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 number of nonlinear damage accumulation theories in the context of composite FRP 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 considered 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-deterioration approaches. The fatigue data used in this investigation are generated from laminated specimens made of cross-ply E-glass woven-roving fibers and vinyl ester resin. Constant-amplitude tests are conducted to obtain the material's S-N curve. Variable-amplitude fatigue tests are carried out using simulated narrow band stochastic stress histories with various root-mean-square stresses. In addition to the experimental results, the predictions based on the nonlinear damage accumulation techniques are compared with those based on the linear (Palmgren-Miner) damage accumulation rule. It is found that, for the cases investigated in this study, the nonlinear damage models most often yield fatigue life predictions that are generally comparable to those predicted by the linear model; predictions in most cases are conservative.