Study On Microscale Finite Element Simulation Model Of Ceramic Tool Materials And Applications

Ceramic tool materials have the advantages of high hardness, high wear resistance, good high-temperature property and chemical stability, which are better than those of traditional cutting tool materials in high-speed machining and in cutting difficult-to-cut materials. But the brittleness of ceramic cutting tools greatly limits the popularization and application of ceramic cutting tools. The traditional method for developing ceramic cutting tools is "trial and error method", which is not only laborious and time-consuming, but also will reduce the hardness and wear resistance sometimes. So there is great significance in search of new methods for the research and development of ceramic cutting tools. The application of computer simulation technology causes the research approach of ceramic tool materials changing gradually from the semiempirical qualitative description to a stage of scientific quantifiable prediction.Based on the Monte Carlo algorithm, a microscale finite element three-dimensional simulation model of ceramic tool materials is established, and then the stress field, the equivalent elastic modulus as well as the crack propagation behaviors of ceramic tool materials are analyzed in this thesis.The three-dimensional microstructure simulation model of ceramic tool materials is established using the Monte Carlo algorithm. The microscale finite element three-dimensional simulation model of ceramic tool materials is built by integrating the Monte Carlo algorithm and the Finite Element Method. The evolution program of grain growth in single-phase and composite ceramic tool materials are compiled using C++ language, and the three-dimensional microstructure Monte Carlo simulation model of ceramic tool materials is built. By the interface code developped in this study, the microstructure after evolution of Monte Carlo three-dimensional simulation model is imported successfully into ABAQUS/CAE module of finite element analysis software, and then the microscale finite element three-dimensional simulation model of single-phase alumina ceramic tool materials and Al2O3TiB2 composite ceramic tool materials are built.The microscale finite element three-dimensional simulation model of single-phase and composite ceramic tool materials' mechanical stress, residual thermal stress and equivalent elastic modulus are created in the thesis. The linear elastic mechanical stress field of the single-phase alumina ceramic tool materials and Al2O3/TiB2 composite ceramic tool materials are simulated by applying uniaxial pressure. The results show that the mechanical stress on grain boundary is bigger and the intergranular failure will be generated under the external applied load. In the composite ceramic tool materials, the contour distribution density of maximum tensile stress on grain boundary is reduced due to the existence of second phase particles, which makes the integral stress distribution in materials more uniformer and reduces partly the stress concentration zone to improve the fracture toughness. Residual thermal stress field and toughening effect of Al2O3TiB2 composite ceramic tool materials are simulated. The results show that there are mainly residual compressive stress in the second phase particles and residual tensile stress in matrix, and the stress mutates strongly between the second phase particles and the matrix. The residual compressive stress reduces gradually, while the residual tensile stress increases, from the second phase to matrix. The maximum residual tensile stress increases with an increase in the volume content of second phase. The maximum residual compressive stress increases at first and then decreases. The residual compressive stress can close crack tip and result in toughening effect, so there is the best value of the second phase volume content. Microscale finite element computation model of equivalent elastic modulus is also created, and the equivalent elastic modulus of Al2O3/TiB2 composite ceramic tool materials is computed and compared with the calculated results by the empirical models. It can be concluded that the results calculated by finite element simulation model are consistent with the results obtained by empirical models, and they lies between the upper and lower limit value obtained by empirical models. These results verify the validity of microscale finite element computation model of equivalent elastic modulus.Microscale extended finite element three-dimensional simulation model of modeⅠcrack's and mixed mode crack's(modeⅠcrack and modeⅡcrack) propagation behaviors in single-phase ceramic tool materials are created respectively. The results show that the crack propagation path of modeⅠcrack's and mixed mode crack's match the actual crack propagation path, and there are stress concentration effects near the crack tip. This is one of the reason leading to the actual fracture strength of ceramic tool materials less than the theoretical fracture strength.