Multiscale modeling of failure in metal matrix composites

A multiscale approach to composite failure, in which detailed information on small-scale micromechanics is incorporated approximately yet accurately into larger-scale models capable of simulating extensive damage evolution and ultimate failure, is applied to the deformation and failure of a Ti-matrix composite. The composite is reinforced with SiC fibers under conditions of matrix yielding and interfacial sliding via Coulomb friction. Specifically, a fully three-dimensional finite element model is employed to investigate the load transfer from broken to unbroken fibers as a function of applied stress and interface friction coefficient. With a von Mises matrix yield criterion, constraint effects permit the matrix to carry some of the transferred load near the fiber break, a feature not captured in previous composite 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 coefficient and, for values of mu comparable to those measured experimentally, the predicted tensile strength is in excellent agreement with the measured value. Analytic models for scaling of the tensile strength to very large sizes are then shown to agree well with strengths obtained from simulations. These 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 Science Ltd. All rights reserved.