A deterministic model of fatigue may be considered to be a mathematical system which will allow one to make accurate predictions about the lifetime of a material or structure, given information about the material properties, details of the geometry, and the actions to which it is subjected. A deterministic model is one such that if the various parameters are specified exactly, then an exact prediction for the lifetime is obtained.
In practice there is a large amount of scatter in observed lifetime data for similar materials under similar conditions. This could be because the true parameters are not known exactly, or because there is a natural variability in the physical system. Such scatter will be addressed in the probabilistic adaptations of some of the deterministic models.
The different types of model may be roughly divided into two categories; namely those which are empirical - based on observed data, and constructed to fit the data - and those that are more theoretical - based on some physical reasoning, or mechanism which is known to affect the lifetime. Details of both empirical and theoretical deterministic models for crack growth are discussed in what follows.