轮箍氢致裂纹的形成、扩展及预防

Initiation,Propagation and Prevention of Hydrogen Induced Cracking in Train Tyres

以近年来发生崩裂的6个车轮轮箍为研究对象,在进行断口观察、周向应力有限元分析、残余应力测量、紧凑拉伸试样的断裂韧性测试和疲劳裂纹扩展门槛值、氢致滞后断裂临界应力和陷阱氢浓度测定的基础上,研究轮箍崩裂的原因和机理并提出预防措施。结果表明:当轮箍中可扩散氢浓度足够高时,在残余应力(或装配应力与残余应力共同)作用下轮箍内部产生氢致裂纹,氢致裂纹在氢压及拉应力的作用下滞后扩展,氢致滞后断裂临界应力随可扩散氢浓度的增加而降低;对于长大到一定尺寸的氢致裂纹,即使不发生氢致滞后扩展,也会在轮箍运行过程中发生疲劳扩展,轮箍的疲劳裂纹扩展门槛值为5.5MPa·m1/2;预防氢致裂纹导致轮箍崩裂的根本方法是将轮箍中总的氢浓度控制在1.8×10-6以下。

The research objects were six train tyres broken in recent years.The fracture surfaces of the broken tyres were observed by scanning electron microscopy （SEM）.The circumferential stress was analyzed by finite element method and the residual stress was measured.The fracture toughness of compact tension specimen was tested.The fatigue crack propagation threshold,the critical stress for hydrogen induced delayed fracture and the trapped hydrogen concentration were determined.Based on the abovementioned,the causes and mechanisms of tyre cracking were analyzed and the preventive measures were suggested.The results showed that hydrogen induced cracking was initiated by residual stress （or both the assembly stress and residual stress） and its delayed propagation was caused by hydrogen pressure and tensile stress if the diffusible hydrogen concentration in the tyre was high enough.The critical stress for hydrogen induced delayed fracture decreased with the increase of diffusible hydrogen concentration.When the size of hydrogen induced cracking grew to certain extent,even though there was no hydrogen induced delayed propagation,fatigue propagation would also occur during operation.The fatigue crack propagation threshold of tyre was 5.5 MPa · m1/2.Controlling the total hydrogen concentration in tyre below 1.8 × 10^-6 was the most effective way to prevent hydrogen induced cracking from inducing tyre broken.