【作者】 鲍雨梅；

【导师】 柴国钟；

【作者基本信息】 浙江工业大学 ， 化工过程机械， 2009， 博士

【摘要】 陶瓷材料具有优良的物理、化学性能,广泛应用于航空、航天、通信、石油化工、电力、冶金、机械及现代生物医学等领域。磨削是目前陶瓷材料普遍应用的加工方法,特别是精密和超精密磨削加工。磨削加工过程是一个材料的损伤过程,磨料通过对被加工材料的有限度损伤而实现加工。由于陶瓷是一种典型的脆性材料,硬度高、耐磨而且韧性低,使得其磨削加工性极差,极易产生表面/亚表面磨削损伤,从而大大降低陶瓷材料零件的寿命,甚至直接导致零件的报废。因此,对工程陶瓷磨削损伤进行全面深入研究和了解是非常重要的。目前,对于陶瓷材料的磨削损伤问题主要从实验和理论研究、数值模拟等三个方面研究其损伤问题,分别从损伤的各种表现形式如微裂纹、残余应力等方面进行研究。本文基于连续损伤力学理论和纳米压痕/划痕测试技术,提出了一种弹性模量退化型陶瓷材料表面/亚表面损伤表征方法,根据球锥形压头下的纳米压痕实验数据,推导得到微纳尺度压痕局部区域的弹脆性损伤本构关系,在此基础上进行了压痕过程的有限元模拟,并采用纳米划痕试验来模拟单颗磨粒的磨削过程,研究其损伤的演化,研究成果将为陶瓷材料精密磨削理论的完善奠定坚实的理论基础。本文的主要工作和成果如下:1.结合Kachanov经典的连续损伤力学理论,定义弹性模量退化型损伤变量来综合描述材料因各种损伤形式而造成的性能劣化,并实现了基于纳米压痕测试的表征材料表面/亚表面损伤的简单可测的方法。2.采用上述的损伤变量定义,结合陶瓷材料的弹性损伤特征,以氧化铝陶瓷材料为例,采用球锥形压头进行纳米压痕测试,得到了氧化铝陶瓷的弹脆性损伤本构关系,并分别进行了球锥形压头和玻氏压头压痕损伤的有限元模拟,证实了该本构关系具有一定的正确性。3.以氧化铝陶瓷材料为例,采用纳米划痕测试方法,通过控制划痕载荷和压头形状,模拟研究了磨削参数(包括磨削用量、砂轮特性等)对磨削后表面/亚表面损伤等的影响规律,结合磨削后划痕周围相同载荷下距划痕中心不同距离处,或者不同载荷下同一距离处测试点的压痕试验,以及表面原位扫描和SEM形貌观测,探讨将陔损伤表征方法用于测量陶瓷磨削损伤的可能性。4.本文基于连续损伤力学和纳米压痕/划痕测试技术对陶瓷材料弹脆性损伤本构关系和磨削损伤表征测量方法进行研究。研究中借鉴了国内外在工程陶瓷磨削损伤、连续损伤力学、微纳米测试技术、磨削过程计算机仿真技术等方面已取得的相关研究成果,同时混凝土、岩石等脆性材料损伤机理、本构模型的研究成果也为本文的研究提供了理论依据。在此基础上,还可以深入开展将本文提出的表面/亚表面损伤表征测量方法应用于其它材料的研究。更多还原

【Abstract】 Ceramics, with very excellent physical and chemical properties, are increasingly used in the fields of aerospace, communication, petrochemical engineering, power, metallurgy, mechanical and modern biomedical engineering. Grinding is the most efficient and effective technique to finish ceramics workpieces, especially precision and ultra-precision grinding. Grinding is a complex abrasive cutting process, involving a material removal by the contact between abrasives and the workpiece with certain damage. Ceramics, typical brittle materials with high hardness, strength and abrasive resistance, are difficult to be machined. The ground components are most likely to contain surface/subsurface damages, influencing strongly the performance and reliability of ceramic components. Therefore, it is essential to study and understand comprehensively the grinding induced damage in ceramic.The current research efforts related to the grinding induced damage of ceramics focus on the experimental, theoretical and numerical aspects including such damage as microcracks, residual stresses. A degraded elastic modulus based characterization method of surface/ subsurface damage for ceramic materials is presented based on continuum damage mechanics (CDM) and nanoindentation/ scrath techniques. An elastic brittle damage constitutive equation is developed according to the nanoindentation results under a conospherical tip. Then the FEM simulation of the indentation loading process is conducted. The nanoscratch tests are employed to simulate the single abrasive grinding to study the damage evolution. The proposed efforts will be a foundation for improving the precision grinding theories of the ceramics. Main research efforts are as follows:1. A degraded elastic modulus based damage variable is defined to describe the damage induced property degradation of the materials based on the traditional Kachanov CDM framework. A simple and feasible characterization method of surface/ subsurface damage is realized based on nanoindentation test.2. An elastic brittle damage constitutive equation of the alumina is developed according to the nanoindentation results under a conospherical tip, considering the elastic damage of brittle ceraics. And then the FEM simulation of the indentation loading process is conducted with conospherical and berkovich tip, to verify the developed constitutive equation.3. The effect of grinding parameters such as grinding depth, griniding wheel characteristics on the grinding induced surface/ subsurface damage is studied simulatively with alumina sample, through nanoscratch tests with controlled peak scratch force and the tip geometry. A series of indentation tests are employed on the points either with different distance from the scratch center under the constant load or the points with the similar distance under ramp force. The surface topography of the sratches and the indents is analyzed through piezo in-situ tip scanning method and the SEM method. The feasibility of applying the proposed damage characteraization method to the grinding induced damage is consequently studied.4. The elastic brittle damage constitutive equation and the characterization method of grinding induced damage for ceramics are studied based on CDM and nanoindentaion/ scratch technique. The research findings in the grinding induced damage of ceramics, CDM, nano testing techniques and simulation of the grinding process are referred as well as the damage mechanisms and constitutive models of brittle materials such as concrete, rock. A further research on extending the proposed characterization method to other materials should be carried out.更多还原