共晶基复相陶瓷的损伤演化规律与断裂特性研究

To reveal the effect of microscopic damage on the constitutive relation and the fracture behaviour of the eutectic composite ceramic, the project includes three parts. Firstly, the micro-damage model of eutectic bodies would be built by analyzing the characteristic of micro non-homogeneous plastic flow, and defining the micro-damage variable which is related to the distribution of the nano/micro-fibres. After the micro-damage evolution law is studied, the micro-damage fracture strength as well as the critical breaking length of the eutectic body can be calculated. Secondly, choosing the meso-cell which is composed of eutectic bodies, inherent defects and particles, the extending energy release rate of the inherent defects can be defined. Considering such rate, combining the releasing rate of both the damage complementary free energy of eutectic body and the damage growth strain energy of the particles, the meso-parameter-related meso-damage model would be built. Then based on the micro-damage fracture strength and the critical breaking length of the eutectic body, damage extending criterion can be determined. In the final part, according to the random orientations and sizes of meso-cells, the damage expanding zone under the complex stress state would be computed. On the basis of the concepts of bridging eutectic body and ending eutectic body, and the bridging stress of eutectic body, the nonlinear properties of the stress-strain relation can be examined, and eventually the constitutive relation with the damage of the composites can be established. In a word, both the analysis method and the conclusion in this project would lay a foundation for the further dynamic mechanical behaviour research of the eutectic composite ceramic, also would provide a theoretical direction for the material's practical application.

为了揭示细微观损伤对共晶基复相陶瓷本构关系和断裂行为的影响，本项目进行三部分研究：首先，基于微观非均匀塑性流动损伤特征，定义与纳微米纤维分布规律相关的微观损伤变量，建立复合共晶体的微观损伤模型，分析微观损伤演化规律，计算复合共晶体的微观损伤断裂应力和临界断裂长度。其次，选取由共晶体、固有缺陷和颗粒组成的细观胞元，定义固有缺陷扩展的能量释放率，结合共晶体损伤余自由能释放率和颗粒的损伤增长应变能释放率,建立与细观结构参数相关的细观损伤模型，基于共晶体的微观损伤断裂应力和临界断裂长度，确定损伤扩展准则。最后，根据复相陶瓷内细观胞元的尺寸和取向的随机性，计算复杂应力状态下的损伤扩展区，基于桥联共晶体和终止共晶体的概念和共晶体桥联应力结果，分析应力-应变关系的非线性特征，建立复合材料的损伤型本构关系。本项目的分析方法和结论将为进一步研究复相陶瓷动态力学行为奠定基础，为材料的实际应用提供理论指导。

为了深入研究共晶基复相陶瓷的断裂特性，将微观结构与复相陶瓷的力学行为联系起来，需要建立合理完善的损伤与断裂的力学模型。为此，本项目进行了四部分研究：基于复合共晶体内的增强相有三种不同的分布形式，建立与增强相形状和分布规律相关的复合共晶体的微观损伤模型，计算微观损伤断裂应力；选择由多个平行共晶体构成的晶团，考虑基于共晶体断裂的局部突然损伤、共晶体间的界面滑移及界面脱粘损伤效应，建立与细观结构参数相关的细观损伤模型，计算晶团细观损伤极限应力；将细观损伤视为各向异性有效介质内的缺陷，基于强度因子分析，建立了细观缺陷稳定性模型；根据细观破坏机理，研究共晶基复相陶瓷的多种增韧机制的作用原理及发挥增韧作用的不同阶段，利用指数型韧性函数建立与裂纹长度相关的本构关系，得到了不同裂纹长度下的裂纹扩展极限应力。研究结果表明：共晶体损伤断裂应力相对增强相具有尺度效应，三角对称增强纤维共晶体抗破坏能力最强；晶团的细观损伤由共晶体断裂、共晶体间界面滑移和共晶体间界面脱粘共同控制；晶团的各向异性对细观损伤扩展有一定程度的影响，共晶体同向排列方式使细观损伤沿平行共晶体方向扩展；晶团内细观损伤发生自发的失稳扩展，并在晶团边界偏转成为晶团外细观缺陷；晶团外的某些尺度的细观缺陷在残余应力与基体本征韧性比值较大时将出现稳定性，增强相的不同分布形式对晶团外细观缺陷的稳定性影响不大；指数型材料韧性函数反映了材料的增韧特性，能够较好的解释裂纹扩展稳定性；细观缺陷对材料极限韧性值影响不大，但会导致增韧区尺寸变大，使韧性函数趋于平缓；裂纹较小时，材料经历一段失稳扩展过程后又趋于稳定，直到外载继续增加破坏其稳定性，材料再次失稳将导致材料断裂。对理论结果进行了有限元仿真和实验验证。本项目的分析方法和结论为材料的实际应用提供理论指导。