金属疲劳裂纹扩展率曲线与S-N曲线之间的关系

目前有两种不同的理论用于预报金属结构的疲劳寿命。一种是基于S－N曲线的累积疲劳损伤理论，另一种是基于裂纹扩展率曲线的疲劳裂纹扩展理论，如果都把一个构件的最终断裂作为疲劳破坏的定义，则S－N曲线和裂纹扩展率曲线均是反映金属在疲劳载荷作用下的基本材料特性。尽管在过去这两种曲线是分别测试的，但它们之间应该存在一些相互关系。本文的主要目的就是讨论它们之间的关系。基于S－N曲线的一个一般表达式和裂纹扩展率曲线的一个有代表性的表达式，本文建立了两种曲线之间的一个正式关系，这表明只需要测试一种曲线，而另一种曲线就可以根据已有的试验结果导出。文章以一个中央裂纹平板作为例子，演示了如何根据一种曲线推导另一种曲线。

Relation between Crack Growth Rate Curve and S- N Curve for Metal Fatigue

Currently two different theories for predicting the fatigue life of metal structures are used.One is the cumulative fatigue damage(CFD) theory based mainly on S- N (or ε - N) curves and the other is the fatigue crack propagation (FCP) theory based on the crack growth rate curve.If the failure is defined as the final fracture of a component,then both S- N curves and crack growth rate curves reflect the fundamental material behavior under fatigue loading.Some relations must exist between them although they were tested separately in the past.The purpose of this paper is to discuss such a relation.Based on the general formats of an S- N curve and a representative crack growth rate curve,a formal relation is established between the two types of curves.This indicates that only one type of curves needs to be tested and the other can be derived from the existing test results.An example of a center crack in a plate of finite width is used to demonstrate how to convert one set of material parameters to another.