Fatigue and Hysteresis Effects in Wood-Based Panels Under Cyclic Shear Load Through Thickness
Keywords:Energy loss, fatigue life, fatigue limit, shear through thickness, wood-based panel
AbstractThe fatigue behavior of wood-based panels (plywood: PW, and oriented strandboard: OSB) under cyclic shear load through the thickness was experimentally investigated. Test specimens were cut into sections of 350-mm length and 240-mm width. Pulsating shear load through the thickness was applied along the length of specimens at stress levels corresponding to 60%~100% of static strength. The hysteresis loops of stress-strain curves were determined by measuring the shear load and the shear strain at the center of the specimen surface throughout the fatigue tests. The area enclosed by a hysteresis loop was defined as the energy loss per cycle, and was obtained for each loading cycle. To discuss the fatigue properties of wood-based panels under shear load through the thickness, the energy loss per cycle was examined in relation to the number of loading cycles. The energy loss per cycle at each stress level showed an almost constant value throughout most of the fatigue life, that is, from 5~10 loading cycles to just before fatigue failure. A significant correlation between energy loss during 5~10 loading cycles and fatigue life was obtained. Therefore, fatigue life could be predicted by monitoring energy loss in the cyclic shear-through-thickness test with approximately 10 loading cycles. As fatigue life lengthened, mean energy loss per cycle was found to decrease and seemed to gradually approach a threshold value. The stress level at which mean energy loss per cycle is equal to the threshold value can be regarded as the fatigue limit. A model equation for the relationship between mean energy loss per cycle and fatigue life was proposed and fitted to the data obtained. The threshold values of mean energy loss per cycle for PW and OSB were found to be 0.446 and 0.350 [kJ/m3/cycle], respectively. The fatigue limit was estimated to be approximately 40% of the static strength for PW and OSB, respectively, on the basis of the nonlinear relationship between mean energy loss per cycle and stress level.
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