Investigations Of The Fracture Mechanics Of Nonhomogeneous Materials Under Thermal Shock Loading

Compared with homogeneous materials consisting of single component, nonhomogeneous materials have the unique excellent properties. Thermal shock is a typical loading condition which is possiblely met by nonhomogeneous materials in service. It might bring about a large temperature gradient and thermal stresses inside the material, which may eventually cause fracture failure. So a good understanding of fracture behavior of nonhomogeneous materials under thermal shock loading will be significant for the design and safety evaluation of nonhomogeneous materials. However, studies on the cracking problems of the nonhomogeneous materials under thermal shock loading are still quite limited by far. In this study, a series of investigations have been conducted, including the extraction of fracture parameters, crack propagation with complex interfaces and the thermal shock resistance of mixed-mode multiple cracks of nonhomogeneous materials under thermal shock loading.In Chapter1, the background and significance of the subject are introduced. Then, a series of studies on the thermal fracture problems of nonhomogeneous materials are reviewed. The shortages about the previous studies on the thermal fracture problems of nonhomogeneous materials under thermal shock loading are discussed. Based on the review and discussion, the main contents of this thesis are determined.In Chapter2, a set of analytical-numerical method combining the transient interaction integral method with the perturbation solution and finite element method is proposed for analyzing the thermal shock crack problems of nonhomogeneou materials. The perturbation solution of the transient temperature field is introduced in the interaction integral to express the thermal stress intensity factors (TSIFs) at different time. Then the interaction integral is imbedded in the finite element method to calculate the the mixed-mode TSIFs with high efficiency. Particularly, the influences of the geometric parameters and the distribution of matrial properties on the TSIFs are investigated by using the method. The present analytical-numerical method can be used to obtain the fracture parameters of nonhomogeneous materials under thermal shocks. The present work is also significant for solving the crack problems of nonhomogeneous materials with general properties. In Chapter3, the fracture behavior of nonhomogeneous coating/substratesystem containing an interface under a thermal shock loading is studied. A method for obtaing the TSIFs is proposed. The transient temerature field is evaluated by using the finite element method (FEM) and the finite difference method (FDM). The present method can be used to obtain the fracture paramenters of nonhomogeneous materials with different type of interfaces. Meanwhile, on considerartion of the fracture toughness of nonhomogeneous materials and the known TSIF, the crack growth law are anaylized and several critical parameters are provided. This method presents a solution to the fundermental problem for simulating thermal shock crack propagation.In Chapter4, the thermal shock resistance of nonhomogeneous materials with periodic cracks is studied in this chapter. According to stress-based and TSIF-based criteria, a thermal shock resistance model is established for nonhomogeneous materials with periodic cracks. The curves of thermal shock resistance are obtained. The maximum temperature jump for the nonhomogeneous materials can be predicted. The influences of the distribution patterns of material properties on the thermal shock resistances are discussed. And the influences of the crack spacing, the crack length and the crack angle on TSIFs are investigated. The present work will be significant for the fracture evaluation of nonhomogeneous materials under thermal shocks.In Chapter5, the thermal shock crack problems of nonhomogeneous materials containing particles are investigated. The IEIM and the extended finite element method (XFEM) are assembled to obtain the transient thermal stress intensity factors (TSIFs). The influences of the material parameters and the particle locations on the transient TSIFs are investigated. The results show that:1) the effect caused by the thermal expansion coefficient on the mixed-mode TSIFs is the dominant one among all thermomechanical properties, while the effect caused by the other material parameters is relatively weak;2) there is a critical distance beyond which the influences of particles on the mixed-mode TSIFs can be ignored. The present work will be significant for the fracture mechanics evaluation and design of nonhomogeneous materials.