MICROMECHANICAL MODELING OF PROCESS-INDUCED RESIDUAL-STRESSES IN TI-24AL-11NB SCS-6 COMPOSITE/

A crucial problem in the application of Metallic and Intermetallic Mat rix Composites (MMCs and IMCs) is the presence of high levels of resid ual stresses induced during the fabrication process. This process-indu ced stress is essentially thermal in nature, and is caused by a signif icant difference in the coefficients of thermal expansion (CTE) of the fiber and the matrix and the large temperature differential of the co oling 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 phenomena like damage a re local in nature even though they affect the macro properties. An el astic-plastic finite element analysis is performed to model the therma l stresses induced during fabrication of Ti-24Al-11Nb/SCS-6 unidirecti onal composite and the effect of these stresses on subsequent transver se 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 literatu re. The influence of fiber-matrix interfacial bonding and fiber arrang ement on the thermomechanical behavior of Ti-24Al-11Nb/SCS-6 composite is also studied.