直流电压降方法在钢材疲劳过载延迟效应研究中的应用

Application of Direct Current Potential Drop Method in Analysis of Fatigue Overload-induced Retardation of Steels

通过引入等效残余应力强度因子ΔKres,提出了一种无材料拟合参数的新型驱动力模型,对裂纹扩展速率与延迟疲劳寿命进行预测;采用直流电压降(DCPD)方法结合有限元标定测得裂纹扩展长度,并与实测值进行比较,验证该方法的准确性;基于DCPD方法结合有限元标定通过过载疲劳试验得到4种钢材过载后的裂纹扩展速率与延迟疲劳寿命,验证预测模型的准确性。结果表明:单峰过载后,4种试验钢均出现过载延迟效应;过载比越大,试验钢过载后的最小裂纹扩展速率越小,且屈服强度越低的试验钢的延迟效果越大。采用DCPD方法结合有限元标定得到的裂纹扩展长度与实测值的相对误差小于3.75%,该方法具有较高的精度;驱动力模型预测得到的裂纹扩展速率的变化趋势与由DCPD方法结合有限元标定得到的试验值相吻合,且预测延迟疲劳寿命均在试验值的2倍误差带内,验证了驱动力模型的准确性。

A new driving force model without material fitting parameters was proposed to predict crack growth rate and overload fatigue life by introducing an equivalent residual stress intensity factorΔKres.The crack growth length was measured by direct current potential drop(DCPD)method combined with finite element calibration,and compared with measured values to verify the accuracy of the method.On the basis of DCPD method and finite element calibration,the crack growth rate and overload fatigue life of four steels after overload were obtained by overload fatigue test to verify the accuracy of the prediction model.The results show that the overloadinduced retardation appeared in four test steels after single-peak overload.The higher the overload ratio,the smaller the minimum crack propagation rate of the test steel after overload,and the lower the yield strength,the greater the retardation effect of the test steel.The relative error between crack growth length measured by DCPD method and finite element calibration and measured values was smaller than 3.75%,indicating the method had high accuracy.The trend of crack growth rate prdicted by driving force model agreed with test values by DCPD method combined with finite element calibration well,and the predicted overload fatigue life was within 2 times the error band of the test value,which verified the accuracy of driving force model.