Modeling Stiffness Degradation in Filamentary Composite Materials

Abstract

The effect of service‐load‐induced internal damage in advanced filamentary composite materials has for some time been a topic of extensive research. It is well known that the stiffness of the material system is degraded as load is applied and damage accumulates. A computational simulation of the processes by which the internal damage propagates was developed for studying the effect of the complex interactions among identified internal damage mechanisms. The approach considers the random distribution of initial matrix flaws (microcracks and micropores) and weak fiber‐matrix interfacial bonding, the random strength properties of the fibers, and load transfer in the vicinity of broken fibers through matrix shear, and it employs an iterative, time‐stepping technique to simulate damage propagation under increasing load and over periods of sustained constant load. The developed model is employed to simulate the response of strands of Kevlar 49/epoxy to specified loading conditions. The statistical nature of the effect of preloading on the stiffness and strength degradation of continuously loaded strands is demonstrated and discussed.