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UBC Theses and Dissertations

Fatigue cracking of lumber bandsaw blades Lu, Hongtao


The focus of this research is on the fatigue cracking problem in the tooth gullet region of wide handsaw blades used in the lumber industry. This thesis presents both the theory and the experiment aspects of this research in terms of the tasks defined as follows. The current literature was reviewed to critically examine the current state-of-the-art in smooth and cracked body analysis techniques and their application in the failure analysis of a bandsaw blade. The advantage of the fracture mechanics approach insolving the problem was recognized and useful information was identified. Experimental testing was conducted to obtain the mechanical properties of the blade material and to establish the cracking resistance curve which defines the stability threshold of cracks inthis material. Experimental testing was also conducted to determine crack propagation behaviour in handsaw blade material subjected to representative loading conditions. Based on the experiment data obtained, a failure analysis of a blade under assumed loading conditions was performed. Critical crack lengths which a blade can tolerate under the assumed loads were calculated. A fatigue crack propagation model has been proposed and used in the failure analysis of commonly used blades. The results offer explanations for cracking problem in the tooth gullet. The failure analysis also shows that careful handling of the blade resharpening process can substantially prolong the fatigue life of a saw blade.

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