Finite element analysis of thermally induced residual stresses in functionally graded materials.

Abstract: Functionally graded materials (FGMs) are advanced materials and their main characteristic is microstructure and composition variation over the volume of the specimen. This variation of the composition results in changing of material properties in the component. In FGMs usually there are two different types of powder materials such as metal and ceramic powders which are mixed to build up the graded region. These grade layers are placed between the metal and ceramic layers and by this approach a smooth and gradual transient from metal to ceramic can be achieved.Sintering is the main technique to manufacture these types of materials. During the sintering process, cooling of the specimen from sintering temperature to room temperature results in generation of thermal residual stresses within the material. These thermal stresses may cause crack propagation and failure of the material.Distribution analysis of these thermally induced stresses within the material has been carried out in this thesis work. Finite element package ABAQUS has been used in order to simulate the distribution of the thermal residual stresses in the materials. In order to achieve the optimal design for different geometries the parametric study also has been performed. For example influence of number of layers, mixing ratio and porosity has been investigated.Based on the finite element results for cylindrical and cuboid models, non-linear composition variation for both geometries has no improving effect in terms of induced thermal residual stresses. Porous material shows less thermal stress than non-porous material. As the amount of porosity for individual layer was considered in simulation process, this approach resulted in decreasing of thermal stresses within the material. Moreover, non-uniform thickness of graded layers was not beneficial for stress reduction. This variation of thickness results in increasing of thermal residual stresses within the material.