MICROMECHANICAL MODELS FOR GRADED COMPOSITE-MATERIALS - II - THERMOMECHANICAL LOADING

Thermoelastic response of several discrete and homogenized models of u nconstrained graded composite layers is examined for both uniform chan ges in temperature and steady-state heat conduction in the gradient di rection. Detailed finite element studies of the overall response and l ocal fields in the discrete models are conducted, using large plane-ar ray domains containing simulated skeletal and particulate microstructu res. Homogenized layered models, with the same composition gradient an d effective properties derived from the Mori-Tanaka and/or self-consis tent methods, are analyzed under identical boundary conditions. Compar isons of temperature distributions, and of overall and local stress an d strain fields predicted by the discrete and homogenized models are m ade in the C/SiC composite system, with very different phase propertie s and relatively steep composition gradient, that was used in the firs t part of this study (T. Reiter, G. J. Dvorak and V. Tvergaard, J. Mec h. Phys. Solids, Vol. 45, pp. 1281-1302, 1997). Homogenized models of combined microstructures which employ only a single averaging method d o not provide reliable agreements with the discrete model predictions. However, close agreement with the discrete models is shown by homogen ized models which derive effective properties estimates from several a veraging methods: In those parts of the graded microstructure which ha ve a well-defined continuous matrix and discontinuous reinforcement, t he effective moduli, expansion coefficients and heat conductivities ar e approximated by the appropriate Mori-Tanaka estimates. In skeletal m icrostructures that often form transition zones between clearly define d matrix and reinforcement phases, the effective properties are approx imated by the self-consistent estimates. The results do not support th e proposition that nonlocal or new micromechanical theories are requir ed for modeling of graded microstructures. (C) 1998 Elsevier Science L td. All rights reserved.