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Relationship of some coniferous wood strength properties to specific gravity variations within growth… Homoky, Stephen George John 1966

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RELATIONSHIP. OF SOME CONIFEROUS WOOD, STRENGTH PROPERTIES TO SPECIFIC GRAVITY VARIATIONS WITHIN GROWTH INCREMENTS by STEPHEN GEORGE JOHN HOMOKY B.S.F. (Sopron Division) University of B r i t i s h Columbia i960 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY i n the Department of Forestry We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 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 the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study . I f u r t h e r agree that permiss ion f o r ex -tens i ve copying 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 gran by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or 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 f i n a n -c i a l gain s h a l l not be a l lowed wi thout my w r i t t e n p e r m i s s i o n . Department of FORESTRY  The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date Mav 16. 19 66 i i ABSTRACT Tensile and compression strength properties of six coniferous woods were studied at the tissue l e v e l . Relationships of these properties to s p e c i f i c gravity variations i n three adjacent growth increments of each species were explored. P a c i f i c yew was excluded from t e n s i l e strength analyses, since the material available d i d not lend i t s e l f t o micro-tensile t e s t i n g . The main purpose of the investi g a t i o n was to examine, at the tissue l e v e l , i n what manner s p e c i f i c gravity influences tension p a r a l l e l and compression perpendicular to grain strengths. Wood s t r e n g t h — s p e c i f i c gravity r e l a t i o n s h i p s for gross wood based on e a r l i e r studied, were compared to tissue r e l a t i o n s h i p s . D i s t r i b u t i o n s of s p e c i f i c gravity and stresses within growth increments of woods having gradual t r a n s i t i o n from earlywood to latewood, as represented by western white pine, and of woods having abrupt t r a n s i t i o n , as Douglas f i r , were also compared. F e a s i b i l i t y of r a d i a l micro-compression t e s t methods established previously for Douglas f i r were re-examined and extended to a l l six species. Experimental material, from f r e s h l y f e l l e d trees was never dried before physical t e s t i n g , except western red cedar. Specimens for t e n s i l e and compression tests were cut from each increment studied. Micro-specific gravity determinations, based on green volume and oven-dry weight, were performed on broken t e n s i l e t e s t specimens after extraction with standard solvents. Physical tests were carr i e d out by established techniques. i i i Regression analysis was employed to e s t a b l i s h equations and curves best describing relationships of maximum micro-t e n s i l e and micro-compression stresses to s p e c i f i c gravity. Test r e s u l t s revealed highly s i g n i f i c a n t r e l a t i o n s h i p between maximum micro-tensile stress and s p e c i f i c gravity, and between maximum micro-compression stress and s p e c i f i c gravity. The l a t t e r r e l a t i o n s h i p i s c u r v i l i n e a r , expressed by an exponential curve f i t t i n g f i v e of the s i x species studied. P a c i f i c yew, also s i g n i f i c a n t l y correlated to s p e c i f i c gravity at 9f? per cent p r o b a b i l i t y , was described by the same basic equation applied to the grouping of the other f i v e woods, but with d i f f e r e n t con-stants. This suggests that s p e c i f i c gravity influences maximum micro-compression stress v a r i a t i o n s i n species of greatly d i f f e r e n t physical and anatomical, c h a r a c t e r i s t i c s i n varying degrees. Comparing ten s i l e and compression s t r e s s — s p e c i f i c gravity variations of gross wood with those of wood tissue, i t was found that i n both properties s p e c i f i c gravity caused greater stress increase of gross wood than of tissue, as i l l u s t r a t e d by respective regression l i n e s . No d e f i n i t e trend of s p e c i f i c micro-compression stress within growth increments was found. S p e c i f i c micro-tensile stress d i s t r i b u t i o n s showed a peak-value close to or at the i n i t i a t i o n of latewood. S p e c i f i c gravity, maximum micro-tensile stress and maximum micro-compression stress i n woods having gradual t r a n s i t i o n from earlywood to latewood vary gradually across the increment, suggesting trends of a second degree parabola. In iv woods where t r a n s i t i o n is abrupt, the increase of these properties i s abrupt at or close to the i n i t i a t i o n of latewood. I f i n such woods the latewood zone i s wide the d i s t r i b u t i o n curve i s sigmoid. Methods for tes t i n g wood tissue i n r a d i a l compression, as well as theories r e l a t e d to the analysis of stress-deformation curves, have been v e r i f i e d . Ultimate load i s recorded at the i n f l e c t i o n point on the curve, beyond the proportional l i m i t . At this phase of compression ultimate compressibility of the tracheids i s achieved. V TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS v LIST OF FIGURES v i i LIST OF TABLES v i i i ACKNOWLEDGEMENT i x INTRODUCTION 1 LITERATURE REVIEW 3 Investigations with Gross Wood . * • • 3 S p e c i f i c gravity r e l a t e d d i r e c t l y to strength . . . 3 Factors influencing s p e c i f i c gravity • • • 6 Investigations with Wood Tissues 8 MATERIALS AND METHODS . . 11 Wood Samples . . . . . . . . 11 Preparation of Test Specimens lfy. Physical Testing 16 S p e c i f i c gravity 16 Micro-tensile t e s t i n g . . . . . . . 18 Micro-compression te s t i n g . 19 Analysis of stress-deformation diagrams • 19 RESULTS • 2 5 DISCUSSION 39 Behavior of Western White Pine 39 Tension-Specific Gravity Relationships . . . . . . . . 1L2 v i Page Compression-Specific Gravity Relationships I4.6 F e a s i b i l i t y of Micro-Compression Test Methods $1 CONCLUSIONS . 52 REFERENCES 56 v i i LIST OF FIGURES Figure Page 1. Resolution of t y p i c a l micro-tensile stress-deformation diagrams for Douglas f i r earlywood and latewood. . . . 20 2. Resolution of t y p i c a l micro-compression s t r e s s -deformation diagrams f o r Douglas f i r earlywood and latewood . 21 3. D i s t r i b u t i o n of s p e c i f i c gravity (green volume), maximum micro-tensile stress, maximum micro-compression stress and s p e c i f i c t e n s i l e stress i n Pinua monticola Dougl. I4.X ij.. Relationship between maximum micro-tensile stress and s p e c i f i c gravity (green volume) for f i v e coniferous species I4.3 5. Relationship of maximum macro- and micro-tensile stress to s p e c i f i c gravity. 6. Relationship between micro-compression stress maximum and at proportional l i m i t f o r six coniferous woods . • I4..8 7» Relationship between maximum micro-compression stress and s p e c i f i c gravity (green volume) f o r six coniferous species • . . . 1^ .9 v i i i LIST OP TABLES Table Page I. Descriptive data of six coniferous woods co l l e c t e d for the study 13 I I . Summary of test r e s u l t s of six coniferous woods. . • 2 9 I I I . S p e c i f i c micro-compression stresses of six coniferous woods. • • 35 IV. Summary of data of small clear t e n s i l e test specimens (Forest Products Laboratories of Canada, Vancouver Branch) 37 ACKNOWLEDGEMENT The author expresses with gratitude his appreciation to Dr. J.W. Wilson, Professor, Faculty of Forestry, f o r hi3 valuable professional assistance i n planning and experimental phases and preparing the the s i s , as well as fo r h i s encouraging and understanding guidance over the past two years at t h i s University; to Dr. R.W. Wellwood, Professor, and Mr. L. Adamovich, Assistant Professor, Faculty of Forestry, f o r hel p f u l suggestions and c r i t i c i s m s ; to Dr. A. Kozak, Assistant Professor, Faculty of Forestry, f o r the s t a t i s t i c a l analysis and computer programming; to Mr. J. Walters, Research Forester, University Research Forest, Haney, B.C., for supplying experimental material; to the National Research Council of Canada and the University of B r i t i s h Columbia f o r f i n a n c i a l support during the two year academic programme; and to the Pulp and Paper Research Inst i t u t e of Canada f o r employment during the summer of 1965 and assistance thereafter. -1 INTRODUCTION There i s a growing demand f o r more economical use of st r u c t u r a l wood material due to the increasing scarcity of available high-grade stock. Conscious e f f o r t i s being made by industry and various s c i e n t i f i c organisations i n order to extend knowledge r e l a t e d to wood q u a l i t y , factors c o n t r o l l i n g physical and mechanical properties, and to set l i m i t s f o r use of wood under s p e c i f i e d service conditions. The information should lead to the better u t i l i s a t i o n of available raw material. It has been established that strength properties of wood vary within the same tree with respect to p o s i t i o n i n the bole, growth rate and r e l a t i v e proportion of latewood within growth increments. Variations within individuals of the same species and among geographical l o c a l i t i e s of the same species are also s i g n i f i c a n t . Among a l l the causative factors which influence the strength properties of wood, s p e c i f i c gravity has been recognised! as the most important single f a c t o r . In order to arr i v e at better d e f i n i t i o n as to what extent s p e c i f i c gravity exerts i t s influence upon wood strength properties, a closer examination of such relationships became imperative. Although i t i s true that d i r e c t r e l a t i o n s between strength and s p e c i f i c gravity or wood density have been recognised ever since man has used wood as a s t r u c t u r a l material, such relationships were considered i n empirical ways u n t i l beginning -2 of the 20th century. It is now common knowledge that most strength properties do not vary linearly with specific gravity. When the laws governing the mechanical behavior of wood as a function of its specific gravity are well formulated, the user of structural timber, as well as the wood scientist possesses a valuable guide for selecting material of the required strength for specific purposes. Since relationships such as these are always based on a large number of tests, i t must be pointed out that no one single measurement can replace a large number of data due to variations that exist between individual measurements. However, such relationships must be valid within s t a t i s t i c a l l y determined confidence l i m i t s . Based on the use of tissues rather than gross samples, six Canadian conifers were studied i n order to examine mechanical behavior of wood within growth Increments; the following objectives were set: 1. ) Re-examination of the influence of specific gravity on tensile strength parallel and compression strength perpendicular to grain, using wood tissues versus gross wood. 2. ) Extension of micro-test methods to Intensive examination of a typical wood having "gradual transition" from earlywood to latewood, for com-parison with accumulated information on Douglas f i r which has "abrupt transition." 3. ) Broader application of the new micro-compression perpendicular to grain test. - 3 -Ij..) D e f i n i t i o n of some wood tissue physical properties within r e s t r i c t i v e l i m i t s of material used. LITERATURE REVIEW A number of workers have attempted to apply s p e c i f i c gravity as an estimator to explain strength property variations i n wood. Various approaches have been t r i e d r e l a t i n g to gross wood and wood t i s s u e . Investigations with Gross Wood S p e c i f i c gravity r e l a t e d d i r e c t l y to strength The f i r s t e f f o r t to express strength properties of wood with respect to variations of i t s s p e c i f i c gravity was made at the beginning of t h i s century. Results from two hundred thousand tests c a r r i e d out at the U.S. Forest Products Laboratory were published i n 1919 (23). Ninety deciduous and 38 coniferous species, not counting regional v a r i e t i e s , were tested. Properties examined were s t a t i c bending, impact bending, compression-parallel to grain, compression perpendicular to grain at proportional l i m i t , hardness, shear, cleavage, tension perpendicular to grain, and shrinkage from green to oven-dry condition. It was shown that maximum bending strength and maximum compression strength p a r a l l e l to grain varied with s p e c i f i c gravity i n a l i n e a r fashion, while compression strength per-pendicular to grain, tension strength perpendicular to grain, work values i n s t a t i e bending, and toughness deviated markedly from the straight l i n e . These properties varied as higher powers of s p e c i f i c gravity giving large Increases i n strength with small increase of s p e c i f i c g r a v i t y . It was therefore necessary to express strength--specific gravity r e l a t i o n s by curve forms and equations i n order to render them f e a s i b l e for p r a c t i c a l a p p l i c a t i o n both f o r green and air-dry material. Strength values p l o t t e d over s p e c i f i c gravity suggest c u r v i l i n e a r d i s t r i b u t i o n except i n the two cases mentioned above. I f a s t r a i g h t l i n e i s suggested, the l i n e does not pass through the o r i g i n . Since strength must be zero at zero s p e c i f i c gravity, the d i s t r i b u t i o n curve must s t a r t from the o r i g i n . For almost every case the d i s t r i b u t i o n curve revealed a parabola of the form f = pG n where f i s the strength value or property, G Is the s p e c i f i c gravity, and p and n are constants. The procedure of f i n d i n g the constants was as follows: ... the equation was transformed into the logarithmic form log f = log p + n log G. This equation represents a straight l i n e having i t s slope equal to n and i t s i n t e r -cept with the y axis equal to p. Con-sequently, to f i n d the constants p and n i t i s only necessary to plot log f against l o g G on ordinary cross-section paper and f i n d the straight l i n e which best averages the points; then n and log p are determined from the slope and intercept of the l i n e (23). In order to f i n d the best f i t for the straight l i n e , the method of l e a s t squares was used. The derived equations are so r e l i a b l e that unknown values of a cer t a i n strength property can be estimated by knowing the s p e c i f i c gravity of the specimen. - 5 -T h i s e m p i r i c a l work has been repeated t o date i n t e x t -books d e a l i n g w i t h mechanical behavior of wood. For sake o f more e f f i c i e n t u t i l i s a t i o n of wood wit h r e s p e c t t o s t r e n g t h - s p e c i f i c g r a v i t y r e l a t i o n s h i p s based on t h i s work, E t h i n g t o n (11) o f f e r s a double sampling technique of s p e c i f i c g r a v i t y on an improved, t e c h n i c a l l y sound b a s i s . The attempt t o r e l a t e mechanical p r o p e r t y v a r i a t i o n s t o s p e c i f i c g r a v i t y has not always been s u c c e s s f u l . Bodig (3 , found no c o r r e l a t i o n between maximum t r a n s v e r s e compression and s p e c i f i c g r a v i t y . The "weak l a y e r t h e o r y " may serve as an e x p l a n a t i o n f o r t h i s phenomenon. It must be borne i n mind t h a t a l l e a r l i e r data on t r a n s v e r s e compression only r e l a t e s t r e n g t h to the p r o p o r t i o n a l l i m i t , s i n c e u l t i m a t e t r a n s v e r s e compression s t r e n g t h had not been r e c o r d e d . P e l l e r i n (21}.), i n the course o f h i s n o n d e s t r u c t i v e -t e s t i n g experiment w i t h damped v i b r a t i o n s , c o r r e l a t e d modulus of r u p t u r e w i t h the combination of dynamic modulus o f e l a s t i c i t y and l o g a r i t h m i c decrement. Seventy per cent of the v a r i a t i o n had been accounted f o r , but i n order to improve the c o r r e l a t i o n , these two parameters were subsequently combined w i t h s p e c i f i c g r a v i t y . The e f f e c t of s p e c i f i c g r a v i t y was i n s i g n i f i c a n t and i t was t h e r e f o r e excluded from f u r t h e r c o r r e l a t i o n s . While s t u d y i n g the a n i s o t r o p y of wood, Y l i n e n (36) found t h a t s p e c i f i c g r a v i t y was a f a r more r e l i a b l e c h a r a c t e r -i s t i c f o r e s t i m a t i o n of e l a s t i c modulus p a r a l l e l t o g r a i n i n com-p r e s s i o n than latewood per cent. -6-F a c t o r s i n f l u e n c i n g s p e c i f i c gravity-Much has been w r i t t e n on the v a r i o u s causes of v a r i a t i o n i n wood s p e c i f i c g r a v i t y . The few examples d i s c u s s e d here a r e o n l y meant t o p r o v i d e a sampling of the l i t e r a t u r e p e r -t a i n i n g t o the s u b j e c t . Drow (10) found wide d i f f e r e n c e s i n latewood per cent and s t r e n g t h p r o p e r t i e s o f two r e g i o n a l v a r i e t i e s of Douglas f i r , Pseudotsuga m e n z i e s i i v a r . m e n z l e s i l and P . m e n z i e s i i v a r . g l a u c a . Z o b e l e_t j a l . (35) s t u d i e d s p e c i f i c g r a v i t y , t r a c h e i d l e n g t h , per cent w a t e r - i n s o l u b l e c a r b o h y d r a t e s , per cent a l p h a -c e l l u l o s e and percentage latewood i n - l o b l o l l y p i n e (Pinus taeda L . ) and found h i g h l y s i g n i f i c a n t d i f f e r e n c e s between s i t e s . S p e c i f i c g r a v i t y f o l l o w e d a d i s t i n c t g e o g r a p h i c a l p a t t e r n . Between-tree v a r i a t i o n f o r s p e c i f i c g r a v i t y and t r a c h e i d l e n g t h was a l s o s i g n i f i c a n t . European l a r c h ( L a r i x dec idua M i l l . ) has been p l a n t e d as an e x o t i c s p e c i e s at three d i f f e r e n t e l e v a t i o n s i n the w e s t e r n Hungarian h i l l s . Wood q u a l i t y s t u d i e s (32) r e v e a l e d t h a t l a t e -wood percentage of a l p i n e t r e e s was lower t h a n t h a t of middle mountain and l o w l a n d samples, a l t h o u g h wood of g r e a t e r r i n g s t r u c t u r e u n i f o r m i t y and d e n s i t y o c c u r r e d i n a l p i n e t r e e s . S i m i l a r r e s u l t s were r e p o r t e d by Burger (7) f o r German Norway spruce ( P i c e a abies (L>) K a r s t . ) and Scots p i n e (Pinus s i l v e s t r i s L . ) . The s lowest growing races of Scots p i n e produced h e a v i e r wood on each s i t e . V a r i a t i o n between stem c l a s s e s o f the shade-t o l e r a n t spruce was n o t i c e a b l e . -7 Cockrell (8) found that stand and s i t e conditions had a greater influence on wood qual i t y than i l l - d e f i n e d categories of second-growth and old-growth. S p e c i f i c gravity was independent of growth rate i n a l l 2 3 ponderosa pine (Pinus ponderosa Laws.) selected from various l o c a l i t i e s . Zobel (33) suggested genetic control,since wide s p e c i f i c gravity v a r i a t i o n was found between trees of the same age and diameter growing close to each other i n a stand of l o b l o l l y pine i n eastern Texas. Strong r e l a t i o n s h i p was found between s p e c i f i c gravity and latewood percentage. Results from extensive studies by Zobel and Rhodes (3I4.) on widely scattered plots revealed that growth rate and tree age had no s i g n i f i c a n t r e l a t i o n s h i p to s p e c i f i c gravity. L i t t l e influence o£ length of clear bole on s p e c i f i c gravity was found, and moistness of s i t e , s i t e index, s o i l c h a r a c t e r i s t i c s and stand basal area indicated no important e f f e c t . The moat important contributing f a c t o r was latewood per-centage. L i t t l e f o r d ( 2 2 ) studied strength properties within trees and between trees of a young stand of rapid-growth Douglas f i r . He concluded that number of rings from p i t h d i d not influence strength properties. In four of the f i v e trees examined, r i n g width had no s i g n i f i c a n t e f f e c t , but latewood per-centage maintained significance i n a l l f i v e trees. Ring width and latewood percentage were most often unrelated to moduli of rupture and e l a s t i c i t y , and maximum crushing strength, only when associated with s p e c i f i c gravity. It was also found that s p e c i f i c gravity did not f u l l y account f o r va r i a t i o n s i n strength properties between trees. In a stand of r a p i d l y growing trees -8-one tree seemed more competent than others i n producing high-strength wood per unit weight. Wellwood (27) reported maximum s p e c i f i c gravity i n western hemlock (Tsuga heterophylla (Raf.) Sarg.) at the base of the tree and minimum at the top. Grown class did not a f f e c t s p e c i f i c gravity v a r i a t i o n s i g n i f i c a n t l y , but a trend was suggested by the data. An inverse r e l a t i o n s h i p was found between s p e c i f i c gravity and s i t e index. Banks (2), studying Pinus l o n g i f o l i a Roxb. i n South A f r i c a , found a very steep r a d i a l density gradient both at ground l e v e l and at the 22 feet l e v e l . Fluctuating r i n g width had no e f f e c t on s p e c i f i c gravity. This i s i n agreement with the r e s u l t s of other workers (10, 2 2 ) . Investigations with Wood Tissues Since wood Is a very complex material, i t becomes necessary to investigate i t s properties within narrow l i m i t s of the gross structure, i.e., the annual increment,in order to gain better understanding of i t s properties and causative factors of property changes. Investigations at the tissue l e v e l provide suitable means for such purposes. Two mechanical properties have been dealt with at the tissue l e v e l : micro-tensile properties have been studied intensively, while e f f o r t s to elaborate on micro-compression are of more recent o r i g i n . In micro-tensile t e s t studies If ju and Kennedy (ill) reported that "per cent c e l l wall was a s l i g h t l y better indicator than s p e c i f i c gravity i n evaluating the amount of material - 9 -r e s i s t i n g applied stresses." Since the two factors are very closely correlated (r = 0.97)» the extra time and e f f o r t involved i n determination of per cent c e l l wall i s not j u s t i f i e d . In a project conducted by Kellogg and I f j u (17), 20 species were examined to r e f l e c t upon the e f f e c t of s p e c i f i c gravity, as well as other causative f a c t o r s , of t e n s i l e strength properties i n the d i r e c t i o n of the grain. The r e s u l t s revealed that s p e c i f i c gravity from 0.22 to 1.18 accounted f o r 75.5 per cent of v a r i a b i l i t y i n ultimate t e n s i l e strength and for 87.8 per cent of v a r i a b i l i t y i n modulus of e l a s t i c i t y . The thermal conductivity factor can be r e l a t e d to f i b r i l angle according to Wangaard (25). It Is postulated by the f i r s t mentioned authors that s p e c i f i c strength and s p e c i f i c s t i f f n e s s might be correlated with an int e g r a l f i b r i l angle. I f t h i s i s correct, the thermal conductivity r a t i o offers a simple technique for evaluating complex s t r u c t u r a l factors impossible to measure d i r e c t l y . Another source of v a r i a t i o n i s the extractive content which may cause p o s i t i v e or negative c o r r e l a t i o n depending on the l o c a t i o n of extractives i n the c e l l : i f extractives are included i n the lumen, weight i s increased without increase i n strength, but i f they are found i n amorphous regions of the c e l l walls some strength properties may be increased. Methods for study of wood c h a r a c t e r i s t i c s on minute specimens have been conducted by the s t a f f and students of the Faculty of Forestry, University of B r i t i s h Columbia, i n cooperation with the Pulp and Paper Research Institute of Canada (29, 30, 31). Intra-increment variations of c e r t a i n species were studied, such as micro-specific gravity, micro--10 t e n s i l e strength, e l a s t i c i t y , micro-photometer measurements of c e l l wall, c e l l wall porosity, and f i b e r c o l l a p s i b i l i t y i n micro-compression perpendicular t e s t s . In micro-tensile strength studies (16, 31) abrupt t r a n s i t i o n from earlywood to latewood of Douglas f i r was established i n a l l properties examined. V a r i a t i o n across increments was greater than that along increments. D i s t r i b u t i o n patterns of a l l properties were sim i l a r across a l l three increments studied but s p e c i f i c gravity was constant across the earlywood zone. Relationships between strength and s p e c i f i c gravity were found to be c u r v i l i n e a r as solved by mathematical transformation of data. Ultimate t e n s i l e stress was highly correlated with modulus of e l a s t i c i t y (r = O.98). Highest values f o r s p e c i f i c strength and s p e c i f i c s t i f f n e s s were detected at the i n i t i a t i o n of latewood. Empirical equations derived for estimating intra-increment strength and s p e c i f i c gravity may be solved f o r "physico-mechanical" latewood. S p e c i f i c gravity variations accounted for more than 92 per cent of v a r i a b i l i t y i n strength properties. Intra-increment investigations can be extended to study s p e c i f i c problems as demonstrated by Kennedy (18). Pour Norway spruce clones were studied for within-increment v a r i a t i o n i n seven wood properties, and the degree to which these properties might be h e r i t a b l e . S p e c i f i c gravity was highly correlated to latewood per cent (r = 0.90). H e r i t a b i l i t y estimates both f o r s p e c i f i c gravity and latewood per cent were i n excess of 0.8. S p e c i f i c gravity values within the increment were p o s i t i v e l y correlated with whole--11-r l n g s p e c i f i c gravity and were also h e r i t a b l e . V a r i a t i o n of te n s i l e strength and s t i f f n e s s increased across the increment. Maximum s t r a i n decreased l i n e a r l y . Tracheid length showed a s l i g h t increase from earlywood to latewood. In r a d i a l micro-compression test of Douglas f i r (12), variations of maximum compression strength, modulus of e l a s t i c i t y and s p e c i f i c gravity within the increment exhibited the same sigraoid-pattern as had been found i n t e n s i l e test studies. Modulus of e l a s t i c i t y was correlated with s p e c i f i c gravity i n a l i n e a r fashion. The influence of s p e c i f i c gravity on maximum compression strength was somewhat stronger than on modulus of e l a s t i c i t y . No d e f i n i t e d i s t r i b u t i o n pattern could be obtained for s p e c i f i c strength or s p e c i f i c s t i f f n e s s . MATERIALS AND METHODS Wood Samples Experimental material was extracted from six i n d i v i d u a l trees representing six coniferous genera. Woods used i n the study are described i n Table I. After f e l l i n g , the boles were bucked and one test disk from each tree was retained f o r examination. In order to prevent excessive drying the disks were wrapped i n polethylene sheets and stored i n a cool storage room at the University of B.C. -12-Several r a d i a l blocks were cut from each disk and the ones with straight g r a i n were chosen for sectioning. The sectioning was carr i e d out i n the following manner: a) . Three adjacent rings which exhibited minimum of curvature and p a r a l l e l alignment with respect to each other were chosen. P a r a l l e l boundaries of r a d i a l blocks were delineated perpendicular to the chosen three r i n g s . b) . After extracting and machining the blocks, the one with the longest straight grain was selected for further processing. Only one radius f o r each wood was examined i n the study. The length of the block was a nominal 5 inches, the depth about 2 1/2 inches with width controlled by curvature of the r i n g s . The narrowest block, not exceeding 0.8 cm (O.32 i n . ) , was cut from P a c i f i c yew due to excessive increment curvature. Such r e s t r i c t i o n s were imperative i n order to secure tissues as homogeneous as possible. c) . The selected block was aspirated i n a pressure cylinder under 80 p s i pressure u n t i l waterlogged, p r i o r to sectioning tangentially on a s l i d i n g microtome. The rings above the f i r s t of the selected three rings were sectioned and d i s -carded, and adjustments were made to ensure p a r a l l e l alignment of knife and wood block. Tangential microsections were cut from the first-formed earlywood to the l a t e s t latewood at nominal t h i c k -ness of 100 microns. The thickness was increased to 180-200 microns i n latewood zones of Douglas f i r and P a c i f i c yew. -1 3 -Table I. D e s c r i p t i v e data of s i x coniferous woods c o l l e c t e d f o r the study Species L o c a l i t y Height Diameter Number of Increments of disk of d i s k increments examined, above i . b . , i n . counted ground from p i t h f t .  Pinus Haney, monticola, B.C. 5.0 12 157 131,132,133 Dougl. (3.0,4.8,2.5)* Pseudotsuga Univ. of m e n z i e s i i , B.C. (Mirk* J ; Endowment 18.0 13 8I4. L8,1^ .9,50 Franco . Lands (li.7.2.4,2.9) Vancouver, B.C. Tauga heterc ( R a f . ) S a r g . " B.C~.' (3.7,3.3»3«8V h e t e r o p h y l l a , Haney, 20.0 10 77 27,28,29 # Abies S t . balsamea, M i c h e l l e I4..5 10 55 19,20,21 (L.) M i l l . des (2.7,2.2,2.2) S a i n t s , Que. Thuja Haney, p l i c a t a , B.C. 8.0 18 6I4. kk>k$> ¥> Bonn (3-3»3»^>3» 3)* Taxus Haney, breve i f o l l a , B.C. i^.5 7 175 135,136,137 Nutt. (2.9,3.0,2.7)^ ^increment widths, ram. Western r e d cedar (Thuja p l i c a t a Dorm) sec t i o n s of acceptable q u a l i t y c o u l d be obtained only when the block was a i r -d r i e d . The microsections numbered from the i n c e p t i o n of one increment t o the In c e p t i o n of the next increment were submerged i n water and s t o r e d i n a r e f r i g e r a t o r i n l a b e l l e d t e s t tubes. - i4 -A r a d i a l microtome section was cut from the t e s t block, dyed and mounted on cover glass. Ring width and latewood per-centage of the increments selected were measured by stage micro-scope to the nearest 0 . 1 mm. Mork's d e f i n i t i o n was used for determining latewood percentage. Preparation of Test Specimens The o r i g i n a l design was to obtain •.separate te s t specimens f o r s p e c i f i c gravity determination, as well as t e n s i l e and compression tests from the same microsection. Preliminary tests proved that this method was not fe a s i b l e p a r t l y because of poor c o r r e l a t i o n obtained between t e n s i l e strength and s p e c i f i c gravity, and p a r t l y because of s c a r c i t y of suitable material i n some microsections. The s p e c i f i c gravity samples were disks 3/3 Inch i n diameter. Much of the area within the microsection was s a c r i f i c e d by punching out disks of such dimension. When smaller disk3, 3/16 Inch i n diameter were used, material was con-served, but the samples had to be obtained from the end of the microsection where density was not always the same as at other locations along the section. This accounted for poor c o r r e l a t i o n between t e n s i l e strength and s p e c i f i c gravity. For the main study i t was decided to use broken t e n s i l e t e s t specimens of known dimensions as has been done previously (II4., 1$, 28). Another problem was to resolve whether or not com-pression test specimens could be extracted from broken t e n s i l e test specimens. The " t " test performed revealed s i g n i f i c a n t difference (t = -2.271}. at the 5 P©r cent l e v e l ) between compression stress of pre-3tressed and unstressed compression specimens. Consequently, -15-the decision was to use separate material f o r t e n s i l e and com-pression tests from the same microsection. A proper number of r e p l i c a t i o n s for t e n s i l e and com-pression tests was computed. Tensile t e s t s c a l l e d f or four r e p l i c a t i o n s at the 90 per cent confidence l i m i t , while com-pression tests required only three at 95 per cent confidence when sampling within a single microsection blank. The allowable error f o r both tests was ten per cent of the mean from r e p l i c a t i o n values, less than or equal to the difference between the larg e s t and smallest strength value found within the microsection. In terms of geometry a single microsection blank, which was 13 mm (0.512 inch) wide, provided 2.5 mm (O.O98 inch) width rectangular s t r i p s . Two st r i p s at both sides served as te n s i l e t e s t specimens while the remaining s t r i p at the center was used f o r compression t e s t specimens. The symmetrical arrangement of the f i v e s t r i p s could not always be adhered to due to i r r e g u l a r i t i e s i n some micro-sections. This was es p e c i a l l y true i n case of western white . pine latewood sections where the numerous and wide r e s i n canals seriously aggravated the a v a i l a b i l i t y of r e l a t i v e l y homogeneous test material. Six microsections i n each r i n g were selected for testi n g , except i n western white pine. This species was studied, by more intensive sampling f o r reasons described. The tissues selected included both earlywood and latewood. Latewood i n several rings was represented by one microsection only, due to small latewood per cent In those r i n g s , i . e . , western red cedar. Selection was based on t h e i r r e l a t i v e proportions i n the -16-increments. Punching out te n s i l e t e s t specimens with an Arbor press and cutting die followed the same procedure described by I f j u et a l . (15). The width of the s t r i p s was 2.5 mm (0.098 inch), the length 2.5 inches. Thickness measurements were made with an S 509-lj. "Microcator" d i a l i n d i c a t o r . Readings were taken at each end, at the center, and at two more intermediate spots of the test specimen. Averages were recorded. Preparation of compression test specimens was accomplished by r o t a t i n g the 2.5 mm wide die 90 degrees, thus obtaining squares 2.5 mm by 2.5 mm with an area of 6.25 mm2 (O.OO37 I n 2 ) . Various specimen sizes were t r i e d by changing the spacing of the die to 3 . 0 mm (0.118 inch) and I4..0 mm (0.158 inch), but comparisons of compression strength values showed similar r e s u l t s . The smallest spacing, 2.5 mm, was chosen, due to l i m i t e d width of the microsections and matching with t e n s i l e specimens. The thickness of each specimen-square was measured and recorded to the nearest micron. A l l test specimens were numbered and kept i n l a b e l l e d , w a t e r - f i l l e d test tubes and v i a l s and stored i n cold u n t i l mechanical t e s t i n g was commenced. The material was never dried between f e l l i n g the trees and physical t e s t i n g , except western red cedar. Physical Testing S p e c i f i c gravity Broken t e n s i l e specimens of constant width and length were used f o r s p e c i f i c gravity determinations. Thickness was 17 measured p r i o r to t e n s i l e t e s t i n g , thus green volume of the specimen was obtained. In order to base s p e c i f i c gravity calculations on c e l l wall substance, the specimens were extracted i n sequence with ethyl ether, ethyl alcohol, and hot d i s t i l l e d water. Eight hours were allowed for ether and alcohol extractions while hot water extractions were done fo r three hours. Tensile and com-pression test specimens were not extracted before t e s t s . Upon completion of extraction, specimens were oven-dried at 100 + 2°C for two and a h a l f hours, transferred to a desiccator and cooled for 30 minutes. Determination of s p e c i f i c gravity based on green volume and oven-dry weight was accomplished by d i v i d i n g weight i n mg by volume i n rnm3. Weight measurements were taken with a Cahn E l e c t r o -balance contained i n a plexiglass glove box. The purpose of t h i s arrangement was to maintain desiccated atmosphere f o r oven-dry specimens with the a i d of s i l i c a - g e l drying media. The dry atmosphere was p r a c t i c a l l y unaffected by the atmosphere outside the glove box since i t was t i g h t l y sealed. Transfer of specimens was f a c i l i t a t e d through an a i r - l o c k attached to the glove box. Opening and closing of the outside and inside a i r - l o c k covers was done as quickly as possible. The desiccator, containing v i a l s with test specimens, was not opened u n t i l i t was securely transferred to the glove box and the inside cover of the a i r lock was t i g h t l y shut. Weighing was carried out using the 10 mg range on the balance, which had a s e n s i t i v i t y of 0.001 mg. Some weight -18-measurements were repeated randomly i n order to check accuracy of the balance. Zeroing and c a l i b r a t i o n was repeated a f t e r every fourth measurement. This method of s p e c i f i c gravity determination at the tissue l e v e l i s as accurate as the one applied by other workers 15, 16) but i s much f a s t e r . Micro-tensile t e s t i n g Tensile t e s t i n g of wood tissues has been developed and described by several authors (llj., 1$, 16, 17, 28). An i d e n t i c a l procedure was followed i n t h i s project with a Table Model T-ML (Slow Speed) Instron testing machine. Tests were performed at room temperature on green specimens. The ehart speed was 1.0 inch per minute and load speed was 0.01 inch per minute. S e n s i t i v i t y of load c e l l was 10 grams. Some modifications of the o r i g i n a l procedure were employed i n that the gage length was 1.0 inch instead of 1 .5 inch. This was necessitated by lack of straight grain over the 1 .5 inch length i n some r a d i a l blocks. Test specimens were maintained i n the green condition during test by continual brush a p p l i c a t i o n of a water f i l m . Tensile test data were not recorded f o r P a c i f i c yew (Taxus b r e v i f o l i a Nutt.) because the sections were so poor, due to lack of homogeneity, that strength v a r i a t i o n among r e p l i c a t e s within raicrosections far exceeded the allowable error. Specimens a f t e r test were returned to t e s t tubes. 19-Miero-eompression t e s t i n g R a d i a l micro-compression t e s t i n g of wood t i s s u e s has been developed and de s c r i b e d r e c e n t l y (12). The same t e s t i n g machine was used f o r compression t e s t s as f o r t e n s i l e t e s t s , but w i t h changed l o a d c e l l . The procedure was as f o l l o w s : the t e s t specimen was removed from the v i a l , p l aced between a 1 mm t h i c k cover g l a s s and a 0.1 ram t h i c k m i c r o s l i d e g l a s s . In order t o ma i n t a i n the specimen I n green c o n d i t i o n i t was mounted i n a f i l m of water between the two gla s s p l a t e s during compression t e s t . This assembly was p l a c e d on the compression d i s c of the t e s t i n g machine wi t h the t h i n m i c r o s l i d e g l a s s f a c i n g the l o a d i n g head. Load was a p p l i e d at a constant speed of 0.002 i n c h per minute, chart speed was 1.0 i n c h per minute. S e n s i t i v i t y of l o a d c e l l was 25 grams. Tests were performed at room temperature. Specimens a f t e r t e s t s were returned t o v i a l s . S e v e r a l microsections y i e l d e d t e s t specimens w i t h too much v a r i a t i o n among r e p l i c a t e s , e s p e c i a l l y i n t e n s i o n t e s t s . Data from such s e c t i o n s were discarded and adjacent s e c t i o n s were t e s t e d . A n a l y s i s of stress-deformation diagrams The procedures f o r o b t a i n i n g data from the I n s t r o n chart traces are i l l u s t r a t e d i n F i g . 1 and 2. These curves were tr a c e d from the charts and reduced to h a l f - s i z e . Since i t i s conventional t o i l l u s t r a t e s t r ess-deformation diagrams w i t h the -20-Deformation.lO6- in 0 02 0-6 10 1-4 Deformation, 10"^  in-EARLYWOOD LATEWOOD 11-6 Tmax.lO3 psi 24-7 1-4 Umax.lO-2 in- 1-6 •86 E.IO6 psi 1 83 35-6 Wmax, in--lb/in-3 93-4 0022 c = correction line,slope % 0022 F i g u r e 1. R e s o l u t i o n of t y p i c a l m i c r o - t e n s i l e s t r e s s - d e f o r m a t i o n diagrams f o r Douglas f i r earlywood and latewood -21-Defor motion JO" 4 ! * Deformotion.lO^in-EARLYWOOD LATEWOOD 5-42 2 Cimox.lO psi 21-96 37-8 Umox. lO" 4 in- 211 00019 E. IO 6 psi 00141 169 Wmox, i n - l b / i n ^ 437 0075 c°correction line, slope % 0293 Figure 2. Resolution of t y p i c a l micro-compression stress-deformation diagrams for Douglas f i r earlywood and latewood -22-v e r t i c a l axis as stress and the horizontal axis f o r deformation, the mirror-images of the automatically recorded Instron diagrams were rotated 90 degrees clockwise. Instead of recording load i n kilograms on the v e r t i c a l axis corresponding values were computed for stress i n pounds per square inch. S i m i l a r l y , deformation as 10~^ inch Is used on the horizontal axis instead of time i n minutes. The following strength properties can be computed by analysing the charts: stress at proportional l i m i t , ultimate stress, modulus of e l a s t i c i t y , ultimate deformation or s t r a i n , work to proportional l i m i t , and work to maximum load. Although only the f i r s t and second property have been dealt with i n this study, methods for computing the other values are presented. Tensile stress-deformation curves consist of an i n i t i a l straight portion, which represents the e l a s t i c range of the specimen, and a curved portion i n the p l a s t i c range. Depending on the test method, load range used, chart speed and load speed an i n i t i a l curvature i s also present i n some cases but not as well pronounced as on compression stress-deformation curves. In compression, the stress-deformation curves exhibit four zones with respect to mechanical c h a r a c t e r i s t i c s : the 0 i n i t i a l zone where adjustment of load to the compression face takes place (3, \\), the e l a s t i c range where load or stress i s proportional to deformation, the p l a s t i c range where pro-p o r t i o n a l i t y no longer exists, and the zone beyond the maximum load where compression i n d e f i n i t e l y approaches a t h e o r e t i c a l zero-deformation. Under conditions of the teat creep s t a r t s -23-beyond the proportional l i m i t and r e l a x a t i o n of load increases gradually at f i r s t , then at a constant rate described by a sigmoid-pattern of the curve which i s sharply pronounced i n earlywood but becomes smoother and f l a t t e r when latewood specimens are tested (12). The i n i t i a l curvature i s disregarded i n analysis (3, Ij .) . The second portion of the curve, i . e . , the e l a s t i c range, i s delineated with a tangent to the curve. Proportional l i m i t i s marked where the curve deviates from t h i s tangent. The load at this point i s obtained by p r o j e c t i o n to the horizontal axis on the Instron chart. Load i n kilograms divided by the crosa-sectional area of the t e n s i l e test specimen, or by the area of the compression test specimen, y i e l d s stress values i n kilograms per square centimeter which i s converted to pounds per square inch by multiplying with a factor (1^.223). Ultimate t e n s i l e load i s simply recorded at the end of the curve where the specimen breaks (Pig. 1) . Ultimate com-pression stress i s found at the i n f l e c t i o n point on the curve i n the p l a s t i c range where load r e l a x a t i o n starts to decrease and the downward-curvature reflexes as shown on Pig. 2 (12, 21). In order to obtain i n f l e c t i o n points on micro-compression stress-deformation diagrams for Douglas f i r and P a c i f i c yew latewood, specimens about 180 to 200 microns thick were required. In determining modulus of e l a s t i c i t y and deformation or s t r a i n at maximum load, a "correction l i n e , " marked as w c " on P i g . 1 and 2 should be established. This l i n e i s the v e c t o r i a l sura of load speed and chart speed. The slope of the l i n e i s dependent upon the load range used. The "c" l i n e i n tension i s determined by gripping a material of very high elastic modulus, e.g., steel or glass, i n the jaws and letting the recording needle draw a line on the chart. In compression, glass is subjected to compression load and a similar line is drawn on the chart. Using the 5 kg range in tension, the slope of the line is 0.22 inch per 10 inches, or the tangent equals 0.022. In compression, this tangent value was found to be 0.075 in the 20 kg range and O.293 i n the 5 kg range. Since the i n i t i a l curvature of the stress-deformation curve is disregarded, the tangent line of the elastic range is extended to the deformation-axis. The intersection denotes the point of "zero-deformation." It is at this point where the correction line originates when deformation is to be computed. Deformation at any phase of the test or at any point on the curve can be computed by projecting the point on the curve to the correction line, parallel to the deformation-axis. The distance, measured in inches and multiplied with the loading speed, provides the deformation in inches. If the selected location on the stress-deformation curve is the end of the curve (in tension) or the point of inflection (in compression), the maximum deformation value is obtained. Modulus of el a s t i c i t y is computed by the conventional 1 • formula E * -Pf-» where E = modulus of elast i c i t y in pounds per square inch, P = load at proportional limit i n pounds per square inch, L = gage length of tensile test specimen or thickness of compression specimen in inches, A = area of specimen subjected to normal load i n square inches, and S = deformation at the proportional limit in inches. Previous work (12) has shown that -25-modulus of e l a s t i c i t y may be calculated from Instron charts when rectangular specimens are used. Work values are determined simply by the conventional formulae V = g ^ E V a n d W m a x = ^ (6) . where Wp-^  = work to proportional l i m i t i n inch-pound, g = stress at proportional l i m i t i n pounds per square inch, V = volume of specimen i n cubic inches, E - modulus of e l a s t i c i t y i n pounds per square inch, W m a x = work to maximum load i n inch-pound per cubic inch, Q4. = load-deformation equivalent of one square inch on the graph paper and A = area under the stress-deformation curve. With respect to A, i t must be pointed out that the area under the compression curve f a l l s within the following boundaries: a) the tangent to the curve from zero-deformation to the pro-po r t i o n a l l i m i t , b) the curve from the proportional l i m i t to the i n f l e c t i o n point, c) ordinate of i n f l e c t i o n point, and d) deforma-t i o n a x i s . If work to proportional l i m i t has to be expressed i n r e l a t i o n to unit volume, the value of Wp]_ i s divided by V, thus the dimension w i l l be inch-pound per cubic inch. RESULTS Micro-specific gravity, based on green volume and oven-dry weight, maximum micro-tensile stress, s p e c i f i c t e n s i l e stress, -26-maximum micro-compression stress and micro-compression stress at the proportional l i m i t (P.L.) were recorded f o r each micro-section tested. Suraraative r e s u l t s are tabulated i n Table I I . Maximum micro-tensile stress data f o r P a c i f i c yew were not used due to large v a r i a t i o n within microsections. The test material of t h i s species did not appear to be homogeneous due to lack of straight grain along the length of the te n s i l e test specimens. Because of narrow sections, only two r e p l i c a t e s could be obtained from each section blank which is fewer than the calculated r e p l i c a t i o n number required. Mean stress values encountered ranged from 6600 to 9800 p s i with 25 to l\.0 per cent error, which f a r exceeded the minimum allowable error of 10 per cent. One determination of micro-tensile stress and micro-compression stress i n increment No. I 3 2 of western white pine had to be discarded due to poor r e p l i c a t i o n of results i n those sections. D i s t r i b u t i o n of micro-specific gravity, maximum micro-tension and micro-compression stresses, as well as s p e c i f i c t e n s i l e stress, i n three adjacent growth increments of western white pine are i l l u s t r a t e d i n P i g . 3. Values for s p e c i f i c com-pression stresses for this species are given i n Table I I I . No de f i n i t e trend was obtained, which i s similar to e a r l i e r attempts with Douglas f i r ( 1 2 ) . P i g . 4 graphically i l l u s t r a t e s r e l a t i o n s h i p of maximum micro-tensile stress to s p e c i f i c gravity. A demonstration of comparison between the maximum micro- and macro-tensile stress r e l a t i o n s h i p s and s p e c i f i c -27-gravity i s given i n F i g . 5. Data for small clear t e n s i l e teat specimens were obtained from the Forest Products Laboratories of Canada, Vancouver Branch ( 1 ) . Data for gross wood are l i s t e d i n Table IV. Since the equation for macro-specimens, and the curve derived therefrom, r e l a t e to compression stress at proportional l i m i t while stresses of tissues are at maximum load, the two d i f f e r e n t strength properties could not be compared d i r e c t l y u n t i l r e l a t i o n s h i p was shown between the two values. Bodig (3, \+) proved that highly s i g n i f i c a n t r e l a t i o n s h i p exists between compression stress at ultimate load and stress at proportional l i m i t of gross specimens. The same r e s u l t was found on the t i s s u e - l e v e l , as i l l u s t r a t e d i n F i g . 6, permitting comparison between the two strength properties. Relationship between maximum micro-eompression stress and s p e c i f i c gravity i s shown i n F i g . 7. The o r i g i n a l curve f o r the v a r i a t i o n of compression stress of small clear specimens at proportional l i m i t with respect to s p e c i f i c gravity was p l o t t e d as F i g . 6 to compare compression s t r e s s - s p e c i f i c gravity r e l a t i o n s h i p s of gross wood and t i s s u e . In F i g . 7 a t h i r d curve i s plotted i l l u s t r a t i n g regression of maximum micro-compression s t r e s s - s p e c i f i c gravity r e l a t i o n s h i p of P a c i f i c yew. The anomaly indicates that t h i s species belongs to an e n t i r e l y d i f f e r e n t population with respect to r a d i a l micro-compression behavior. The equations shown with the figures were derived by regression analyses and straight l i n e s or curves were f i t t e d to plotted data. A l l regressions have been conditioned to zero--28-intercept. A l l analyses were performed at the 95 per cent con-fidence l i m i t . Although a l l test data have been included i n the analyses, only s i x data points i n each increment of western white pine have been plo t t e d on the figures i n order to avoid over-crowding of dots. Table I I . Summary of tes t r e s u l t s of six coniferous woods g P o s i t i o n S p e c i f i c Maximum S p e c i f i c Maximum Micro-S • r i n g , % gravity micro-tensile micro-tensile micro-compression compression (green volume) stress, stress, stress, stress at g 103 p s i 10-3 p s i 10 2 p s i proportional H _ l i m i t , IO 2 p s i Pinus rapnticola Dougl. 4»5 O.ij.03 10.82 26.86 8.6 O.39I IO.I3 25.91 20.8 0.1j05 9.55 23.58 28.4 0.389 11.01 28.31 36.6 O.383 10.34 27.01 48.8 0.377 10.67 28.3I H 56.8 0 . 5 l 2 12.74 30*91 65.2 0.452 14.13 31.27 73.O 0436 14.05 32.23 81.6 0.536 14.II 26.33 90.7 0.596 17.13 28.74 100.0 0.668 16.68 25.00 2.8 O.368 8.95 24.32 3.73 3.26 5.3 0.415 9.42 22.70 3.94 3.4^ 7 . f 0.410 9.43 23.01 E.o4 2.54 14.9 0.399 9.73 24.39 4.16 3.64 22.0 0.404 H . 7 5 29.08 4.11 3.00 29.3 0 4 l 7 H . 2 8 27.05 3.76 3.29 36.8 0.412 12.92 31.37 > 96 2.77 4 4 2 0.420 13.42 31.96 4.3| 3.81 £9.2 0.470 12.15 25.85 4.12 > ° i 4* Table II continued cf P o s i t i o n Specif i c 1 ring> % gravity 2 o (green volume) 8* av r-i 3 r-l CO 89.7 97.2 100.0 4.8 8.6 19.5 29.1 9.0 8.8 58.6 63.7 7 5 a 83.4 88.5 94.1 10.7 .5 50.5 65.0 '91.1* 13.1 22.0 1*1.9 0.601 0.616 0.575 0.670 O..36O O.36O 0.157 0*418 0.4.28 0.381 0.522 0 4 0 9 0.485 0 4 7 1 0.497 0.720 0.285 0.479 0.436 0.606 0.845 0.897 0.3144. 0.336 0.411 Maximum S p e c i f i c Maximum Micro-micro-tensile micro-tensile micro-compression compression stress, stress, stress, stress at 103 p s i 103 p s i 10 2 p s i proportional l i m i t , 1 0 2 p s i Pinus monticola Dougl, 14.01 15.02 15.64 15.75 2^38 23.34 27.39 9*40 9.53 9.86 11.78 12.96 12.91 14.65 15.66 15.63 17.22 I8.83 19.22 26.10 26 .48 27.61 28.19 30.27 33.88 34.71 38.68 32.22 36.55 37.89 26.70 6.08 5.3 2 6.19 5 . 4 2 7.31 4-85 2.38 2.08 2.38 1.82 1.99 1.74 2.75 1.66 2.90 2.59 2.87 2.O3 3.07 2.69 3.18 2 . 4 6 3 . 4 S 2.99 3.51 2.3O 3.68 3 . 2 2 6.38 4.51 Paeudotsuga menziesii (Mirb.) Franco 3-49 9.12 9.31 16.53 22.39 22.06 12.26 19.04 21.35-' 27.27 26.50 24.59 2.48 3.57 4 .89 7.53 11.72 5.11 7.26 10.06 14.85 21.62 2 4 . 4 7 3.92 2.71 3.12 3.3O 1 O I o 1A eg co Table II continued . % P o s i t i o n S p e c i f i c Maximum Sp e c i f i c M a x i m u m M i c r o -% . r i n g , % gravity micro-tensile micro-tensile micro-compression compression ^jg (green volume) stress, stress, stress, stress at M - 1°-* p s i 103 p s i 10 2 p s i proportional _ ; l i m i t , 10 2 p s i Pseudotsuga menziesii (Mirb.) Franco 60.3 0.779 6 3 . 8 0.770 9 ? . 6 0.810 10.6 0 O 1 5 32.9 O.378 IJ9.6 O.374 70.8 0 .B54 81.7 0.867 9 2 . 9 0.842 _ / B I 6 - f 3 21.35 7.59 5 . 9 9 1 9 . 4 6 25.27 15.62 11.47 ~~ ' " n " 24.78 30.59 13.83 9 . 8 4 5 . 4 4 17*28 4 . 0 4 6 . 9 4 I 8 . 3 6 4*26 13.12 35.09 5 .53 21.51 25.19 10.99 26 .82 23.76 9.98 2 0 . 0 0 30.93 12.71 Tsuga heterophylla (Raf.) Sarg. 14.7 O.338 10.02 29 .64 ~ 3.07 2 .39 2 0 . 0 O.33O 10.18 3O.85 3.40 2 .78 3 6 . 4 0.554 12.97 2 3 . 4 l 4.72 7.60 61.0 0.544 18.11 33.30 8.62 7.69 76.4 0.620 2 I .3O 34*35 9.48 8.26 100.0 0.761 21.97 28.86 12.27 9.26 5 . 1 0.277 . 7 . 1 2 25.70 3.23 2.57 2 3 . 8 0.525 14*12 26.90 8.84 6 . 3 3 5 2 . 7 0.610 17.92 29.38 8.65 7.50 70.8 O.637 18.68 29 .13 9.92 6 . 9 9 ™ 90 .0 0.652 21 .8k 3 3 4 9 10.85 7.31 9 6 . 2 0.641 22.65 35.33 10.01 7.06 4 . 8 O .3I7 6.47 2 0.kl 1*97 1.82 14.5 O.503 10.35 2 5 . 6 8 3.67 2 . 7 8 29.7 0 J 3 9 l 2 - 5 6 23.31 7.71 4 . 9 4 o 59 .7 0.619 19 .33 31.23 9.69 £.37 " 7 4 4 0.653 19.55 29 .95 10.86 , 6 . 9 0 100 0 0.689 19.91 2 8.89 H . 9 5 : 8 ^ 1 KM a <D s • © o u & o Table II continued P o s i t i o n S p e c i f i c r i n g , % g r a v i t y (green volume) Maximum Sp e c i f i c Maximum Micro-micro-tensile micro-tensile micro-compression compression stress, stress, stress, stress at 1 0 3 p s i 103 p s i i o 2 p s i proportional l i m i t , 102 p s i Abies balsamea (L.) M i l l . ON r-i 16.4 3^.1 51+. 0 73.7 91.8 99.1 0.278 O.3O6 0*396 O.Jkl 0.568 0.1+89 1.78 5.81 8.94 10.74 15.37 14.05 6.39 18.98 22.58 24.34 31.43 24.73 2 . 8 2 2 . 8 0 3.72 6.25 6.49 IO.32 2.00 2.05 2 . 7 3 4 . 7 1 .55 83 o 15.4 25.2 43.9 56.5 8 0 . 8 93.9 O . 3 O 6 0.264 O.323 O.389 0.530 0.651 7.51 5.69 7.60 9.70 13.48 19.91 3.01 3.14 . 1 6 6.43 9.45 r-i OJ 14.5 2 8 . 7 46.5 6 0 . 8 7 8 . 9 9 3 . 8 5.27 8.02 9.18 10.55 11.80 17.87 19.39 25222 2 8 . 8 6 3I.3I 26 .93 28 .73 3.O3 3.17 3.45 3.62 3-85 9.90 Thuja p l i c a t a Donn 11.4 34.8 50.7 6 2 . 6 74.8 96.1 0.225 O.232 0 .226 0 . 2 6 2 0.284 0.579 3.09 4.05 5.01 6.84 6.72 25.81 13.72 17.48 22.18 26.12 23.66 44.59 1.67 1.68 1.64 1.85 2.16 5.75 I.23 1.14 1.41 1.39 2.28 3.41 Table I I continued P o s i t i o n S p e c i f i c © © o Wei o vO rH r i n g , % 10.8 3 9 4 47.6 72.7 88.0 100.0 11.4 37.7 66.2 84.1 96 .3 3.9 16 .0 36.3 51.0 61 .0 100.0 6.6 20.0 40.5 57.4 81.4 95.5 Maximum S p e c i f i c Maximum Micro-gravity micro-tensile micro-tensile micro-compression compression (green volume) stress, stress, stress, stress at 103 p s i 103 p s i IO 2 p s i proportional l i m i t , IO 2 0.200 0.224 0.216 0.265 0.343 0.472 0.219 0.229 0.248 0.261 0.262 0.515 0.592 0.753 0.580 0.669 0.731 0.729 0.657 0.572 0.580 0.652 0.700 0.699 2.66 3.00 3.52 6.16 7.40 12.33 13.29 13.38 16.28 23.23 21.58 26.12 1.46 2.00 2. 4.46 4.34 4.77 5.0k 7.o4 21.41 20.37 18.95 19.25 19.31 26.88 41*57 l . k j 1.65 1.71 2.05 2.10 5.64 Taxus b r e v i f o l i a Nutt. 15.29 27.15 I6.39 21.16 18.28 27; 08 17.22 l4 .79 17.30 17.56 20.03 21.16 p s i 1.05 1.86 0.93 1 . 4 l 1.78 3.94 0.91 1.18 1.07 1.59 1.57 4.16 17.75 11.22 14.72 12.59 17.91 12.90 9.85 11.67 11.54 15.02 14.63 1 u> vo I Table II continued  •g P o s i t i o n S p e c i f i c Maximum S p e c i f i c Maximum Micro-g # r i n g , % gravity micro-tensile micro-tensile micro-compression compression ®5§ (green volume) stress, stress, stress, stress at 2 103 p a l 103 p s i 10 2 p s i proportional H l i m i t , 10 2 p s i Taxua b r e v i f o l i a Nutt. 6 4 24.9 h.34 67.1 87.3 100.0 0.553 0.570 0.588 .0.61*1 0.559 11.36 15.89 13.96 19.34 11.91 4.26 8 . O 3 10.92 9.72 4 . 1 1 7 4 4 9.63 Table I I I S p e c i f i c micro-compression s t r e s s e s of s i x coniferous woods +5 fl <D 6 • <D ,0 U & o P o s i t i o n I n r i n g , % i s S p e c i f i c micro- § . compression © ,°. s t r e s s , o 10 2 p s i £ P o s i t i o n S p e c i f i c a i n r i n g , micro- fj . $ compression® J! s t r e s s , o 10 2 p s i £ P o s i t i o n In r i n g , i S p e c i f i c micro-compression s t r e s s , 10 2 p s i Pinus monticola Dougl. i.6 20.8 28.ii 36.6 5.8.8 56.8 6 5 . 2 73.0 81.6 90.7 100.0 8.18 7.73 5.86 8.82 9.53 7.97 8.62 9.17 10.68 9.36 11.% 5.3 7.7 4 . 9 22.. 0 29.3 36.8 54- 2 14-9.2 51.6 59.2 69.1 74-3 8I4..6 89.7 91+.6 97.2 100.0 •10.1' 9.UB 9.85 19.43 10.18 9.01 9.61 9.65 8.77 9.95 10.69 11.86 11.5.7 10.67 10.67 10.81 10.90 .8 .6 19.5 29.1 9.0 8.8 58.6 63.7 75.1 83A 85.? 94.1 6.62 6.62 5.57 6.57 6.91 l\zl 7.87 7 .0 7 . 4 0 8.16 Pseudotsuga m e n z i e s i i (Mirb.) Franco oo 10.91 9 . 5 2 11 . 5 1 11 . 4 9 1 4 . 1 3 16 . 4 2 _=t 1 3 . 1 22.0 4 1 . 9 6O.3 63.8 92.6 11.40 ll.kO 11.87 9 . 7 4 20.29 17.07 o 1A 10.6 2.9 • • 9 * S 70.8 81.7 92.9 1 2 . 8 3 11 .27 14 .79 12.87 1 1 . 5 1 1 5 . 1 0 Table III continued © B • © o a * P o s i t i o n i n r i n g , % S p e c i f i c micro-compression stress, IO 2 p s i -p © s • © o u& o « P o s i t i o n i n r i n g , ' % S p e c i f i c "g micro- ® compression © o* stress,. &521 10 2 p s i £ Po s i t i o n i n r i n g , % S p e c i f i c micro-compression stress, 10 2 p s i Tsuga heterophylla (Raf.) Sarg. 20.0 36.14. 61.0 76.i|. 100.0 16.4 3^.1 54.0 73.7 91.8 99.1 I O . 3 O 8.52 15.8* 15.29 16.12 o j 5.1 23.8 52.7 70.8 90.0 96.2 11.66 16.8k 14-58 15.57 16.64 15.62 oj 4.8 H|.5 29.7 59.7 lOOiO Abies balsamea (L.) M i l l . lO.lij. 9.15 9.39 Hf. 17 11.113 21.10 o oj I5.ii 25.2 43.9 56.5 80.8 93.9 9.84 11.89 10.65 10.86 12.13 14.52 rH eg l k . 5 2§.7 46.5 60.8 78.9 Itf. 8 6.21 9.11 l 4 . 3 0 15.65 16.66 17.34 11.14 9.97 10.85 10.7k 8.79 15.92 1 1 3 r.3 11 50.7 62.6 74.8 96.1 3.9 16.0 36.3 51.0 61.0 100.0 Thuja 7.2% 7.26 7.06 7.61 9.93 10.8 72.7 88.0 100.0 Taxus b r e v i f o l l a Nutt. 25.83 36.O6 28.26 3J.63 25.01 37.15 vO H "TIF 20.0 k0.5 81.4 95.5 26.21 25.86 29.83 26.93 28.61 30.27 ro H 24.9 43.4 67.1 87.3 100.0 6.53 7.21 6.90 7.85 8.02 10.95 '.88 20, 27. 23.74 30.17 21 .3I 27.81 Table IV. Summary of data of small clear t e n s i l e test specimens (Forest Products Laboratories of Canada, Vancouver Branch) Tree No. Lab. No. Rings per inch Latewood fo Moisture content, Specific % gravity (green volume) Maximum ten s i l e stress, 10 2 p s i Pseudot3u ga menziesii (Mirb.) Francol 1 51*336 41 54352: 7 10 11 12 10 4 42 tt >° LO 50 30.5 29.8 104.0 32.2 32.0 29.4 27.1 OJ4.78 oi4c?9 0.441 0.471 0.367 0.499 14.22 17.51 12.01 17.68 20.07 8.70 18.58 2 54098 99 54100 3101 02 03 Ok o> 54106 -* 5 8 9 6 8 7 8 28 31 31.7 30.7 36.3 32.I 42.0 32.5 70.0 31.2 34.6 0.370 O.46O 0.424 0.469 0.499 0.509 O.486 0.474 0.485 10.17 19.76 11.51 18.32 19.19 15.71 16.15 16.46 16.65 k 53563 64 66 67 68 69 70 71 72 10 9 5 5; 9 9 11 11 7 52 62 37 2 7 50 50 34.0 k l . ! 34.5 34.1 32.2 34*5 ^ ! l 0.596 ° o ! ^ 0.565 0.648 0.635 0.520 0.531 0.600 27.67 23.57 17.73 20.65 25.07 25.l4 13.21 20.15 17.84 Table IV continued Tree Noi Lab. No. Rings per inch Latewood - * Moisture content, fo S p e c i f i c gravity (green volume) Maximum te n s i l e stress, ]f>2 pai Picea giauca (Moeneh) Voss 1 49 37 22 49 16 17 17 28.6 112.6 28.1 0.370 0.358 0.358 9.87 10.05 12.16 58716 17 18 36 17 38 .28 18 23 27.5 32.4 29.7 0.451 0 .4l5 0.486 9.74 7.42 14.35 29 1 35 16 20 19 17 37.7 30.3 28.2 29.4 I3.6O 13.87 13.65 13.01 % P 0 3 0 J . 62 64 58365 0.339 0.342 0.351 0.346 58636 58859 60 62 6, 65 25 31 20 21 23 28 24 21 15 15 20 18 20 19 15 3I.3 30.5 29.6 25.2 3O.6 29.5 28.3 30.9 18 17 16 18 15 17 22 16 22 15 23 20 37.2 29.0 52.6 37.6 55.6 42.7 0*361 0.362 0.392 0.366 0.408 O.373 0.368 O.350 0.37 0.345 0.351 0.330 0.363 0.351 lk . 6 3 15.17 16.11 14.96 16.09 16.70 10.82 12.37 13.9k 12.16 16.18 12.07 17.68 12.55 1 O r i g i n of (second-growth) Douglas f i r : Coombs, B.C. 2 O r i g i n of white spruce: Nordegg, A l t a - 3 9 -DISCUSSION Behavior of Western White Pine Western white pine was chosen as one of six Canadian conifers i n order to observe the behavior of a species with gradual t r a n s i t i o n from earlywood to latewood i n micro-tension and micro-compression. The procedures employed during strength tests, as well as for s p e c i f i c gravity determinations, were i d e n t i c a l to those with the other f i v e species, although the sampling was more intensive. Every second microsection was examined i n each of the three increments studied. The reason for t h i s was that western white pine has not been previously studied as regards i t s intra-increment physical properties. C o l l e c t i o n of r e l a t i v e l y more test data seemed j u s t i f i e d i n order to obtain r e l i a b l e d i s t r i b u t i o n patterns for a species with gradual t r a n s i t i o n . A r e l a t i v e l y low s p e c i f i c gravity value of O . 3 6 has been found f o r gross specimens (based on green volume and oven-dry weight) ( 6 ) . The range of intra-increment variations extended from O . 3 5 7 to 0 . 7 2 0 but the widest portion of the increments, from Ofo to about 70$ p o s i t i o n , included a s p e c i f i c gravity range from O . 3 5 0 to 0 . 5 0 0 , leaving the remaining 3 0 $ or l e s s of increments with higher s p e c i f i c g r a v i t i e s (Pig. 3 ) . This phenomenon i s of primary importance when d i s t r i b u t i o n patterns i n western white pine are compared to those found i n species with abrupt t r a n s i t i o n , -5 .0-f o r instance Douglas f i r . A species with gradual t r a n s i t i o n and low s p e c i f i c gravity exhibits a gradually r i s i n g d i s t r i b u t i o n pattern of i t s s p e c i f i c gravity across the growth increment, suggesting a second-degree curve, whereas species with abrupt t r a n s i t i o n show sigmoid-shaped d i s t r i b u t i o n s , as demonstrated i n e a r l i e r studies (12, 16). The explanation is obvious. A tree with abrupt t r a n s i t i o n and wide range of s p e c i f i c gravity develops tissues of varying c e l l - w a l l thickness. Increase of thickening r i s e s abruptly at the inception of latewood, therefore s p e c i f i c gravity changes take place with s i m i l a r i n t e n s i t y . This abrupt change i s indicated by the sharp r i s e of the d i s t r i b u t i o n curve at approximately O.lj.0 and 0 .50 s p e c i f i c gravity l e v e l s . When no more appreciable increase of c e l l wall substance i s r e a l i s e d and therefore s p e c i f i c gravity approaches a constant l e v e l , the "S" shape commences to f l a t t e n out (12, 16). In comparison, western white pine exhibits r e l a t i v e l y high s p e c i f i c gravity values close to the end of the increment only, thus the "flattening-out" of the curve cannot occur. Moreover, since c e l l - w a l l thickening i n western white pine takes place at a nearly constant rate, the upward-curvature of the d i s t r i b u t i o n curve w i l l not be pronounced as sharply as i n species with abrupt t r a n s i t i o n . It Is easy t o v i s u a l i s e that i f the s p e c i f i c gravity d i s t r i b u t i o n s of these two species, i . e . , western white pine and Douglas f i r , were super-imposed on each other, the former would occupy only part of the l a t t e r . It follows that i n case of c o r r e l a t i o n between s p e c i f i c gravity and strength properties, strength d i s t r i b u t i o n patterns across growth increments would indicate d i s t r i b u t i o n s similar to -41-0 2 4 Radial distance, mm Earlywood Latewood Figure 3. D i s t r i b u t i o n of s p e c i f i c g r a v i t y (green volume), maximum micro - t e n s i l e s t r e s s , maximum micro-compression st r e s s and s p e c i f i c t e n s i l e stress i n Pinus monticola Dougl. those of s p e c i f i c gravity. It must be noted, however, that i n some species a s l i g h t increase of s p e c i f i c gravity i n the higher l e v e l s causes substantial increase of c e r t a i n strength properties ( 2 3 ) . In western white pine, micro-compression strength varies from 200 to 790 p s i only and micro-tensile strength values encompass a range of 9000 to 19 ,200 p s i , whereas In Douglas f i r micro-compression and micro-tension values vary from 3IO to 1560 p s i and from 3OOO to 26 ,800 p s i , respectively, within a wide s p e c i f i c gravity range from 0.285" to 0.897 (Fig. 3 and Table I I ) . Preparation of western white pine sections f o r t e s t i n g was aggravated by large and numerous r e s i n canals, e s p e c i a l l y i n latewood t i s s u e s . Longitudinal r e s i n canals were excluded from tes t specimens as much as possible, since such c a v i t i e s , with diameters of 135-150 microns, would have caused great error In cross section and volume determinations, and possibly i n physical test values. Tension-Specific Gravity Relationships Micro-tensile stress was s i g n i f i c a n t l y correlated with s p e c i f i c gravity, described by the equation Y = 273J4.O.6X. The c o r r e l a t i o n c o e f f i c i e n t was found to be O.82I4.5 (Pig. 1+). S p e c i f i c gravity accounted f o r 68$ of the v a r i a b i l i t y among the f i v e woods tested i n micro-tension. However, i t was found that the r e l a t i o n s h i p with small clear macro-specimens was also s i g n i f i c a n t (r = O.7I4.) but s p e c i f i c gravity accounted f o r only 55 per cent of the v a r i a b i l i t y . It must be pointed out that the standard t e n s i l e test f o r macro-specimens i s d i f f i c u l t to control and the available data were r e s t r i c t e d to a r e l a t i v e l y narrow 1 1 1 1 1 1 1 1 ' 1 ' 1 ' 1 ' 1 ' - • Pinus monticola Dougl- + © Pseudotsugamenziesii (Mirb)Franco O / -A Tsuga iteterophylla (Raf)Sarg-A Abies balsamea (L ) Mill- A A -— •*• Thuja plicata Donn-A * V / O - — — • o m O . . • -— — ±S • ° o si* ° y = 2734 x n=H4 r = 0-82 r 2 = 0-68 SEE=±3296 psi — mmmmu -< 1 , 1 , A 1 , i i 1 i 1 i 1 i l i l 0 I -2 -3 -4 -5 -6 -7 -8 -9 10 Specific Gravity (areen volume) F i g u r e 4. R e l a t i o n s n i p between maximum m i c r o - t e n s i l e s t r e s s and s p e c i f i c g r a v i t y ( g r e e n volume) f o r f i v e c o n i f e r o u s . s p e c i e s s p e c i f i c gravity range (O.33O to 0.61*8) although care was taken to select data with as wide a s p e c i f i c gravity range as possible. The trend of the two regression l i n e s i n P i g . 5 is evident, with steeper slope for gross wood data. The scatter of maximum micro-tensile stress values (Fig. I*) s t a r t s to increase between O.lj. and 0.5 s p e c i f i c gravity. Although values i n the lower s p e c i f i c gravity ranges exhibited less scatter, most species f e l l below the calculated regression l i n e , e s p e c i a l l y western red cedar, the species with the lowest density. The f i v e species tested i n micro-tension exhibited d i f f e r e n t behavior. Micro-tensile stress of western hemlock increased gradually from 0 to about the 75$ p o s i t i o n (6000 p s i to 20,000 psi) and showed tendency to remain nearly constant there-a f t e r . Western red cedar maintained constant l e v e l of t e n s i l e stress (2500 p s i - 1*000 psi) to about 55$ p o s i t i o n . Stress beyond the 70$ p o s i t i o n i n the increment increased abruptly from 5000 p s i to 26,000 p s i (Table I I ) . The sharp increase of t e n s i l e stress would have been more sharply pronounced had more data been coll e c t e d between 75 and 100 per cent positions. In that case the boundary of the physico-mechanical latewood would have been designated. S p e c i f i c t e n s i l e stress d i s t r i b u t i o n i n Douglas f i r and white pine reached the peak before the i n i t i a t i o n of latewood. Similar r e s u l t s with Douglas f i r were reported by other workers (15, 3D . The same phenomenon was found with hemlock and balsam f i r (Table I I ) . The peak occurred well i n the latewood or at the end of the increment i n western red cedar, but one must consider the very low latewood percentage (less than 10 per cent) which -Fr VJ1 Specific Gravity (green volume) F i g u r e 5. K e i a t i o n s h i p o f maximum macro- and m i c r o - t e n s i l e s t r e s s t o s p e c i f i c g r a v i t y could have shifted the s p e c i f i c strength peak to a higher per-centage p o s i t i o n . In cedar only one latewood tissue was tested i n each increment. This may also explain the p o s i t i o n of the peak. Balsam f i r micro-tensile stress increased gradually across the increments tested with somewhat stronger tendency at or around the 80 per cent p o s i t i o n . Maximum micro-tensile stress i n thi s species increased from 2000 p s i to 20,000 p s i . Two types of f a i l u r e have been observed i n micro-tension: f a i l u r e across the c e l l wall i n earlywood and f a i l u r e i n the middle lamella i n latewood at which time tracheids are separated (1%, 17). Generally, f a i l u r e i n the middle lamella occurs i n thick-walled f i b e r s and tracheids (13). These tests showed the same behavior. P a c i f i c yew supplied the best example for t h i s fact since f a i l u r e i n the middle lamella occurred even i n the earlywood zone. Compression-Specific Gravity Relationships Maximum micro-compression stress was found to be s i g n i f i c a n t l y correlated with s p e c i f i c gravity, with r = 0.92. S p e c i f i c gravity accounted for 85 per cent of the v a r i a b i l i t y . 1.528 The equation Y = 1599»3X i s b a s i c a l l y the same as the one 2 2*5 established f o r small clear specimens (23): P = 2900 G where P i s compression strength at proportional l i m i t of gross wood i n p s i , and G i s s p e c i f i c gravity. P i g . 6 shows a l e s s -pronounced upward-trend of maximum micro-compression stress than i n case of gross wood. An exponential function of the form Y = a 1 0 b x would also describe the re l a t i o n s h i p , but the o r i g i n a l form Y = ax b -1*7-was adhered to since the objective was the re-examination of t h i s function at the t i s s u e - l e v e l * The scatter s t a r t s to increase at 0 . 5 s p e c i f i c g r a v i t y . P a c i f i c yew exhibits unique behavior i n that stresses are found i n the higher ranges from 1 2 0 0 to 2 7 0 0 p s i at r e l a t i v e l y low le v e l s of s p e c i f i c gravity, i . e . , from 0 . 5 2 to 0 . 7 5 . P a c i f i c yew was chosen f o r the experiment to extend the s p e c i f i c gravity range as close to 1 . 0 as possible, since yew i s one of the densest conifer^,with 0 . 6 s p e c i f i c gravity (based on green volume). It was found that i t s s p e c i f i c gravity i s high both i n earlywood and latewood with not much increase i n the l a t t e r . S p e c i f i c gravity does not seem to influence maximum micro-compression strength i n a manner similar to the other f i v e species tested. Small tracheid diameter i n t h i s wood ( 1 5 - 2 0 microns), coupled with thick c e l l walls, c e r t a i n l y does d i f f e r e n t i a t e i t from the other f i v e species tested. There might be other influencing factors as well, e.g., lumen diameter-to-wall thickness r a t i o , f i b r i l o r i e n t a t i o n and chemical composition. The equation Y = 1*2)4.0.6X " J expresses maximum micro-compression stress of P a c i f i c yew as a function of s p e c i f i c gravity, with r = 0 . 9 0 . The r e l a t i o n s h i p i s highly s i g n i f i c a n t . S p e c i f i c gravity i n t h i s single species accounts fo r 8 l per cent of v a r i a b i l i t y . Since behavior of P a c i f i c yew d i f f e r s greatly from that of the other f i v e species tested one can i n f e r that the s t r u c t u r a l c h a r a c t e r i s t i c s of a species have a s p e c i a l bearing upon i t 3 strength-specific gravity r e l a t i o n s , k closer examination of P i g . 7 suggests that a l l species tested exhibit 4 6 8 10 12 14 16 Micro-compression Stress at Proportional Limit, 10*- psi Figure 6. Relationship between micro-compression stress maximum and at proportional l i m i t for six coniferous woods y (5 s p e c i e s ) = 1599 x 1 5 2 8 y (r- brevifolia) = 4 2 4 0 x 1 9 3 0 n= 113 n = 18 r = 0 - 9 2 r = 0 - 9 0 r 2 = 0 - 8 5 r 2 = 0 81 S E E - 1 1 2 6 - 6 p s i S E E = ± 1 9 8 0 p s i Pinus monficola D o u g I-© Pseudotsuga menziesii ( M i r b ) F r a n c o / / / A Tsuga heterophylla ( R a f - ) S a r g - / / * Abies balsamea ( L - ) M i l l - B J / r • / S p e c i f i c Grav i ty (green v o l u m e ) Figure 7. Relationship between maximum micro-compression stress and s p e c i f i c gravity (green volume) f o r six coniferous species -50-indivielual behavior. However, f i v e of the six species do not d i f f e r from each other s i g n i f i c a n t l y as regards t h e i r respective strength-specific gravity r e l a t i o n s . Pooling the data seemed j u s t i f i e d as indicated by the highly s i g n i f i c a n t c o r r e l a t i o n c o e f f i c i e n t (r = 0 . 9 2 ) . E a r l i e r studies on micro-tensile and micro-compression strength (12, 16) showed c u r v i l i n e a r relationships between strength and s p e c i f i c gravity of Douglas f i r . The relationships could be expressed l i n e a r l y only after mathematical transformation of test data. Considering th i s phenomenon i t i s easy to v i s u a l i s e that, i f the d i s t r i b u t i o n s of strength values of in d i v i d u a l species were p l o t t e d over respective s p e c i f i c gravity values on the same graph, a family (or families) of curves would develop. Depending on the s p e c i f i c gravity range and the manner of t r a n s i t i o n from earlywood to latewood (gradual versus abrupt) of a single species tested, the curve would be sigmoid or a complex function. Both s p e c i f i c gravity and maximum micro-compression stress d i s t r i b u t i o n s across three adjacent growth increments of western hemlock, balsam f i r and western red cedar suggest trend of second-degree curves but i n d i f f e r e n t ways. Test data shown i n Table I I indicate that, i n hemlock and balsam f i r latewood, the increase of maximum micro-compression stress and s p e c i f i c gravity was gradual. In cedar the increase of these properties, similar to maximum micro-tensile stress variations i n that species, was abrupt. Although only six observations have been recorded f o r s p e c i f i c gravity and maximum micro-compression stress f o r each of three adjacent increments of Douglas f i r , the t y p i c a l sigmoid-pattern was resolved. . J - 5 1 -It has been generally recognised and strongly emphasized that there are other factors besides s p e c i f i c gravity influencing wood strength properties. However, questions s t i l l remain to be answered as to what extent those properties exert their influence on wood strength (8). F e a s i b i l i t y of Micro-Compression Test Methods Micro-compression tests prove that methods of te s t i n g , data recording and analysis of stress-deformation diagrams established e a r l i e r (12) are f e a s i b l e . The theory of compressibility and that of ultimate load-point on the stress-deformation curve are correct. Com-p r e s s i b i l i t y and the l o c a t i o n of the ultimate load-point are explained as follows: the tes t material i s viewed as an aggregate of hollow tubes, the tracheids, i n horizontal p o s i t i o n with respect to the l i n e of ac t i o n of the compressive load. When load is applied to the specimen, the tube walls, i . e . , the tracheid walls react with resistance due to the inherent e l a s t i c properties of the c e l l wall substance. When load reaches the proportional l i m i t the e l a s t i c resistance collapses and much of the ensuing deformation becomes irrecoverable. The cavity of the tube, i . e . , the c e l l lumen i s further compressed and the distance between the i n t e r i o r walls of the lumen i n the d i r e c t i o n of load decreases. Load relax a t i o n takes place at thi s phase of compression. When the i n t e r i o r walls come into f u l l contact with each other load starts to increase due to the more compact sub-stance which exerts higher resistance to the external load but th i s substance has already l o s t i t s e l a s t i c properties (12). \ - 5 2 -This i s i n agreement with Kollmann's statement (20) that a c e r t a i n l e v e l of compression, i . e . , when the i n t e r i o r walls of the lumens come into contact the compressibility of the c e l l wall substance i s (approximately) reached. It i s at this point that maximum load i s recorded because the event i s marked by the i n f l e c t i o n point on the stress-deformation curve (Pig. 2) ( 1 2 ) . Kunesh (21) , studying r a d i a l compression behavior of gross wood, termed th i s point as F i r s t Load I n f l e c t i o n Point, since several more points occur on the stress-deformation diagram designating so-called "micro-s t r e s s - s t r a i n curves" ( 3 ) . He points out that t h i s i s the most important l o c a t i o n on the stress-deformation diagram a f t e r the proportional l i m i t . The high c o r r e l a t i o n c o e f f i c i e n t (r = O.98) for the r e l a t i o n s h i p between maximum micro-compression stress; and compression stress at proportional l i m i t ( F i g . 6) also supports these theories. Agreement with Kollmann (19) was found i n that the specimen was being compressed Into a dense cake beyond the maximum-load point. The micro-compression stress-deformation curve beyond the maximum-load point approaches a t h e o r e t i c a l zero-deformation change. CONCLUSIONS 1. Maximum micro-tensile stress i s well correlated with s p e c i f i c gravity i n l i n e a r manner expressed by the equation Y = 27340.6X, withr»0.82 at 95 per cent p r o b a b i l i t y . S p e c i f i c -5> gravity accounts for 68 per cent of v a r i a b i l i t y . 2. Comparison between the v a r i a t i o n of maximum t e n s i l e stress of gross wood, and that of tiss u e , over s p e c i f i c gravity i s poor due to large scatter of stress values encountered with gross specimens. The slope of the regression l i n e of the gross specimens i s steeper than that of tissues. 3. S p e c i f i c micro-tensile stress has maximum value close to or at the i n i t i a t i o n of latewood. Maximum micro-compression stress i s s i g n i f i c a n t l y correlated with s p e c i f i c gravity. The regression Is c u r v i l i n e a r , expressed by the equation Y = 1 5 9 9 . 3 X 1 * ^ 2 8 with r = 0.92 at 95 per cent p r o b a b i l i t y . S p e c i f i c gravity accounts f o r 85 per cent of v a r i a b i l i t y . The scatter of stress values increases at 0 .5 s p e c i f i c gravity. 5* Comparison between compression stress of gross wood at proportional l i m i t and maximum micro-compression stress indicates that trend of stress increase with increasing s p e c i f i c gravity i n gross wood i s more pronounced than i n wood tis s u e . Consequently, wood tissue i n r a d i a l compression exhibits d i f f e r e n t behavior from gross wood. 6. The d i s t r i b u t i o n pattern of P a c i f i c yew maximum micro-compression stress over s p e c i f i c gravity suggests that a family of curves exists when woods of greatly d i f f e r e n t physical and anatomical c h a r a c t e r i s t i c s are tested and compared at the tissue l e v e l . Although r e l a t i o n s h i p between maximum micro-compression stress and s p e c i f i c gravity of t h i s species i s s i g n i f i c a n t , with r = 0.90, and s p e c i f i c gravity accounts for - 5 V 81 per cent of v a r i a b i l i t y , the equation Y = l|2l*0.6X designates a trend d i f f e r e n t from that found i n the group of the other f i v e species tested, 7 . S p e c i f i c micro-compression stress does not suggest any d e f i n i t e trend. 8. Although s p e c i f i c gravity accounts f o r most of the v a r i a b i l i t y of strength, other variables ought to be examined as well, especially i n species l i k e P a c i f i c yew. 9 . Distributions of s p e c i f i c gravity, maximum micro-te n s i l e stress and maximum micro-compression stress i n woods having gradual t r a n s i t i o n from earlywood to latewood show gradually r i s i n g trends i n latewood contrasted to woods having abrupt t r a n s i t i o n and wide latewood zone. Western white pine, a wood with gradual -transition, i s densest at the end of the l a t e -wood therefore d i s t r i b u t i o n curves of s p e c i f i c gravity and strength properties studied do not f l a t t e n out. This i s i n con-t r a s t to d i s t r i b u t i o n patterns i n Douglas f i r , a t y p i c a l wood with abrupt t r a n s i t i o n and wide s p e c i f i c gravity range where the flattening-out of curves does take place. In Douglas f i r the abrupt t r a n s i t i o n from earlywood to latewood, coupled with the r e l a t i v e l y constant l e v e l of s p e c i f i c gravity i n the latewood zone, i s responsible f o r the sigmoid-shape of d i s t r i b u t i o n curves. 10. The established methods for t e s t i n g wood tissue i n r a d i a l compression are f e a s i b l e . Theories of compressibility and of maximum-load point on the stress-deformation curve are v a l i d . Microsection thickness i n the latewood zone should be increased from 100 microns to about 200 microns i n order to obtain chart traces indicating maximum-load point. -55-1 1 . Maximum micro-tensile stress of western hemlock shows tendency to remain nearly constant beyond the 75$ p o s i t i o n . In balsam f i r gradual increase of t h i s property has been observed. Western red cedar, a species with abrupt t r a n s i t i o n but very low latewood percentage, exhibits sharp increase both i n micro-tension and micro-compression. -56-REFERENCES 1. Anonymous. 1956-1959. Tensile test data of small clear wood specimens collected i n the period between 1956 to 1959. Project No. V - l - 1 . Unpublished data. Canada Department of Forestry, F.P.L., Vancouver, B.C. 2. Banks, CH. 1955» The mechanical properties of the mature wood of Pinus l o n g i f o l i a , Roxb. grown i n the Union of South A f r i c a . J.S. A f r i c a n Forestry Assoc. 26:18-31. 3. Bodig, J. I963. A study of the mechanical behavior of wood In transverse compression. Ph.D. Thesis, Sc. Forestry, Univ. Wash., pp. 321. . 1965. The e f f e c t of anatomy on the s t r e s s - s t r a i n r e l a t i o n s h i p i n transverse compression. Forest Prod. J. l5(5):197-202. 5. . 1965. E f f e c t s of growth ch a r a c t e r i s t i c s on the mechanical properties of Douglas f i r i n r a d i a l com-pression. Holzforsch. 3:83-88. 6. Brown, H.P., Panshin, A.J. and C.C. F o r s a i t h . 1952. Text-book of Wood Technology. V o l . I I . New York, McGraw H i l l Book Co. Inc., pp. 783. 7. Burger, H. I9I4.I• Holz, Blattmenge und Zuwachs, von Fichten una Fohren verschiedener Herkunft auf verscniedenen Kulturorten. Mitt. Schweiz. Centralanstalt f o r s t l . Versuchsw. 22:10-62. 8. C o c k r e l l , R.A. 19i}-3» Some observations on density and shrinkage of poriderosa pine wood. Trans. Am. Soc. Mech. Engs. 65:729-739. 9. Desch, H.E. 19V?. Timber, i t s Structure and Properties. Macmillan and Co., Ltd., pp. 299. 10. Drow, J.T. 1957* Relationship of l o c a l i t y and rate of growth to density and strength of Douglas f i r . Report No. 2078. U.S.D.A. F.P.L. Madison, Wis., pp. 56. 11. Ethington, R.L. 1956. Structural property estimation from wood density samples f o r western woods. Forest Prod. J. 15(10): 1+22-425. 12. Homoky, S.G. 1965. Intra-increment r e l a t i o n s h i p of micro-compression perpendicular properties i n Douglas f i r . Unpub. Rept., Fac. For., Univ. B.C., pp. 69. - 5 7 -13. I f j u , G. 1961}.. Tensile strength behavior as a function of c e l l u l o s e i n wood.' Forest Prod. J. llj.(8):366-372. 1%. — — and R.W. Kennedy. 1962. Some variables a f f e c t i n g microterisile strength of Douglas f i r . Forest Prod. J. 12(5):213-217. 15. ; — W e l l w d o d , R.W. and J.W. Wilson. 1965. Improved microtechnique for wood t e n s i l e strength and r e l a t e d properties. Forest Prod. J. 15(1) : l3-lq.. 16. — = — . 1965. Relationship between c e r t a i n intra-increraent physical measurements i n Douglas f i r . Pulp Paper Mag. Can. 66:T%75-T483. 17. Kellogg, R.M. and G. I f j u . 1962. Influence of s p e c i f i c gravity and c e r t a i n other factors on the t e n s i l e properties of wood. Forest Prod. J. 12(10) :!j:63-ij/70. 18. Kennedy, R.W. 1965* Intra-increment v a r i a t i o n and h e r i t a b i l l t y of s p e c i f i c gravity, p a r a l l e l - t o grain t e n s i l e strength, s t i f f n e s s and tracheid length i n clonal Norway spruce. Proc. Third T.A.P.P.I. Forest Biology Conference. U.S.D.A., Madison, Wis., Nov. 1965* 19. Kollmann, F. 1959. Zur Frage der Querdruckfestlgkeit von Holz. Holzvorschung und Holzbewertung. 5*103-121. 20. : — — - I 9 6 3 . Das Verhalten von Holz bei a l l s e i t i g e r Druckeinwirkung. Research Note No. 6 S. 233/39. Institute of Wood Research and Wood Technology, Univ. of Munich, Germany, pp. 223-239. 21. Kunesh, R.H. 1965* Strength and e l a s t i c properties of wood. F i f t h P a c i f i c Area National Meeting A.S.T.M. Paper No. 72, pp. 20. 22. L i t t l e f o r d , T.W. 1961. V a r i a t i o n of strength properties within trees and between trees i n a stand of rapid-growth Douglas f i r . Project No. V-1028. Canada Depart-ment of Forestry, F.P.L. Vancouver, B.C., pp. 20. 23. Newlin, J.A. and T.R.C. Wilson. 1919. The r e l a t i o n of the shrinkage and strength properties of wood to i t s s p e c i f i c gravity. ¥.S.D.A., F.P.L. B u l l e t i n No. 676, pp. 33. 21}.. P e l l e r i n , R.F. 1965. A v i b r a t i o n a l approach to ... non-destructive t e s t i n g of structural lumber. Forest Prod. J. 15(3):93"101« 25. Wangaard, F.F. 19%3. The e f f e c t of wood structure upon heat conductivity. Trans, of the Am. Soc. Mech. Eng. 2:127-135. -58-2 6 . Wangaard, P . P . 1950. The Mechanical Properties of Wood. New York, John Wiley and Sons, Inc., pp. 377. 27. Wellwood, R.W. I960. S p e c i f i c gravity and tracheid length variations i n second-growth western hemlock. Forest Prod. J. 10(5):36l-368. 28. • •  1962. Tensile t e s t i n g of small wood samples. Pulp Paper Mag. Can. 6 3:T6l -T67. 29. Wilson, J.V/. 196k. Wood Characteristics I I I : Intra-increment physical and chemical properties. Summary of studies i n progress at U.B.C. Pulp Paper Res. Inst. Can. Res. Note No. Ij.5, pp. 9. 30. : and G. I f j u . 1965. Wood Characte r i s t i c s VI: Measuring density and strength properties of minute wood specimens. Pulp Paper Res. Inst. Can. Tech. Rept. No. I4.23, pp. 13. 31. — — ; . 1965. Wood Char a c t e r i s t i c s V I I : " " Intra-increment r e l a t i o n s h i p of Douglas f i r wood density* t e n s i l e strength and s t i f f n e s s . Pulp Paper Res. Inst. Can. Rept. No. pp. 2ij.. 32. Worschitz, F. 1930. Vergleichende Untersuchungen ttber das Dickenwachstura, das spezifische Gewicht der Larche (Larix decidua) des westungarischen Htigellandes. Zentr. ges. Forstw. 56:170-183. 33. Zobel, B.T. 1956. Genetic, growth, and environmental factors a f f e c t i n g s p e c i f i c gravity of l o b l o l l y pine (Pinus taeda). Forest Prod. J. 6:l|i|2-447. 3I4.. and R.R. Rhodes. 1955- Relationship of wood s p e c i f i c gravity i n l o b l o l l y pine to growth and environmental f a c t o r s . Texas Forest Service, Tech. Rept. No. 11, pp. 32. 35. :—, Thorbjorsen, E. and F. Henson. i960. Geographic, s i t e and i n d i v i d u a l tree v a r i a t i o n i n wood properties of l o b l o l l y pine. Silvae Genet. 9:ll|.9-l58. 36. Y l i n e n ; A . 1954* Uber die Beziehungen Zeischen Spathdlzanteil, Rohwichte, Jahrringbreite, Feuchtigkeitsgehalt und den Elastizitatsmoduln beim finnischen Kiefernholz. Holz a l s Roh-und Werkstoff. 12(7):253"258. 

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