Fatigue life and allowable design stresses for wood composites used in furniture

Zhaozhen Bao, Purdue University

Abstract

The fatigue behavior of several wood composites was investigated in order to evaluate the relationship between stress level and fatigue life in order to provide a reasonable basis for determining allowable design stresses for these materials as they are used in furniture. Particleboard, OSB, MDF, and hardwood plywood were included in the study. A total of 276 specimens was tested, half in static bending and half in fatigue. Static bending tests were carried out on a Riehle universal testing machine; fatigue tests were conducted on an air-driven loading system especially constructed for the purpose. Fatigue specimens were subjected to cyclic stress levels of 30%, 40%, 50%, 60%, and 70% of average MOR values. All specimens survived at least 1 million test cycles at a stress level of 30% of average MOR. Fatigue failures at fewer test cycles began to occur as stress levels increased to 40% of average MORs. A rapid decrease in fatigue life was observed for all materials as the stress levels reached 50% of average MOR. Results indicated that there were no significant differences between edgewise and flatwise fatigue performance for the same type of materials. Hardwood plywood beams showed very strong fatigue resistance as compared to the remaining types of materials. Specimens which had been subjected to 1 million test cycles at 30% of MOR without failure showed no significant change in MOR and MOE in subsequent static load tests. For furniture designs in which cyclic loading must be taken into account, it appears that allowable design stresses may be based on some percentage of MOR in order to satisfy safety and service requirements. In particular, allowable design stress values ranging from 30% to 40% of the average MOR is suggested as the basis for allowable design stresses.

Degree

Ph.D.

Advisors

Eckelman, Purdue University.

Subject Area

Wood|Technology|Mechanical engineering

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