带有疲劳裂纹的35CrMo构件电磁热止裂强化

Crack Arrest of 35CrMo Component with Fatigue Crack by Electromagnetic Heating

利用超强脉冲放电装置对含有疲劳裂纹的35Cr Mo钢试件进行电磁热止裂试验。放电后裂纹尖端熔化,裂尖钝化成微小的椭圆形,降低了裂尖处的应力集中;对放电后裂尖处的椭圆形钝化区与基体区的化学成分进行对比分析发现:椭圆形钝化区中Mn、Si、Mo质量分数增高,晶粒得到细化,提高了裂纹尖端微小区域内组织的硬度和强度;利用自主研发的多轴加载疲劳试验机对放电前后试件进行三点弯曲疲劳寿命测试,结果表明,经过电磁热止裂强化后的试件,疲劳寿命得到提高,较未放电的试件平均寿命提高了13%;采用热-电耦合的数值分析方法模拟求得放电瞬间裂纹尖端处的温度场;通过理论计算脉冲放电瞬间裂尖处微小区域的应变能密度因子,由于电热应力强度因子的作用,降低了裂尖处的应变能密度因子,有效阻止了裂纹的继续扩展,为电磁热止裂技术的应用奠定基础。

A specimen of 35CrMo with fatigue crack is used to perform electromagnetic heating crack arrest experiment using a self-made ZL-2 super pulse current generation equipment. The crack tip melted after discharging, and the crack tip melt into a tiny ellipse, reducing the stress concentration. Comparing chemical ingredient in the oval region near crack tip with the base material after crack arresting, the content of Mn, Si, Mo raises, and the grains are refine , increasing the hardness and strength of materials around the crack tip. Specimens before and after discharging are tested by multi axial load fatigue testing machine under three-point bending fatigue load, and the results show that the average fatigue life of specimens after discharge are increased by 13%. Based on the coupled thermal-electrical theory, a numerical simulation method is proposed to study the temperature field. The strain energy density factor in the small region around crack tip is theoretically calculated. Because of the electrothermal stress intensity factor, the strain energy density factor is reduced that prevent the cracks expanding, and lays the foundation for the application of electromagnetic thermal arrest techniques.