Micromechanics-based deformation and failure prediction for longitudinally reinforced titanium composites

Two models to account for fiber breakage in longitudinally loaded composite materials have been incorporated into NASA Glennʹs Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) (Arnold SM, Bednarcyk BA, Wilt TE, Trowbridge D. MAC/GMC Users Guide: Version 3.0. NASA/TM- 1999-209070, 1999). The first is Curtinʹs widely used effective fiber breakage model (Curtin WA. Ultimate strengths of fibre-reinforced ceramics and metals. Composites 1993;24(2):98–102; Curtin WA. Theory of mechanical properties of ceramic-matrix composites. J Am Ceram Soc 1991;74(11):2837–45). This model treats all fibers in the composite as one effective fiber whose properties degrade in accordance with the statistical strength distribution of the actual fibers. The second is a new discrete model that considers failure of many individual fibers in a composite repeating unit cell. This model explicitly includes the important feature of local stress unloading in fractured fibers, even as global loading of the composite continues. MAC/GMC was employed to simulate the longitudinal tensile deformation and failure behavior of several silicon-carbide-fiber/titanium-matrix (SiC/Ti) composites using both models. Through comparison with experiment, MAC/GMC, in conjunction with the incorporated fiber breakage models, is shown to be quite realistic and capable of accurate predictions for various temperatures, fiber volume fractions, and fiber diameters.