A NEW MULTIPARAMETER APPROACH TO THE PREDICTION OF FATIGUE-CRACK GROWTH

A new multiparameter approach is proposed for the prediction of the co mbined effects of multiple variables on fatigue crack growth. The meth od, which is based on multiple linear regression analysis, involves th e statistical formulation of mathematical expressions for the crack gr owth rate, da/dN, as a function of multiple variables, e.g. stress int ensity 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 i s then verified by comparing predicted and measured fatigue crack grow th and crack growth rate data obtained from tests on a quenched and te mpered Q1N (HY80) pressure vessel steel. Error ranges and reliability functions are presented within a probabilistic mechanics framework, an d the implications of the results are discussed for the development of generalized fatigue life prediction methods.