On the strength of discontinuous silicon carbide reinforced aluminum composites

Abstract The incorporation of dSiC into aluminum matrices results in substantial improvements in yield strength relative to the matrix material, but little change in the proportional limit. The Orowan strengthening mechanism was shown to be insufficient to account for the increase in yield strength of the composite. An increased dislocation density of the matrix due to a difference in the thermal expansion of the SiC and the matrix does predict an increase in composite strength, but is unable to explain why the proportional limit of the composite remains similar to that of the matrix or why the strength of the SiCw/6061Al is anisotropic. The conventional shear lag theory predicts yield strength values that are less than those observed. This is particularly so for the SiCp/Al composites, where the yield strength of the composite is predicted to be equal to that of the matrix independent of SiC volume fraction. If, however, the shear lag theory is modified to take into account the tensile transfer of load, the predicted composite strength is of sufficient magnitude to explain the strengthening effect of both the SiC whisker and platelet material. In addition, the modified shear lag theory can be used to rationalize why the proportional limit of the composite is similar to that of the matrix.