LONG-TERM STRENGTH AND DAMAGE ANALYSIS OF LAMINATED COMPOSITES

A modified version of the probabilistic model developed by the authors for damage evolution analysis of laminates subjected to random loadin g is utilized to predict long-term strength of laminates. The model as sumes that each ply in a laminate consists of a large number of mesovo lumes. Probabilistic variation functions for mesovolumes stiffnesses a s well as strengths are used in the analysis. Stochastic strains are c alculated using the lamination theory and random function theory. Dete rioration of ply stiffnesses is calculated on the basis of the probabi lities of mesovolumes failures using the theory of excursions of rando m process beyond the limits. Long-term strength and damage accumulatio n in a Kevlar(R)/epoxy laminate under tension and complex in-plane loa ding are investigated. Effects of the mean level and stochastic deviat ion of loading on damage evolution and time to failure are discussed. It is found that the effect of the deviation in loading is more pronou nced at lower mean loading levels. Long-term cumulative damage at the time of the final failure at low loading levels is higher than at high loading Levels. The analytical results are qualitatively compared wit h the available experimental observations.