低サイクル疲労寿命の支配因子の検討

抄録

In this paper, an effective and convenient method for estimating low cycle fatigue life based on the smail crack growth law was proposed, and the factors controlling fatigue life were clarified. Also, plastic-strain-controlled low cycle fatigue tests were carried out on pearlitic spheroidal graphite cast lron (PDI) and its matrix material (0.85% carbon steel ; JIS SK5). The effect of detects on fatigue life and the factors controlling fatigue life were examined from a microscopic point of view. The main results obtained are as follows : (1) Low cycle fatigue life is controlled by three factors : crack initiation length, crack propagation limit length and relative crack growth rate. (2) Fracture of PDI starts from a microshrinkage that exists on the neighboring surface in the case of a cylindrical specimen ; thus, the crack initiation length of PDI is longer than that of SK5. (3) Cracks caused by defects shorten the crack propagation limit length. (4) The relative crack growth rate is accelerated by the increase in crack opening displacement range at a crack tip.