Analytical Evaluation of the Thermal Residual Stresses in SiC/Al Composites

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An analytical investigation of the difference in the constitutive behavior of SiC-Al composites under uniaxial compressive and tensile loading was carried out and the associated changes of the residual stresses were studied. It is suggested that the observed asymmetric response of the constitutive behavior is primarily due to the existence of residual stresses in the composite, and the residual stresses are initially introduced due to the differences in the coefficients of thermal expansion (ΔCTE), and subsequently changed after the external load is applied. A two-dimensional finite element analysis of a hexagonal array of SiC whiskers in an Al matrix was performed, the result of which testifies to the appropriateness of the proposed explanation. It is concluded that the 2-D finite element analysis is an economical way of adequately reproducing the most prominent features of the material's constitutive behavior. Based upon the theory of mechanics of composite material, simplified analytical models were developed which can be used to investigate the influences of the whisker-matrix interface shear load transfer and the volume mismatch on the residual stresses. It is concluded that the mechanism of load transfer in terms of normal stress at the whisker tip, which is governed by the volume (bulk) mismatch between the matrix and the whisker, is predominantly responsible for altering the specific pattern of the residual stresses under the applied load. In contrast, the effect of shear load transfer at the longitudinal whisker-matrix interface is only restricted to a very small region in the vicinity of the whisker and does not significantly influence the overall proposed asymmetric constitutive behavior.

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