The Development of Life Prediction Techniques for Structural Ceramics

One of the major challenges involved in the use of ceramic materials in advanced vehicular heat engines is ensuring adequate strength and durability. This Department of Energy supported activity has developed methodologies to predict the structural behavior of ceramic components. The effort involved the characterization of injection-molded and hot isostatic pressed PY6 silicon nitride and the development of analytical life prediction techniques. Three failure modes are addressed: fast fracture, slow crack growth, and creep rupture. The technique deals with surface as well as internal component failures. The life prediction methodologies for fast fracture and slow crack growth have been verified using two types of confirmatory specimens: (1) flat circular disks subjected to bending stresses, and (2) high-speed rotating spin disks. Correlation was achieved for a variety of test conditions and failure mechanisms. The predictions associated with surface failures proved to be optimistic, requiring re-evaluation of the components’ initial fast fracture strength. Correlation was achieved for the spin disks that failed in fast fracture from internal flaws. Time-dependent, elevated-temperature spin disk failures were also successfully predicted.