A new multiparameter approach to the prediction of fatigue crack growth

A new multiparameter approach is proposed for the prediction of the combined effects of multiple variables on fatigue crack growth. The method, which is based on multiple linear regression analysis, involves the statistical formulation of mathematical expressions for the crack growth rate, da/dN, as a function of multiple variables, e.g. stress intensity factor range, Delta K, crack closure stress intensity factor, K-cl, and stress ratio, R. A general empirical approach is proposed for the estimation of the fatigue crack growth rate as a function of the above variables. The predictive capability of the empirical approach is then verified by comparing predicted and measured fatigue crack growth and crack growth rate data obtained from tests on a quenched and tempered Q1N (HY80) pressure vessel steel. Error ranges and reliability functions are presented within a probabilistic mechanics framework, and the implications of the results are discussed for the development of generalized fatigue life prediction methods.