电位法测量微缺口试样的数值分析

Numerical Analysis of Potential Drop Test on Micro-Notched Specimen

疲劳寿命受到材料内部缺陷的制约,可以通过电位法试验获得微缺口试样的疲劳裂纹扩展规律,进而分析缺陷对材料疲劳寿命的影响。在试验前,需要预先研究试验的主要影响因素。利用COMSOL有限元软件,研究了电流输入点位置和电势差测点位置对试验精度和试验复现性的影响,计算得到不同裂纹前缘形状对应的电位法校核曲线。结果表明:(1)电流输入点位置位于试样平行于裂纹面的上下表面时,可以保证试验的复现性。(2)当测点位于裂纹面的垂直对称面上,且测点距离裂纹面垂直距离为0.06~0.1倍试样宽度时,可以同时满足测试精度和复现性。(3)当裂纹宽度和裂纹深度的比值>3时,可以不考虑裂纹前缘形状对校核曲线的影响,当裂纹宽度和裂纹深度的比值≤3时,裂纹前缘形状对校核曲线的影响较大。

The fatigue life is limited by the defects of the material.Crack propagation behavior of the micronotched specimen can be studied by the potential drop method.Thus,the influence of the defects on the fatigue life was analyzed.Before the test,the numerical analysis was conducted,using COMSOL finite element software,to investigate the main influencing factors of the test.The effects of the current input position and probe position on the accuracy and reproducibility of the test are studied.And the potential drop method’s calibration curves are calculated for different crack front shapes.The results suggest that:(1)When the current input position is on the upper and lower surfaces of the specimen which paralleled to the crack surface,the reproducibility of the test can be guaranteed.(2)When the probe position is located on the vertical symmetry plane of the crack surface,and the vertical distance of the probe position is 0.06~0.1 times of the specimen width from the crack surface,the test accuracy and reproducibility can be satisfied at the same time.(3)If the ratio of crack width to crack depth is larger than 3,the influence of crack front shape on the calibration curve can be neglected.But if the ratio is smaller than or equal to 3,the crack front shape will influence the calibration curve significantly.