Fatigue of Composite Materials Subjected to Variable Loadings

A model describing the fatigue behavior of composite materials under variable loadings is presented. Theapproach is based on a two-parameter model fulfilling the principal responsesÕ features of compositematerials subjected to constant amplitude cyclic loadings. It is shown that when coupled with the equivalentresidual strength assumption the model can describe the strength degradation of composite materialssubjected to variable amplitude loadings without simplifications or substantial reductions of the loadingspectrum. Compared to the linear MinerÕs rule, the results highlight the importance of the sequence of loadsand the approach discriminates the ascending, descending and random patterns. It is shown that for thecase under study the ordered descending (high to low) sequence showed the worst scenario in terms ofdamage accumulation extent, while the random spectrum resulted in an intermediate response betweenordered ascending and descending sequences.