Fatigue Behavior in Wood Under Pulsating Compression-Torsion-Combined-Loading

Abstract

We have experimentally investigated the effects of cyclic compression-torsion-combined loading on the fatigue behavior and stress-strain properties of wood. Pulsating compression and torsion loadings were applied along and around the longitudinal axis of the rectangular bar specimen (Japanese cypress). According to the relationships between stress and strain during fatigue tests, the secant modulus of the stress-strain curve changed with an increase in the number of loading cycles, and the differences between the curves for compression and shear were observed. We found that the experimental results of fatigue tests were influenced by the combined-stress ratios. Compressive stiffness tended to maintain its initial values during almost all loading cycles to failure. Shear stiffness decreased with increasing number of loading cycles, and the final decrease of shear stiffness was larger as compressive stress became dominant. The failure mode was affected by the combined stress states; typical torsion failure was observed in combined stress states with dominant application of shear stress. In contrast, typical compression failure was observed in combined stress states with dominant application of compressive stress. The failure mode under compressive-shear combined stress states was not affected by the stress level, although, as previously demonstrated, it was affected by the stress level under tensile-shear states.