INFLUENCE OF FIBER ARCHITECTURE ON THE INELASTIC RESPONSE OF METAL-MATRIX COMPOSITES

This three-part paper focuses on the effect of fiber architecture (i.e , shape and distribution) on the elastic and inelastic response of uni directionally reinforced metal matrix composites (MMCs). The first par t provides an annotated survey of the literature; it is presented as a n historical perspective dealing with the effects of fiber shape and d istribution on the response of advanced polymeric matrix composites an d MMCs. A summary of the state of the art will assist in defining new directions in this quickly reviving area of research. The second part outlines a recently developed analytical micromechanics model that is particularly well suited for studying the influence of these effects o n the response of MMCs. This micromechanics model, referred to as the generalized method of cells (GMC), can predict the overall inelastic b ehavior of unidirectional, multiphase composites, given the properties of the constituents. The model is also general enough to predict the response of unidirectional composites that are reinforced by either co ntinuous or discontinuous fibers, with different inclusion shapes and spatial arrangements, in the presence of either perfect or imperfect i nterfaces and/or interfacial layers. Recent developments on this promi sing model, as well as directions for future enhancements of the model 's predictive capability, are included. Finally,the third part provide s qualitative results generated by using GMC for a representative tita nium matrix composite system, SCS-6/TIMETAL 21S. The results presented correctly demonstrate the relative effects of fiber arrangement and s hape on the longitudinal and transverse stress-strain and creep behavi or of MMCs, with both strong and weak fiber/matrix interfacial bonds. Fiber arrangements included square, square-diagonal, hexagonal and rec tangular periodic arrays, as well as a random array. The fiber shapes were circular, square, and cross-shaped cross-sections; The effect of fiber volume fraction on the stress-strain response is also discussed, as is the thus-far. poorly documented strain rate sensitivity effect. In addition to the well-documented features of the architecture-depen dent behavior of continuously reinforced two-phase MMCs, new results a re presented about continuous multiphase internal architectures. Speci fically, the stress-strain and creep responses of composites with diff erent size fibers and different internal arrangements and bond strengt hs are investigated; the aim was to determine the feasibility of using this approach to enhance the transverse toughness and creep resistanc e of titanium matrix composites (TMCs).