Effects of an interfacial region on the transverse behavior of metal-matrix composites -- A finite element analysis

An interfacial region (i.e., an interface coating or a reaction product) between the fiber and matrix is known to exist in most metal-matrix composites. Since the load transfer between the fiber and matrix depends on the properties and conditions of this interfacial region, the mechanical behavior of the composites is strongly affected by its characteristics. In this study, finite element analysis has been used to investigate the distribution of residual thermal stresses in the interfacial region, characteristics of interfacial crack initiation and propagation, and mechanical response of the composites under transverse tensile loading. The matrix material is taken to be Ti-6Al-4V (wt%) and behaves elasto-plastically, while the SiC-fiber is assumed to be elastic. The interface is treated as a thin layer with a finite thickness between the fiber and matrix. Three separate interfacial conditions (i.e., a graded carbon coating, a Y2O3 coating and an uncoated interface) have been considered to evaluate the influence of the (independent) thermal and mechanical properties of the interfacial region. For comparison, an infinitely strong bond at the interface is also assessed. The results indicate that the properties of the interfacial region affect the stress distribution, the interfacial crack initiation and propagation, and the mechanical response of the composites. Based on these results, the thermal and mechanical properties of the coating for improved performance of the composites under transverse loading conditions are proposed