Micromechanics-based stress rupture life prediction of polymer composites

Abstract

This paper develops a Monte Carlo simulation technique to predict the stress-rupture lifetime of longitudinally loaded unidirectional polymer composites based on fiber and matrix properties. Matrix viscoelasticity is cited as the primary cause of rupture failure. Time-dependent matrix deformation leads to an increase in the overstressed length of unbroken fibers in the vicinity of a cluster of fiber fractures. A general time-dependent load-sharing framework that is able to account for an arbitrary sequence of fiber fractures is developed. Matrix deformations are based on the shearlag assumption. The time-dependent load sharing is incorporated into a Monte Carlo simulation for stressrupture lifetime. Even though the only material variability included in the simulation is the fiber strength distribution, very broad lifetime distributions are computed. The reasons for broad rupture lifetime distributions are discussed. It is shown that the strength-life equal rank assumption does not apply for unidirectional polymer composites loaded in longitudinal tension because of fundamental differences between quasi-static and stress-rupture failure behavior. Encouraging comparisons are made to the experimental rupture lifetime of carbon fiber/polymer matrix composites.