Correlation of uniaxial yielding and substructure in aluminum-stainless steel composites

Abstract

Stress-strain behavior and associated structural detail have been characterized in aluminum-stainless steel vacuum hot-pressed composites subjected to uniaxial tension or compression. Particular emphasis was placed on the premacroyield region. Volume fractions of reinforcement 0.041, 0.11, 0.153, 0.212, 0.248, and 0.328 have been examined with the load applied parallel to the direction of wire reinforcement. Dislocation configurations have been characterized as a function of overall composite strain, volume fraction of reinforcement, and distance into the matrix from the matrix-wire interface. In tensile loading, experimental values of the precision elastic limit, microyield stress (strain 2.5 x 10-6) and macroyield stress (strain 1 x 10-3) are in close agreement with values calculated from the rule of mixtures. Similar agreement is found in compression for the initial elastic modulus, however, the experimental precision elastic limit and microyield stress are higher than the calculated values by a factor ~2, and the macroyield stress is higher by a factor of 5 to 8. At a given level of strain and volume fraction of reinforcement, dislocation configurations, and dislocation densities are independent of distance from the matrix-wire interface. Alternatively, dislocation configurations and dislocation densities are essentially independent of volume fraction of reinforcement at a given level of strain. It is concluded that the matrix responds to its percentage of the applied stress as if it were the only phase present, there being no long-range matrix-wire interaction perturbing the matrix dislocation substructure. Compressive loading of composites in the direction of reinforcement constitutes a form of buckling test.