DIMENSIONAL STABILITY OF METAL-MATRIX LAMINATES

The dimensional stability of metal matrix composite laminates under thermal fluctuations and thermomechanical load cycles is examined. The system considered as a model material is a Gr/Al (+/- phi)s laminate. The analysis is performed by the finite-element method while the underlying constitutive equations of unidirectional composites are provided by the periodic-hexagonal-array (PHA) micromechanical model. A computationally more efficient and equally accurate method based on fiber-dominated analysis of unidirectional composites by the self-consistent method is also presented. The results show that laminates of the model system with phi = 12-degrees are dimensionally stable in the elastic range when subjected to pure temperature changes. Plastic deformation of the matrix causes permanent dimensional changes, which can be reduced by heat treatment of the composite. Under thermomechanical loads, (+/- phi)s laminates are not in general dimensionally stable. Dimensional stability of the laminate was enhanced by plastic deformation of the matrix for in-phase thermal and mechanical load cycles and reduced for out-of-phase cycles.