Residual Stresses and Resulting Damage Within Fibers Intersecting A Free Surface

Abstract

ABSTRACTFinite element as well as indentation fracture mechanics modeling have been used to analyze the evolution of fiber damage that was observed at the ends of fibers intersecting a free surface in sapphire-reinforced TiAl matrix composites. Experimental observations indicate that, under certain conditions, surface cracks introduced during cutting will propagate along the fiber axis due to thermally-induced residual stresses. Finite element computations predict that significant thermally-induced residual tensile stresses exist near the ends of sapphire fibers which are embedded within TiAl-based matrices and are oriented normal to a free surface. Crack growth behavior induced by microhardness indentations is used to experimentally verify the FEM predictions. The results indicate that a biaxial tensile residual stress state exists near the fiber ends due to a thermal expansion mismatch. The magnitude of the residual stresses are a sensitive function of interfacial bond strength and elastic/plastic properties of the interfacial region and may be sufficient to propagate pre-existing cracks.