THE EFFECT OF PARTICLE-SHAPE AND STIFFNESS ON THE CONSTITUTIVE BEHAVIOR OF METAL-MATRIX COMPOSITES

This paper deals with the effective constitutive behavior of ductile m etals reinforced by aligned spheroidal inclusions with linear-elastic properties. For simplicity, both the matrix and the inclusions are ass umed to be incompressible and isotropic, so that the overall constitut ive behavior of the metal-matrix composites is incompressible and tran sversely isotropic. Based on a recently proposed variational method fo r estimating the effective behavior of nonlinear composites, results a re obtained for the initial yield surfaces and overall stress-strain r elations in terms of the three essentially distinct loading modes for this class of composites: Axisymmetric tension (relative to the symmet ry axis of the inclusions), longitudinal shear (along the symmetry axi s) and transverse shear (perpendicular to the symmetry axis). It is fo und that particle shape has a significant effect on the effective resp onse of the composites, and that this effect is markedly different for the three loading modes. For the axisymmetric mode, oblate and prolat e shapes have the largest strengthening effects; for the transverse mo de, oblate shapes are most effective; and for the longitudinal mode, n early spherical shapes are best. Particle stiffness also has a strong effect on the initial yielding behavior of the composites, which is ma gnified for the more severe aspect ratios. On the other hand, the stif fness of the particles does not seem to significantly affect the stres s-strain behavior of the composites for strains greater than about fiv e times the yield value.