Multiscale modeling of damage and failure in aluminum-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 an aluminum matrix composite reinforced with Al2O3 fibers, Specifically, 3D finite-element models are used to predict the load transfer from broken to unbroken fibers as a function of applied stress and matrix yield strength. The stress concentrations around a single fiber break are then employed in a Green's function model that predicts the evolution of multiple fiber damage under increasing applied load up to failure in moderate-sized composites. These studies explicitly demonstrate the local critical damage level that must be attained to drive global failure. Analytic models for scaling of the tensile strength to large sizes typical of test coupons and components are then employed. The general method is applied to predict failure in an aluminium matrix reinforced with Al2O3 fibers. Good agreement at small composite sizes is obtained, but the scaling of strength with size is weaker than is observed in experiments. Possible reasons for these deviations are discussed, focusing on the appropriate constitutive response for highly constrained metal yielding at small scales. The analytic models for strength also provide information on reliability versus size and are usable in stochastic finite element models. The overall multiscale model can guide the choice of damage metrics and instability points within macroscale damage mechanics models. (C) 2001 Elsevier Science Ltd. All rights reserved.