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通过对 1 8Cr2 Ni4WA钢在不同应力比和不同载荷下的疲劳裂纹扩展速率试验 ,拟合得Paris关系式 ,然后对试验断口进行疲劳条带宽度 S(微观裂纹扩展速率 )测量 ,将疲劳条带宽度值代入拟合的 Paris关系式中 ,反推计算断口试样的疲劳应力变幅。结果表明 ,疲劳条带宽度只在疲劳裂纹扩展的一定阶段与宏观裂纹扩展速率相等 ,选择该阶段的数据点进行疲劳应力变幅反推计算 ,相对误差在 1 0 %以下 ;数据点是否位于宏、微观裂纹扩展速率相等的阶段 ,可由 S～ yπa双对数座标 S形曲线判定 ,并发现由于裂纹扩展速率的误差传递系数小于 0 .5,计算结果对裂纹扩展速率测量的相对误差不敏感
The Paris relationship was fitted by fatigue crack growth rate test of 18Cr2 Ni4WA steel at different stress ratios and different loads, and then the fatigue band width S (microscopic crack growth rate) was measured on the test fracture. The fatigue band The width value is substituted into the fitting Paris relation, and the fatigue stress amplitude of the fracture specimen is calculated back-calculated. The results show that the fatigue band width is only equal to the macroscopic crack growth rate at a certain stage of fatigue crack growth, and the data points at this stage are used to calculate the fatigue stress amplitude reversal. The relative error is below 10% , And the stage of microcrack propagation rate is equal, it can be judged by S-yπa double-logarithmic S-curve. It is found that the calculated result is insensitive to the relative error of crack growth rate measurement because the error transfer coefficient of crack propagation rate is less than 0.5