Comparative study of nonlinear damage accumulation model in stochastic fatigue of FRP laminates

The objective of this investigation is to verify the applicability of a num ber of nonlinear damage accumulation theories in the context of composite F RP laminates subjected to simulated stochastic loadings. Although nonlinear damage accumulation methods for composite materials have been investigated for a few decades, most comparisons with experimental results have conside red only two-stress-level loadings; none has considered stochastic loadings . The nonlinear damage models considered in this study are primarily those obtained as a result of the strength-deterioration and stiffness-deteriorat ion approaches. The fatigue data used in this investigation are generated f rom laminated specimens made of cross-ply E-glass woven-roving fibers and v inyl ester resin. Constant-amplitude tests are conducted to obtain the mate rial's S-N curve. Variable-amplitude fatigue tests are carried out using si mulated narrow band stochastic stress histories with various root-mean-squa re stresses. In addition to the experimental results, the predictions based on the nonlinear damage accumulation techniques are compared with those ba sed on the linear (Palmgren-Miner) damage accumulation rule. It is found th at, for the cases investigated in this study, the nonlinear damage models m ost often yield fatigue life predictions that are generally comparable to t hose predicted by the linear model; predictions in most cases are conservat ive.