The effects of reinforcement additions and heat treatment on the evolution of the poisson ratio during straining of discontinuously reinforced aluminum alloys

The effects of reinforcement additions and heat treatment on the evolution of the Poisson ratio were determined for a 7xxx aluminum alloy reinforced with 15 vol pct SiC_p, a 2xxx alloy with 20 pct SiC_p, and a 2014 alloy with 15 pct A1₂O₃. The Poisson ratio of the monolithic alloy was 0.31 to 0.32 in the elastic regime. At the onset of the plastic regime, the Poisson ratio of the monolithic materials rose rapidly to about 0.45 and then gradually increased to 0.47 by 3.5 pct strain. For discontinuously reinforced aluminum (DRA) materials, the Poisson ratio in the elastic regime was considerably lower than that exhibited by the matrix alloy, while the magnitude of the difference was dependent upon the type, volume fraction, and elastic properties of the reinforcement. In addition, th evolution of the Poisson ratio for DRA material depends upon heat treatment and level of strain due to damage evolution(e.g., SiC_p cracking, matrix failure,etc.) which accompanies straining in these materials. Both the magnitude and extent of change in the Poisson ratio with increasing strain in the composite is rationalized by the accumulation of damage which accompanies increasing strain.