Determination method of equivalent initial flaw size for crack initiated at hole chamfering
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摘要:
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。
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关键词:
- 原始疲劳质量(IFQ) /
- 应力强度因子 /
- 有限元 /
- 裂纹扩展方程 /
- 当量初始缺陷尺寸(EIFS)
Abstract: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 initiated 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 relatively 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.
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图 3 有无倒角下的2种裂纹形态
Figure 3. Shape of two types of cracks initiated at holes with and without chamfering
图 7 2种裂纹形态下应力强度因子的对比
Figure 7. Comparison of stress intensity factors of two types of cracks
图 13 无量纲化应力强度因子随裂纹尺寸变化曲线
Figure 13. Changing curve of non-dimensional stress intensity factor with crack size
表 1 7B04-T74铝合金力学性能
Table 1. Mechanical properties of 7B04-T74 aluminum alloy
参数 弹性模量
E/GPa泊松比
ν屈服强度
σs/MPa抗拉强度
σb/MPa数值 70 0.33 450 518 
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表 2 2种应力水平下Z分布参数估计
Table 2. Z distribution parameter estimation for two stress levels
应力水平 
应力水平1 0.806 0.250 应力水平2 1.043 0.443
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