S38C车轴表层梯度材料的疲劳裂纹扩展性能研究

Research on Fatigue Crack Propagation Properties ofS38C Axle Surface Gradient Materials

为研究S38C车轴表层梯度材料的疲劳裂纹扩展性能,直接从现车车轴截取试样,保持实际车轴表层具有的显微组织、硬度及其残余应力呈梯度变化的情况,采用三点弯曲加载方法,检测疲劳裂纹在硬化层、过渡层和芯部基体的扩展性能。结果表明,随着表层裂纹长度的增加,疲劳裂纹扩展速率呈现先增加后减小最后增加的趋势。通过测量不同表层深度位置的残余应力分布,发现距车轴表面深度0~3 mm内存在较大的残余应力压应力,使得疲劳裂纹扩展需要更大的驱动力,而距车轴表面深度3 mm后转变为拉应力,对疲劳裂纹扩展没有影响。

In order to study the fatigue crack growth characteristics of the gradient material of the surface layer of the S38C axle,the samples of S38C axle were taken directly from the existing axle to maintain the gradient of the microstructure,hardness and residual stress of the actual axle surface.The three-point bending loading method was used to detect the propagation characteristics of fatigue cracks in the hardened layer,the transition layer and the core matrix.It is found that as the crack length increases,the fatigue crack growth rate is increased first then decreased,and finally increased.By measuring the residual stress distribution at different surface depths,it is found that there is a large residual stress compressive stress within 0 to 3 mm from the surface of the axle,which makes the fatigue crack growth need a greater driving force.However,the residual stress changes into tensile stress after 3 mm from the axle surface depth,which has no effect on the fatigue crack propagation.