Abstract
Fatigue behavior of wood under cyclic tension-torsion combined loading was investigated. Material used for experiments was a rectangular bar of Japanese cypress (Chamaecyparis obtusa Endl.). Two types of loading pattern (Type 1 and Type 2) shown in Fig.1 were applied to specimen. Based on the failure criterion obtained from static tests, three combined-stress-ratios (TA, Tb, and TC) were determined for the fatigue tests, where the shear stress component was dominant in the combined-stress state TA and the tensile stress component in TC. The obtained results were owed to the combined-stress-ratios, wave-forms and the applied stress levels, and were summarized as follows. Difference in SN plot between Type1 and Type2 at higher stress levels was observed. Fatigue life in TC stress state under Type2 was shorter than that under Type1,and that in TA stress state waslonger. The more ratic of tensile stress component in combined stress state increased, the more tensile stiffness during cyclic loading decreased at the late stage in fatigue life. Torsional rigidity under Type2 decreased all over the fatigue process more than that under Type1,owing to much damage by torsional creep.
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