Life prediction of fiber-reinforced composites: macro- and micro-mechanical modeling

In homogenous materials the life of a component is controlled by damage associated with a single crack while that of non-homogenous materials is the result of a distributed damage state. The life prediction of composite materials is thus carried out using damage mechanics two common approaches of which are, macro- and micro-mechanical modeling. The former assumes homogeneity at the lamina level while the latter evaluates failure processes at the fiber-matrix level.

In the first part of this study the remaining strength life prediction methodology MRLife, modified for ceramic composites (CCLife), is integrated into the finite element package CSTEM. to create an integrated design tool for ceramic matrix composites. Using this tool, a case study is carried out to predict the life of a notched Nicalon™/Silicon Carbide 2-D woven laminated composite coupon with a temperature distribution subject to fatigue loading. Global failure of the notched plate is predicted based on a Whitney-Nuismer type average strength criterion.

In the second part of this study, simulation of events occurring at the fiber-matrix level are used to develop micro-mechanical models for the time-dependent behavior of fiber-reinforced composites due to shear creep of the fiber-matrix interface and slow crack growth in the fibers. At first, simulations of the time-dependent failure of the composite are performed using a modified Monte-Carlo fast-fracture model the results of which are then used to validate the analytical models developed for the two mechanisms. Finally, an analytical model for the time-dependent failure of a composite due to the combined effects of the two mechanism, shear creep and slow crack growth is presented. The potential for including the time-dependent failure model into CCLife is evaluated by comparing these results with those form CCLife results under the same conditions.