Reaction Rate Engineering Models of Fatigue Crack Growth

A macro model is presented of fatigue cracks growth FCG in a thin center crack panel of polycrystalline ductile metal subject to an axial periodically varying tensile load. The macro model is base upon a fundamental micro result from reaction rate theory. The deterministic version of this model applies to the mean time to reach a given crack length. Variability is introduced at the macro level to produce a probabilistic version. The parameters of this physically based model are directly related to the physical properties of the material, the temperature T, and the load. The form of the periodic load and T are important quantities in predicting crack growth. Analysis of FCG data for periodically varying loads reveals that three material parameters are required. The minimum amount testing required for predictive purposes is also discussed as is an interesting method for accelerating tests. Because of the physical basis of the model, it provides new insight into the FCG process.