The effect of cryogenic cooling on the tensile properties of metal-matrix composites

Abstract

Tensile specimens machined from metal-matrix, oriented-fiber composites (aluminum alloy reinforced with high strength stainless steel wire) were heated to 260°C and cooled in air to produce a tensile residual stress state in the matrix. Some of the test pieces were cooled to the temperature of boiling nitrogen, held at temperature for fifteen minutes, and then air warmed to room temperature. All test pieces were subsequently strain cycled in tension and the resulting stress-strain behavior was recorded. The results indicated cryogenic refrigeration extended the first stage (totally elastic) behavior of these materials. It was shown that the beneficial effects of the cryogenic treatment resulted from an alteration of the residual stress state brought about by plastic flow of the matrix. Finally, it was shown that these effects could be computed by rigorous analytical methods.