在薄壳淬火硬化层中疲劳裂纹的扩展

Fatigue Crack Propagation in the Hardened Layer by Shell-hardening

薄壳淬火半轴具有很高的疲劳强度和使用寿命,即使存在淬火裂纹时也是如此。本文在进行X射线残余应力分析及疲劳裂纹宏观、微观观察的基础上,分析讨论了薄壳淬火半轴扭转疲劳裂纹的扩展行为,并与调质半轴对比。作者认为薄壳淬火半轴硬化层存在很高的残余压应力,是其疲劳强度高的主要原因。在残余压应力场中,由于有效应力强度因子下降及裂纹闭合力增大,而使裂纹扩展速率降低;在一定载荷水平下,淬火裂纹可以不扩展。从断裂力学的观点来看,零件中存在裂纹是普遍现象,并非任何裂纹都会引起早期失效。薄壳淬火半轴的技术要求应与调质半轴区别对待,对薄壳淬火半轴应允许存在一定程度的淬火裂纹。

It has been found that the shell-hardened rear axles possess ahigh fatigue strength,even though there are some quenching cracks in it.This paper based upon the x-ray stress analyses and macro-micro observation offatigue cracks,the torsional fatigue crack propagation behaviours of shell-hardened rear axle were discussed.The authors consider that the main reason ofthe high fatigue strength is the high residual compressive stress in thehardened layer of shell hardened rear-axle.Within residual compressive stressfield the rate of crack propagatiom(da/dn)decreases due to reduction inefficient stress intensity factor of cracks(K_(?))and increasing in crack closureforce,thus at the loads below certain level the quenching cracks may not begrown.It is emphasized that the technical specification for shell hardend rear-axles should be distinct from that of ordinary quenching-tempring,in theformer some quenching cracks should be allowed。