Fatigue Strength of Wood Under Pulsating Tension-Torsion Combined Loading

Fatigue strength of wood under cyclic tension-torsion combined loading was investigated experimentally. The material used for the experiments was a rectangular bar of Japanese cypress. Pulsating tension-torsion combined loadings were respectively applied along and around the longitudinal axis of the specimen, which coincided with the longitudinal direction of the wood. The obtained results of fatigue tests were found to be influenced by the combined-stress ratios and the applied stress levels, and were summarized as follows: 1) All data were located in a slightly wide band on the S-N plot in spite of different combined-stress ratios, but the slope of the S-N curves became low when tensile stress was dominant. 2) Failure modes of the test specimen depended on whether tensile or shear stress was dominant in the biaxial stress ratios. 3) Hill's criterion for the static strength was suitable for evaluating the fatigue strength under combined-stress ratios