非对称交变应力下疲劳强度条件的探讨

Study of Fatigue Strength Condition for Non Symmetrical Circulation

对当前广泛应用于机械设计的非对称循环下构件的疲劳强度条件进行分析，求导合理的疲劳强度条件．由材料力学可知，在简化的构件持久极限图上，同一循环特征下，构件的工作安全系数是由同一射线上的两点得到的．但由于构件的综合影响系数只对应力幅值（纵坐标）有影响，因此材料的持久极限与构件的持久极限一般不会落在同一射线上．由此可知，当前通用的非对称交变应力的疲劳强度条件是不正确的．通过对构件持久极限图的分析，进行了推导，得出了构件工作安全系数的正确表达式，并分析了两者之间的误差．结论指出，按原有的疲劳强度条件进行设计有时会造成较大的浪费．

The fatigue strength condition of component parts under non symmetrical circulation is analysed for the tranditional design of mechanism in order to infer an expression about the fatigue strength condition. In terms of material mechanics, the working safe coefficient of components under the same circle feature is found by two points on the same projecting line in the endurance limit figure. Because the combined influence coefficient of components has only an effect on the stain amplitude (the vertical coordinate),the endurance limits of materials and components can't be located on the same projecting line. In view of this,the tranditional fatigue strength condition under non symmetrical circulation is incorrect. Through the analysis of the figure of the endurance limit of components, a correct expression about the working safe coefficient of components is obtained.And further, the error between the expressions of two strength conditions is analysed. The conclusion shows that the design according to the original fatigue strength condition would cause greater losses.