划痕缺陷对 30Ni4CrMoA 试样疲劳寿命影响的试验与理论模型

The smooth samples of 30Ni4CrMoA high strength structural steel and the test parts with depth scratch defects of different depths were prepared, and the fatigue life of the test parts with scratch defects of different depths and different stress levels were obtained. Based on the theory of continuous damage mechanics and the original high-cycle fatigue damage evolution equation, an expression for influence of scratch coefficient was proposed, which comprehensively considered the influences of scratch depth and stress level, according to the relationship between the maximum stress analysis at scratch root and scratch depth, as well as the change law of sample fatigue life with scratch depth and stress level. A new equivalent fatigue damage evolution equation considering the effects of scratches was established. Based on this equation, the fatigue life of 30Ni4CrMoA sample with scratches can be predicted by the closed solution directly according to the fatigue life expression in the integral form, without establishing the finite element model of scratches. The theoretical prediction results are in good agreement with the experimental results, which verifies the effectiveness and applicability of the proposed method. Finally, the relationship between the scratch influence coefficient and notch fatigue coefficient and the influence of stress gradient at scratch root were discussed.