Micromechanical modelling of deformation and failure in Ti–6Al–4V/SiC composites

Abstract

The tensile behaviour and the associated fracture micromechanisms were determined in a Ti–6Al–4V alloy uniaxially reinforced with 35 vol. % Sigma 1140+SiC monofilaments. Damage in the form of fiber fracture was localized in a given section of the composite, and the critical micromechanical parameters which control the composite behavior (namely the matrix elasto-plastic response, the fiber elastic modulus and strength, the interfacial sliding resistance, and the residual stresses originated by the thermal expansion mismatch between matrix and fibers) were determined using various experimental and analytical techniques. They were used as input data to simulate the composite deformation and fracture. The composite stress–strain curve was determined by the self-consistent method. The failure locus was determined by computing the probability of nucleating clusters containing one, two, three or more broken fibers. The analysis was based on the stress concentration introduced by one fiber failure in its neighbours, which was determined from the finite element analyses of a representative volume of the composite containing one fiber break, and included the effects of matrix plasticity, residual stresses, and interfacial sliding. This result was extended to analyze the stress concentration around a cluster of broken fibers by a superposition technique. The average composite strength and the extent of damage were accurately predicted by the model when failure was dictated by the nucleation of a cluster containing two neighbour broken fibers. These results demonstrate the potential of the new model to assess the strength and ductility of fiber-reinforced composites which fail under local load sharing conditions by the unstable propagation of a cluster of broken fibers.