摘要
目的:探讨平均应力或应力比对S-N曲线的影响,并期望得到不同应力比或平均应力下统一的S-N曲线的数学形式。方法:1.基于Kachanov的疲劳损伤演化律,考虑循环载荷作用下高周疲劳的实际情况,提出疲劳损伤演化模型;2.采用高镇同(1981)的实验数据,验证不同平均应力下S-N曲线的数学表达式;3.利用等效对称应力幅和等效对称寿命的概念,研究不同平均应力下的S-N曲线数学表达式。结论:1.提出任意循环比或平均应力下S-N曲线的统一数学表达式;2.给出疲劳极限、比例系数和平均应力间的关系;3.引入等效对称循环应力和寿命的概念,可以将任意循环比或平均应力下的疲劳等效为对称疲劳。
It is well known that the mean stress or stress ratio of fatigue loadings has a strong effect on the shape of S-N curves. An understanding of the relationships among S-N curves corresponding to different mean stresses or stress ratios would be very useful in engineering applications. In this study, based on continuum damage mechanics, a mathematical expression of an S-N curve is deduced from a new damage evolution law. This mathematical expression can well represent the whole S-N curve, not only the linear part in bi-logarithmic diagrams, but also the transitional part near the fatigue limit. The effect of mean stress on an S-N curve is represented by two state parameters. The relationships between these state parameters and the mean stress are proposed and examined. By using these relationships, the concepts of equivalent symmetric amplitude and equivalent symmetric cycles are introduced. We have found that all S-N curves under non-symmetric states can be rearranged into the same curve as that of symmetric fatigue by adopting these equivalent parameters.
基金
Project supported by the National Natural Science Foundation of China(No.10772116)
关键词
损伤力学
S-N曲线
演化律
等效方法
疲劳极限
Damage mechanics
S-N curve
Evolution law
Equivalent method
Fatigue limit
