加载波形对LZ50车轴钢疲劳裂纹扩展行为的影响

在三角波、正弦波、方波3种加载波形下对LZ50车轴钢紧凑拉伸试样开展疲劳裂纹扩展试验,采用扫描电镜观察断口形貌,并结合试验数据分析加载波形对裂纹尺寸增量和扩展速率的影响。结果显示:加载频率较高时,疲劳裂纹扩展行为对波形的敏感性较低,断口形貌基本相同;加载频率较低时,波形对疲劳裂纹扩展行为的影响增大,断口形貌出现差异;稳态扩展区以疲劳条带为主要扩展机制,三角波加载下的疲劳条带间距明显小于其他2种波形,其失稳扩展区形貌以韧窝为主,且韧窝较其他2种波形下的小且浅。同时,基于LS-DYNA软件和节点位移外推法对CT试样在3种加载波形下的应力强度因子进行计算和分析。结果表明:仿真分析波形对疲劳裂纹扩展的影响机制与试验结果基本一致。

Loading Waveform Effect on Fatigue Crack Growth Behavior of LZ50 Axle Steel

Fatigue crack growth tests using LZ50 steel compact tensile specimens were performed under three different loading waveforms,i.e.triangular wave,sinusoidal wave and square wave.The characteristics of fatigue fracture were observed by scanning electron microscopy,and the effects of different loading waveforms on crack size increment and crack growth rate were analyzed based on the experimental data.The results show that the sensitivity of fatigue crack growth behavior to the waveform is relatively low and the fracture morphology of specimens is basically the same at high loading frequency.The influence of waveform on the fatigue crack growth behavior increases and the fracture morphology of specimens is different at low loading frequency.Meanwhile,the main mechanism in critical crack propagation region is fatigue striations,and the spacing of fatigue striations under triangular wave is significantly smaller than that under the other two waves.The main morphology in unstable propagation region is dimple,the shape of which is smaller and shallower under triangular wave than that under the other two waves.Stress intensity factor under the three different loading modes was calculated and analyzed based on simulation using LS-DYNA software and the node displacement extrapolation method.The results demonstrate that the influence mechanism of the loading waveforms on fatigue crack growth behavior obtained by simulation analysis is essentially consistent with the experimental results.