一种新的多轴疲劳寿命预测模型

基于SAE 1045中碳钢和40CrNiMo合金钢的疲劳试验结果,分别建立了单轴和多轴疲劳应变-寿命模型,寻求了两种模型的关系,发现:就所研究的两种材料而言,如果假设单轴疲劳应变-寿命模型(Manson-Coffin方程)中的疲劳强度指数和疲劳延性指数不变,而对疲劳强度系数乘以1.093 7、疲劳延性系数乘以0.751 2,以von Mises等效应变幅取代单轴拉压应变幅,则修正后的单轴模型等价于多轴模型。修正后的多轴疲劳寿命预测模型中,弹性线上移,塑性线下移的事实表明:对于同样大小的应变幅,单轴疲劳中的弹性应变分量大于多轴疲劳中的弹性应变分量,而单轴疲劳中的塑性应变分量小于多轴疲劳中的塑性应变分量。利用修正后的模型可以预测多轴疲劳寿命。

A New Predication Model for Multi-Axial Fatigue Life

Based on the fatigue test results of SAE 1045 medium carbon steel and 40CrNiMo alloy steel,the axial and multi-axial fatigue life predication models are founded respectively.Relationship between the two kinds of models is studied.It is found that,so far as the two kinds materials are concerned,if the fatigue strength exponent and the fatigue ductility exponent are constant,while the fatigue strength coefficient times1.0937 and the fatigue ductility coefficient times 0.7512,the von Mises equivalent strain amplitude replaces the axial push-pull strain amplitude,then the modified axial fatigue life predication model is equivalent to the multi-axial fatigue life predication model.In the modified prediction model of multi-axial fatigue,the fact that the elastic line shifts up while the plastic line down indicates that given the same strain amplitude,the elastic strain component in uni-axial fatigue is larger than that in multi-axial fatigue while the plastic strain component in uni-axial fatigue is smaller than that in multi-axial fatigue.Therefore the revised axial fatigue life predication model can be used to predict the multi-axial fatigue life.