Size and heterogeneity effects on the strength of fibrous composites

Probabilistic fiber composite strength distributions and size scalings depe nd heavily on both the stress redistribution mechanism around broken fibers and properties of the fiber strength distribution. In this study we perfor m large scale Monte Carlo simulations to study the fracture process in a fi ber composite material in which fibers are arranged in parallel in a hexago nal array and their strengths are given by a two-parameter Weibull distribu tion function. To calculate the stress redistribution due to several broken fibers, a realistic 3D shear-lag theory is applied to rhombus-shaped domai ns with periodic boundary conditions. Empirical composite strength distribu tions are generated from several hundred Monte Carlo replications, particul arly for much lower values of fiber Weibull modulus gamma, and larger compo site sizes than studied previously. Despite the localized stress enhancemen ts due to fiber failures, predicted by the shear-lag model, composite respo nse displays a transition to equal load sharing like behavior for approxima tely gamma less than or equal to 1. Accordingly, the results reveal distinc t alterations in size effect, failure mode, and weak-link scaling behavior, associated with a transition from stress-driven to fiber strength-driven b reakdown. (C) 1999 Elsevier Science B.V. All rights reserved.