ＡＺ３１Ｍｇ合金圧延材の高応力振幅下における疲労特性に及ぼす負荷開始方向の影響

抄録

The influence of the start loading direction (from tension and compression) on the fatigue life was investigated by performing the axial fatigue test. An axial fatigue tests were conducted with a stress ratio R = -1 and a stress amplitude σ_a= 100 MPa to 140 MPa. We used the rolled AZ31 magnesium alloy machined in the direction L parallel to the rolling direction in this study. The 0.2% proof stresses of tension and compression are 129 MPa and 78 MPa, respectively. This rolled AZ31 magnesium alloy shows an anisotropy. At all stress amplitudes, the fatigue life of the start from tension loading becomes longer than that of the start from compression loading. In the case of the stress amplitude of 140 MPa, the fatigue life of the start from tension loading was 3,717 cycles, and the fatigue life of the start from compression loading was 3,393 cycles. In particular, stress amplitude of 100 MPa, the fatigue life of the start from tension loading was 30,472 cycles, and the fatigue life of the start from compression loading was 26,360 cycles. In the case of a stress amplitude of 100 MPa, there is a great difference between the fatigue life of the start from the tensile and the compression loading, and the difference of fatigue life was approximately 4,000 cycles. Therefore, it is considered that the start loading direction affects the fatigue life in the L direction under high stress amplitude. The fracture surface of the specimens were observed using SEM. The fatigue crack initiated at the surface of the specimen. Fatigue crack propagated in the T direction.