MICROMECHANICAL MODELS FOR GRADED COMPOSITE-MATERIALS

Elastic response of selected plane-array models of graded composite mi crostructures is examined under both uniform and linearly varying boun dary tractions and displacements, by means of detailed finite element studies of large domains containing up to several thousand inclusions. Models consisting of piecewise homogeneous layers with equivalent ela stic properties estimated by Mori-Tanaka and self-consistent methods a re also analysed under similar boundary conditions. Comparisons of the overall and local fields predicted by the discrete and homogenized mo dels are made using a C/SiC composite system with very different Young 's moduli of the phases, and relatively steep composition gradients. T he conclusions reached from these comparisons suggest that in those pa rts of the graded microstructure which have a well-defined continuous matrix and discontinuous second phase, the overall properties and loca l fields are predicted by Mori-Tanaka estimates. On the other hand, th e response of graded materials with a skeletal microstructure in a wid e transition zone between clearly defined matrix phases is better appr oximated by the self-consistent estimates. Certain exceptions are note d for loading by overall transverse shear stress; The results suggest that the averaging methods originally developed for statistically homo geneous aggregates may be selectively applied, with a reasonable degre e of confidence, to aggregates dth composition gradients, subjected to both uniform and nonuniform overall loads. (C) 1997 Elsevier Science Ltd.