Intrinsic fatigue curves applied to damage evaluation and life prediction of laminate and fabric material

Abstract

Modeling of the stochastic fatigue behavior of specimens is made from a knowledge of the intrinsic character of fatigue referred as the intrinsic fatigue curve (IFC). The idea is to predetermine the fatigue behavior of specimens' population such that each sample functions of IFC would correspond to the intrinsic fatigue character of a specimen. The existence proof of IFC is derived from Kolmogorov's theorem for a random function. The form of IFC is obtained for log-normal life distribution functions of specimens subjected to constant-amplitude load histories. Proposed is a linear damage accumulation rule for estimating the life distribution function of a specimen subjected to irregular load histories. For a stationary loading process, the life distribution function is also shown to be log-normal. The relations between the quantile SN curves and IFC are established. The ways of creating IFC from test data and quantile SN curves are illustrated by numerical examples for laminate and fabric material.