| Residual stresses in metal-matrix composites are investigated both with a numerical model and by average elastic residual strain measurements by neutron diffraction. The composite is modeled as a periodic array of cylindrical cells, each consisting of the matrix alloy with the reinforcement embedded in the center. Although the problem is approached from a purely continuum viewpoint, full account is taken of thermo-elasticity, temperature dependence of material properties, and finite deformations. Thermally induced residual stresses are inherent in most metal-matrix composites because of the mismatch in thermal expansion coefficients between the reinforcement and matrix. The effects of fiber spacing, volume fraction and aspect ratio on residual stresses resulting from a quench of the composite are analyzed. The results show that the side-to-side spacings of fibers is the most important parameter affecting the magnitude of the residual stresses, while the overall level of plastic deformation in the matrix is governed primarily by reinforcement volume fraction. The effect of thermally induced residual stresses on the mechanical properties and ductility of Al-SiC composites is also analyzed. The residual stresses have only a small effect on the predicted ductility of the composite, even when a relatively weak interface is assumed. The model predictions are compared to measurements of average elastic residual strains by neutron diffraction for both 15 vol.% whisker and 20 vol.% particulate Al-SiC composites subjected to a rapid quench followed by different loading histories. Remarkable agreement in the aluminum data is obtained for the whisker composite, while only qualitative agreement is obtained for the particulate composite. A simulation of creep in thermally cycled Al-SiC composites is presented and compared to existing experimental data. The model predicts the salient features of the experiments but underestimates the magnitudes of composite creep rates. Finally, the limits to composite unit cell models and continuum plasticity theory in micro-mechanical modeling of metal-matrix composites are discussed. |
