MICROMECHANICAL ANALYSIS FOR THERMOVISCOPLASTIC BEHAVIOR OF UNIDIRECTIONAL FIBROUS COMPOSITES

A three-dimensional micromechanics formulation for fiber-reinforced composites containing viscoplastic matrix materials is presented. The micromechanics model is based on the relaxation of the coupling effect between the normal and shear stresses. Three variations of Bodner's theory of viscoplasticity are used to predict the thermoviscoplastic behavior of unidirectional metal-matrix composites; first, the original isotropic-hardening model of Bodner and Partom; second, Ramaswamy's extension of the theory through the inclusion of a back stress; and third, Stouffer and Bodner's extension of the theory through a special form of directional hardening. Comparisons with numerical solutions and experimental data of other researchers are made to demonstrate the accuracy of the model. Micromechanical analyses of metal-matrix composites under both in-phase and out-of-phase thermomechanical fatigue-loading conditions are also presented for comparison with experiments and previous models.