A micromechanical model was developed to predict the thermomechanical deformation of unidirectional filamentary metal matrix composites. The composite is represented by two concentric cylinders, the inner one simulating the fiber and the outer one the matrix. Both elastic and elastic-plastic analyses were performed. In the model the fiber was assumed to be linear-elastic and the matrix a work-hardening elastoplastic material. The elastoplastic analysis was based on the deformation theory of plasticity in conjunction with the von Mises yield criterion. The matrix cylinder in the model was divided into a number (N) of concentric layers with each layer having different values of tangent modulus and Poisson's ratio depending on the amount of plastic deformation. An elastic analysis of a composite cylinder with (N + 1) layers was then performed and served as a subroutine for a computer program.
The computer program was applied to the study of thermal deformation in the longitudinal and transverse directions of a filamentary silicon carbide/aluminum composite subjected to thermal cycling up to 177~ (350~ Longitudinal and transverse thermal strains were measured using strain gages. The critical temperature at which the strain-temperature curves become nonlinear was experimentally determined and predicted by the model. Above this critical temperature the longitudinal thermal expansion coefficient decreases while the transverse one increases. The complete three-dimensional state of stress in the fiber and the matrix was computed. It was determined that in addition to the longitudinal stresses high transverse stresses were also developed in the matrix. The experimental thermal strain curves verified the theoretical predictions.