高频谐振载荷作用下疲劳裂纹尖端变形场分析

Finite element analysis of displacement and strain fields at crack tip under high frequency resonant loading

为研究高频谐振式疲劳裂纹扩展试验中,带有I型预制裂纹的CT紧凑拉伸试件裂纹尖端位移、应变场的变化规律,利用动态有限元方法,采用ANSYS和MATLAB软件编写程序,计算了CT试件在高频恒幅正弦交变载荷作用下,在一个应力循环及裂纹扩展到不同长度时裂纹尖端区域的位移、应变场并分析了其变化规律.为验证有限元计算结果的准确性,进行了高频谐振式疲劳裂纹扩展试验,采用动态高精度应变仪测量了CT试件疲劳裂纹扩展到5mm时在一个应力循环内裂纹尖端点的应变.研究结果表明:在稳态裂纹扩展阶段,高频谐振载荷作用下I型疲劳裂纹尖端区域位移、应变均为和载荷同一形式的交变量;随着裂纹的扩展,I型疲劳裂纹尖端的位移、应变幅不断增大;裂纹尖端测量点应变有限元计算结果和实验结果最大误差为2.93%.

This work researched the variation law of displacement field and strain field at fatigue crack tip of compact tension specimen with type I pre-notch based on dynamic finite element method （FEM） in the high frequency resonant fatigue crack propagation test. The displacement field and the strain field at CT specimen fatigue crack tip in one stress cycle and at different crack lengths under constant amplitude high frequency sinusoidal alternating loading condition are calculated and the related variation laws of the displacement field and the strain field are analyzed. In order to validate the FEM result, the high frequency resonant fatigue crack propagation test was performed, and the dynamic strain gauge is used to measure the strain at crack tip of CT specimen with crack length of 5mm during one stress cycle. The research results show that during crack stable propagation stage, the displacement and the strain at type I fatigue crack tip are the same form with the high frequency resonant load; the displacement and strain increase with the crack growth. The maximum error of the strain at crack tip between the calculated result by FEM simulation and the experimental result is 2.93 %.