渗碳淬硬层疲劳裂纹闭合模型

A FATIGUE CRACK CLOSURE MODEL IN CARBURIZED AND HARDENED CASE

本文在Newman裂纹闭合模型的基础上,以裂纹面附加残留位移为主要线索,综合考虑了渗层组织、强度、初始残留应力分布及残余奥氏体转变对裂纹闭合行为的影响,提出了一个渗碳硬层疲劳裂纹闭合计算模型。文中利用该模型对疲劳裂纹扩张过程中卸载后裂纹面接触应力的分布、渗层裂纹闭合效应进行了成功地计算;借助于实测的渗碳层da/dn—ΔK_(eff)关系,较好地预测了渗层裂纹扩张速率的变化规律;并在定量分析残余奥氏体转变、初始残留应力分布对闭合行为的影响方面进行了有益的尝试。

A model of fatigue crack growth through the residual stress field of carburized and hardened 20CrNiMo steel is developed on the basis of Newman's crack closure model with consideration of the residual displacements remained in the wake of an advanced crack. In this model the original carburized residual stress, the strength distribution and the effect of retained austenite transformation induced the crack closure are considered. This model predicts successively the variation of contact stresses on crack surfaces, the crack closure parameters and the fatigue crack growth rates in terms of the measured data of da/dn—ΔK_(off) relation. Quantative analyses on the effects of retained austenite transformations and original stress distributions on the crack closure behaviors and fatigue crack growth rates are respectively made by using this model.