This research is funded to study the relationship of micro- mechanics and the toughening mechanism of ceramics. Many techniques have been tried to improve bonding between dissimilar materials with applications to composite materials, layered electronic devices, and protective coatings. Research will be conducted to study a number of aspects of fracture along interfaces including the parameters controlling toughness of a brittle adherent layer, the role of combined mode loading on debonding, and bond toughening by deflected crack trajectories within an adhesive layer. Theoretical work will be carried out on micro-cracking and crack- bridging, two basic mechanisms which can in principle be manipulated by micro-structural processing to improve the toughness of polycrystalline ceramics. The objective of this work is to quantify the mechanisms so that reliable toughness predictions can be made based on microstructural characterizations. A basic study of cavitation in plastically deforming solids under triaxial stressing will be conducted. Stress levels at which "explosive" void growth occurs will be sought. These stress states represent intrinsic material stability limits which appear to have been attained in recent experiments under highly constrained flow.
