铝合金缺口试样疲劳寿命预测新方法研究

Research on New Methods of Aluminum Alloy Fatigue Life Prediction Notched Specimens

借鉴基于断裂力学的Walker裂纹扩展公式的形式,对主ΔSs-N方法中的裂纹扩展公式进行修正,得到一种新的考虑了平均应力影响的等效结构应力ΔSg.由于焊接结构中存在着高值残余应力,平均应力对于焊接接头的疲劳寿命影响并不显著,但对于非焊接缺口件,平均应力的影响是显著的.对11种铝合金缺口试样进行有限元分析,建立以ΔSg为参数的ΔSg-N曲线族,并对得到的数据进行二元线性回归分析,得到不同置信度下的主ΔSg-N曲线.将其与试验得到的以名义应力S和等效结构应力ΔSs为参数的ΔSs-N曲线族进行对比,发现ΔSg-N曲线存在着良好的归一性.

A new equivalent structural stress ΔSgwas obtained when the crack propagation formula in masterΔS-N method was corrected by using the Walker crack propagation formula for reference,the effect of mean stress was also included in this stress. High-value residual stress is found in the welded structures. The fatigue life is not too much influenced by mean stress,but for the non-welded notched specimen,it is significant. 11 kinds of finite element model of aluminum alloy notch specimens were analyzed. The master ΔSg-N curve under different degrees of confidence was obtained through the equation of bivariate linear regression. At last,the ΔSg-N curve was compared with the nominal stress S obtained by test and the equivalent structural stressΔSsin Verity,and the normalization is obvious.