残余压应力场中疲劳短裂纹扩展速率的预测

PREDICTION ABOUT SHORT FATIGUE CRACK GROWTH IN COMPRESSIVE RESIDUAL STRESS FIELD

通过对Newman中心孔裂纹闭合模型加以改进,引入经有限元分析计算得到的残余应力再分布曲线,建立了用于单边圆缺口短裂纹闭合力及扩展速率预测的改进模型。为了验证模型的合理性,对40Cr调质态板状试样的缺口部位进行喷丸,测定裂纹扩展时的残余应力再分布,实测短裂纹的闭合力及扩展速率。结果表明,模型计算与实验测定符合较好。残余压应力提高了裂纹闭合力,减小了最大应力强度因子,从而降低了有效应力强度因子幅值,使裂纹扩展速率下降。

A model based on Newman's calculation was suggested.The central hole model was replaced by single edge notch and compressive residual stress was induced.Residual stress redistribution during crack growth was calculated with finite element method.The short fatigue crack growth rate in this residual stress field was predicted.The experiment was carried out on a high temperature tempered medium carbon steel,of which the notched area was shot peened.Residual stress was measured with x-ray diffractometer to detect its redistribution.Crack closure force and short crack length were moni- tored during fatigue.Experimental results show that the prediction curve agrees well with the tested data.The compressive residual stress increases the crack closure force and reduces the maximun stress intensity factor as well.The craek growth rate decreases with the reduction of the effective stress in- tensity factor.