【作者】 朱小辉；

【导师】 黄传真；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2011， 硕士

【摘要】 陶瓷刀具材料具有高硬度、高耐磨性、良好的高温性能和化学稳定性,在高速切削和难加工材料加工领域具有传统刀具无法比拟的优势,但陶瓷刀具的脆性大,极大地限制了陶瓷刀具的推广和应用。传统的开发陶瓷刀具的方法多采用“试凑法”,这种方法不仅费时费力,而且在提高断裂韧度的同时,有时还会降低材料的硬度和耐磨性,因此寻找全新的开发方法对陶瓷刀具的研制和发展具有重要的意义。由于计算机模拟技术的应用,使得陶瓷刀具材料的研究从半经验定性描述逐渐进入到定量预测控制的更为科学的阶段。本文基于蒙特卡洛算法,建立了陶瓷刀具材料微观尺度有限元三维模拟模型,对陶瓷刀具材料的应力场、等效弹性模量和裂纹扩展行为进行了模拟。采用蒙特卡洛算法建立了陶瓷刀具材料三维微观组织模拟模型；集成蒙特卡洛算法和有限元法,建立了陶瓷刀具材料的微观尺度有限元三维模拟模型。利用C++语言编写了单相和复相陶瓷刀具材料的晶粒生长演化程序,建立了陶瓷刀具材料三维微观组织蒙特卡洛模拟模型。通过本文开发的接口程序,将蒙特卡洛三维模拟模型演变后的微观组织成功地导入有限元分析软件ABAQUS/CAE模块之中,建立了单相氧化铝陶瓷刀具材料和复相Al2O3/TiB2陶瓷刀具材料的微观尺度有限元三维模拟模型。分别建立了单相和复相陶瓷刀具材料机械应力、残余热应力、等效弹性模量的微观尺度有限元三维模拟模型。模拟研究了单相氧化铝陶瓷刀具材料和复相Al2O3/TiB2陶瓷刀具材料在单轴压力作用下的线弹性机械应力场；结果表明,晶界处的应力较大,在外载荷作用下,容易产生沿晶断裂；在复相陶瓷刀具材料内,由于第二相颗粒的存在,晶界处的最大拉应力等值线分布密度降低,使材料内部整体应力分布趋于均匀,在一定程度上缩小了应力集中,可提高材料的断裂韧度。模拟研究了复相A1203陶瓷刀具材料的残余热应力场及其增韧效应；结果表明,第二相颗粒内主要是残余压应力,基体内主要是残余拉应力,在第二相与基体的界面处,应力产生突变,由第二相到基体,残余压应力逐渐减小,残余拉应力逐渐’本研究得到了国家自然科学基金(50975161)和济南市高校自主创新计划(200906013)资助增大；最大残余拉应力随着第二相体积含量的增大而增大,最大残余压应力则是先增大后降低,由于残余压应力可以促使裂纹尖端闭合,产生增韧作用,因此第二相组份存在一个最优的体积含量。建立了等效弹性模量的微观尺度有限元计算模型,计算了复相Al2O3陶瓷刀具材料的等效弹性模量,并与通过经验模型获得的等效弹性模量进行了对比；结果表明,有限元计算结果与经验模型获得的结果相符合,并介于经验模型计算的等效弹性模量上限值和下限值之间,证明了等效弹性模量的微观尺度有限元计算模型的正确性。分别建立了单相陶瓷刀具材料中Ⅰ型裂纹和复合型裂纹(同时存在Ⅰ型和Ⅱ型裂纹)扩展行为的微观尺度扩展有限元三维模拟模型。模拟结果表明,Ⅰ型裂纹和复合型裂纹的模拟扩展路径与实际扩展路径相符,而且在裂纹尖端存在应力集中效应,这是导致材料真实断裂强度小于理论断裂强度的原因之一。更多还原

【Abstract】 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.更多还原