Investigation On The Thermal Fracture Mechanics Of Nonhomogeneous Materials With Interfaces

The applications of the nonhomogeneous materials are more and more widely applied in many fields, such as the3-D braided composites, the functionally graded materials (FGMs), and the electronic packaging devices. Although the nonhomogeneous materials have many advantages, the complex structure may arouse new difficulties in obtaining the thermal fracture parameters. How to obtain the thermal fracture parameters in the material with complex interfaces effectively is a key problem in this investigation. This thesis will study the thermal fracture problems in nonhomogeneous materials with complex interfaces.In Chapter1, the thermal fracture problems of nonhomogeneous materials are reviewed first. Then the study of the thermal interface crack problems, the T-stress problems and the thermal fracture problems in nonhomogeneous piezoelectrics are also presented. Next, the interaction energy integral and the extended finite element method used in this thesis are introduced. Finally, the main contents of this project are introduced. This thesis aims to present an effective method for investigating the thermal fracture in nonhomogeneous materials with complex interfaces.In Chapter2, the thermal fracture problems in nonhomogeneous materials with interface are studied. A domain independent formulation of the interaction energy integral is obtained after a series of derivation. The domain-independence of the integral is valid when the integral domain contains an interface or many interfaces, so the application ranges of the interaction energy integral are enlarged greatly. Then, the validity of the present method is verified by comparison of the present results with analytical solutions. The convergence and the domain-independence of the present method are also verified. At last, the influences of the discontinuous material properties on the thermal stress intensity factors (TSIFs) are investigated. Numerical results show that the discontinuous Young’s modulus and the thermal expansion coefficient affect the TSIFs greatly. However, the discontinuous thermal conductivity may not arouse jump value of the TSIFs. By using the present method, the thermal fracture problems in nonhomogeneous materials containing complex interfaces, such as the fiber reinforced composites, can be solved effectively and show great significance in engineering applications.In Chapter3, the thermal interface crack problems in nonhomogeneous materials with complex interfaces are studied. First, a modified interaction energy integral method is proposed for obtaining the TSIFs of interface crack in nonhomogeneous materials with complex interface. Then, the validity and the domain independent of the present method are verified. Finally, the thermal fracture problems of the packaging devices containing complex interfaces are studied. The results show that the TSIFs will jump when the interface crack tip lies in the vicinity of the complex interfaces. The present method is an important complementary for the thermal interface crack problems.In Chapter4, an important fracture parameter—T-stress is studied when the nonhomogeneous materials are subjected to thermal loading. The formulation of the T-stress for complex structures is present first. The T-stress can be proved to maintain the domain-independence when the crack tip is near an interface. The present interaction energy integral shows good validation (the present results agree well with those in published articles) and the domain independence of the T-stress is verified (the difference of the T-stress for different integral domains are very small). The influences of the different material properties on the T-stress are analyzed. We found that the Young’s modulus and the thermal expansion coefficient will affect the T-stress greatly. However, the influence of the thermal conductivity on the T-stress is not too significant.In Chapter5, thermal fracture problems in nonhomogeneous piezoelectrics are studied. As a kind of smart materials, piezoelectrics have been widely applied in many fields. First, an interaction energy integral for obtaining the TSIFs and the electrical displacement intensity factor (EDIF) are developed in this Chapter. Then, the domain-independence of the interaction energy integral is proved and verified. Finally, we investigated the influence of different materials properties, including mechanical properties, thermal properties and electrical properties on the TSIFs. The method proposed in this chapter can be regarded as a guiding role for solving the thermal fracture problems of nonhomogeneous piezoelectrics.