Stress-State dependence of strain-hardening behavior in 2014 Al/15 vol Pct Al₂O₃ composite

Abstract

The purpose of this investigation was to examine if the effective stress-strain function for discontinuously reinforced aluminum (DRA) matrix composites is independent of stress state, as they are for aluminum alloys. The rationale for such work is provided by the need to develop constitutive equations for applications in metal forming and forging problems. Experimental effectiveas curves at room temperature were determined for a particulate-reinforced composite, 2014 Al/15 vol pct A1₂O₃, and the matrix material, 2014 Al, under a variety of stress states. The tests consisted of uniaxial tension, equibiaxial tension (bulge test), and compression tests. To eliminate the effects of prior precipitation, all samples were given a solution-heat-treatment prior to tests. It was found that for the composite the effective yield stress in uniaxial tension was higher than that in equibiaxial tension but slightly lower than that in compression. However, the effective yield stresses for the matrix material in uniaxial tension and equibiaxial tension were nearly the same. The strain-hardening rate of the composite under equibiaxial tension was higher than that under either uniaxial tension or compression. It is suggested that nondeformable dead zones can develop around the particles during deformation whose shape changes with the applied stress state, and this is partly responsible for the observed differences in behavior.