Interfacial Shear Behavior and Its Influence on Fiber Damage in Sapphire-Reinforced Gamma Titanium Aluminide Composites

摘要

The interfacial shear behavior and its influence on fiber damage in sapphire-reinforced TiA1 composites was investigated using a combination of microscopic characterization, indentation crack growth results, fiber pushout testing, fiber displacement measurements, and computational analyses. Two inter-related phenomena were studied: (1) residual stresses and resulting damage within fibers intersecting a free surface and (2) fiber/matrix interfacial strength behavior. In the first aspect of this study, experimental observations, finite element analysis, as well as analytical computations were all used to analyze the evolution of fiber damage that was observed in fibers intersecting a free surface in sapphire-reinforced Ti-48Al-IV composites. Experimental observations indicate that, under certain conditions, surface cracks introduced during specimen preparation will propagate along the fiber axis due to thermally-induced residual stresses. Finite element computations predict that significant thermally-induced residual tensile stresses exist in sapphire fibers embedded within TiA1-based matrices when they intersect and are oriented normal to a free surface. Indentation crack growth behavior within the sapphire fibers provided experimental validation of the predicted stress state. Finally, the application of an exact elastic analysis indicates that tensile stresses also exist within fibers oriented parallel to and near a free surface.