Plasticity of continuous fiber-reinforced metals

Continuous parallel alumina fiber-reinforced metals produced by pressure infiltration are tested in tension/compression along the fiber axis with a goal of measuring the influence exerted by long fibers on the flow stress of their matrix. In this configuration, the equistrain rule of mixtures, modified to take into account stresses due to differential lateral contraction, can be used to back-calculate the matrix flow stress from that of the composite. This method provides the least physically ambiguous measurement of matrix flow stress in the composite; however, experimental uncertainty can be high. This uncertainty is evaluated in detail for the present experiments, in which matrix in situ stress-strain curves are measured for cast 3M NEXTEL 610 and DUPONT FIBER FP reinforced pure and alloyed aluminum- and copper-based matrices of varying propensity for recovery and cross-slip. Within experimental uncertainty, data show no enhanced matrix work-hardening rates such as those those that have been measured with tungsten fiber-reinforced copper. It is found that the fibers alter the matrix plastic flow behavior by increasing the flow-stress amplitude of the matrix, and by rendering initial yield in compression more progressive than in initial tension. Essentially, all observed features of matrix/fiber interaction can be rationalized as attributable to dislocation emission in the matrix caused by thermal mismatch strains within the material during composite cooldown from processing temperatures.