Abstract
Fatigue behavior and stress-strain properties of wood under a cyclic tension-torsion combined loading were investigated experimentally. Materials used for the experiments were rectangular bars of Japanese cypress (Chamaecyparis obtusa Endl.). Tension and torsion loading were applied along and around the longitudinal axis of the specimen coincided with the longitudinal direction of the wood, respectively. The obtained results were summarized as follows : 1) All data were found to locate in a slightly wide band on the S-N plot in spite of different biaxial combined stress ratios, but the slope of the S-N curves became low in which tensile stress was dominant. 2) Failure modes of the test specimen depended on which tensile or shear stress was dominant in the biaxial stress ratios. 3) Hill's criterion for the static strength showed in better agreement to evaluate the fatigue strength under biaxial combined stress ratios. 4) The longitudinal and transverse elasticity kept the initial states and decayed suddenly just before fatigue failure. However their tendencies owed to the biaxail combined stress ratios and the applied stress levels.
