Residual Stresses in Fibrous Metal Matrix Composites: A Thermoviscoplastic Analysis

Abstract

The vanishing fiber diameter model together with the thermoviscoplasticity theory based on overstress are used to analyze the thermomechanical rate (time)-dependent behavior of unidirectional fibrous metal—matrix composites. For the present analysis the fibers are assumed to be transversely isotropic thermoelastic and the matrix constitutive equation is isotropic thermoviscoplastic. All material functions and 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. Assumed but realistic material elastic and viscoplastic properties as a function of temperature which are close to Gr/Al and B/Al composites permit the computation of residual stresses arising during cool down from the fabrication. These residual stresses influence the subsequent mechanical behavior in fiber and transverse directions. Due to the viscoplasticity of the matrix time-dependent effects such as creep and change of residual stresses with time are depicted. For Gr/Al residual stresses are affecting the free thermal expansion behavior of the composite under temperature cycling. The computational results agree qualitatively with scarce experimental results.