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Effect of resin impregnated core veneer on shear strength of Douglas-fir plywood Chow, Sue-Zone 1966

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EFFECT OF RESIN IMPREGNATED CORE VENEER ON SHEAR STRENGTH OF DOUGLAS-FIR PLYWOOD by SUE-ZONE CHOW B.Sc,  National  Taiwan U n i v e r s i t y ,  Taiwan, 1959  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY i n the Department of FORESTRY  We accept t h i s t h e s i s a's conforming t o the required  THE  standard  UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1966  In p r e s e n t i n g t h i s t h e s i s  in p a r t i a l  f u l f i l m e n t of  requirements f o r an advanced degree at the U n i v e r s i t y of Columbia, for  I agree t h a t the L i b r a r y  r e f e r e n c e and s t u d y .  I further  s h a l l make i t  freely  the  British available  agree that p e r m i s s i o n f o r  ex-  t e n s i v e c o p y i n g of t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department or by h i s  representatives.  understood t h a t c o p y i n g o r p u b l i c a t i o n of t h i s t h e s i s f o r cial  g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n  Department  of  The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date  A^le^  /o? ,  / f 6 <Z  It  is  finan-  permission.  (i) ABSTRACT  The i n f l u e n c e o f l a t h e checks on shear s t r e n g t h o f Douglas f i r plywood was i n v e s t i g a t e d by means o f impregnating l a t h e checks o f r o t a r y - c u t veneer t o v a r i o u s depths u s i n g a phenol-formaldehyde  resin.  Comparative  t e n s i l e shear s t r e n g t h t e s t s were conducted  on a T a b l e Model I n s t r o n machine and photographs  taken a t  v a r i o u s stages o f l o a d a p p l i c a t i o n t o i l l u s t r a t e the v a r i e d manner o f f a i l u r e . S t r e n g t h o f r o t a r y - c u t veneer plywood was about 60 t o 70% t h a t o f sawn veneer plywood, but a f t e r the l a t h e checks o f core veneer were impregnated by r e s i n t h e r e was no s i g n i f i c a n t d i f f e r e n c e between them.  The shear s t r e n g t h  (Y) was found t o be  h i g h l y c o r r e l a t e d w i t h p e n e t r a t i o n depth o f adhesive i n t o l a t h e checks  (X).  The l i n e a r r e l a t i o n s h i p between these f a c t o r s was:  Y a 228.22 + 1.28052X ( S E . 21.82; r = 0.893). £  Per cent wood f a i l u r e estimated by c o n v e n t i o n a l methods f a i l e d t o r e l a t e t o shear s t r e n g t h .  Rather,, the per cent wood  f a i l u r e o c c u r r i n g w i t h i n 10$ o f the i n i t i a t i o n o f an annual increment was found t o be a b e t t e r i n d i c a t o r o f shear s t r e n g t h . Use o f photography  helped t o e x p l a i n more c l e a r l y  d i s t r i b u t i o n and wood f a i l u r e i n the specimens.  stress I t was found  t h a t the u l t i m a t e s t r e n g t h was reached i n c o n v e n t i o n a l plywood when the l a t h e checks were j u s t  opening.  (ii) Core-impregnated  plywood was used i n a t e s t t o compare  the t e n s i l e shear r e s i s t a n c e when t i g h t - s i d e and l o o s e - s i d e o f veneer was next t o the glue l i n e .  N e i t h e r s t r e n g t h nor wood  f a i l u r e were s i g n i f i c a n t l y d i f f e r e n t between the two. shear s t r e n g t h f o r plywood made of impregnated  Tensile  core veneer and  u n t r e a t e d f a c e veneer was two t o t h r e e times as h i g h as t h a t of c o n v e n t i o n a l plywood.  The p e r cent wood f a i l u r e i n core veneer  and shear s t r e n g t h v a r i e d i n v e r s e l y .  Results obtained i n t h i s  study i n d i c a t e d t h a t i t i s f e a s i b l e t o develop a plywood which has shear s t r e n g t h as h i g h as 500 p s i w h i l e remaining to  manufacture.  economical  (iii) ACKNOWLEDGEMENT  The author wishes t o express h i s g r a t i t u d e t o Dr. R.W. Wellwood o f the F a c u l t y o f F o r e s t r y a t the U n i v e r s i t y o f B r i t i s h Columbia,  under whose d i r e c t i o n t h i s t h e s i s was  accomplished. A p p r e c i a t i o n i s a l s o due t o Dr. J.W. Wilson f o r h i s a d v i c e and review of t h i s t h e s i s , t o Dr. A. Kozak f o r h i s h e l p i n s t a t i s t i c a l a n a l y s i s , and t o Mrs. Chow f o r a s s i s t a n c e i n p r e p a r a t i o n o f the manuscript. Thanks a r e a l s o due t o t h e author*s p a r e n t s , and t o P r o f e s s o r T.T. Wang o f the Department o f F o r e s t r y a t N a t i o n a l Taiwan U n i v e r s i t y , Taipei,' Taiwan, f o r encouraging the author to study i n t h i s c o u n t r y . P a c i f i c Veneer and Plywood D i v i s i o n o f Canadian F o r e s t Products L i m i t e d s u p p l i e d t h e l o g and P a c i f i c Resins L i m i t e d p r o v i d e d t h e g l u e s used i n t h e experiment. generosity  Their  i s g r a t e f u l l y acknowledged. The author i s a l s o a p p r e c i a t i v e o f f i n a n c i a l  assistance  obtained from t h e F a c u l t y o f F o r e s t r y , U n i v e r s i t y o f B r i t i s h Columbia,  Vancouver,  of Canada.  Canada, and t h e N a t i o n a l Research  Council  (iv) TABLE OF CONTENTS Page TITLE PAGE ABSTRACT  i  ACKNOWLEDGEMENT  i i i  TABLE OF CONTENTS  iv  LIST OF TABLES  v i i  LIST OF FIGURES  x  INTRODUCTION  1  REVIEW OF LITERATURE  3  A. Lathe Checks i. ii.  3  Formation  3  I n f l u e n c e on shear s t r e n g t h o f plywood  k  B. Wood F a i l u r e i.  6  Importance  ii.  6  U n c e r t a i n t y o f r e l a t i o n s h i p between wood f a i l u r e and shear s t r e n g t h  iii;  1  R e l a t i o n s h i p between wood f a i l u r e and l a t h e checks  8  C. R e l a t i o n s h i p o f R e s i n - P e n e t r a t i o n  t o Shear  Strength o f Plywood. i. ii. iii.  1  6  9  P e r m e a b i l i t y o f D o u g l a s - f i r wood Resin properties Resin impregnation  9 10  and shear s t r e n g t h  12  (v) Page MATERIALS AND METHODS  13  A. Experimental Design  13  B. Materials  16  i.  Veneer collection  16  a.  Log  16  b.  Peeling and sawing  16  c.  Selection and grouping of veneers 17  ii. iii. iv.  (1) .  Group A  1?  (2) .  Group B  17  (3) .  Group C  18  Staining  19  Drying  19  Impregnation  20  C. Plywood Panel Construction  23  D.  25  Preparation and Test of Specimens i.  Sample size  ii.  Trimming of samples and measurements  iii.  Measurements of lathe checks, adhesive  25 25  penetration depth and the angle of lathe  iv. v.  E.  checks  26  Testing  27  Estimation of wood failure and position of failure  28  Photographic Technique  28  (vi) Page RESULTS A. Shear Strength"  29 2 9  i.  Group A  3 0  ii.  Group B  3 1  iii.  Group C  3 1  B. Per Cent Wood F a i l u r e  3 2  i.  Group A  3 2  ii.  Group B  3 3  iii.  Group C  3 3  C. Photographic Evidence DISCUSSION  3 3 3 3  A. I n f l u e n c e o f Lathe Checks on Shear S t r e n g t h  3 4  B. I n f l u e n c e o f Lathe Checks on Wood F a i l u r e  4 l  C. I n f l u e n c e o f R o t a r y - c u t t i n g on Shear S t r e n g t h and Wood F a i l u r e i n T i g h t - s i d e and L o o s e - s i d e of Veneer  42  D. I n f l u e n c e of Resin-Impregnation on Shear Strength and Per Cent F a i l u r e o f Core Veneer CONCLUSIONS LITERATURE CITED  4 3 46 5 0  (vii) LIST OF TABLES  Page  Table  I.  Summation of average shear s t r e n g t h s and per cent wood f a i l u r e s ,  56  Table  II.  A n a l y s i s of v a r i a n c e : Average shear s t r e n g t h s i n Groups A,B and C (dry test).  57  A n a l y s i s of v a r i a n c e : Average shear s t r e n g t h s i n Treatments 5. 8 and 9 of Groups A, B and C, r e s p e c t i v e l y (dry test)„  58  Duncan s m u l t i p l e range t e s t : Average shear s t r e n g t h s i n Treatments 5» 8 and 9 of Groups A, B and C, r e s p e c t i v e l y (dry t e s t ) .  58  A n a l y s i s o f v a r i a n c e : Average shear s t r e n g t h s i n Treatments 5» 8 * i d 9 of Group A, B and C, r e s p e c t i v e l y (boil test).  59  Table  Table  Table  IIIA.  IIIB.  IVA.  1  a  Table  IVB.  Table  V.  Table  VIA.  Duncan's m u l t i p l e range t e s t : Average shear s t r e n g t h s i n Treatments 5» 8 and 9 of Groups A, B and C, r e s p e c t i v e l y (boil test), 59 Summation of averaged data of Group A.  60  A n a l y s i s of v a r i a n c e : Average p e n e t r a t i o n depths of adhesive i n t o l a t h e checks i n Treatments 1 t o k Group A.  61  Duncan's m u l t i p l e range t e s t : Average p e n e t r a t i o n depths of adhesive i n t o l a t h e checks i n Treatments 1 t o k, Group A.  6l  A n a l y s i s of v a r i a n c e : Average shear s t r e n g t h s i n Treatments 1 t o 5» Group A (dry t e s t ) .  62  Duncan's m u l t i p l e range t e s t : Average shear s t r e n g t h s i n Treatments 1 to 5. Group A (dry t e s t ) .  62  f  Table  Table  Table  VIB.  VILA.  VIIB.  (viii) Page Table  Table  Table  Table  Table  Table  Table  Table  VIIIA.  VIIIB.  IX.  X.  XIA.  XIB,  XIIA.  XIIB.  A n a l y s i s o f v a r i a n c e : Average shear s t r e n g t h s i n T r e a t m e n t s 1 t o 5. Group A ( b o i l t e s t ) .  63  Duncan s m u l t i p l e range t e s t : shear s t r e n g t h s i n Treatments Group A ( b o i l t e s t ) .  63  1  Average 1 t o 5»  A n a l y s i s o f v a r i a n c e : Average shear s t r e n g t h s i n T r e a t m e n t s 6 t o 8, Group B ( d r y t e s t ) .  64  A n a l y s i s o f v a r i a n c e : Average shear s t r e n g t h s i n T r e a t m e n t s 6 t o 8. Group B ( b o i l t e s t ) .  64  A n a l y s i s o f v a r i a n c e : Average shear s t r e n g t h s i n T r e a t m e n t s 9 t o 12, Group C ( d r y t e s t ) .  65  Duncan's m u l t i p l e r a n g e t e s t : shear s t r e n g t h s i n Treatments Group C ( d r y t e s t ) .  65  Average 9 t o 12,  A n a l y s i s o f v a r i a n c e : Average shear s t r e n g t h s i n T r e a t m e n t s 9 t o 12, Group G ( b o i l t e s t ) .  66  Duncan's m u l t i p l e r a n g e t e s t : shear s t r e n g t h s i n Treatments Group C ( b o i l t e s t ) .  66  Average 9 t o 12,  Table  XIII.  A n a l y s i s o f v a r i a n c e : Average p e r cent wood f a i l u r e by c o n v e n t i o n a l methods i n T r e a t m e n t s 1 t o 5t G r o u p A , 67  Table  XIV.  A n a l y s i s o f v a r i a n c e : Average p o s i t i o n o f wood f a i l u r e i n a n a n n u a l i n c r e m e n t f r o m i t s i n i t i a t i o n i n T r e a t m e n t s 2 t o 5» Group A . 67  Table  XVA.  A n a l y s i s o f v a r i a n c e : Average p e r c e n t wood f a i l u r e o c c u r r i n g i n e a r l y wood i n T r e a t m e n t s 2 t o 5» Group A .  68  Duncan's m u l t i p l e r a n g e t e s t : Average p e r c e n t wood f a i l u r e o c c u r r i n g i n earlywood I n T r e a t m e n t s 2 t o 5» Group A ,  68  Table  XVB.  (ix) Table  Table  Table  XVI.  XVIIA.  XVIIB.  Page  Analysis of variance: Average per cent wood f a i l u r e s by conventional method i n Treatments 6 to 8 , Group B (These are a l l of Group B).  69  Analysis of variance: Average per cent wood failure.' by conventional methods i n Treatments 9 to 1 2 , Group C.  70  Duncan's multiple range t e s t : Average per cent wood failure?, by conventional methods i n Treatments 9 to 1 2 , Group C. 7 0  (x) LIST OF FIGURES  Fig.*  5  Fig.*  1 .  C r i t i c a l zones o f s t r e s s i n veneer c u t t i n g without a nosebar .  FlgJ Fig;  Fig.  ;  1  ;l  7 1  2.* Lathe check o r i e n t a t i o n i n plywood shear t e s t specimens.  Fig.  Page  7 2  3 » P o s i t i o n o f sample veneer i n the l o g .  7 3  4 ; ' Camera setup and t e s t i n g a p p a r a t u s . 5 » R e l a t i o n s h i p between shear s t r e n g t h o f plywood and p e n e t r a t i o n depth o f adhesive i n t o l a t h e checks.  7 ^ 7 5  6 . S t r e s s - s t r a i n curve f o r plywood made of sawn veneer, w i t h accompanying photographs a t the p o s i t i o n s noted - Treatment 5 .  7 6  7 « S t r e s s - s t r a i n curve f o r plywood made o f r o t a r y - c u t veneer, w i t h accompanying photographs a t t h e p o s i t i o n s noted (Sample 1 ) - Treatment 1 .  8 1  1  Fig.  !  1  Fig.'  Fig.'  8.  f  S t r e s s - s t r a i n curve f o r plywood made o f r o t a r y - c u t veneer, w i t h accompanying photographs a t the p o s i t i o n s noted (Sample 2 ) - Treatment 1 „  9 . Comparison o f s t r e s s - s t r a i n curves f o r plywoods made o f sawn veneer ( S ) , r o t a r y - c u t veneer w i t h l a t h e checks f u l l y impregnated by r e s i n (L),' and r o t a r y - c u t veneer (R).  Fig. " 1 0 . 1  ;  8 8  9 3  S t r e s s - s t r a i n curve f o r plywood made o f r o t a r y - c u t veneer, w i t h l a t h e checks f u l l y Impregnated by r e s i n , ' w i t h accompanying photographs a t the p o s i t i o n s . noted (Sample 1 ) - Treatment 4 . 9 4 1  (xi) Page Fig.  1  11.'  F i g . 12.  Fig;* 13'.'  S t r e s s - s t r a i n curve f o r plywood made o f r o t a r y - c u t veneer w i t h l a t h e checks f u l l y impregnated by r e s i n , w i t h accompanying photographs a t the p o s i t i o n s noted (Sample 2) - Treatment 4.  98  S t r e s s - s t r a i n curve f o r plywood made o f r o t a r y - c u t veneer w i t h l a t h e checks f u l l y impregnated by resin,- w i t h accompanying photographs a t the p o s i t i o n s noted (Sample 3) - Treatment 4.  103  Test specimens a f t e r f a i l u r e .  10?  INTRODUCTION  Many s t u d i e s have been done d u r i n g  recent  years t o  determine the f a c t o r s i n f l u e n c i n g the t e n s i l e shear  strength  of plywoods.  Of these f a c t o r s , l a t h e checks are always regarded  to be of the g r e a t e s t questions  concerning  answered c l e a r l y .  importance.  However, s e v e r a l fundamental  the i n f l u e n c e of l a t h e checks have not  F o r example, how  deeply does the g l u e  i n t o l a t h e checks i n p r o p o r t i o n to t h e i r t o t a l depth? v a r y i n g depths of glue m i g r a t i o n of plywood?  How  i n f l u e n c e the shear  does the c r i t i c a l area  been  migrate  Will strength  of a shear specimen having  l a t h e checks behave under the a p p l i e d l o a d , In comparison with that of a check-free questions the new  ( i . e . sawn veneer) specimen?  I f these  c o u l d be s a t i s f a c t o r i l y answered, i t i s b e l i e v e d  that  knowledge could l e a d to b e t t e r techniques t h a t would  improve s t r e n g t h p r o p e r t i e s of plywoods. The q u a l i t y has  value  of wood f a i l u r e as a c r i t e r i o n of plywood  been a subject  have been expressed.  on which many c o n f l i c t i n g  T h i s may  be due  of the mechanism of wood f a i l u r e I t has  to l a c k of understanding  i n r e l a t i o n to shear  long been recognized  are a f f e c t e d by the p e e l i n g p r o c e s s .  The  l o o s e - and t i g h t - s i d e i n strength  t i g h t - s i d e might have been compressed beyond the  l i m i t by the nose bar, and  strength.  t h a t veneer p r o p e r t i e s  of a veneer are expected to be d i f f e r e n t The  opinions  properties. proportional  the t e n s i l e s t r e n g t h p a r a l l e l to  the  2 g r a i n of the l o o s e - s i d e might of these v a r i a b l e s In view was  be  r e d u c e d by l a t h e  on p l y w o o d s p e c i m e n s  has not been  o f the above, the f i r s t  t o i n v e s t i g a t e how  checks.  purpose  A  done.  of t h i s  m e c h a n i c a l b e h a v i o u r o f plywood  study  in tensile  shear, p e r p e n d i c u l a r t o the g r a i n o f the c o r e plies,, would influenced depths  (a) by p r e s e n c e  o f l a t h e checks and  of adhesive penetration  (b) by  into l a t h e checks.  were d e t e r m i n e d w i t h p l y w o o d i n w h i c h  test  be  different  Shear s t r e n g t h s  t h e f a c e p l i e s were n o t  treated. The which  s h e a r t e s t i n g was  directly  up p h o t o g r a p h s  done on a n  r e c o r d s t h e s t r e s s - s t r a i n c u r v e on a c h a r t . o f the samples,  a p p l i c a t i o n , were a l s o  in different  t a k e n and  wood f a i l u r e a t known p o s i t i o n s The  second  of the t i g h t - and tensile  I n s t r o n machine  purpose  loose-side  stages of  load  used f o r a n a l y s e s of s t r e s s on t h e s t r e s s - s t r a i n  was  Close-  to determine  of veneer  the  and  curve.  contribution  i n the face p l i e s  to the  s h e a r s t r e n g t h o f p l y w o o d made w i t h r e s i n - i m p r e g n a t e d  core veneer, with f a i l u r e  f o r c e d by  specimen  design to occur i n  face p l y . Another resin-impregnated i n which  o b j e c t i v e was core veneer  t o examine t h e i n f l u e n c e o f  on t h e s h e a r s t r e n g t h o f  t h e f a c e p l i e s were n o t t r e a t e d , w i t h f a i l u r e  the  plywood forced  occur i n core. It lead  i s hoped t h a t  t o t h e development  s t r e n g t h and  still  will  the r e s u l t s  of t h i s  o f a plywood which remain  has  economical to  experiment improved  will  shear  manufacture.  to  3 REVIEW OF LITERATURE A.  Lathe Checks  I".  Formation  ,  The i n f l u e n c e of p e e l i n g technique on veneer qualityhas r e c e i v e d c o n s i d e r a b l e study i n recent years ( 1 2 , 23» 3 0 3*+t  3 5 , 39, k0 ^5.  46.).  r  f  F l e i s c h e r (23) o b t a i n e d e x c e l l e n t  close-up photographs of veneer c u t t i n g and showed t h a t an i n c r e a s e i n nose-bar p r e s s u r e was e f f e c t i v e i n r e d u c i n g both the s e v e r i t y of l a t h e checks and roughness of the veneer. E x c e s s i v e compression i n the case of some softwoods, however, r e s u l t e d i n s h e l l i n g o r s l i v e r i n g , due t o a s e p a r a t i o n between earlywood and latewood.  V a r i a t i o n s i n frequency and depth of .  checks, i n veneer t h i c k n e s s and i n s u r f a c e q u a l i t y i n p e e l e d veneers were observed by M c M i l l i n (46).  He found t h a t , as  nose-bar p r e s s u r e was i n c r e a s e d stepwise so t h a t  compression  of the veneer i n c r e a s e d from zero t o 15% of veneer t h i c k n e s s , the depth of l a t h e checks decreased, w h i l e t h e i r frequency (of checks) i n c r e a s e d . The mechanism of veneer f o r m a t i o n a t the c e l l u l a r l e v e l was s t u d i e d comprehensively by Leney  ( 3 9 , *K>). When h i s -  study i s combined w i t h the e x p l a n a t i o n p o s t u l a t e d by Koch ( 3 5 ) . it  i s seen t h a t s t r e s s e s i n the zone a d j a c e n t t o the c u t t i n g  edge of the k n i f e can be c l a s s i f i e d simply i n t o t e n s i o n , shear and compression.  These c r i t i c a l zones of s t r e s s  are presented diagrammat1cally i n F i g . 1.  concentration  Because of s t r e s s e s ,  t h r e e types of r u p t u r e may occur, s i n g l y o r i n combination, as  veneer i s formed.  Leney  (39, 40) i d e n t i f i e d these types o f  r u p t u r e as t e n s i o n checks, shear checks, and compression  tearing.  "Tension check i s due t o t e n s i o n s t r e s s e s r e s u l t i n g from combination of c a n t i l e v e r beam a c t i o n , compression j u s t behind the c u t t i n g edge, and shear s t r e s s e s caused by the c u t t i n g edge r e s i s t i n g the movement of the wood. Shear checks from behind the c u t t i n g edge when h i g h compressive s t r e s s e s combined w i t h r e s u l t i n g f r i c t i o n r e s i s t the movement of the c h i p up the k n i f e . Compression t e a r i n g was a t t r i b u t e d t o a d u l l k n i f e r e s i s t i n g the movement o f the wood past the c u t t i n g edge." ( 3 9 ) .  \  About  the same time C o l l i n s  ( 1 2 ) p o s t u l a t e d t h a t l a t h e checks  i n D o u g l a s - f i r veneer were produced by an u n s t a b l e "snap a c t i o n " i n an a r e a s t r e s s e d under t e n s i o n normal t o the break. first,  At  the s t r e s s would be n e a r l y normal t o the c u t , but would  change r a p i d l y t o a d i r e c t i o n n e a r l y p a r a l l e l t o t h e c u t , ii.  I n f l u e n c e on shear s t r e n g t h o f plywood. T e n s i l e s t r e n g t h p e r p e n d i c u l a r to the g r a i n i n r o t a r y -  cut veneer has been s t u d i e d by Kivimaa (3*0 „  He found t h a t  i n c r e a s e o f nose-bar p r e s s u r e i n c r e a s e d the t e n s i l e s t r e n g t h of veneer but reduced the depth o f l a t h e checks. Curry  ( 1 5 ) and Yavorsky and Cunningham ( 7 1 ) p o s t u l a t e d  t h a t a l a r g e component o f shear e x i s t e d i n the plane o f the core veneer of t h r e e - p l y specimens.  E x i s t e n c e o f l a t h e checks  i n the core veneer e x e r t e d a pronounced shear s t r a i n i n t h i s r e g i o n .  e f f e c t on the amount of  A s i m i l a r o p i n i o n was r e p o r t e d by  N o r r i s , Warren and McKinnon ( 4 8 ) .  They added t h a t l a t h e checks  reduced the e f f e c t i v e a r e a o f each p l y by r e d u c i n g the c r o s s - s e c t i o n area.  5 of  wood  subjected  introduce decrease  a  zone  the  to of  stress  shear  (5),  (22),  Feihl  that,  i n plywood  ation  of  lathe  checks  specimen  could  cause  pulled  found  that  birch  plywood  explained  as  distribution  of  tests.  The  tension  shear  He  closed  have  pulled  open.  (Fig.  properties  the  important  role and  of  this  surface  veneer  was  However,  paratively  of  to  small  and  gum  the  sawn  was  checks  on  i n the test  by  major  concluded  found that  pulled by  those  for  (22)  Feihl  who  of  This  yellow  was  in  the  to different  better  than  with  with  shear  than  strength  specimens  than  open  submitted be  test  rolling  differences  to  orient-  i n the  i n the  and  Huffman the  cuts  the  Bethel  and  nature.  specimens was  by  face,  done  contradictory  Douglas-fir  factors  the  lathe  the  The  f a c t o r was  times that  average that  of  influencing  plywood.  i s attributed to  1.5  the  lathe  mainly  single  suggested  attributable  further  checks  checks  2).  quality.  he  Bethel  f o r specimens  investigated  factor  about  checks  should  done  differences  higher strength  (5^),  strength most  very  shear  pulled  Palka  of  stresses  test.  to  s i m i l a r study  caused  bending  respect  lower  A  of a  being  core  significant  influence was  lathe  that  (5*0-.  Palka  poplar  with  closed.  the  concentration  and  of  S t r e n g t h was  those  furthermore,  i n v e s t i g a t i o n s were a l s o  found  strength.  and,  strength.  Practical Huffman  stress  veneer the  rolling  He  concluded  type.  effect shear  rotary-cut  of  in rolling  mechanical  e f f e c t of  lathe  countered  by  the  that  dominant  lathe  veneer  reduction  partly  The  strength  the  and/or  several  checks of  sawn  blocks. shear  checks  was  adhesive  resistance com-  p e n e t r a t i n g i n t o them.  The l a t t e r was more pronounced f o r  b l o c k s p r e p a r e d under h i g h g l u i n g p r e s s u r e ( 3 5 0 p s i ) . B.  Wood F a i l u r e  i.  Importance T e s t s of g l u e bonds a r e made i n a n attempt t o p r e d i c t  t h e b e h a v i o u r t o be e x p e c t e d of t h e plywood i n s e r v i c e . i n s t a n c e s t h e c r i t e r i o n f o r acceptance  I n most  or r e j e c t i o n i s that the  t e s t specimen must have a g l u e bond s t r e n g t h a t l e a s t e q u a l t o t h a t o f t h e wood i n t h e specimen.  T h i s l i n e of r e a s o n i n g l e d  t o t h e use of percentage wood f a i l u r e as t h e b a s i s f o r e v a l u a t i n g bond s t r e n g t h ( 7 2 ) . I n Canada p e r cent x-jood f a i l u r e i s a c c e p t e d as a s t a n d a r d f o r e s t i m a t i n g glue-bond  q u a l i t y (10) f o r t e s t i n g  e x t e r i o r - t y p e D o u g l a s - f i r plywood bonded w i t h w a t e r p r o o f formaldehyde  resin.  phenol-  A c c o r d i n g t o Canadian s p e c i f i c a t i o n s ( 1 0 ) :  " I f t h e average wood f a i l u r e of t e n t e s t specimens from a t e s t p i e c e i s l e s s t h a n 60 p e r c e n t , o r i f more t h a n one t e s t specimen i s l e s s t h a n 30 V cent, t h a t t e s t piece fails. I f more t h a n one t e s t p i e c e from a t e s t panel f a i l s , then that panel f a i l s . " er  Importance o f p e r cent wood f a i l u r e , t h e r e f o r e , c a n be seen. ii.  U n c e r t a i n t y of r e l a t i o n s h i p between wood f a i l u r e and shear s t r e n g t h The  importance  of wood f a i l u r e was not emphasized i n  e a r l i e r r e s e a r c h i n England o r t h e U.S.A. ( 5 0 , 6 6 ) . Shear s t r e n g t h o f plywood was based upon b r e a k i n g l o a d s o b t a i n e d from m e c h a n i c a l t e s t s of g l u e j o i n t s .  Truax ( 6 5 ) , in. d i s c u s s i n g  7  r e s u l t s of h i s experiments,  s t a t e d t h a t under good g l u i n g  c o n d i t i o n s t h e j o i n t s t r e n g t h was not s e r i o u s l y i n f l u e n c e d by t h e p e r c e n t a g e o f wood f a i l u r e developed by t h e t e s t . was l a t e r confirmed  (49),  by N o r t h c o t t  This  who used D o u g l a s - f i r  v e n e e r s bonded w i t h phenol-formaldehyde r e s i n . By 1 9 3 8 s e r i o u s c o n s i d e r a t i o n was b e i n g g i v e n t o t h e use o f p e r cent wood f a i l u r e as a c r i t e r i o n o f bond q u a l i t y for  plywood s p e c i f i c a t i o n p u r p o s e s , i f not f o r r e s e a r c h purpose  (50).  The amount of wood f a i l u r e was e x p e c t e d t o be r e l a t e d t o  the s e r v i c e l i f e of plywood ( 5 7 ) • A r e v i e w of v a r i o u s d a t a and r e p o r t s f r o m d i f f e r e n t sources, together w i t h h i s experimental (49,  r e s u l t s , l e d Northcott  5 0 ) t o p o s t u l a t e t h a t t h e r e was a p o o r e r  correlation  between b r e a k i n g l o a d and s e r v i c e l i f e t h a n between p e r cent wood f a i l u r e and s e r v i c e l i f e .  He f u r t h e r showed t h a t s t r e n g t h  v a l u e s f r o m m e c h a n i c a l t e s t s gave more r e l i a b l e e s t i m a t e s of bond s t r e n g t h t h a n r e s u l t s o b t a i n e d by t h e p e r cent wood f a i l u r e method. Shen ( 5 9 ) found t h a t p e r cent wood f a i l u r e i n spruce plywood was not a s a c c u r a t e a n i n d i c a t o r f o r e s t i m a t i n g t h e g l u e l i n e q u a l i t y as was t h e b r e a k i n g Palka ( 5 ^ ) .  load.  using D o u g l a s - f i r veneers,  postulated that  an i n c r e a s e of shear s t r e n g t h was a s s o c i a t e d w i t h h i g h e r wood failure.  The s i m p l e c o r r e l a t i o n c o e f f i c i e n t between shear  s t r e s s and wood f a i l u r e p e r c e n t a g e was 0 . 5 ^ f o r sawn veneer p a n e l s and O . 7 6 f o r r o t a r y - c u t v e n e e r p a n e l s .  8  ((5.2,;  In a recent r e p o r t , N o r t h c o t t and co-workers  53)  concluded t h a t , w i t h i n c e r t a i n l i m i t s , t h e p e r cent wood f a i l u r e was a p o t e n t i a l l y good estimate of plywood d u r a b i l i t y . They suggested that i t was reasonable t o accept p e r cent wood f a i l u r e as a worthwhile p r e d i c t o r of bond d u r a b i l i t y with h o t pressed, phenolic-glue-bonded D o u g l a s - f i r plywood.  The p e r  cent wood f a i l u r e was expected t o be more s e n s i t i v e t o i n i t i a l bond d e g r a d a t i o n than was the breaking l o a d . From the r e s u l t s and o p i n i o n s above, i t may be concluded t h a t the r e l a t i o n s h i p of p e r cent wood f a i l u r e t o breaking l o a d i n t e n s i o n shear t e s t has not been adequately d e f i n e d . C e r t a i n v a r i a t i o n s i n wood, g l u e , i n g l u i n g , o r i n t e s t and measuring  method, may cause t h e amount of wood f a i l u r e of a  glue j o i n t t o v a r y c o n s i d e r a b l y (59). wood s p e c i e s (51)»  The d e n s i t y of wood (3),  whether heartwood or sapwood (59)»  latewood  percentage, veneer t h i c k n e s s , g l u i n g pressure^, moisture content • of veneer (54),  angle of g r a i n i n r e l a t i o n t o the g l u e - l i n e  t h i c k n e s s of g l u e - l i n e  (11)  and k i n d of g l u e used  (19K  (4),•  were  f a c t o r s found i n f l u e n c i n g the p e r cent wood f a i l u r e of shear specimens. iii.  R e l a t i o n s h i p between wood f a i l u r e and l a t h e I t had been observed (48)  that the number of l a t h e  checks w i t h i n one l i n e a l i n c h of veneer was independent  checks  (from i t s c r o s s - s e c t i o n )  of veneer t h i c k n e s s and t h a t t h e i r depth,  expressed as a p r o p o r t i o n of the veneer t h i c k n e s s , i n c r e a s e d with t h i s t h i c k n e s s .  Consequently, plywood panels made from  t h i c k veneers had a lower shear s t r e n g t h than panels of the same t h i c k n e s s  made from t h i n veneers (15).  e f f e c t , along with Palka's f i n d i n g (5^)  Considering  this  that r e d u c t i o n i n wood  f a i l u r e accompanied i n c r e a s i n g veneer t h i c k n e s s ,  i t i s possible  t h a t i n c r e a s e of l a t h e check; depth would cause r e d u c t i o n I n p e r cent wood f a i l u r e . Prom r e s u l t s obtained  by B e t h e l and Huffman  (5),  o r i e n t a t i o n of l a t h e checks w i t h r e s p e c t t o the saw cut i n f l u enced the p e r cent wood f a i l u r e a s w e l l as shear s t r e n g t h ?  (p.5).  Regardless of whether specimens were t e s t e d a f t e r b o i l i n g o r i n dry c o n d i t i o n , the average wood f a i l u r e of specimens f o r which l a t h e checks were t o be p u l l e d open was lower than that of s p e c i mens f o r which l a t h e checks were t o be p u l l e d C.  R e l a t i o n s h i p of R e s i n - p e n e t r a t i o n  closed.  t o Shear S t r e n g t h of  Plywood i.  Permeability  of D o u g l a s - f i r wood  E r i c k s o n and co-workers (21)  i l l u s t r a t e d that  per-  m e a b i l i t y of sapwood i n the l o n g i t u d i n a l and r a d i a l a n a t o m i c a l d i r e c t i o n was g r e a t e r than that of heartwood. permeability Griffin  (26)  The s u p e r i o r  of latewood over earlywood was e x p l a i n e d by as due t o the g r e a t e r c a p i l l a r y f o r c e s i n the  lumina of latewood and the g r e a t e r degree of a s p i r a t i o n i n p i t s of earlywood than of latewood. Krahmer and CSte ( 3 8 ) d e s c r i b e d  three n a t u r a l p r o -  cesses which modify the c o n d i t i o n of bordered p i t - p a i r s .  One  was p i t a s p i r a t i o n , the second was p i t o c c u l t a t i o n w i t h e x t r a c t i v e s ,  10 and the third process was pit incrustation.  Pit membranes of  Douglas-fir studied were not heavily incrusted like those of western red-cedar, but pit aspiration was commonly found in the heartwood of both species. Recently, Koran (37) showed that the presence of extraneous materials in the capillary structure was an important factor prohibiting penetration.  The influence of origin of the  material was reported by Miller (47).  He found that heartwood  of Douglas-fir from eastern Oregon was generally much less permeable than that from the western half of the State.  Craig (14)  reported that trees from high elevations had lowest permeability while trees from medium elevations had the highest variation in permeability. The styrene impregnation technique applied in this study had been developed by Erickson and Balatinecz (20). They found that in radial impregnation the liquid moved mainly in the ray tracheids.  Ray parenchyma cells were mostly imper-  meable. In tangential impregnation, the penetration was comparatively slow.  Movement was through tracheid bordered pits  and into and across ray tracheids to some extent.  The higher  permeability of sapwood over heartwood in Douglas-fir was also demonstrated. i i . Resin properties Impregnating veneer with a synthetic resin to stabilize the dimensions, and increase the strength of plywood made from i t , can be effectively accomplished only when resin-forming  11 c o n s t i t u e n t s p e n e t r a t e the c e l l w a l l s t r u c t u r e and become bonded to the a c t i v e groups i n the wood upon f o r m a t i o n o f the r e s i n (62). Hence, use o f a h i g h m o l e c u l a r weight o r p r e p o l y m e r i z e d r e s i n , or non-polar r e s i n - f o r m i n g  constituents,  i s not d e s i r a b l e because  d e p o s i t i o n w i t h i n the coarse c a p i l l a r y s t r u c t u r e o f wood renders i t less efficient. A comparison o f commercial water s o l u b l e phenolformaldehyde r e s i n o i d s f o r wood impregnations has been made by (8).  Burr and Stamm  of p r e p o l y m e r i z a t i o n  By u s i n g an a l k a l i n e c a t a l y s t , the degree o f the impregnant was s u f f i c i e n t l y lowered  so as t o be s o l u b l e i n water i n a l l p r o p o r t i o n s .  T h i s system  was s u p e r i o r t o the raw mix, s i n c e the r e s i n was l e s s v o l a t i l e and very small amounts were l o s t d u r i n g d r y i n g p r i o r t o c u r i n g of r e s i n ( 6 l ) .  Another advantage o f the phenol-formaldehyde  system was t h a t i t swelled wood about 25% beyond the s w e l l i n g i n water, thus f u r t h e r opening up the s t r u c t u r e .  A f t e r cure of  the r e s i n , the r e t a i n e d volume o f wood was c l o s e t o the normal water-swollen volume o f t h a t wood.  The a p p l i c a t i o n of u r e a -  formaldehyde r e s i n was found l e s s s u c c e s s f u l  (61), mainly because  the lower polymer was only about 20% s o l u b l e i n water and the resin-forming  s o l i d tended t o p r e c i p i t a t e i n the c o a r s e v o i d  s t r u c t u r e o f the wood as i t was d r i e d , r a t h e r than c o n t i n u i n g t o d i f f u s e i n t o the f i b e r w a l l s .  A l s o , the cured u r e a r e s i n was f a r  l e s s water r e s i s t a n t than the phenol-formaldehyde r e s i n .  1 2 G a p - f i l l i n g p r o p e r t i e s of s e v e r a l wood adhesives  was  compared by Goto, Kawamura and Sakuno ( 2 5 ) . They found t h a t phenol-formaldehyde  g l u e was  the b e s t , while r e s o r c i n o l and  p o l y v i n y l a c e t a t e were next. iii.  R e s i n impregnation and shear s t r e n g t h An i n t e r e s t i n g experiment  examining  the i n f l u e n c e of  adhesive on the s t r e n g t h of plywood has been done by Curry ( 1 6 ) . Plywoods were made from veneers r a n g i n g i n t h i c k n e s s from 1 / 1 0 i n c h t o 1 / 5 0 i n c h , u s i n g phenol-formaldehyde types of adhesive, and t e s t e d . t h i c k n e s s was  I t was  r e s i n and two  other  found t h a t when the veneer  not l e s s than 1 / 1 6 i n c h , the c o n t r i b u t i o n of  adhesive t o the t o t a l s t r e n g t h of plywood was  little.  But f o r  plywoods made from t h i n n e r veneers, the i n f l u e n c e of adhesive became more s i g n i f i c a n t .  Neglect of adhesive i n f l u e n c e c o u l d  l e a d t o c o n s i d e r a b l e e r r o r when c a l c u l a t i n g s t r e n g t h v a l u e s because  of the s t r u c t u r e of the wood being m o d i f i e d by the  presence of a d h e s i v e s .  Though the p e n e t r a t i o n of adhesive had  i r r e g u l a r and i n d e f i n i t e borders, r a y t i s s u e was trated.  deeply pene-  A s i m i l a r f i n d i n g t h a t the shear s t r e n g t h of. wood  the d e c i d i n g f a c t o r f o r shear s t r e n g t h of g l u e j o i n t was  was  specimens  shown i n a r e p o r t by Marian and Stumbo ( 4 3 ) . Since wood i s t y p i c a l l y nonhomogeneous, whereas r e s i n  i s s t r i c t l y homogeneous, impregnating r e s i n i n t o i t i n c r e a s e d u n i f o r m i t y and thereby s t r e n g t h ( 6 l ) . S t r e n g t h p r o p e r t i e s of wood which had been r e s i n impregnated,  then compressed, were o b t a i n e d by Stamm and  13 Seborg  (63).  and Dadswell and co-workers  showed t h a t phenol-formaldehyde r e s i n was  (17).  The  results  effective i n increasing  the compressive and shear s t r e n g t h s , whereas toughness  was  decreased. In Impreg (wood impregnated w i t h r e s i n but not comp r e s s e d ) , treatment w i t h s y n t h e t i c r e s i n s was  found t o  only the compressive s t r e n g t h p r o p e r t i e s p a r a l l e l and to the g r a i n , and hardness, w h i l e u l t i m a t e t e n s i o n  improve perpendicular  parallel  t o g r a i n , toughness and Izod impact s t r e n g t h were decreased. However, because of t e c h n i c a l p r o g r e s s , and improved chemicals, g r e a t e r toughness of t r e a t e d wood has been o b t a i n e d ( 2 7 ) . S o l e c h n i k and co-workers  (60),  on the o t h e r hand,  found t h a t bending r e s i s t a n c e of wood impregnated w i t h condensation products of/phenol-formaldehyde r e s i n was  increased  by l l - 2 5 # .  MATERIAL AND  A.  METHODS  Experimental Design In t h i s experiment, shear s t r e n g t h and per cent wood  f a i l u r e were e v a l u a t e d i n 12 treatments d i v i d e d i n t o t h r e e groups.  Each treatment had 12 specimens randomly taken from  k duplicate panels.  The treatments were as f o l l o w s :  14 GROUP A - E v a l u a t i o n of shear s t r e n g t h f o r specimens having d i f f e r e n t depths of adhesive p e n e t r a t i o n i n t o l a t h e checks  i n core veneers due t o v a r y i n g p e r i o d s of  adhesive  impregnation.*  Treatment 1 - Conventional plywood made of r o t a r y - c u t veneers bonded by AMRES 2211  phenol-formal-  dehyde glue o n l y . Treatment 2 - Plywood made of r o t a r y - c u t veneer w i t h 5minute r e s i n (No. 4880) impregnation of core  veneer.  Tireatment 3 - Plywood made of r o t a r y - c u t veneer w i t h 10minute r e s i n impregnation  of core  veneer.  Treatment 4 - Plywood made of r o t a r y - c u t veneer w i t h 30minute r e s i n impregnation  of core  veneers.  Treatment 5 - Plywood made of sawn veneer without  resin  impregnation, u s i n g AMRES 2211 g l u e o n l y . GROUP B - E v a l u a t i o n of shear s t r e n g t h f o r specimens having resin-impregnated  core veneer w i t h f a i l u r e f o r c e d by  specimen d e s i g n t o occur i n f a c e p l y . Treatment 6 - Plywood made of r o t a r y - c u t veneer tight-side  with  of f a c e p l y being adjacent t o f u l l y  resin-impregnated  core  veneer.  * H e r e a f t e r , the word " r e s i n " w i l l r e f e r t o r e s i n No. 4880. The term "glue" w i l l r e f e r t o i n d u s t r i a l use AMRES 2211. And "adhesive" w i l l r e f e r t o e i t h e r g l u e o r r e s i n a c c o r d i n g to the t e x t .  15 Treatment 7 - Plywood made of r o t a r y - c u t veneer  with  l o o s e - s i d e of f a c e p l y being a d j a c e n t t o f u l l y resin-impregnated  core  veneer.  Treatment 8 - Plywood made of sawn veneer w i t h f u l l y impregnated  core  resin-  veneer.  GROUP C - E v a l u a t i o n of shear s t r e n g t h f o r specimens having resin-impregnated  core veneer w i t h f a i l u r e f o r c e d t o  occur i n c o r e . Treatment 9 - Plywood made of sawn veneer w i t h core impregnated by m e t h a n o l - r e s i n mix, f l a t t e n e d and o d r i e d a t 140 P. and bonded by g l u e . Treatment 10- Plywood made of r o t a r y - c u t veneer with core impregnated  by m e t h a n o l - r e s i n mix, and bonded  d i r e c t l y i n t o plywood. Treatment 11- Plywood made of r o t a r y - c u t veneer with core impregnated  by m e t h a n o l - r e s i n mix, f l a t t e n e d  and d r i e d a t l40°F. and bonded by g l u e . Treatment 12- plywood made of r o t a r y - c u t veneer with core impregnated by w a t e r - r e s i n mix, f l a t t e n e d and , o d r i e d a t 140 F. and bonded by g l u e . A n a l y s i s of v a r i a n c e and Duncan's m u l t i p l e range test  (41) were performed  -the.  upon^data o b t a i n e d .  B.  Materials  i.  Veneer  collection  a. Log A Douglas-fir Francd) l o g , 10.5 was  (Pseudotsuga m e n z i e s i i  (Mirb.)  f e e t i n l e n g t h and about 23 inches i n diameter,  chosen from the log-pond of the P a c i f i c Veneer and  D i v i s i o n , Canadian F o r e s t o r i g i n was  Vancouver  Products L t d . , New  Westminster.v. I t s  I s l a n d but the exact l o c a t i o n was  known. A 6-inch long s e c t i o n was  Plywood  not  cut from one end of the l o g  and l a t e r sawn i n t o the t a n g e n t i a l plane. The remaining 10-foot l o g was B. P e e l i n g and  peeled on a commercial  lathe.  sawing  Before p e e l i n g , every t e n t h growth r i n g from the p i t h was  c l e a r l y marked by India ink at each end of the l o g  (Fig. 3). was  One quadrant of the 80- t o 100-year p a r t of the l o g  sprayed w i t h b l u e p a i n t to serve as a r e f e r e n c e  subsequent  sampling.  from t h i s zone.  mark f o r  Sawn and r o t a r y - c u t veneers were taken  Thus, the l o c a t i o n and h o p e f u l l y the p r o p e r t i e s  of r o t a r y - c u t and sawn veneers were c l o s e l y matched. P e e l i n g took place two hours and 15 minutes a f t e r the honing of the k n i f e . s e t t i n g of the machine was P e e l i n g speed K n i f e angle H o r i z o n t a l gap  A c c o r d i n g to the data a v a i l a b l e , the as f o l l o w s : 170  fpm.  90 deg. 0.125 i n .  17 The log was chucked at the pith.  This enabled the  longitudinal axis of veneer to be parallel to the grain direction.  The resulting veneer was 1/7 inch in thickness.  Facilities of the Vancouver Forest Products Laboratory of the Canada Department of Forestry were used to saw the short log tangentially into sheets of 1/7-inch thickness and 4-by 6-inch surface dimension. C. Selection and grouping of veneers (1) . Group A Four 36-by 30-inch rotary-cut veneers taken from the end of the bolt adjacent to the log used for sawn veneer were sawn into strips of 6-by 24-inches along the grain (total of 6 strips)•  Four strips were randomly chosen to serve as core  veneers. Each strip was sawn into four 6-by 6-inch veneers which were randomly assigned to four treatments. Hence, each treatment was applied to four veneers marked alphabetically.  The other  strips were also sawn into 6-by 6-inch veneers to be used later as face veneers. Twelve 4-by 6-inch sawn veneers were randomly chosen. Four of them were used as core and eight as face plies.  This  assignment allowed each treatment to have 12 veneers to be made into 4 panels. (2), Group B Five consecutive parallel strips of 6-by 24-inch rotary-cut veneer were cut into 6-by 6-inch samples yielding a total of 20. Sixteen of these were randomly chosen and  18 separated i n t o two equal groups o f 8 each.  Both groups served  as f a c e p l i e s , one t o t e s t the s t r e n g t h of t i g h t - s i d e of veneer, the o t h e r f o r t e s t of l o o s e - s i d e .  A l l 4-by-6-inch sawn veneers  were chosen t o be f a c e veneers f o r t e s t of shear s t r e n g t h of face p l y .  These t h r e e c l a s s e s o f m a t e r i a l p r o v i d e d comparison  w i t h r e s u l t s of o t h e r treatments o f r o t a r y - o u t veneers. E i g h t 6-by 6 - i n c h and f o u r 4- by 6 - l n c h samples of 1/10-inch t h i c k sapwood veneers were taken from another t r e e to serve as c o r e s of plywoods.  In a p r e l i m i n a r y t e s t of t h i s  study these veneers had proved t o be e a s i l y p e n e t r a t e d by the impregnating r e s i n .  T h i s assignment a l l o w e d each treatment t o  have 12 veneers t o be made i n t o 4 p a n e l s , a l l of which f o r c e f a i l u r e upon s t r e s s i n g t o occur i n the f a c e  (3).  would  plies.  Group C Twelve 6-by 6 - i n c h r o t a r y - c u t sapwood veneers from  the l o n g l o g were randomly  s e l e c t e d from a p i l e o f veneers  which had been c u t i n t o c o n s e c u t i v e p a r a l l e l s t r i p s .  They  were s e p a r a t e d i n t o t h r e e equal groups of f o u r veneers, and l a t e r used as c o r e veneers f o r r e s i n - i m p r e g n a t i o n . Twenty-four r o t a r y - c u t veneers o f the same dimensions as the core veneers were o b t a i n e d from matched heartwood of the same l o g , and used as f a c e p l i e s .  The above mentioned  veneers were a p p l i e d t o Treatments 10, 11 and 12. Samples f o r Treatment  9 were made o f sawn veneers.  E i g h t sawn sapwood veneers were taken and marked t o i n d i c a t e t h e i r p o s i t i o n w i t h r e s p e c t t o the cambium. impregnated w i t h r e s i n .  They were then  Pour o f them were s e l e c t e d f o r use  19 as core veneers. in sections i i i  The reason f o r t h i s arrangement i s d e s c r i b e d and  i v . E i g h t non-impregnated  sawn veneers  of heartwood were used as f a c e p l i e s . Again, t h i s  assignment  allowed each treatment to have 12 veneers to be made Into k panels. ii.  Staining In order to render l a t h e checks e a s i l y observable,  the p e e l e d core veneers of Group A were submerged i n about 0.5%  by weight of C a l c o z i n e Rhodamin BPX  solution  (red) f o r  12 hours, then a i r - d r i e d f o r two weeks. Under m i c r o s c o p i c o b s e r v a t i o n , i t was  found t h a t the  dye p e n e t r a t e d to the t i p of the l a t h e checks, but d i d not d i s p e r e i n t o the wood surrounding the l a t h e checks. A prel i m i n a r y t e s t of t h i s study showed that the presence of the dye had no e f f e c t on r e s i n impregnation and g l u i n g . iii.  Dry ing A f t e r more than two weeks a i r - d r y i n g  i n the working  room of the l a b o r a t o r y , the moisture content of veneer  averaged  8.37$.  Veneers  of a l l treatments were l i g h t l y  sanded by hand  to secure smooth s u r f a c e s which were then cleaned by a s t r o n g vacuum c l e a n e r to remove f i n e wood p a r t i c l e s otherwise would h i n d e r adhesion. Veneers were p i l e d , by s t i c k s between every tow veneers, and about flat them.  that supported  50 pounds of  i r o n p l a t e s were p l a c e d on top of the p i l e to f l a t t e n  20 They were further dried in a small oven at l40°F for 6 hours. This temperature was used to minimize the degradation of wood strength which otherwise might result upon exposure to higher temperature. The consequent moisture content of veneer averaged  5«50%  which was believed to be suitable for  the resin impregnation process ( 6 l ) .  A high moisture content  might result in the moisture in the wood diffusing out of the veneer as the resin-forming material diffused in. stated ( 6 l ) , this tends to dilute the resin.  As Stamm  The volume of  the resin increased so that eventually some had to be discarded. The core veneers of Treatments 2, 3 and 4 in Group A, and of a l l treatments of Group B and Group C, were stored in a plastic bag and later dried with the core veneers soon after the latter were impregnated, iv.  Impregnation Two phenol-formaldehyde resins, No. 4000 and No. 4880,  obtained from Pacific Resins Ltd., New Westminster, B.C. were tested in a preliminary study to determine their feasibility for the purpose intended. Resin specifications were as follows: Resin No. Non-volatile fractions Viscosity (Centistokes) Specific gravity  4880  63.3% 600 1.202  Resin No. 4000 37.5% 15 1.135  21 Resin No. 4000 was found to be more easily impregnated into the wood but, perhaps due to its short chain length, the resin did not hold the lathe checks strongly.  Upon testing,  the tension shear strength of treated plywood was found to be not significantly different from that of conventional, untreated plywood. Use of this resin was therefore abandoned. Work was then concentrated on the use of resin No.  4880.  Since the solids content of this resin was  63.3$,  dilution was necessary. However, like most short chain phenolformaldehyde resins  (6l),  resin No.  in water at pH less than about 9.  4880  was not readily soluble  The resin was diluted by  distilled water to 40$ solids content. Three per cent of sodium hydroxide by weight was added to retain pE^O.5^ of Victoria blue dye by weight was added so that the cured resin could later be distinguished by stereomicroscope when within the lathe checks (lathe checks were indicated by red colour). The pH of the mixture, as indicated by a Beckman glass electrode pH meter, was 9»lt which proved adequate for the purpose of the experiment. The core veneers of Treatments 2, 3 and 4 of Gromp A, a l l treatments of Group B, and Treatment 12 of Group C, were immersed into the resin one sheet at a time. Each veneer, suitably weighted, was placed vertically in the container. The container was then placed in a pressure cylinder and 90 psi air pressure was applied. Treatments 2,3 and 4 of Group A were kept in the cylinder for 5» 10 and 30 minutes, respectively.  22 T h i s o p e r a t i o n was  expected t o r e s u l t i n v a r y i n g depths of  r e s i n p e n e t r a t i o n i n t o l a t h e checks.  Next, veneers were  removed from the c y l i n d e r a t the a p p r o p r i a t e times and d r i e d . Veneers of Group B and Treatment 12  of Group C remained i n the  c y l i n d e r and were impregnated f o r 20 hours.  The per cent r e s i n  content of the veneers was determined on the oiren-dry b a s i s by comparison with t h r e e e x t r a veneers which served as c o n t r o l s and which were checked v i s u a l l y by s t e r e o s c o p e a t 20 X magniR e s i n contents a f t e r 20 hours impregnation were  fication. to  31«5%  of oven-dry weight of wood.  These per cent r e s i n  contents were considered s u f f i c i e n t t o s a t u r a t e the c e l l (6l).  wall  M i c r o s c o p i c o b s e r v a t i o n supported t h i s . In  the  29.0%  o r d e r t o speed the time of impregnation and at  same time o b t a i n a r e a s o n a b l e amount of r e s i n i n the wood,  a b e t t e r s o l v e n t was  sought which could d i l u t e the r e s i n , a l l o w  i t s u n i f o r m d i s t r i b u t i o n i n wood substance, and d r y f a s t . Methanol was found t o be such a s o l v e n t . r e s i n , 0.5% The f i n a l  F o r c o l o u r i n g the  by weight of V i c t o r i a b l u e dye was a g a i n added.  s o l i d s content of the mixture was a g a i n made t o 40%.  Core veneers of Treatments 9» 10 and 11  were t r e a t e d .  Three  hours was found t o be long enough f o r impregnating sapwood veneers from the o u t e r part of the stem. n a t i o n was  Ease of r e s i n  impreg-  observed t o decrease w i t h an i n c r e a s e i n the  d i s t a n c e of wood substance from t h e cambium. # (Weight of impregnated veneer a f t e r d r y i n g s oven-dry h e i g h t of v e n e e r ) / oven-dry weight of veneer X 100  23 In o r d e r t o completely impregnate a l l the veneers, time of impregnation was prolonged t o 5 hours.  T h i s enabled  the veneer t o have a r e s i n content of 20-22$ of i t s oven-dry weight.  Again, t h i s was  confirmed by m i c r o s c o p i c o b s e r v a t i o n .  Together w i t h core veneers of the other treatments and a l l f a c e veneers, the impregnated veneers, with the e x c e p t i o n of Treatment  10, were p l a c e d i n the oven and d r i e d  at l40°F. f o r j6 hours. was  T h i s temperature and time f o r d r y i n g  chosen f i r s t l y because the b o i l i n g p o i n t of methanol i s o  °  148 F. ( 6 4 . 5 C.).  I f the d r y i n g temperature were h i g h e r than  l48°F. the b o i l i n g of the solvent would expel the r e s i n from the c e l l w a l l s .  Secondly, f i n a l s e t t i n g of the r e s i n  was  expected t o be done i n a hot p r e s s a t a temperature of 300°F. T h i r d l y , 36" hours d r y i n g a t t h i s temperature would not the s t r e n g t h of D o u g l a s - f i r wood ( 5 8 ) .  Two  parallel  were p l a c e d between the veneers as they were s t a c k e d .  degrade  sticks Several  heavy i r o n p l a t e s were p l a c e d on the top t o f l a t t e n the veneers. A f t e r d r y i n g , the moisture content of both nated and non-impregnated C.  Plywood  impreg-  veneers averaged 2.02$.  Panel C o n s t r u c t i o n  AMRES 2211 phenol-formaldehyde g l u e was used i n the major p a r t of the experiment f o r bonding p a n e l s .  The adhesive  was mixed and a p p l i e d a c c o r d i n g t o the manufacturerJs cation.  Except f o r core veneers of Treatment  specifi-  10, which were not  oven-dried, a l l the oven-dried impregnated veneers were l i g h t l y sanded a second time to p r o v i d e a smooth s u r f a c e , and cleaned by a strong vacuum c l e a n e r .  24  The g l u e was u n i f o r m l y spread on a l l veneers, w i t h the e x c e p t i o n of core veneers of Treatment  10, t o ensure a  spread of 50 pounds p e r thousand square f e e t p e r double g l u e line.  Veneers of a l t e r n a t i n g g r a i n d i r e c t i o n s were c a r e f u l l y  arranged, so t h a t f a c e p l i e s were e x a c t l y p e r p e n d i c u l a r t o t h e i r respective centre p l y . Use of methanol as s o l v e n t f o r r e s i n might  directly  enable assembling impregnated veneers i n t o plywood without t h e d r y i n g process p r i o r t o the a p p l i c a t i o n of heat and p r e s s u r e . An attempt was made t o determine the f e a s i b i l i t y of t h i s sis.  Impregnated  hypothe-  10 were exposed t o room  veneers of Treatment  temperature f o r 30 minutes b e f o r e a p p l i c a t i o n of the AMRES 2211 glue.  At the same time,the f a c e veneers were spread w i t h the  g l u e on t h e i r l o o s e - s i d e and a l l o w e d t o stand f o r 10 minutes. R e s u l t s of t h i s p r e l i m i n a r y experiment proved t h a t veneers could be s t r o n g l y g l u e d using a p r e s s i n g time t h e same as that of c o n v e n t i o n a l plywood, which i s normally 5 minutes. Treatment  6 was designed t o t e s t  shear s t r e n g t h  p a r a l l e l t o g r a i n i n plywood where the t i g h t - s i d e of f a c e veneer was arranged t o be i n contact w i t h the core veneer. The assembled veneers were p r e s s e d a t Temperature  150 p s i and 300°P.  a t the g l u e - l i n e was measured by a p o r t a b l e  potentiometer and time r e c o r d e d when constant temperature was reached. plywood  I t was found that : m i n u t e s  was s u f f i c i e n t f o r  of c o r e - d r i e d veneer, and f i v e and one-half minutes  f o r cores of Treatment  10, where the sudden b o i l i n g  i n the c e n t r e p l y was c l e a r l y  visible.  of methanol  25 Immediately upon l e a v i n g the hot press the  panels  were stacked i n a t h e r m o s t a t i c a l l y c o n t r o l l e d oven (212°P.) f o r one hour, then p l a c e d i n another hours.  oven a t l40°F. f o r 24  The purpose of t h i s "hot stack" was  t o c o o l the plywood  g r a d u a l l y and to a l l o w complete c u r i n g of g l u e - l i n e s .  The  panels were then kept i n the l a b o r a t o r y f o r two weeks b e f o r e sampling. D.  P r e p a r a t i o n and T e s t of Specimens i.  Sample s i z e S i n c e t e s t s of t e n s i o n shear were conducted  T a b l e Model I n s t r o n T e s t e r , i t was  necessary t o c o n s i d e r the  maximum l o a d i n g c a p a c i t y of the machine (50 sample s i z e .  was  trimmed t o 0.5  inch.  s i z e s of samples  notches- depending  F o r Groups A and B, l e n g t h was  f o r Group C about 0.5  about one  inch on  i n c h , and  I f specimens of Group C were not  i n c h i n l e n g t h (between two  the core f o r samples of Treatments 9 and  notches), f a i l u r e i n  12 was  o b t a i n because of the r e s i n - s t r e n g t h e n e d core ii.  i n determining  A width of about 0.2  chosen, w i t h the l e n g t h between two  treatments.  Kg)  I n a p r e l i m i n a r y study, d i f f e r e n t  were t e s t e d t o f i n d a s u i t a b l e one.  on a  i m p o s s i b l e to veneer.  Trimming of samples and measurements Four panels of each treatment  of s i z e s d e s c r i b e d above.  were cut i n t o sample  The depth of notch was  two-thirds  of the core veneer t h i c k n e s s w i t h the arrangement of l a t h e checks t o be p u l l e d open (5,  22), as shown i n F i g . 2.  This i s  26 b e l i e v e d t o be the most s e n s i t i v e method to t e s t r o l l i n g of plywood.  Twenty-four samples were randomly  chosen.  shear Half  were used f o r t e s t when specimens were dry and the o t h e r h a l f for test after boiling.  The procedure f o r p r e p a r a t i o n of the  l a t t e r was a c c o r d i n g t o the CSA  standard 0121-1961 (10).  "Shear specimens . . . s h a l l be b o i l e d i n water f o r 4 hours, then d r i e d f o r 20 hours a t a temperature of 145 ± 5°F. They s h a l l be b o i l e d a g a i n f o r a p e r i o d of 4 hours and t e s t e d w h i l e wet." iii.  Measurements of l a t h e checks, adhesive p e n e t r a t i o n depth and angle of l a t h e checks The end s e c t i o n s of each sample were l i g h t l y  sanded u s i n g a b e l t sander.  T h i s enabled the s t a i n e d p a r t of  wood to be observed and p r o v i d e d h i g h e r accuracy i n measurement of dimensions. The l i n e a r dimensions of samples were taken to an accuracy of 0.001  i n c h u s i n g a micrometer  caliper.  A stereomicroscope (5 X m a g n i f i c a t i o n ) was  used to  measure veneer t h i c k n e s s e s , depth of l a t h e checks, depth of glue p e n e t r a t i o n  (Treatment 1) and r e s i n p e n e t r a t i o n  2, 3 and 4) and t o estimate per cent wood f a i l u r e .  (Treatments The depth  of l a t h e checks and of the p e n e t r a t i o n s were measured perpend i c u l a r l y from the deepest p o i n t of l a t h e check and t h a t of the p e n e t r a t i o n s t o the g l u e - l i n e  (48).  As mentioned  above,  l a t h e checks had been s t a i n e d by C a l c o z i n e Rhodamine BPX r e s i n was black  (red),  c o l o u r e d by V i c t o r i a b l u e and the c o l o u r of g l u e was  (Fig. 13).  T h e r e f o r e , depth of checks and t h a t of the  p e n e t r a t i o n s were e a s i l y  identified.  27 I n Group A, depth of each l a t h e check between the notches was "read" t o g i v e average depth.  Veneer t h i c k n e s s  was o b t a i n e d by a v e r a g i n g t h r e e r e a d i n g s of core veneer t h i c k n e s s i n each sample.  I n o r d e r t o r e l a t e t h e depth t o veneer t h i c k n e s s ,  the average depth of l a t h e check was d i v i d e d by vener t h i c k n e s s t o g i v e a p e r cent depth of l a t h e check.  The depth of adhesive  p e n e t r a t i o n was d i v i d e d by t h e depth of l a t h e check t o g i v e per cent depth of adhesive p e n e t r a t i o n (Table V ) . I n c l i n a t i o n of l a t h e check was o b t a i n e d by measuring with a t r a n s p a r e n t p r o t r a c t o r t h e angle of the t h r e e longest l a t h e checks t o the g l u e - l i n e .  The recorded v a l u e s were averaged  to represent the l a t h e check i n c l i n a t i o n of the sample and a r e shown i n T a b l e V. iv.  Testing A l l t e s t s were performed w i t h the same T a b l e Model  Instron T e s t i n g instrument.  F o r a c c u r a c y , the t e s t  pieces  were c a r e f u l l y a l i g n e d p a r a l l e l t o t h e a x i s of l o a d i n g .  The  g r i p s h o l d i n g the sample were u n i f o r m l y t i g h t e n e d by means of a torgue-wrench s e t f o r 60 foot-pounds f o r d r y samples and 35 foot-pounds f o r wet samples, which prevented t h e crushing of specimens b e f o r e and d u r i n g  testing.  Load was a p p l i e d w i t h a continuous motion of the moveable crosshead a t a r a t e of 0.02  i n c h p e r minute.  Load  was r e c o r d e d a u t o m a t i c a l l y throughout the t e s t on a c h a r t . The u l t i m a t e l o a d , l o a d t o u n i t s t r a i n w i t h i n t h e p r o p o r t i o n a l l i m i t , and u l t i m a t e s t r a i n a r e a v a i l a b l e from t h i s r e c o r d ( F i g . 4).  28 v.  E s t i m a t i o n o f wood f a i l u r e and p o s i t i o n of f a i l u r e The p e r cent wood f a i l u r e o f broken specimens was  e v a l u a t e d by two methods:  (1) the c o n v e n t i o n a l way, which i s  d e f i n e d as being an estimate o f the amount o f wood f i b r e adhering t o the s u r f a c e s o f a f r a c t u r e d g l u e j o i n t , as a percentage  expressed  o f the t o t a l j o i n t a r e a , and (2) i n measuring  the p o s i t i o n w i t h i n an annual  increment,  i n relation  to i t s  i n i t i a t i o n , a t which f a i l u r e o c c u r r e d , recorded as a p e r cent of the width.  Amount o f wood f a i l u r e i n t h i s p o s i t i o n was a l s o  estimated and expressed as a percentage  of t h e t o t a l j o i n t  The e s t i m a t i o n was done under a stereomicroscope  area.  a t a magnification  of 20 X. E.  Photographic  Technique  In o r d e r t o take photographs of the development of f a i l u r e i n plywood d u r i n g l o a d i n g , a SAS A s a h i Pentax camera was  p l a c e d i n f r o n t of the l o a d i n g s i d e o f the I n s t r o n machine.  An e x t e n s i b l e bellows u n i t was a t t a c h e d t o the camera t o magnify the o b j e c t , w i t h the l e n s focused on the c r i t i c a l shear area o f the sample  ( P i g . 4 ) . F o r the purpose of o b s e r v i n g the whole  c r i t i c a l area, the d i s t a n c e between the two notches to about 0.4 i n c h .  was shortened  When t h e sample was p l a c e d i n the machine  and b e f o r e a p p l i c a t i o n o f l o a d , the f i r s t photograph was taken for reference.  As soon as the machine s t a r t e d , the e f f e c t of  t e n s i o n s t r e s s and s t r a i n on the sample was observed the viewer.  When a s l i g h t change was observed,  through  t h e pen of the  r e c o r d i n g c h a r t and the movement o f l o a d i n g arms were  stopped.  T h i s avoided t h e v i b r a t i o n o f the machine i n f l u e n c i n g the camera. The photograph was then taken and a number was marked  29  on the stress-strain curve as a reference point of the photograph being taken (Fig. 5 to 1 2 ) . A sequence of photographs was taken until the sample failed. A preliminary study was done to observe the effect of stopping the machine during test, since such action permitted stress relaxation and a possible alteration in the ultimate point of failure.  The study showed that the stress-strain  curves and shear strengths obtained in tests during which the machine was stopped for about 5 seconds were similar to results obtained in an uninterrupted test, hence the effect of these interruptions was ignored in this study. RESULTS A.  Shear Strength The shear strengths of various groups and treatments  were found to be significantly different (Tables I, II).  Since  the results of Group C gave data that varied greatly between treatments, a direct comparison of the strength of groups is not  considered reasonable.  Instead, the strength of specimens  made of lathe -check-free sawn veneer from each group (i.e., Treatment 5 from Group A, Treatment 8 from Group B and Treatment 9 from Group C) were compared (Tables III, IV). The analyses of variance showed that the average strength of Treatment 5. Group A was significantly lower than that of Treatments 8 and 9 from the two other groups, whereas that of Treatment 9, Group C was not significantly different from Treatment 8, Group B, in the dry condition.  30  The v a r i a t i o n s between treatments of each group a r e as f o l l o w s : i.  Group A The d i f f e r e n c e s of depth of r e s i n p e n e t r a t i o n  l a t h e checks i n Treatments 1 - 4  into  and d i f f e r e n c e s of shear s t r e n g t h  i n a l l treatments were found t o be h i g h l y s i g n i f i c a n t  (Tables VI,  VII and V I I I ) . As shown i n T a b l e V, average depths of adhesive penet r a t i o n i n t o l a t h e checks were 16, 47, 88 and 97$ f o r Treatments 1, 2, 3 and 4 r e s p e c t i v e l y .  Average shear s t r e n g t h s were  252,  280, 343, 356 and 343 p s i f o r Treatments 1, 2, 3, k and 5 respectively. Regardless of the f a c t that the l a t h e checks of Treatment  1 were p e n e t r a t e d by g l u e only and those of Treatments  2, 3 and 4 were p e n e t r a t e d by r e s i n , a mathematical r e l a t i o n s h i p between p e n e t r a t i o n depth and shear s t r e n g t h of specimens computed.  T h i s was done because i t i s b e l i e v e d t h a t  was  since  e i t h e r the g l u e or the r e s i n can h o l d l a t h e checks s t r o n g l y during the  l o a d , t h e i r r e l a t i o n s h i p t o the s t r e n g t h of specimen i s  same.  T h i s r e l a t i o n s h i p was found t o be h i g h l y c o r r e l a t e d  as shown by the l i n e a r e q u a t i o n f o r t h e d r y c o n d i t i o n ( F i g . 5 ) . Y = 228.22 + 1.28052 X  ( S E = 21.82; r a 0.893) E  where Y = shear s t r e n g t h and X = p e n e t r a t i o n depth as per cent of depth of l a t h e check.  31 The wet  average  strength values  specimens f o l l o w e d the were 133,  they  175,  T r e a t m e n t s 1, ii.  Group  2,  the  3,  same p a t t e r n a s  226  4 and  5  (Table  shear  strength p a r a l l e l  core  the average  shear  557,  506  p s i i n dry  boil  test,  544  and  respectively.  t h e r e were no either test  significant ( Table  For dry  g r o u p was  possibility  plywood,  test,  The  370,  and  Analyses  for  the  X  T r e a t m e n t s 3,  results  347  a  indicated  7 and 382  and  8 were p s i i n the  treatments  strengths of t h i s  those  f o r Treatments 1 and 4 and  of developing  ).  shear  higher than  to  o f v a r i a n c e showed t h a t  o f any  Average s t r e n g t h s o f Group B a r e about those  designed  d i f f e r e n c e s between the  IX and  tests,  were s i g n i f i c a n t l y  2,  two and  group  treatment to three  1.5  o f Group  times  times  as  as  high  as  5.  Group C T h i s Group d i f f e r e d  two  specimens;  VIII).  s t r e n g t h s o f T r e a t m e n t s 6,  that  iii.  of dry  of  to the g r a i n i n u n t r e a t e d  f o r e v a l u a t i n g the  strong resin-impregnated  h i g h as  those  psi, respectively,  previously stated, this  f a c e p l i e s and  in  229  and  from t e s t s  B As  test  236,  obtained  different  core veneer Also,  the  f r o m Group A a n d  s o l v e n t s were u s e d t o  i n order to obtain a  s a m p l e s were d e s i g n e d  Group B  impregnate r e s i n  strong resin-wood to f a i l  i n the core  i n that  into  the  complex. veneer.  A.  32 The average shear s t r e n g t h s of the specimens of Treatments  9, 10, 11 and 12 were 589,156,376  respectively, i n dry test.  530  psi,  The a n a l y s e s of v a r i a n c e showed  t h a t there were h i g h l y s i g n i f i c a n t ments (Table X I ) .  and  d i f f e r e n c e s between t r e a t -  Treatment 9 was s i g n i f i c a n t l y h i g h e r than  Treatments 10 and 11 a t the 1% l e v e l , and Treatment  12 a t the  5% l e v e l . Average wet s t r e n g t h s of Treatments 9,  12  were  291>125,187  and  267 p s i , r e s p e c t i v e l y .  and 12 were not s i g n i f i c a n t l y d i f f e r e n t Treatments 10 and 11 a t the 1% l e v e l . t h a n Treatment B.  10,  11 and  Treatments  9  but were h i g h e r than Treatment  11 was h i g h e r  10 a t the 5% l e v e l (Table X I I ) .  Per Cent Wood F a i l u r e i.  Group A Average p e r cent wood f a i l u r e s  v e n t i o n a l method d i d not show s i g n i f i c a n t They were 94, t o 5*  96,  89,  94 and 96%,  estimated by t h e cond i f f e r e n c e s (Table X I I I ) .  r e s p e c t i v e l y , f o r Treatments 1  P o s i t i o n s of f a i l u r e w i t h i n an annual increment were  found t o be 7»  5.  6" and 7% f o r Treatments 2 t o 5 r e s p e c t i v e l y .  T h e i r d i f f e r e n c e s were not s i g n i f i c a n t  (Table X I V ) .  The average p e r cent wood f a i l u r e s these p o s i t i o n s were 63, respectively.  75.  occurring i n  80 and 95% f o r Treatments 2 t o 5»  The a n a l y s i s of v a r i a n c e showed t h a t Treatment 5  (sawn veneer plywood) was s i g n i f i c a n t l y h i g h e r i n p e r cent wood f a i l u r e a t t h e 1% l e v e l than Treatment 2, and the  5% l e v e l , but not s i g n i f i c a n t l y d i f f e r e n t  (Table XV).  Treatment 3 a t from Treatment 4  33 ii.  Group B The p o s i t i o n of f a i l u r e w i t h i n an annual  was  increment  found to be i n c o n s i s t e n t from sample t o sample.  Average  p e r cent wood f a i l u r e s estimated by the c o n v e n t i o n a l method were 84, 79 and 80$ f o r Treatments  6, 7 and 8,  respectively.  T h e i r d i f f e r e n c e s were not s i g n i f i c a n t : (Table X V I ) . iii.  Group C The per cent wood f a i l u r e i n t h i s group was  to be s i g n i f i c a n t l y d i f f e r e n t between t r e a t m e n t s . of  magnitude of the data were 97»  10, 11, 12 and 9, r e s p e c t i v e l y C.  95. 76 and  found  The  order  62$ f o r Treatments  (Table X V I I ) .  Photographic Evidence Photographs  of plywood samples made of sawn veneers,  r o t a r y - c u t veneers w i t h l a t h e checks f u l l y p e n e t r a t e d by  resin,  andTiwAmpregnated r o t a r y - c u t veneers were s a t i s f a c t o r y .  The  s e t t i n g of camera and t e s t i n g apparatus are shown i n F i g . 4. The  s t r e s s - s t r a i n curves and the p o i n t s a t which  the.photographs  were taken are shown i n F i g . 6, 7, 8, 10, 11 and 12. photographs Fig.  of a l l t e s t  The  specimens a f t e r f a i l u r e a r e shown i n  13. DISCUSSION The study of Group A was  designed t o compare the  shear s t r e n g t h of r o t a r y - c u t veneer specimens h a v i n g l a t h e checks i n core veneer p a r t i a l l y or f u l l y p e n e t r a t e d by adhesive,  34 w i t h t h e specimens made of sawn veneer.  Consequently,  tensile  shear s t r e n g t h s of Group A specimens depend mainly on the shear r e s i s t a n c e p e r p e n d i c u l a r t o the g r a i n of wood.  Group B was  designed t o e v a l u a t e shear r e s i s t a n c e of specimens with the core veneer f u l l y impregnated by r e s i n and where f a i l u r e was f o r c e d t o occur i n a f a c e p l y .  T h e r e f o r e , t h e s t r e n g t h s of  specimens i n Group B depends on shear r e s i s t a n c e p a r a l l e l t o the g r a i n of wood.  On the o t h e r hand, Group C was designed  f o r e v a l u a t i o n of shear s t r e n g t h of specimens having r e s i n impregnated  core veneer,  with f a i l u r e f o r c e d t o occur i n the  core, so t h a t s t r e n g t h s of t h i s , group depend*!solely on the comb i n a t i o n of r e s i n and wood. Hence, the order of magnitude of shear s t r e n g t h as shown by T a b l e I I I i s considered r e a s o n a b l e .  From t h i s , i t  i s c l e a r t h a t t h e h y p o t h e s i s of t h i s t h e s i s i s sound.  That  i s , plywood made of r e s i n impregnated core veneer and u n t r e a t e d f a c e veneers  can be a product having  shear s t r e n g t h s about  1.5  times as h i g h as t h a t of sawn-veneer plywood, and two t o t h r e e times as h i g h as t h a t of c o n v e n t i o n a l plywood made of r o t a r y - c u t veneer. F u r t h e r d i s c u s s i o n of v a r i a t i o n s w i t h i n groups i s i n c l u d e d below. A.  I n f l u e n c e of Lathe  checks on Shear S t r e n g t h  The assumption which leads t o t h e t h e o r e t i c a l a n a l y s i s of f a i l u r e i n l a p j o i n t s was g i v e n by V o l k e r s e n i n 1938  (18).  A c c o r d i n g t o him, the d i s t r i b u t i o n of shear s t r e s s e s i n t h e  35 adhesive l a y e r a r i s e s s o l e l y from d i f f e r e n t i a l s t r a i n i n g i n the l a p j o i n t . Reissner  T h i s h y p o t h e s i s was  in 1 9 ^  (24).  by Goland  and  They s t a t e d t h a t t e a r i n g s t r e s s e s ,  which were ignored by Volkersen, Baud (72)  modified  should be taken i n t o account.  employed an i s o t r o p i c model of plywood t e s t specimen  which t r a c e d the s t r e s s d i s t r i b u t i o n by p h o t o e l a s t i c means. Thereby, he confirmed t h a t t e a r i n g or t e n s i l e s t r e s s e s e x i s t normal to the plane of the glue notch.  In t h i s r e g i o n ,  o f the glue  joint.  j o i n t i n the v i c i n i t y of  shear components occur i n the  plane  However, the main p o r t i o n of the t e s t  section i s subjected  o n l y to t e n s i l e and  Consequently, the plane of the g l u e stress.  the  compressive s t r e s s e s .  j o i n t i s f r e e of shear  S i m i l a r r e s u l t s were r e p o r t e d by  I s h i h a r a and  co-  (33),  workers  F u r t h e r a p p l i c a t i o n of a s t r a i n - i n d i c a t i n g b r i t t l e l a c q u e r t o wood and wood-glue combinations were i n v e s t i g a t e d by Yavorsky and  Cunningham (71)•  They found t h a t a l a r g e  component of shear e x i s t e d i n the plane of the core veneer of t h r e e - p l y specimens. the notches was  1  The  presence of s t r e s s c o n c e n t r a t i o n s  demonstrated by the formation  of i n i t i a l  i n these areas a t low l o a d s , whereas the c e n t r a l r e g i o n f r e e of cracks Any  u n t i l considerable  imperfection  at  cracks was  l o a d had been a p p l i e d .  i n veneers w i l l t h e r e f o r e cause a  r e d u c t i o n of t e n s i l e shear r e s i s t a n c e i n plywood.  T h i s can  be  seen from the photograph of sawn veneer plywood i n t h i s experiment.'  3 6  In  Pig.' 6 , photograph  upper notch.' the  2, the f i r s t c r a c k o c c u r r e d i n the  The s t r e s s - s t r a i n curve ( F i g . 6 ) i n d i c a t e d t h a t  sample was s t r e s s e d j u s t over the p r o p o r t i o n a l l i m i t a t  that point.  Instead o f the c r a c k opening, a d e f e c t between the  notches was p u l l e d open by continuous l o a d i n g  (photograph 3 ) .  Soon a f t e r , ' the u l t i m a t e s t r e n g t h was reached and the sample f a i l e d suddenly i n the zone l o c a t e d w i t h i n 10% from the i n i t i a t i o n o f an annual increment.  L a t e r , the d e f e c t noted  above was observed under stereomicroscope, on the end s u r f a c e , and i d e n t i f i e d as r a y t i s s u e .  I t i s known t h a t r a y i s the weakest  t i s s u e of wood when l o a d i s a p p l i e d i n  the! direction  p e r p e n d i c u l a r t o g r a i n i n the r a d i a l face  ( 6 8 ) .  The d e f e c t might  be due t o the s e p a r a t i o n between r a y s and prosenchyma i n d r y i n g , where latewood prosenchyma o f h i g h p o t e n t i a l shrinkage i s i n c o n t a c t w i t h r a y s o f r e l a t i v e l y s m a l l r a d i a l shrinkage p o t e n t i a l (28.56).  The occurrence o f wood f a i l u r e i n earlywood was found in  shear ( 4 3 ) , t r a n s v e r s e compression  tests.  ( 7 ) and bending ( 3 6 )  But t h i s i s the f i r s t r e p o r t o f shear f a i l u r e  occurring  w i t h i n an annual increment i n the zone l o c a t e d w i t h i n 1 0 % o f its  initiation.  T h i s was r e p o r t e d as t h a t r e g i o n having maximum  l i g n i n content i n an annual increment of D o u g l a s ^ f i r ( 7 0 ) . R e s u l t s f o r the plywood made f r o m ^ r o t a r y - c u t veneer (Fig.  7 and F i g . 8 ) were completely d i f f e r e n t from those of sawn  veneer plywood ( F i g . 6 ) . the  The f i n e b l a c k d e c l i n e d l i n e s i n  core veneers o f these f i g u r e s a r e the r e d l a t h e checks i n  samples  7 to 9 of F i g . 1 3 . '  Photographs  2 o f F i g . 7 and F i g . 8  37 showed no cracks  i n t h e f a c e veneers i n v i c i n i t y o f the notches,  but the l a t h e checks had opened s l i g h t l y . the f i n a l rupture  s t r e s s was reached.  When t h i s  occurred,  Photograph 3 showed  t h a t the r e a l wood f a i l u r e s t a r t e d a t t h a t p o i n t .  A l l this  evidence i n d i c a t e s that l a t h e checks d e f i n i t e l y reduce shear s t r e n g t h o f plywood. A comparison between the s t r e s s - s t r a i n curves o f plywood from sawn and r o t a r y - c u t veneers ( P i g . 9)» showed t h a t the former f a i l e d a b r u p t l y  soon a f t e r maximum s t r e s s was reached  whereas t h e l a t t e r had a l o n g e l o n g a t i o n  i n the specimen.  This  might be caused by the opening of l a t h e checks which d i v i d e d the c r i t i c a l area and r e s u l t e d i n the formation of s t r e s s i n t h i s a r e a The was  extent  (1).  t o which l a t h e checks i n f l u e n c e  demonstrated by the r e s u l t s o f Group A.  variance  failure  A n a l y s e s of  showed t h a t d i f f e r e n c e s i n shear s t r e n g t h between  treatments o f Group A were h i g h l y s i g n i f i c a n t and  o f s e v e r a l flows  VIII).  Treatment 1  (conventional  (Tables V, V I I  plywood) gave s i g n i f i c a n t l y  lower r e s u l t s than d i d any other treatment; whereas d i f f e r e n c e s between Treatments 3 , 4 and 5 were not s i g n i f i c a n t , they were s i g n i f i c a n t l y higher  than Treatment 2 (Table V I I ) .  c o u l d be e x p l a i n e d as being  due t o the v a r y i n g  This  penetration  depths o f adhesive i n t o l a t h e checks i n the core veneers. was  observed t h a t the p e n e t r a t i o n depth o f glue  checks o f c o n v e n t i o n a l and  It  into lathe  plywood (Treatment 1) was 16% (Tables V  VI) o f the average depth o f l a t h e checks.  This indicated  38 t h a t the l o a d a r e a was decreased by about 45$ of the area was s u b j e c t e d t o f u l l  55$* so t h a t o t h e r  load.  The p e n e t r a t i o n of adhesive i n t o l a t h e checks of D o u g l a s - f i r heartwood was d i f f i c u l t .  Even when u s i n g a s h o r t  c h a i n r e s i n , and impregnating under 90 p s i a i r p r e s s u r e f o r 5 minutes, as i n Treatment  2, the p e n e t r a t i o n depth of r e s i n  was l e s s than h a l f the l a t h e check depth.  This i s explained i n  the f o l l o w i n g way: ( i ) Nature of veneer. The curved nature of l a t h e checks, and the shear type of l a t h e checks  ( P i g . 1) which were concealed  deep i n the veneer and t h e r e f o r e n o n - a c c e s s i b l e t o adhesive, should be c o n s i d e r e d . ( i i ) E f f e c t of pH of wood. The pH of mixed phenol-formaldehyde  i s about  commercial  12, but t h a t of D o u g l a s - f i r  heartwood i s only 3 t o 4.5. I t was found  (13) t h a t the pH of  both f i l m and l i q u i d p h e n o l i c r e s i n decreased w i t h i n c r e a s i n g assembly  time.  High veneer moisture contents accentuated the  decrease. A c c o r d i n g t o stamm ( 6 l ) , t h e decrease of pH causes reduced s o l u b i l i t y and glue t r a n s f e r . I t i s understandable  that,  s i n c e pH of D o u g l a s - f i r i s so low, when the glue i s spread i t s pH w i l l r a p i d l y decrease.  T h i s i s p r o v i d e d t h a t the rough  s u r f a c e s a t the entrances of l a t h e checks may absorb some amount of glue (6) and the e x c e s s i v e depth of l a t h e checks can a l t e r the p r o p o r t i o n between the amount of glue and the s u r f a c e area of l a t h e checks.  Consequently,  * , % depth of l a t h e c h e c k s  ( 1 Q 0  _ £  d  the b u f f e r i n g  e  p  t  h  o  f  £  d  h  e  s  l  v  e  penetration  39 p o t e n t i a l of wood i s s u f f i c i e n t l y g r e a t to overpower the of glue  (44).  The  further penetration (iii)  pH.  v i s c o s i t y of glue g r e a t l y i n c r e a s e s and  no  occurs.  I n f l u e n c e of e x t r a c t i v e s .  The  e f f e c t of e x t r a c t i v e s  on glue bonds has been e x p l a i n e d by Huffman (32), who  stated:  "The e x t r a c t i v e s may a c t as d e t e r r e n t s t o adequate p e n e t r a t i o n of the f l u i d adhesive, they may r e t a r d the d i s s i p a t i o n of water or o t h e r s o l v e n t s from the glue l i n e , and t h e i r chemical composition may a c t as a b a r r i e r to proper w e t t i n g or t o the f o r m a t i o n of molecular bonds", " k i l n d r y i n g r e s u l t e d i n c o n c e n t r a t i n g the e x t r a c t i v e s i n the outer l a y e r s " . Hancock (29)  found that i n the case of D o u g l a s - f i r veneer  t r e a t e d a t h i g h temperature, f a t t y a c i d s c o n c e n t r a t e d s u r f a c e , r e d u c i n g the w e t t a b i l i t y of veneer.  This  at  the  chemical  b a r r i e r w i l l no doubt slow the p e n e t r a t i o n r a t e and  depth  of g l u e . These i n f l u e n c e s , and  the e f f e c t of high temperature  of the hot p r e s s , a c c e l e r a t e d the l o s s of water and of g l u e .  The  polymerization  p o s s i b i l i t y of glue f u r t h e r p e n e t r a t i n g i n t o l a t h e  checks i s thus g r e a t l y reduced. As mentioned above, there i s a h i g h l y  significant  l i n e a r r e l a t i o n s h i p between the depth of adhesive i n t o the l a t h e checks (X) and the shear s t r e n g t h  penetration (Y), such t h a t :  Y * 228.22 + 1.28052 X. The depth of r e s i n p e n e t r a t i o n and  shear s t r e n g t h i n Treatment  2 were s i g n i f i c a n t l y h i g h e r than those of Treatment 1.  Similarly  f o r Treatments 3 and 4, which had s i m i l a r s t r e n g t h s , the depth was  about two  times h i g h e r than Treatment 2, and  times h i g h e r than t h a t of Treatment 1.  f i v e to s i x  I t i s i n t e r e s t i n g to  1+0 note t h a t shear s t r e n g t h of Treatments 3 and significantly different  (Tables VII and V I I I ) ; but  p e n e t r a t i o n depth of the l a t t e r was t h a t of the former (Table V I ) . follows:  4 were not  s i g n i f i c a n t l y higher  T h i s c o u l d be  When the p e n e t r a t i o n  the  depth was  than  i n t e r p r e t e d as  beyond 80$  the  shear  s t r e n g t h of plywood made of r o t a r y - c u t veneer remained unchanged and no d i f f e r e n t from t h a t of plywood made of sawn veneers (Tables V I I and The  VIII).  r e l a t i o n s h i p between p e n e t r a t i o n depth and  s t r e n g t h can a l s o be observed from the photographic F i g u r e 10  3 of the same F i g u r e have been due  i t may  be  i n the face p l y .  to the r e s i n s t r e n g t h e n i n g  causing misalignment of sample (2), F i g u r e 11  demonstrated t h a t when a crack occurred  over the p r o p o r t i o n a l l i m i t .  ply,  sample  or by d e f e c t i n the  v i c i n i t y of the notches (photograph 3)t  face i n the  the specimen was  already  When the shear l a t h e check*  s l i g h t l y opened, the maximum s t r e s s was  reached.  The  then f a i l e d suddenly i n the c r i t i c a l a r e a through the and  failure  the c e n t e r the  by  From photograph  i m p l i e d that the f a c e  by the s l i g h t angle between the l o a d a x i s and  ply."  results.  shows t h a t the l a t h e checks were completely h e l d  r e s i n , so t h a t f a i l u r e o c c u r r e d  may  shear  was  sample earlywood  the broken shear l a t h e check. F i g u r e 12  shows the response of sample to the  when the l a t h e checks and by r e s i n .  other d e f e c t s were completely  A small c r a c k was  load held  shown near to the upper n o t c h i n  * Shown by r e d c o l o r i n NO. 5 sample of F i g . 13, i t s p o s i t i o n i n photograph A, NO. 5 Is" i n d i c a t e d by an arrow, w h i l e i n photograph B, the red c o l o r i s v i s i b l e .  41 the f a c e p l y ( F i g . 1 2 , photograph 2) a t which stage the specimen was  s t r e s s e d over the p r o p o r t i o n a l l i m i t .  Complete  o c c u r r e d a t the i n i t i a t i o n o f one annual increment. was  failure The r e s i n  so s t r o n g t h a t the course o f b r e a k i n g had passed o r d e v i a t e d  around the t i p of g l u e .  As a r e s u l t the s t r e s s - s t r a i n curves  of plywood made from sawn veneers, and r o t a r y - c u t veneers w i t h l a t h e checks f u l l y B.  impregnated by r e s i n , were s i m i l a r .  I n f l u e n c e of Lathe Checks on Wood F a i l u r e D i f f e r e n c e s i n average per cent wood f a i l u r e i n  v a r i o u s treatments o f Group A as estimated by the c o n v e n t i o n a l method were not s i g n i f i c a n t  (Table X I I I ) .  However, the c h a r a c t e r  and p o s i t i o n o f t h e f a i l u r e i n Treatment 1 ( c o n v e n t i o n a l  plywood  made o f r o t a r y - c u t veneer) v a r i e d g r e a t l y from t h a t o f Treatments 3, 4 and 5 (plywood made o f veneer w i t h l a t h e checks completely impregnated by r e s i n and plywood made o f sawn v e n e e r ) .  In  Treatment 1, the wood broke between the t i p s o f t h e l a t h e checks i n core veneer.  The wood g r a d u a l l y r o l l e d open a f t e r the  u l t i m a t e s t r e n g t h was reached.  But i n Treatments 3, 4 and 5*  f a i l u r e o c c u r r e d suddenly i n t h e b e g i n n i n g of earlywood. From t h i s i t can be seen t h a t the p e r cent wood f a i l u r e of plywood made of r o t a r y - c u t veneer was not i n t i m a t e l y r e l a t e d t o the u l t i m a t e s t r e n g t h .  Instead,  the p e r cent wood f a i l u r e o c c u r r i n g w i t h i n one or more annual increments i n the zone l o c a t e d w i t h i n 1 0 % from i t s i n i t i a t i o n gave a b e t t e r i n d i c a t i o n o f u l t i m a t e  strength.  T h i s p o s i t i o n i n the annual r i n g was found t o have the lowest t e n s i l e strength Douglas^fir.  (69) and compression s t r e n g t h  (31) i n  A n a l y s i s of v a r i a n c e showed t h a t average p e r  42 cent wood f a i l u r e of sawn veneer plywood r e g i o n was 3,  (Treatment 5)  i n this  s i g n i f i c a n t l y h i g h e r than i n Treatment 2 and  Treatment  but not s i g n i f i c a n t l y d i f f e r e n t from Treatment 4 (Table XV).  This r e s u l t c l e a r l y  i n d i c a t e d t h a t wood w i t h no l a t h e  checks  and wood w i t h l a t h e checks h i g h l y impregnated by r e s i n r e s u l t e d i n h i g h e r per cent wood f a i l u r e . C.  I n f l u e n c e o f R o t a r y - c u t t i n g on Shear S t r e n g t h and Wood  F a i l u r e i n T i g h t - s i d e and L o o s e - s i d e of Veneer A s t a t i s t i c a l a n a l y s i s of r e s u l t s showed t h a t t h e r e were no s i g n i f i c a n t d i f f e r e n c e s e i t h e r i n shear s t r e n g t h o r wood f a i l u r e among a l l  treatments of Group B.  i n d i c a t e d t h a t a t the normal i s not s t r e s s e d beyond  This f i n d i n g  i n d u s t r i a l l a t h e s e t t i n g s , veneer  the p r o p o r t i o n a l l i m i t .  However, the  p o s i t i o n of wood f a i l u r e w i t h i n the annual r i n g was no l o n g e r i n the b e g i n n i n g of earlywood, which was v a r i e d from to  specimen  specimen. The shear s t r e n g t h of Group B samples averaged over  500  p s i i n dry t e s t  (Table 1).  data from v a r i o u s sources (63),  and S t i e d a  T h i s i s much lower than  (9,67),  A c c o r d i n g t o Stamm and  (64), shear v a l u e s are h i g h l y dependent  the method o f t e s t i n g .  comparable Seborg upon  Data, t h e r e f o r e , a r e not  comparable  u n l e s s the method used and s i z e of specimens a r e  identical.  R e s u l t s of t h i s experiment i n d i c a t e a new t h a t even i f the specimens do not f a i l  finding:  i n core veneer, t e n s i o n  shear s t r e n g t h of plywood made from r e s i n impregnated core veneer and non-impregnated  f a c e veneers, w i l l be two to t h r e e  43 times as h i g h as t h a t o f "conventional plywood made o f comparable rotary-cut D.  veneers.  I n f l u e n c e o f R e s i n Impregnation on Shear Strength and Per  Cent F a i l u r e o f Core Veneer Two t h i n g s have now become c l e a r .  First,  the a r e a o f  wood w i t h i n an annual r i n g l e a s t a b l e t o r e s i s t s t r e s s e s i s i n t h e zone l o c a t e d w i t h i n 10% from i t s i n i t i a t i o n .  Second,  the shear s t r e n g t h o f latewood of D o u g l a s - f i r i s g r e a t e r than, or a t l e a s t equal t o , t h a t o f phenol-formaldehyde g l u e - l i n e . T h e r e f o r e , as shown by t h i s experiment, there i s no doubt t h a t the a p p l i c a t i o n of r e s i n t o strengthen earlywood, as i n Treatments 9 and 12, w i l l  Increase shear s t r e n g t h of the wood.  Average  s t r e n g t h In d r y t e s t o f Treatments 9 and 12 were 588 and 530 p s i , respectively.  These f i g u r e s were n o t s i g n i f i c a n t l y  different  from the average s t r e n g t h s o f Group B, but were s i g n i f i c a n t l y h i g h e r than r e s u l t s f o r Treatments 10 and 11, and Treatment 5 (plywood made of sawn veneer without resin-impregnated  core  veneer). The p e r cent core veneer f a i l u r e , however, was h i g h e r i n Treatments 10 and 11 than i n 9 and 12 (Table X V I I ) . A q u e s t i o n a r i s e s i n t h a t , s i n c e r e s i n should remedy the l a t h e d e f e c t , why were there s i g n i f i c a n t d i f f e r e n c e s i n shear s t r e n g t h s between Treatments 9, 10, 11 and 12?  An  e x p l a n a t i o n i s g i v e n below: (i).  The h i g h e s t s t r e n g t h i n Treatment 9 was due,  f i r s t l y , to, the methanol-mixed r e s i n being u n i f o r m l y  distributed  44 i n the wood t i s s u e and, secondly, t o the sawn veneer having minimum d e f e c t s . T h e r e f o r e , f a i l u r e i n the core veneer  was  only 62$ by standard wood f a i l u r e e s t i m a t i o n procedures, ( i i ) . Samples of Treatment  12 were made from r o t a r y -  cut veneers, and hence c o n t a i n e d many l a t h e checks. m i c r o s c o p i c o b s e r v a t i o n , i t was  Through  found t h a t l a t h e checks were  f i r m l y h e l d , but the d i s t r i b u t i o n of r e s i n i n the wood was as even as i n the samples  of Treatment  9.  These, f a c t o r s were  b e l i e v e d to account f o r the s t r e n g t h v a l u e s of Treatment being lower than those of Treatment  not  12  9.  ( i i i ) . I t i s i n t e r e s t i n g to note t h a t the specimens of Treatment 10 have the lowest shear s t r e n g t h s but h i g h e s t wood f a i l u r e values. was  possible.  (l45°F.)  T h i s experiment  assembly  Because the b o i l i n g p o i n t of s o l v e n t was  i n comparison w i t h the hot press temperature  p r e s s i n g time was plywood.  indicated that d i r e c t  too low  (300°F),  shortened t o that used i n making c o n v e n t i o n a l  Even so, r a p i d b o i l i n g of methanol  expelled  from the wood and a l s o pushed the l a t h e checks open.  resin This  r e s u l t e d i n core-impregnated plywood b e i n g weaker than u n t r e a t e d plywood  (Treatment 1 ) . The c y c l i c b o i l i n g process ( 10, 55 ) c o u l d a l s o have  caused weakening of the wood.  A f t e r samples were exposed to the  f i r s t c y c l e of b o i l i n g and d r y i n g a t l45°F.for  20 hours,  most of the l a t h e checks i n Treatment 1 were opened wide. Continuous b o i l i n g and d r y i n g s u b j e c t e d the samples  to the  s t r e s s e s of s h r i n k i n g and s w e l l i n g , consequently the l a t h e checks were enlarged, r e s u l t i n g i n f u r t h e r decrease of loaded  45 area.  In Table 1 i t i s shown t h a t the shear s t r e n g t h of b o i l e d  samples of Treatment 1 was  s i m i l a r to that of Treatment  10.  Here, l a t h e checks had been a l r e a d y opened by methanol when the plywood was made. (iv). dry t e s t was  The s t r e n g t h of samples from Treatment 11 i n  equal t o , o r h i g h e r than, t h a t of Treatments 3,  4  and 5 of Group A, but lower than t h a t of Treatments 9 and 12. Prom o b s e r v a t i o n of the manner and per cent wood f a i l u r e , was  this  b e l i e v e d due t o s e v e r a l l a t h e checks i n specimens not being  s t r o n g l y h e l d when the plywood was made.  It i s also possible  t h a t the s e t t i n g o f the oven-temperature was f o r d r y i n g the m e t h a n o l - r e s i n mix.  too h i g h  (l40° F.)  I f t h i s i s so, the f a s t  e v a p o r a t i o n or b o i l i n g of methanol from wood would cause the l a r g e r l a t h e checks to open.  Another reason might be that the  v i s c o s i t y of m e t h a n o l - d i l u t e d r e s i n was  r a t h e r low, and d i d not  h o l d the l a r g e r d e f e c t s . The o r d e r of magnitude  of shear s t r e n g t h i n the b o l l  t e s t i n treatments of every group was dry t e s t .  s i m i l a r t o t h a t of the  Unexpectedly, the v a l u e s of Treatments 9 and 12,  which were h i g h e s t i n dry t e s t , were much lower than the average of Group B, and Treatments 3, r e s u l t s a r e of d o u b t f u l v a l u e . was  4 and 5 of Group A.  These  The r e l a t i v e l y degraded  strength  thought due t o the c r i t i c a l a r e a i n the samples of Group C  being trimmed  to o n e - h a l f t h a t of Group B.  During b o i l i n g , the  dimension of impregnated core veneer was almost c o n s t a n t , but  46 the u n t r e a t e d  f a c e veneers tended t o s w e l l .  T h i s mutual  a c t i o n between core and f a c e p l i e s weakened the wood and glue t r a n s i t i o n zone (43). Consequently, i n t e n s i o n shear specimens which Were a l t e r n a t e l y d r i e d and wetted, the s m a l l e r the c r i t i c a l area the h i g h e r the s t r e s s c o n c e n t r a t i o n i n t h i s w i l l be .  T h i s i s proved when examining the t e s t e d specimens  of treatment 9. which showed t h a t f a i l u r e occurred and glue  area  i n the wood  transitions. I t i s h i g h l y p o s s i b l e t h a t methanol can be used as a  s o l v e n t f o r r e s i n impregnation  of sawn veneer.  For rotary-cut  veneer, i f a method of f a s t d r y i n g the s o l v e n t a t low temperature can be developed, a s t r o n g product assembly.  can be obtained by d i r e c t  T h i s o f f e r s c o n s i d e r a b l e commercial  Otherwise impregnation  possibilities.  as i n Group B would be r e q u i r e d .  CONCLUSIONS 1. The presence of l a t h e checks caused the t e n s i o n shear s t r e n g t h of plywood made of r o t a r y - c u t veneers t o be lower than t h a t made of sawn veneers.  Shear s t r e n g t h of c o n v e n t i o n a l  plywood w i t h an average of 16% depth of glue p e n e t r a t i o n i n t o l a t h e checks was only about 70% t h a t of plywood made of sawn veneers i n d r y , and about 60% i n wet, c o n d i t i o n . 2. In plywood made of sawn veneer, c r a c k i n g o c c u r r e d v i c i n i t y of one notch,  i n the  i n d i c a t i n g t h a t t h e specimen was  s t r e s s e d beyond the p r o p o r t i o n a l l i m i t .  Ultimate  strength  47 was  reached when sudden f a i l u r e o c c u r r e d i n earlywood of  an annual  3.  ring.  During l o a d i n g , c r a c k i n g d i d not occur i n the v i c i n i t y of  the notch, but opening of l a t h e checks i n the c r i t i c a l a r e a s was  observed i n c o n v e n t i o n a l plywood made of r o t a r y - c u t  U l t i m a t e s t r e n g t h was  veneer.  reached when l a t h e checks were j u s t  opening.  4.  When a l l l a t h e checks were completely impregnated w i t h r e s i n ,  shear s t r e n g t h and manner of f a i l u r e of plywood were not different  from t h a t of plywood made of sawn veneer.  s t r e n g t h i n c r e a s e d about 40% as a r e s u l t of t h i s  5.  Shear s t r e n g t h was  resin,  treatment.  h i g h l y i n f l u e n c e d by depth of adhesive  p e n e t r a t i o n i n t o l a t h e checks. factors i s linear.  Shear  R e l a t i o n s h i p between these  When core veneer was  f u l l y impregnated  shear s t r e n g t h of sawn-veneer plywood was  about  two by  1.5  times as h i g h as that of u n t r e a t e d plywood.  6.  There was no s i g n i f i c a n t d i f f e r e n c e i n the per cent wood  f a i l u r e as estimated by c o n v e n t i o n a l method, f o r plywood made from r o t a r y - c u t and from sawn veneer.  Use of  photography  i l l u s t r a t e s t h a t r e l a t i n g per cent wood f a i l u r e t o shear s t r e n g t h i s more meaningful of r o t a r y - c u t veneers.  i n plywood made of sawn than t h a t  48 7.  The weakest plane to r e s i s t shear s t r e s s i n sawn veneer  was found t o be i n the zone w i t h i n 10% o f i n i t i a t i o n of an annual increment.  A p p l i c a t i o n of per cent wood f a i l u r e  occurring  i n t h i s area, f o r evaluatingi the s t r e n g t h o f plywood, i s c o n s i d e r e d a more s e n s i t i v e means than use o f c o n v e n t i o n a l methods o f e s t i m a t i o n ; i . e . , an estimate o f t h e amount o f wood f i b e r s adhering to s u r f a c e s o f a f r a c t u r e d glue r e g a r d l e s s o f p o s i t i o n o f f a i l u r e i n an annual  8.  joint increment.  I t was found h i g h l y f e a s i b l e t o employ medium c h a i n  l e n g t h phenol-formaldehyde  r e s i n , w i t h methanol as s o l v e n t , to  strengthen the earlywood p o r t i o n o f veneers.  Advantages of  t h i s process a r e : (i)  a product w i t h h i g h s t r e n g t h p r o p e r t i e s r e s u l t s , and  (ii)  veneers can be d i r e c t l y assembled  i n t o plywood  w i t h the same hot p r e s s p e r i o d as t h a t of c o n v e n t i o n a l plywood. However, i t must be noted t h a t the i n f l u e n c e o f l a t h e  checks  l i m i t s the a p p l i c a t i o n o f t h i s technique t o plywood o f r o t a r y - c u t veneer.  I f a method of f a s t d r y i n g o f methanol from  wood a t low temperature  c o u l d be o b t a i n e d , a s t r o n g product  c o u l d be produced by d i r e c t  9.  impregnated  assembly.  Shear s t r e n g t h p a r a l l e l t o g r a i n o f the t i g h t - s i d e and  l o o s e - s i d e o f r o t a r y - c u t veneer, o b t a i n e d by t e s t o f standard t e n s i o n shear specimens,  showed no s i g n i f i c a n t  difference.  49 T h i s r e s u l t i n d i c a t e d t h a t plywood made of r e s i n  impregnated  core veneer, and u n t r e a t e d f a c e veneers, can be a product having shear s t r e n g t h s two to t h r e e times h i g h e r than t h a t of c o n v e n t i o n a l plywood.  50 LITERATURE CITED 1.  Bach, L. 1966. Personal communication. For. Prod. Lab. Vancouver, Canada.  2.  Bensend, D.W. and R.L. Preston. 19^6. Some causes of v a r i a b i l i t y i n the results of plywood shear t e s t s . U.S. Forest Service, For. Prod. Lab. Rept. No. R l 6 l 5 , 10 pp.  3.  Bergln, E.G. 1953. The.significance of wood f a i l u r e i n glued j o i n t s . Dept. of Forestry, For. Prod. Lab., Canada. Reprinted from Canadian Woodworker. March, 1953» 2 pp.  4.  . 1953. The gluing c h a r a c t e r i s t i c s of various eastern Canadian wood species. Dept. of Forestry, For. Prod. Lab., Canada. Reprinted from Canadian Woodworker, December, 1953, 3 PP.  5.  Bethel, J.S. and J.B. Huffman. 1952. Influence of lathe check orientation on plywood shear test r e s u l t s . School of Forestry, North Car. State C o l l . Tech. Rept. No. 1, 9 PP.  6.  Blomquist, R.F. i960. Proceedings of the symposium on adhesives f o r the wood industry. U.S. Forest Service, For. Prod. Lab. Rept. No. 2183, 83 pp.  7.  Bodig, J . 1965. The e f f e c t of anatomy on the i n i t i a l s t r e s s - s t r a i n relationship i n transverse compression. Forest Prod. J . 15:197-202.  8.  Burr, H.K. and A.J. Stamm. 195^. Comparison of commercial water - soluble phenol-formaldehyde resinoids f o r wood impregnation. U.S. Forest Service, For. Prod. Lab. Rept. No. 1384, 12 pp.  9.  Canadian Forest Products Laboratory. 1956. Strength and related properties of woods grown i n Canada. Technical Note. No. 3, 7 PP./\  10.  Canadian Standards Association. CSA Standard 0121-1961, 15 PP.  11.  Cockrell, R.A. and H.D. Bruce. 1946. Effect of thickness of glue l i n e on strength and d u r a b i l i t y of glued wood j o i n t s . U.S. Forest Service, For. Prod. Lab. Rep. No. Rl6l6, 2 6 pp.  12.  C o l l i n s , E.H. i960. Lathe check formation i n Douglas f i r veneer. Forest Prods. J . 10:139-140.  13.  Commonwealth S c i e n t i f i c and Industrial Research Organization. 1964. Plywood and gluing: Gluing Phenolic bonds. D i v i s i o n of Forest Products, Melbourne, A u s t r a l i a . Annual report  1963-1964, p. 44.  196l.  Dept. of Forestry,  Douglas f i r  plywood.  51 14.  C r a i g , D.W. 1963. The p e r m e a b i l i t y o f Douglas f i r heartwood from v a r i o u s geographic sources i n the State of Washington. MP T h e s i s , U n i v e r s i t y o f Washington, 90 pp.  15.  Curry, W.T. 195^. The s t r e n g t h p r o p e r t i e s o f plywood. II. E f f e c t o f the geometry o f c o n s t r u c t i o n . D.S.I.R., H.M.S.O., London. Research B u l l . No. 33, 28 pp.  16.  . 1957. The s t r e n g t h p r o p e r t i e s o f plywood. III. The i n f l u e n c e o f the adhesive. D.S.I.R., H.M.S.O., London. Research B u l l . No. 39, 27 pp.  17.  Dadswell, H.E., F i t z g e r a l d , J.S. and N. Tamblyn. 1952. I n v e s t i g a t i o n s o f p h e n o l i c r e s i n s f o r making improved wood, 1942-44. I I . The i n f l u e n c e o f r e s i n composition on the p r o p e r t i e s and s t r u c t u r e o f the improved wood. Aust. J . A p p l . S c i . 3 ( D : 7 1 - 8 7 .  18. ' E l e y , D.D. 290 pp.  I96I.  Adhesion.  Oxford U n i v e r s i t y Press,  Oxford.  19.  E r i c k n e r , H.W. 1955. The g l u i n g c h a r a c t e r i s t i c s o f 15 s p e c i e s o f wood with c o l d - s e t t i n g u r e a - r e s i n g l u e . U.S. F o r e s t S e r v i c e , F o r . Prod. Lab. Rept. No. 1342, 2 pp.  20.  E r i c k s o n , H.D. and J . J . B a l t i n e c z . 1964. L i q u i d flow paths i n t o wood u s i n g p o l y m e r i z a t i o n technique- Douglas f i r and s t y r e n e . F o r e s t Prod. J . 14:293-299-  21.  , Schmitz, H. and R.A. Goertner, 1938. D i r e c t i o n a l p e r m e a b i l i t y o f seasoned woods t o water and some f a c t o r s which a f f e c t i t . J . A g r i c . Res. 56:711-746.  22.  F e i h l , 0. 1958. D e t e r m i n a t i o n o f the i n f l u e n c e o f l a t h e checks on s t r e n g t h o f y e l l o w b i r c h plywood t e s t specimens by means o f two shear t e s t methods. Dept. F o r e s t r y , F o r . Prod. Lab. Can. Pro;}. 0-144-5. Progress r e p o r t No. 1 (unpublished).  23.  F l e i s c h e r , H.O. 1949. Experiments i n r o t a r y veneer c u t t i n g . Proc. F o r e s t Prod. Res. Soc. 3:137-155-  24.  Goland, M. and E. R e i s s n e r . 1944. The s t r e s s e s i n cement joints. J . A p p l . Mech., Trans. Ameri. Soc. Mech. Engr.  66:17.  25.  Goto, T., Kawamura, M. and T. Sakuno. 1963. Studies on the g a p - f i l l i n g property o f wood adhesives. B u l l . Wood Res. I n s t . , Kyoto Univ. Japan, 31:59-74.  26.  G r i f f i n , G.J. 1919Bordered p i t s i n Douglas f i r : A study o f the p o s i t i o n o f the t o r u s i n mountain and lowl a n d specimens i n r e l a t i o n ' t o creosote p e n e t r a t i o n . J .  For. 17:813-822.  52 27.  Gurvitch, J.E. 1957. The past developments and future prospects for compreg. Forest Prod. J. 7(9):16A-17A.  28.  Hale, J.D. 1957* The anatomical basis of dimensional changes in moisture content. Forest Prod. J. 7:140-144.  29.  Hancock, W.V. 1964. The influence of native fatty acids on the formation of glue bonds with heat treated wood. Ph.D. thesis, Faculty of Forestry, Univ. of B.C. 176 pp.  30.  Hoadley, R.B. 1963. Influence of certain variables on veneer-cutting behaviour. Forest Prod. J. 13:528-548.  31.  Homoky, S.G.J. 1965. Intra-increment relationship of micro-compression perpendicular properties in Douglas f i r . Unpublished Rept. Faculty of Forestry, Univ. of B.C.  32.  Huffman, J.B. 196l. Proceedings of the conference on theory of wood adhesion. Edited by A.A. Marra, Dept. of Wood Sci. and Technology. The Univ. of Michigan. P.2:2:4:7.  33.  Ishihara, S., Sasaki, H. and T. Maku. 1963. Fatigue test of some glue joints. Bull. Wood Res. Inst. Koyoto Univ. Japan. 31:75-86.  34.  Kivimaa, E. 1956. Investigating rotary veneer cutting with the aid of a tension test. Forest Prod. J. 6:251-255.  35.  Koch. P. 1964. Wood Machining Processes. The Ronald Press Co. New York, U.S.A., 530 pp.  36.  Kollman, F. and R. Hiltscher. 1955. Stress-optical investigations on laminated bending test beam models. Holz Roh Werkstoff. 13:209-211.  37.  Koran, Z. 1964. Air permeability and creosote retention of Douglas f i r . Forest Prod. J. 14:159-166.  38.  Krahmer, R.L. and W.A. Cote, Jr. I963. Changes in the coniferous wood cells associated with heartwood formation. Tappi, 46:42-49.  39.  Leney, L. i 9 6 0 . Mechanism of veneer formation at the cellular level. Univ. of Missouri. Res. Bull. No. 744. 111pp.  40.  _. i 9 6 0 . A photographic study of veneer formation. Forest Prod. J. 10:133-139.  41.  Li, J.C.R. 1964. Statistical Inference I. Edwards Brothers, Inc. Ann Arbor, Michigan, 658 pp.  53 42.  L u t z , J . 1964. How growth r a t e a f f e c t s p r o p e r t i e s o f s o f t wood veneer. F o r e s t Prod. J . 14:97-102.  43.  Marian, J.E. and D.A. Stumbo. 1962. Adhesion i n wood. Part I. P h y s i c a l f a c t o r s . H o l z f o r s c h . 16:134-148.  44.  Marra, A.A. 1 9 6 l . Proceedings o f the conference on theory o f wood adhesion. E d i t e d by A.A. Marra. Dept. o f Wood S c i . and Technology. The Univ. o f Michigan. P.l:3:13.  45.  McKenzie, W.M. 1962. The r e l a t i o n s h i p between the c u t t i n g p r o p e r t i e s o f wood, and i t s p h y s i c a l and mechanical p r o p e r t i e s . F o r e s t Prod. J . 12:287-294.  46.  M c M i l l i n , G.W. 1958. The r e l a t i o n o f mechanical p r o p e r t i e s of wood and nosebar p r e s s u r e i n the p r o d u c t i o n o f veneer. F o r e s t Prod. J . 8:23-32.  47.  M i l l e r , D.J. I 9 6 I . Permeability F o r e s t Prod. J . 11:14-16.  48.  N o r r i s , C.B., Warren, F. and P.P. McKinnon. 1961. The e f f e c t of veneer t h i c k n e s s and g r a i n d i r e c t i o n on the shear s t r e n g t h of plywood. U.S. F o r e s t S e r v i c e , F o r . Prod. Lab. Rept. No. 1801, 30 pp.  49.  N o r t h c o t t , P.L. 1952. The development o f the g l u e l i n e cleavage t e s t . F o r e s t Prod. J . 5:216-224.  50.  '\ 1955. Bond s t r e n g t h as i n d i c a t e d by wood f a i l u r e o r mechanical t e s t . F o r e s t Prod. J . 5:118-123.  51.  " 1958. Wood f a i l u r e - w i t h i n s p e c i e s and between s p e c i e s . F o r e s t Prod. J . 8:180-181.  52.  , and H.G.M. Colbeck. i 9 6 0 . Prediction of plywood bond d u r a b i l i t y . F o r e s t Prod. J . 10:403-408.  53.  , Hancock, W.V. and H.G.M. Colbeck. I963. Evidence o f need f o r wood f a i l u r e standard. Adhesion. STP. No. 360 o f the ASTM. 13 pp.  54.  Palka, L.C. 1964. F a c t o r s i n f l u e n c i n g the s t r e n g t h p r o p e r t i e s o f Douglas f i r plywood normal t o g l u e l i n e . t h e s i s . F a c u l t y o f F o r e s t r y , Univ. o f B.C., 73 pp.  55.  Pearson, W.J. 1956. P r e l i m i n a r y r e p o r t on a proposed method of e s t i m a t i n g s e r v i c e l i f e o f e x t e r i o r grade plywood. F o r e s t Prod. J . 6:221-224.  o f Douglas f i r i n Oregon.  MF  54 56.  Pentoney, R.E. 1953. Mechanisms a f f e c t i n g t a n g e n t i a l v s . r a d i a l s h r i n k a g e . Proc. F o r e s t Prod. Res. Soc. 2(2):27-32.  57.  P e r k i n s , N.S. 1950. P r e d i c t i n g e x t e r i o r plywood mances. Prod. F o r e s t Prod. Res. Soc. 4:352-363.  58.  Salamon, M. 1963. Q u a l i t y and s t r e n g t h p r o p e r t i e s of Douglas f i r d r i e d a t h i g h temperature. F o r e s t Prod. J .  perfor-  13:339-344. 59.  Shen, K.C. 1958. The e f f e c t s of d r y e r temperature, sapwood and heartwood, and time e l a p s i n g between d r y i n g and g l u i n g on the g l u i n g p r o p e r t i e s o f Engelmann spruce veneer. MF t h e s i s . F a c u l t y of F o r e s t r y , Univ. of B.C., 36 pp.  60.  Solechnik, N., Y a i s o l e c n , J . and A . I . Novoselskays (Novoselskaja). 1959. Impregnation of wood w i t h condensation products of phenol and formaldehyde. Naucnye Doklady Vyssej Skoly L e s o i n Zenernoe Delo. No. 1:245-250. From a b s t r . i n Chem. A b s t r . 54:9284 (i960).  61.  Stamm, A . J . 1964. Wood and C e l l u l o s e S c i e n c e . Press Co., New York, 549 pp.  62.  , and R.M. Seborg. 1955. F o r e s t Products Laboratory r e s i n - t r e a t e d wood (impreg). U.S. F o r e s t S e r v i c e , F o r . Prod. Lab. Rept. No. 1 3 8 0 , 8 pp.  63.  . 1951. F o r e s t Products Laboratory r e s i n - t r e a t e d , laminated, compressed wood (compreg). U.S. F o r e s t S e r v i c e , F o r e s t Prod. Lab. Rept. No. 1381, 12 pp.  64.  S t i e d a , C.K.A. 1965. P e r s o n a l communication. Dept. F o r e s t r y , F o r . Prod. Lab. Vancouver.  65.  Truax, T.R. B u l l . 1500,  66.  , Browne, F.L. and D. Brouse. 1929. Significance of mechanical wood-joint t e s t s f o r the s e l e c t i o n of wood working g l u e s . U.S. F o r e s t S e r v i c e , F o r e s t Prod. Lab. Reprinted from Ind. Eng. Chem. Jan. 1929.  67.  U.S. Department of A g r i c u l t u r e . A g r i c . handbook No. 72. P, 70.  68.  Wardrop, A.B. and F.W. Addo-Ashong. 1963. The anatomy and f i n e s t r u c t u r e of wood i n r e l a t i o n to i t s mechanical failure. C.S.I.R.O., Department of F o r e s t Prod. Reprinted from "Tewksbury Symposium on F r a c t u r e s " , 1963.  1929. 78 pp.  The g l u i n g of wood.  1955.  U.S.  The Ronald  Canada Dept. A g r i c .  Wood Handbook,  55 69.  Wilson, J.W. and G. I f j u . 1965. Wood c h a r a c t e r i s t i c s VII: Intra-increment r e l a t i o n s h i p of Douglas f i r wood d e n s i t y , t e n s i l e s t r e n g t h and s t i f f n e s s . P.P.R.I.C. Woodl. Res. Index No. 170, p. 19.  70.  Wu, Y.T. 1964. Intra-increment l i g n i n content of f i v e western Canadian c o n i f e r o u s woods. MP t h e s i s , F a c u l t y of F o r e s t r y , Univ. of B.C., 48 pp.  71.  Yavorsky, J.M. and J.H. Cunningham. 1955• S t r a i n d i s t r i b u t i o n i n maple g l u e b l o c k shear specimen as i n d i c a t e d by a b r i t t l e l a c q u e r . F o r e s t Prod. J . 5:80-84.  72.  , and N.G. Hundley. 1955. Survey of f a c t o r s a f f e c t i n g s t r e n g t h t e s t s of g l u e joints. F o r e s t Prod. J . 5:306-311.  56  Table I.  roup  Summation o f average shear s t r e n g t h s and per cent wood f a i l u r e s  Treatment  specimens  Conventional Wood f a i l u r e *  Shear s t r e n g t h  Number o f  dry t e s t  Remarks  b o i l test  psi  S.D.  psi  S.D.  %  A  1  12  252  20  133  14  94  A  2  12  280  17  175  14  96  A  3  12  343  23  236  24  89  S.D. Standard  A  4  12  356  21  226  18  94  deviation  A  5  12  343  34  229  26  96  B  6  12  557  82  370  34  84  B  7  12  506  78  347  47  79  B  8  12  544  83  382  45  80  C  9  12  589  65  291  38  62  C  10  12  156  46  125  49  97  c  11  12  376  65  187  33  95  c  12  12  530  56  267  31  76  * Dry t e s t only  ON  57 Table I I .  A n a l y s i s of v a r i a n c e :  Average shear  s t r e n g t h s i n Groups A» B and C (dry t e s t ) .  Source  Degrees of freedom  Sum of squares  Mean square  Groups  1108500  55^250  183.74 **  Treatments  1458400  162050  53.72 **  398170  3017  Error  132  Total  143  **  Significant  a t the 1%  2965070  level  58  Table I I I A.  A n a l y s i s of variance:  s t r e n g t h s i n Treatments respectively  5t  Average  shear  8 and 9 o f Groups A.' B and C,  (dry t e s t ) .  Degrees of freedom  Sum o f squares  Mean square  P  2  411157  205578  50.34  Error  33  134744  4083  Total  35  545901  Source Treatments  **  ** S i g n i f i c a n t a t the 1% l e v e l Table I I I B. Duncan's m u l t i p l e range t e s t : s t r e n g t h s i n Treatments respectively  Groups  (dry  5. 8 and 9 o f Groups A, B and C,  test).  A  Treatments Means ( p s i )  Average shear  3^3  B  C  8.  9.  544  589  Any two means not underscored by the same l i n e a r e significantly different.  Any two means underscored by  the same l i n e a r e not s i g n i f i c a n t l y  different.  59 Table I V A.  A n a l y s i s of variance:  i n Treatments (boil  test).  5»  Average  shear s t r e n g t h s  8 and 9 o f Groups A. B and C, r e s p e c t i v e l y  :  Source  Degrees Sum o f of freedom squares  Mean square  P  7.32  2  141668  70834  Error  33  319458  9681  Total  35  461126  Treatments  ** S i g n i f i c a n t  a t the 1% l e v e l  Table I V B.' Duncan's m u l t i p l e range t e s t : s t r e n g t h s i n Treatments respectively  (boil test).  A  c  B  Treatments  5.  9.  8.  229  291  382  Any  two means not underscored by the same l i n e a r e  significantly the  shear  5; 8 and 9 o f Groups A, B and C,  Groups  Means ( p s i )  Average  different.  Any two means underscored by  same l i n e a r e not s i g n i f i c a n t l y  different.  Table V.  Treatment  Summation o f averaged data of Group A  Lathe Checks Number Angle Depth (per i n . ) (deg.) (%)  Penetration depths(%) S.D.  1  14  56  66  2  13  54  65  16* 47**  3  15  55  4  14  55  Wood f a i l u r e  Dry t e s t B o i l t e s t (psi) (psi)  A B3 C^ D^ (%) (%) (%) (%) 2  9  252  133  94  8  280  175  96  63  7  1.9  64  88** 7  343  236  89  75  5  1.5  66  97**  356  226  94  80  6  2.4  343  229  96  95  7  3.0  3  5  1.  Shear s t r e n g t h  P e n e t r a t i o n depth o f adhesive i n t o l a t h e checks.' * by AMRES g l u e o n l y  ** by r e s i n No. 4880 only  S.D. Standard d e v i a t i o n  2.  C o n v e n t i o n a l wood f a i l u r e  3.  Wood f a i l u r e o c c u r r i n g i n C (see page 28)  4.  P o s i t i o n o f wood f a i l u r e i n an annual increment from i t s i n i t i a t i o n  5. ' Standard d e v i a t i o n of C  61  Table VI A.- A n a l y s i s o f v a r i a n c e :  Average p e n e t r a t i o n depths  of adhesive i n t o l a t h e checks i n Treatments 1 t o 4, Group A.  Source  Degrees of freedom  Sum o f squares  Mean square  F  3  50078.0  16693.0  301.7 **  Error  44  2434.3  55.3  Total  47  52512.O  Treatments  #* S i g n i f i c a n t  Table VI B.  a t the 1% l e v e l  Duncan's m u l t i p l e range t e s t :  Average  penetration  depths o f adhesive i n t o l a t h e checks i n Treatments 1 t o 4, Group A.  Treatments Means (%)  1.' 16  2. 47.1  3. 88  4.* 97  Any two means not underscored by the same l i n e a r e significantly the  different.  Any two means underscored by  same l i n e a r e not s i g n i f i c a n t l y  different.  62 Table V I I A. A n a l y s i s o f v a r i a n c e ; Average i n Treatments  Source  1 t o 5» Group A (dry t e s t ) .  Degrees of freedom 4  Treatments  Sum of squares  Mean square  1015^0  25384  Error  55  31136  Total  59  132670  ** S i g n i f i c a n t  shear s t r e n g t h s  44.84  566  a t the 1% l e v e l  Table V I I B. Duncan's m u l t i p l e range t e s t : Average s t r e n g t h s i n Treatments  Treatments Means ( p s i )  Any  shear  1 t o 5»' Group A (dry t e s t ) .  1.  2.  252  280  5.  3.  4.  343  343  356  two means not underscored by the same l i n e a r e  significantly different. the  **  Any two means underscored by  same l i n e a r e not s i g n i f i c a n t l y  different.  63 Table V I I I A.  A n a l y s i s of variance:  i n Treatments 1 t o 5»  Group A ( b o l l t e s t ) .  Mean square  F  95204  23801.0  59.96 **  55  21831  396.9  59  117035  Degrees of freedom  Sum o f squares  4  Error Total  Source Treatments  Average shear s t r e n g t h s  ** S i g n i f i c a n t  a t the 1% l e v e l  Table V I I I B.  Dunoan's m u l t i p l e range t e s t :  s t r e n g t h s i n Treatments 1 t o 5.  Treatments Means ( p s i )  Any  Average shear  Group A ( b o i l t e s t ) .  1,  2.  4,  5.  3.  133  175  226  229  236  two means not underscored by the same l i n e a r e  significantly  different.  Any two means underscored by  the same l i n e a r e not s i g n i f i c a n t l y  different.  64  Table IX.  A n a l y s i s of variance:  i n Treatments  Source  6 to 8  t  Average shear s t r e n g t h s  Group B (dry t e s t ) .  Degrees of freedom  Sum o f squares  Mean square  2  16459  8229.7  Error  33  216070  6547.6  Total  35  232529  Treatments  Table X.  Analysis of variance:  i n Treatments  Source  6 t o 8.  Sum o f squares  test).  Mean square  2  7475  3737.6  Error  33  59288  1796.9  Total  35  66763  Treatments  NS N o n - s i g n i f i c a n t  NS  Average shear s t r e n g t h s  Group B ( b o l l  Degrees of freedom  1.26  2.08  NS  65 Table X I A. i n Treatments  Analysis of variance:  Average  shear s t r e n g t h s  9 t o 12, Group G (dry t e s t ) .  Degrees of freedom  Sum o f squares  Mean square  3  1340400  446810  Error  44  150970  3431  Total  47  1491400  Source Treatments  ** S i g n i f i c a n t  Table X I B.  a t the  Treatments Means ( p s i )  level  Duncan's m u l t i p l e range t e s t :  s t r e n g t h s i n Treatments  10.' 156  130.22  Average  shear  9 t o 12. Group C (dry t e s t ) .  11.  376  12.  530  589  Any two means not underscored by the same l i n e a r e significantly the  different.  Any two means underscored by  same l i n e a r e not s i g n i f i c a n t l y  different.  **  66  Table X I I A.  Analysis of variance:  Average  i n Treatments  9 t o 12,  test).  Group C ( b o i l  shear s t r e n g t h s  Degrees of freedom  Sum o f squares  Mean square  3  208210  69403  Error  44  64981  1477  Total  47  273190  Source Treatments  ** S i g n i f i c a n t  Table X I I B.  a t the 1% l e v e l  Duncan*s m u l t i p l e range t e s t :  s t r e n g t h s i n Treatments  Treatments Means ( p s i )  46.99  10. 125  9 t o 12.  Average  shear  Group G ( b o i l t e s t ) .  11. I87  12. 267  9. 291  Any two means not underscored by the same l i n e a r e significantly the  different.  Any two means underscored by  same l i n e a r e not s i g n i f i c a n t l y  different.  **  6?  Table X I I I .  Analysis of variance:  Average per cent wood-  f a i l u r e by c o n v e n t i o n a l methods In Treatments 1 t o 5 . Group A.  Source  Degrees  Sum o f  Mean  of freedom  squares  square  4  386.1  96.53  Error  55  3279.8  59.63  Total  59  3665.9  Treatments  Table XIV.  A n a l y s i s of v a r i a n c e :  P  1.62  NS  Average p o s i t i o n o f wood  f a i l u r e i n an annual increment from i t s i n i t i a t i o n i n Treatments 2 t o 5, Group A.  Source  Degrees  Sum o f  Mean  of freedom  squares  square  3  37.06  12.35^  44 47  224.75 261.81  5.108  Treatments Error Total  NS N o n - s i g n i f i c a n t  P  2.42  NS  68  Table XV A.  Analysis of variance;  Average p e r c e n t wood  f a i l u r e s : o c c u r r i n g i n earlywood* i n Treatments 2 t o 5» Group A,  Sum o f squares  Mean square  3  6254.1  2084.7  Error  44  18147.0  412.4  Total  47  24401.0  Source  Degrees o f freedom  Treatments  5.05  ** S i g n i f i c a n t a t t h e 1% l e v e l  T a b l e XV B.  Duncan's m u l t i p l e range t e s t :  Average p e r  c e n t wood f a i l u r e n o c c u r r i n g i n earlywood-* i n Treatments 2 t o 5. Group A.  Treatments  2.  Means ($)  63  3. 75  4. 80  5. 95  f W i t h i n 10$ o f an a n n u a l increment from i t s i n i t i a t i o n . ' Any two means n o t u n d e r s c o r e d by t h e same l i n e a r e significantly different.  Any two means u n d e r s c o r e d by  the same l i n e a r e n o t s i g n i f i c a n t l y d i f f e r e n t .  **  69  Table X V I A n a l y s i s o f v a r i a n c e :  Average p e r cent wood  f a l l u r e r by c o n v e n t i o n a l methods i n Treatments 6 t o 8? Group B (These a r e a l l o f Group B)  Source  Degrees of freedom  Sum o f squares  2  Error Total  Treatments  NS N o n - s i g n i f i c a n t  Mean square  F  145.5  72.75  0.48  33  4999.5  151.50  35  51^5.0  NS  70  Table XVII A.  Analysis of variance:  Average p e r cent wood  failure?;; by c o n v e n t i o n a l methods i n Treatments 9 t o 12.  j  Group C.  Source  Degrees of freedom  Sum o f squares  Mean square  F  3  10114.0  3371.2  17.98 **  Error  44  8250.1  Total  47  18364.0  Treatments  187.5  ** S i g n i f i c a n t  a t the 1% l e v e l  Table XVII B.  Duncan s m u l t i p l e range t e s t : 1  Average p e r  cent wood f a i l u r e s by c o n v e n t i o n a l methods i n Treatments 9 to 12.  Group C;  Treatments Means {%)  9. 62  12,  11.'  76  95  10.' 97  Any two means not underscored by the same l i n e a r e significantly  different.  Any two means underscored by  the same l i n e a r e not s i g n i f i c a n t l y  different.  71  Zone  8.  Zone 2. Zone  (From K o c h , R The  Tension Shear  3 . Compression  tearing  1964. Wood machining  Ronald  Press  fig- I- Critical cutting  processes.  Co , New York. p. 4 4 5 )  zones  of stress in  without a  nosebor.  veneer  72 Specimen cut to pull open. 6  Specimen cut to  pull closed  / /  / / /  / / /  /  /  / /  B  Fig. 2 - Lathe check orientation shear test  specimens.  in  plywood  73  0  <  30  ^  e  e  40  '2.2"  For oN  face veneers  Only for  o n d  core veneers  eneers of Qroup the core v  0  50.  60  ocf  f Group A-  C.  ample F\.3- Potion of s g  veneer* *  e ,09  '  7k  F i g . k.  Camera setup and t e s t i n g  apparatus  75 Correlation coefticient  0.893  Standard error of estimate Y = 228 22  +  21 82 psi  128052 X  Resin No. 4880 A  0  10  AMRES  20  30  2211 glue  40  50  60  70  80  90  100  X Penetration Fig. 5  depth of adhesive into lathe  Relationship between shear strength of and  checks  (%)  plywood  penetration depth of adhesive into lathe checks.  76  400  3  350 300 250 •  200  150  00-  50  0.05  0-15  010  020  Strain (in./irU  Fig-6. Sfr@ss-strain cury® for plywood mad© of sawn v$netr,with eeeomponying pM®^mpfo® at —Treatment  5.  positions psofdd  77  Pig.  6 - Photograph 1  F i g . 6 - Photograph 2  . F i g . 6 - Photograph 3  80  Fig.  6 - Photograph  4  81  400  350  300 250  0  0.05  0 10  0.15  020  Strain (in./in.)  Fig. 7. Stress-strain curve for plywood made of rotary-cut veneer,with accompanying photographs at the positions noted (Sample I)  --Treatment 1.  Fig.  7  - Photograph 1  83  F i g . 7 - Photograph  2  84  P i g . 7 - Photograph 3  P i g . 7 - Photograph 4  86  P i g . 7 - Photograph 5  87  F i g . 7 - Photograph 6  88  400 350  Rg. 8 . Stress-strain curve for plywood made of rotary-cut  veneer, with accompanying  photographs at the positions noted (Sampl® 2), — T r e a t m e n t 1 .  89  Fig.  8  -  Photograph 1  90  F i g . 8 - Photograph 2  91  P i g . 8 - Photograph 3  92  F i g . 8 - Photograph 4  93  4004  0  0.05 0  0.05 Strain  0  005  010  (in/in)  Fig. 9. Comparison of stress-strain curves for plywoods of sawn fully  veneer (S), rotary-cut veneer  impregnated  0.15  by resin (L),  with  made  lathe checks  and rotary-cut veneer(R).  94  4 0 0 •  350-  0  0.10  0.05  0.15  020  Strain (in./in.)  Fig-10. Stress-strain curve r o t a r y - c y t veneer 8fnpr@gfHQf@d  for plywood made of with lath®  checks fully  by resin, with @ee@ra ponying  photographs of the positions inoted (Sample I). --Treatment  4.  95  P i g . 10 - Photograph 1  96  Fig.  10 - P h o t o g r a p h 2  97  P i g . 10 - Photograph 3  400  0  0.05  0.10  0.15  Strain (in./in.) Fig. II. Stress-strain curve for plywood made of rotary-cut veneer with lathe impregnated  checks fully  by resin, with accompanying  photographs at the positions noted(Sample-2) —Treatment 4.  99  P i g . 1 1 - Photograph 1  100  F i g . 11 - Photograph 2  101  F i g . 11 - Photograph 3  102  F i g . 11 - Photograph 4  103  0  0.05  0.10  Strain  0.15  0.20  (in./in.)  Fig. 12. Stress-strain curve for plywood mode of rotary-cut  veneer  impregnated  with lathe checks fully  by resin, with accompanying  photographs o f fht positions noted (Sample 3) —Treatment 4  t  104  F i g . 12 - Photograph 1  Pig.  12 -  Photograph  2  Pig. 12 - Photograph 3  107 No. 1,  2 and 3*  Plywood made o f sawn veneer  (No. 2 i s the sample f o r F i g . 6) No. 4, 5 and 6.  Plywood made o f r o t a r y - c u t veneer  with l a t h e checks impregnated by r e s i n (No. 5 and No. 6 a r e the samples f o r F i g . 11 and 12) No. 7t  8 and 9.  Plywood made o f u n t r e a t e d  rotary-cut  veneer (No. 7 and No. 9 a r e the samples f o r F i g . 7 and 8)  A  8  F i g . 13.  Test  specimens a f t e r f a i l u r e  

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