孔边倒角裂纹当量初始缺陷尺寸的确定方法

孔边倒角裂纹是含孔下陷细节的常见裂纹形态，为进行含孔下陷细节的经济寿命评定，需要确定倒角裂纹的原始疲劳质量（IFQ）。首先，为探究倒角对裂纹前缘应力强度因子的影响，进行了有、无倒角2种情况下应力强度因子的有限元分析。计算表明倒角对相对小裂纹的应力强度因子影响显著。其次，为合理表征该种裂纹的IFQ，将初始缺陷当量为萌生于倒角和试件表面交点，前缘为圆弧的初始裂纹，以萌生点到裂纹前缘沿孔径向的距离作为裂纹特征尺寸。最后，采用相对小裂纹扩展方程描述倒角裂纹的扩展规律，反推得到倒角裂纹的当量初始缺陷尺寸（EIFS）分布。统计分析表明，采用本文定义的裂纹特征尺寸得到的EIFS分布参数与应力水平无关。

Determination method of equivalent initial flaw size for crack initiated at hole chamfering

Cracks often initiate at the chamfering for sagging holes.The initial fatigue quality ( IFQ) of this type of crack needs to be determined prior to economic life assessment.Firstly, finite element models with and without chamfering are developed so as to investigate the effect of chamfering on the stress intensity factors at the crack front.The results show that the chamfering imposes great influence on the stress intensity factors of relatively small crack.Secondly, in order to characterize the IFQ of sagging holes, a circular-front crack in-itiated at the intersection of the chamfering and specimen surface is taken as the initial flaw, with the radial distance of crack front from the initiation site as the crack size.Finally, the crack growth equation for relative-ly small cracks is employed to characterize the crack growth behavior, and the equivalent initial flaw size ( EIFS) distribution is obtained through back-extrapolation.Statistical analyses show that the EIFS distribution parameters obtained by using the proposed crack size definition are independent of stress levels.