Abstract: A random fatigue load cycle counting method is suggested for cycle by cycle calculation of crack growth analysis. This method makes it possible to consider exactly the effect of load sequence in crack growth model calculation. As a tool of crack growth model predictions, it can be used in the analyses of various types of models and can solve the problem in previous counting method, with which the load sequence can't be exactly maintained, and some peak or valley position will be changed and therefore affects the retardation calculation. With the proposed counting method, crack growth model calculation will be more reasonable and properly fit the actual damage mechanism, which is significant for various crack analysis models to be developed, improved and evaluated.

Key words: fatigue, crack growth, random spectrum load, Iife prediction, load counting