FRACTURE MECHANICS APPROACH FOR THE EFFECT OF STRESS RATIO OF CARBURIZED STEELS.

To make a quantitative analysis of the effect of stress ratio on the fatigue properties for carburized steel, the fatigue properties and fatigue fracture mechanism were examined for 2 carburized steels. Carburizing, quenching and tempering were performed at one condition, and the fatigue strength was evaluated up to 10**8 cycles under uniaxial loading of two stress ratios, R equals minus 1 and 0, at room temperature in laboratory air. The threshold stress intensity factor when a mode I crack begins to grow was linearly related to (1-R)** gamma for the two carburized steels, and by a similar relation, the fatigue life can be predicted in the long life region over about 10**6. The lope on the Haigh diagram was discussed by fracture mechanics.