SM50Aにおける疲労き裂発生・進展の応力繰返し速度依存性

概要

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The effect of stress frequency on fatigue crack initiation and propagation in SM50A steel, which has strain rate dependence in the plastic region, was studied. Fatigue crack initiation and propagation tests were carried out at 0.02 Hz, 0.2 Hz, 1Hz and 20 Hz, at R=0, at room temperature, and the number of cycles to crack initiation and the crack propagation rate were measured. The local stress-strain behavior at the part of stress concentration was analyzed and the simulation of fatigue crack propagation was performed by FEM employing the elasto/visco -plastic overlay model. The comparison between the experimental results and the visco-plastic strain behavior calculated by analysis was made. The following results were obtained. (1) The number of cycles to crack initiation and the crack propagation rate depend on the stress frequency in such a way that for lower frequency, a shorter life of the crack initiation and a higher crack propagation rate were obtained. (2) The dependences of the crack initiation life and the crack propagation rate on stress frequency can be explained by the visco-plastic strain range based on the material viscosity in the plastic region at the notch root and the crack tip. (3) A parameter closely related to fatigue crack initiation and propagation rate is the visco -plastic strain range at the notch root and the crack tip in visco-plastic materials.
1988-07-15