Study on Fracture Mechanical Behavior of Functionally Graded Materials under Thermo-Mechanical Loads

Abstract: Functionally Graded Materials (FGMs) have been widely used in the high temperature environments to alleviate the thermal stresses and residual stresses effectively because of its high temperature structural and excellent corrosion-resistant properties. Due to the reasons from the design, manufacture, service environment, etc., all kinds of cracks or defects may cause the failure of FGMs. Therefore, it is very important to investigate the fracture behaviors for the FGMs under thermo-mechanical loads for the design, optimization and application. However, it is very complex to analysis the thermo-mechanical behavior owing to its non-uniform characteristics. Until now, various types of simplified mathematic models and idealized boundary conditions for FGMs can be theoretically solved. However, the numerical methods are further effectively to investigate the fracture behavior of FGMs especially for the more complicated models or boundaries. In this paper, Finite Element Method (FEM) was used to analyse the fracture mechanical performance of FGMs subjected to mechanical loads and thermal loads. The major researches as follows:(1) The surface fracture was studied for Zirconia / Ni-Cr alloy FGMs strip with a semi-elliptical surface crack subjected to the thermal shock load, and studied the influence of crack depth, aspect ratios and thermal boundary conditions on the normalized stress-intensity factors along a crack-front.(2) Studied on the semi-elliptical surface crack problems with Zirconia / Ni-Cr alloy FGMs strip subjected to thermal shock loads and mechanical loads.(3) Changed the material properties, looking for effects with the different properties of materials under thermo-mechanical loading on the stress intensity factors, and propose some recommendations to design the FGMs with higher thermal shock resistance.The fracture problems of FGMs were reviewed in Chapter One, including the advances of theoretical analysis, numerical simulation and experimental researches. In Chapter Two, numerical solution of thermo-elasticity and the basic concepts of fracture mechanics on non-uniform gradient material were introduced. In Chapter Three , a fracture issue which contained a semi-elliptical surface cracks in functionally graded material strip under thermal shock loading was Investigated. In Chapter four, this fracture issue was discussed while FGMs subjected to thermal shock loading and mechanical loading. In Chapter five, the impact to the stress intensity factor was investigated with the variational material properties…
Key words: functionally graded materials; semi-elliptical surface crack; stress intensity factor; transient temperature thermal load; thermo-mechanical load; material properties

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