Fracture mechanics of functionally gradient materials and material interfaces and layered orthotropic materials will be studies. The emphases in the program will be on the fracture related issues in new material systems in which strength, toughness, fatigue and corrosion properties along with the residual stresses may be controlled by controlling the composition profile during processing. Functionally gradient materials are essentially fine composites or nano composites which are synthesized to achieve a desired thermomechanical property variation in the material by grading the volume fractions of the constituent materials through the thickness. This new process of grading the properties of the interfacial regions and coatings by gradually varying the material composition through the thickness appears to have some very important advantages. First, the process smooths the stress distribution and drastically reduces the stress concentration factors thereby reducing the likelihood of failure due to residual and thermal stresses. Secondly, it improves the bonding strength, in most cases quite considerably. The third advantage of the new technique is the improvement one obtains in fracture toughness and fatigue and corrosion crack growth parameters of the material. The second part of the program deals with the investigation of the influence of material orthotropy, particularly the structure and thickness of interfacial zones in bonded layers on the crack driving force in delamination and fracture penetration problems.
