低周疲劳试验寿命预测模型分析及其对断口硬度影响

Analysis on life prediction model and hardness of fracture surface based on low cycle fatigue test

为能够对材料的疲劳失效有更加科学的预测,采用Instron 8803液压伺服疲劳机对45#钢在±0.5%,±1.0%,±1.2%,±1.5%,±2.0%5个应变幅值下进行低周疲劳试验,对疲劳试验数据进行分析,并对寿命预测模型进行验证评测,发现三参数幂函数能量法具有更加广泛的适用性;使用Hitachi S-3400N扫描电镜观察比较不同应变幅下疲劳断口微观形貌,分析裂纹源形成原因及扩展趋势;用Matsuzawa显微硬度计测量疲劳断口截面径向及轴向硬度值变化,以评测循环加载对疲劳特征区强化程度的差异,发现断口径向硬度值沿近中心位置至边缘呈波动递增趋势,而轴向硬度值随与断口的距离增大变化不大,且经过疲劳强化后,断口径向截面平均硬度明显高于原始状态。

In order to predict the fatigue failure of materials more scientifically, an Instron 8803hydraulic-servo fatigue-testing machine is used to study the low-cycle fatigue behavior of stainless steel 45#at strain amplitudes ±0.5%, ±1.0%, ±1.2%, ±1.5% and ±2.0%. After analyzing the variation in mechanical behavior and evaluating the life prediction model,it was found that threeparameter power function was more applicable. At the micro scale, each area of damage failure is shown by using a Hitachi S-3400 N scanning electron microscope to compare different figures and to discover crack initiation points and crack propagation trend. The hardness varying in both radical and longitudinal directions near the fatigue break area is measured with a Matsuzawa microhardness tester to study the difference between fatigue characteristic areas after cyclic loading. It is found that the hardness increased from the center to the edge along the radial direction and the hardness remained almost the same along the longitudinal direction. After the fatigue test,the average hardness of radical fracture section was significantly higher than that of the original state.