Multiscale modeling of failure in metal matrix composites

A multiscale approach to composite failure, in which detailed information o n small-scale micromechanics is incorporated approximately yet accurately i nto larger-scale models capable of simulating extensive damage evolution an d ultimate failure, is applied to the deformation and failure of a Ti-matri x composite. The composite is reinforced with SiC fibers under conditions o f matrix yielding and interfacial sliding via Coulomb friction. Specificall y, a fully three-dimensional finite element model is employed to investigat e the load transfer from broken to unbroken fibers as a function of applied stress and interface friction coefficient. With a von Mises matrix yield c riterion, constraint effects permit the matrix to carry some of the transfe rred load near the fiber break, a feature not captured in previous composit e models. The single-break results for stress concentrations are then used as the discrete Green's functions for load transfer in the full composite, and the predicted load transfer around a seven-fiber-break cluster is shown in good agreement with finite element results. The Green's function model is then used to predict overall damage evolution and composite failure for an IMI-834 Ti/SCS-6 SiC system for various interface friction coefficients. The composite tensile strength is rather insensitive to the friction coeff icient and, for values of mu comparable to those measured experimentally, t he predicted tensile strength is in excellent agreement with the measured v alue. Analytic models for scaling of the tensile strength to very large siz es are then shown to agree well with strengths obtained from simulations. T hese results suggest that the hierarchical coupling approach used here may be useful for approaching a wide variety of damage and failure problems in fiber composites. (C) 2001 Acta Materialia Inc. Published by Elsevier Scien ce Ltd. All rights reserved.