Fracture Process Zone Modeling of Small Cracks in Structural Ceramics Under Static and Cyclic Loading

摘要

This project focused on the study of the effects of microstructural features on the fracture process of room and high temperature structural ceramic materials that operate under cyclic loading environments. The ability to model these effects and the prediction of the damage behavior also become an important consideration, as it provides a direct link to the design cycle for both, processing and design engineers. The project evaluated cyclic effects, high cycle fatigue behavior, and elevated temperature effects under these conditions. Evaluations of the effects of cyclic loading are performed using pre-cracked tensile test specimens (PFT). It is observed that hysteretic load-displacement loops arise as the primary characteristic of the behavior, although gross-slip behavior is seen under certain circumstances. The results on this study conclude that the most important parameters responsible for the observed behavior, whether hysteretic of gross residual displacement behavior, are contact point and unbroken ligament densities. The results show a direct link between the behavior observed and the microstructural features that are active; mainly elastic bridges and that dissipate frictional energy. It is also concluded that a distribution of residual stresses and grain stiffness is required to correlate with the observed behaviors. Evidence of both, large and small scale debris is also found after cyclic loading. Large-scale debris is primarily found in small grain size aluminas, whereas small-scale debris observed in high cyclic fatigue specimens. Small-scale debris is primarily the result of mechanical wear.