RESIDUAL-STRESS EVOLUTION DUE TO COOL-DOWN IN VISCOPLASTIC METAL-MATRIX COMPOSITES

Two issues are considered in the current paper : (1) the effect of coo l down from processing temperature on the thermally induced residual s tresses in a representative volume element (RVE) of a periodic continu ous fiber metal matrix composite monolayer; (2) the initiation of micr ocracks due to subsequent mechanical loading. A nonlinear incremental finite element program that accounts for thermoviscoplasticity in the matrix is utilized for the micromechanical analysis. The uncoupled hea t conduction equation is solved for the spatial temperature distributi on in the RVE for given cooling rates. Results indicate that spatial t hermal gradients can induce significant stresses at rapid cooling rate s. Furthermore, comparisons between thermoelastic and thermoviscoplast ic predictions of residual stresses at the interface between the fiber and the matrix demonstrate that incorporating viscoplasticity may be significant in predicting certain damage mechanisms such as interfacia l and radial matrix cracking. Finally, average stress-strain curves ar e obtained for the cases of mechanical loading with or without residua l stresses, and predictions are made for the location and time at whic h interface debonding initiates.