Viscoelastic Fracture Mechanics Of Functionally Graded Materials

Functionally graded materials are a new generation of engineered materials wherein the microstructural details are spatially varied through non-uniform distribution of the reinforcement phase(s), by using reinforcement with different properties, sizes and shapes, as well as by interchanging the roles of reinforcement and matrix phases in a continuous manner. Functionally graded materials are ideal candidates for applications involving severe thermal gradients, ranging from thermal structures in advanced aircraft and aerospace engines to computer circuit boards. In order to meet the demands of new technologies, particularly in microelectronics, aerospace and high temperature applications, the great bulk of the work, especially the fracture mechanics, has been in research on functionally graded materials.Linear elastic fracture mechanics (LEFM) is considered when there lacks total plasticity, which interests many researches. Great progress has been obtained by means of analytical method and numerical calibrating. Numerical calibrating can overcomes some defects from analytical method, such as strict demand on the geometrical shapes and the loading conditions of materials. Finite element method is an important application of numerical calibrating. In addition, many materials of engineering importance exhibit significant nonlinear viscoelastic behavior in physical environments and under mechanical loading of practical interest, especially under high-temperature conditions. Viscoelastic behavior manifests itself in various ways, including creep under constant load, stress relaxation under constant deformation, time-dependent recovery of deformation following load removal, time-dependent creep rupture and frequency-dependence of fatigue strength.In this thesis, the finite element method is applied first to solve the linear elastic crack tip field. Further, the viscoelastic crack tip field is investigated by means of the correspondence principle. Totally speaking, the thesis includes the following parts:(1) Introduction of functionally graded materials and linear elastic fracture mechanics is presented.(2) Applying the finite element method commercial software ABAQUS, the functionally graded strip model is set up. Then, there gives an introduction of this...