Development of Supporting System of Design to Release Thermal Stresses in the Functionally Gradient Materials with a Crack

点击翻译按钮获取中文摘要

This research project consists of two parts : [I] Theoretical treatises of thermal stresses in the functionally gradient materials(FGMs), [II] Developments of programming system to release the thermal stresses in FGMs with a crack by Finite Element Methods(FEM).PART[I] Theoretical treatises of thermal stresses in the functionally gradient materials.(1) The governing equation of transient heat conduction for the functionally gradient materials is nonlinear. We could solve the nonlinear transient one dimensional heat conduction equation by use a new transformation of a variable and the perturbation method. The large tensile stress occurs on the ceramic surface of the functionally gradient plate at the earlier stage of cooling. But this large stress region is restricted within a very thin layr.(2) We could solve the steady and unsteady thermal stress problems of the FGMs with an internal crack whose all material properties are some exponential functions of a variable. When the Young's mod … More ulus and the coefficients of linear thermal expansion in the FGMs largely change, Stress intensity factors K_I and K_<II> vary drastically. If we can optimally select the composition of FGM such that the Young's modulus of ceramic in FGM is higher than that of metal, but the heat conductivity and the coefficients of linear thermal expansion are lower than that of metal, the stress intensity factors K_I and K_<II> decrease drastically.PART[II] Developments of programming system to release the thermal stresses in the FGMs with a crack by FEM.(1) We could develop programming system to release the thermal stresses in the FGMs with a crack by FEM.(2) From the results of calculation for the time variation of the stress intensity factor of the functionally gradient plate with an edge crack by FEM, we obtained the following results. A very large stress intensity factor K_I occurs on the ceramic surface. The region of the large stress intensity factor K_I is restricted within a very thin layr. A length of crack growth is restricted within a very thin layr. Less