Thermoviscoplasticity Based on Overstress Applied to the Analysis of Fibrous Metal-Matrix Composites

The vanishing fiber diameter (VFD) model together with the thermovisco plasticity theory based on overstress (TVBO) are used to analyse the thermomechanical behavior of unidirectional fibrous metal-matrix composites. Fiber and matrix can both be transversely-isotropic, thermoelastic-viscoplastic. All material constants can depend on current temperature. Yield surfaces and loading/unloading conditions are not used in the theory in which the inelastic strain rate is solely a function of the overstress, the difference between stress and the equilibrium stress, a state variable of the theory. The three- dimensional equations are derived and specialized for various simple loading cases such as isothermal uniaxial and biaxial proportional and nonproportional loadings. The predic tions of this viscoplasticity theory during loading compare favorably with results from the rate-independent plasticity theory. In addition it is capable of predicting creep, relaxation and rate sensitivity.