Micromechanical modeling of process-induced residual stresses in Ti-24Al-11Nb/SCS-6 composite

A crucial problem in the application of Metallic and Intermetallic Matrix Composites (MMCs and IMCs) is the presence of high levels of residual stresses induced during the fabrication process. This process-induced stress is essentially thermal in nature, and is caused by a significant difference in the coefficients of thermal expansion (CTE) of the fiber and the matrix and the large temperature differential of the cooling process. Residual stresses may lead to the development of matrix cracking, and may also have an adverse effect on the thermomechanical properties of the composites, e.g., stress-strain behavior, fracture toughness, fatigue, and creep. A micromechanical analysis is needed to study the effects of residual stresses, since phenomenon like damage are local in nature even though they affect the macro properties. An elastic-plastic finite element analysis is performed to model the thermal stresses induced during fabrication of Ti-24Al-11Nb/SCS-6 unidirectional composite and the effect of these stresses on subsequent transverse loading. The state of residual stress induced in this intermetallic composite is found to be quite different from that in Ti-6Al-4V/SCS-6 metal matrix composite which is extensively discussed in the literature. The influence of fiber-matrix interfacial bonding and fiber arrangement on the thermomechanical behavior of Ti-24Al-11Nb/SCS-6 composite is also studied.