Fatigue life prediction of composite materials under realistic loading conditions (variable amplitude loading)

Two of the most widely used methods for the fatigue life prediction of composite materials under variable amplitude (VA) loading patterns are presented in this chapter. The first method is based on the theoretical formulation and use of a damage summation rule to predict life under VA loading without recourse to experimental observation of the damage accumulation process. An alternative to this classic fatigue life prediction methodology are the residual strength fatigue theories, where residual strength is used as the damage metric. Comparison of the remaining strength of the material to the static strength allows the estimation of the fatigue cycles until failure. The basic fatigue modeling introduced in previous chapters of this book for interpretation of the fatigue data ( Chapter 2), residual strength theories ( Chapter 3), and constant life diagrams ( Chapter 6) is combined here to establish fatigue life prediction methodologies.