US-Turkey Cooperative Research: Three-Dimensional Effects in the Fracture of Functionally Graded Materials

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0322271 LambrosDescription: This project supports a cooperative research between Dr. John M. Lambros, Department of Aeronautics and Astronautics, University of Illinois, Urbana, Illinois and Dr. Gunay Anlas, Department of Mechanical Engineering, Bogazici University, Istanbul, Turkey. Functionally Graded Materials (FGMs) are materials possessing a continuous spatial variation of properties and typically are composed of a metal/ceramic combination in which their relative volume fractions are continuously varied. FGMs are candidate materials for simultaneously providing both structural support and thermal, impact or wear protection. Their widespread use has not materialized thus far, partially because of a lack of understanding of the mechanics of such continuously inhomogeneous materials, and in particular their fracture response. Although several analytical and numerical results exist in the literature, these are primarily two-dimensional and most often involve symmetric (i.e. mode I) conditions. Far fewer experimental studies exist, but the relation between theory and experiment is tenuous at best since the validity of theoretical results, usually asymptotic in nature, in experimental situations is not clear. Emphasis will be placed on three less studied aspects of the fracture of FGMs: (i) the development of three dimensional stresses at a crack tip in an FGM as dependent on the property gradient, (ii) the extent of validity of asymptotic fields in actual situations of cracked FGMs, and (iii) the influence of near tip mixed mode conditions (whether from loading or material gradient asymmetry) on both of the above. Two (2D) and three (3D) dimensional finite element simulations will be performed on physically relevant geometries (three and four point bend, edge crack, compact tension) of cracked graded plates. The results will shed light on the development of through thickness stresses ahead of the tip and will provide an inner boundary for the region of validity of the asymptotic theory. The results will be verified by comparison with experiments on the polymer-based model FGM that Dr. Lambros has developed. The research will help extend fundamental understanding of the processes involved in the fracture of FGMs, especially in regard to three dimensional stress development, dominance of asymptotic fields and mixed mode near tip conditions. Scope: Dr. Alnas' expertise is in the areas of theoretical and numerical analysis of fracture of composites, interfaces and graded materials. Most of the 2D and 3D simulations will be performed in Turkey using ABAQUS as the main platform. Additional experiments, as well as some simulations directly linked to them, will be performed at UIUC. A short planning trip and at least two meetings a year will be held alternately in the United States and Turkey. Drs. Lambros and Anlas will be accompanied by their respective graduate students. Bogazici University graduate students will have the opportunity to work with the experimental set-ups at UIUC. Advanced courses involving FGMs will be developed in Turkey and UIUC. American researchers and graduate students at UIUC will have a chance to cooperate with their Turkish partners.