Abstract
Abstract The effects of thermal expansion mismatch on the residual stress and flow response of microballoon-reinforced metal composites have been examined using finite element analyses of a unit cell model. The calculations indicate that residual tensile stresses can develop within some regions of the microballoons, despite the fact that the thermal expansion coefficient of the microballoon material is lower than that of the matrix. The magnitude of the residual tension increases as the microballoons are brought closer together. The levels of residual tension predicted by finite elements are in qualitative agreement with experimental observations of cracking in Al2O3 microballoons embedded in an Al alloy matrix. The effects of the thermal expansion mismatch on yielding within the matrix both after cooling from the processing temperature and after mechanical loading have also been studied numerically. Preliminary comparisons have been made between the finite element predictions and experimental measurements on two Al/A12O3 microballoon composite, with different microballoon wall thicknesses. The inferred thermal strain from such comparisons is in broad agreement with the reported thermal expansion coefficients of the constituents and an effective temperature change of ∼ 130 K following casting (within a factor of ∼ 2 or 3). The discrepancies are rationalized on the basis of the pre-existing cracks within the microballoons.
Published Version
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