Predicting Composite Fatigue Life Using Constituent-Level Physics

Abstract

Use of composite materials is widespread in large aerospace structures. Many of these applications require the composite structure to perform under cyclic loading. Thus, fatigue life prediction in composite structures is an important part of composite design. In this paper, we present a comprehensive physics-based methodology for accurately predicting fatigue life in composite structures, which has been incorporated into the commercial software, Helius:Fatigue™. This methodology uses minimal coupon-level data for characterization (standard static tests plus two S-N fatigue curves). The basic framework for our approach is to use multicontinuum theory (MCT) to extract relevant constituent stresses from a composite stress or strain field and apply the kinetic theory of fracture (KTF) to predict fatigue life of the matrix constituent. Using KTF in conjunction with a damage variable allows the fatigue life of a composite to be accurately predicted. To demonstrate this approach, we evaluate the fatigue life of a composite plate with a hole in uniaxial tension fatigue.