Thermomechanical cyclic deformation of metal-matrix composites

A constitutive model is developed for unreinforced Al2xxx-T4 and silicon-carbide particulate (SiC_p) reinforced Al2xxx-T4. Its capabilities are also outlined for predicting the cyclic, isothermal, and thermomechanical behaviors of the composite and its constituents. The constitutive model for unreinforced Al2xxx-T4 is also a unified model, because it combines creep and plastic strains as inelastic strains. The unified model for the matrix is combined with Eshelby's equivalent inclusion theory, which is modified to handle finite volume fraction and inelastic deformation, to simulate the behavior of the reinforced material. The behavior of Al2xxx-T4 (reinforced with 20% volume fraction of SiC_p) was simulated at temperatures ranging from 20 to 300°C and strain rates of 3.10^-5 1/s to 3.10^-3 1/s. The model predicts the strengthening of the composite relative to the unreinforced matrix for isothermal and thermomechanical loading conditions. The internal stress-strain behavior of the constituents (volumetric average) is reported. It is demonstrated that the matrix and the particulates experience a multiaxial stress state under uniaxial loading of the composite. The coefficient of thermal expansion mismatch between the reinforcement and the matrix contributes further to the multiaxial stress state. When the mechanical strain and temperature are in-phase, the transverse stress component in the matrix is out-of-phase with the longitudinal stress component. When the temperature and mechanical strain are out-of-phase, the transverse and longitudinal stress components are in-phase. The results on internal stress-strain fields provide insight into the interpretation of fatigue behavior of particle-reinforced composites at elevated temperatures.