An experimental and numerical study of cyclic deformation in metal-matrix composites

The cyclic stress-strain characteristics of discontinuously reinforced metal-matrix composites are studied both experimentally and numerically. The model systems used for investigation are aluminum alloys reinforced with SiC particulates and whiskers. Finite element analyses of the fatigue deformation of the composite are performed within the context of axisymmetric unit cell formulations. Two constitutive relations are used to characterize the matrix of the composite: the fully dense Mises model of an isotropically hardening elastic-viscoplastic solid and the Gurson model of a progressively cavitating elastic-viscoplastic solid (to simulate ductile matrix failure by the nucleation and growth of voids). The brittle reinforcement phase is modeled as elastic, and the interface between the ductile matrix and the reinforcement is taken to be perfectly bonded. The analyses provide insights into the effects of reinforcement shape and concentration on (1) constrained matrix deformation under cyclic loading conditions, (2) cyclic hardening and saturation, (3) the onset and progression of plastic flow and cavitation within the matrix, and (4) cyclic ductility. The numerical predictions of flow strength, strain hardening, evolution of matrix field quantities, and ductility under cyclic loading conditions are compared with those predicted for monotonic tensile deformation and with experimental observations. formerly Visiting Scientist, Division of Engineering, Brown University