复杂应力状态下陶瓷基复合材料细观损伤机理与数值模拟研究

Ceramic matrix composites (CMCs) are the key material for development of advanced aero and space plane. These materials exhibit obviously multi-axial mechanical properties. The damage behavior of material depends on the damage mechanism at microscopic level. Thus, it’s important to study the damage mechanisms of CMCs under complex stress states for understanding the failure process of these materials. Since the damage process is complicated, the researches about the damage mechanism of CMCs under complex stress states are quite limited. The key factors which control the initiation and evolution of damage under complex stress states have not been found. The reliable method of modeling the damage is also absents. In order to solve this problem, in this project, the tension-torsion test and biaxial test will be performed to find out the key factors which control the initiation and evolution of damage of plain weave CMCs under complex stress state, and then the damage mechanisms are revealed. A method derived from microscopic level is used. The mechanical properties of fiber bundle with matrix, matrix and interface under complex stress states are studied and the corresponding models are constructed. The microstructure of material is studied and the three-dimension geometrical models are constructed by using micro X-ray CT. The finite element method and the mechanical models of components are used to simulate the process of damage when material is under complex stress states. Finally, the numerical modeling of the damage of plain weave CMCs under complex stress states is achieved.

陶瓷基复合材料（CMCs）是研制先进航空航天飞行器热端部件的关键材料，该材料具有明显的多轴力学特性，且失效行为与其细观失效机理密切相关。因此研究CMCs在复杂应力状态下的失效机理对于准确把握其失效行为是极为重要的。由于该材料的细观失效过程十分复杂，目前国内外针对该问题的研究进展十分缓慢，尚未找到其在复杂应力状态下损伤萌生与发展的关键因素，更没有可靠的损伤模拟方法。本项目以平纹编织CMCs为对象，开展材料的拉扭和双轴实验，研究控制损伤萌生与发展的关键因素，揭示材料在复杂应力状态下的失效机理。采用“自底向上”的模拟方法，通过实验研究带基体纤维束、基体和界面在复杂应力状态下的力学行为，并建立数学模型；采用微焦点XCT技术研究材料细观结构特征，建立细观结构模型；应用有限元法模拟材料在复杂应力状态下的细观损伤过程。最终实现复杂应力状态下平纹编织CMCs细观损伤的数值模拟。

陶瓷基复合材料（CMCs）是研制先进航空航天飞行器热端部件的关键材料，该材料具有明显的多轴力学特性，且失效行为与其细观失效机理密切相关。因此只有充分掌握CMCs在复杂应力状态下的失效机理才能准确把握其失效行为。目前国内外针对CMCs细观失效机理的研究进展十分缓慢。.本项目首先开展了CMCs复杂应力状态下的力学试验。分别使用圆管试样和十字型试样开展拉扭和双轴拉伸试验，获得了复杂应力状态下的宏观力学响应规律。搭建了声发射及非接触变形联合测试系统及CMCs基体裂纹在线观测系统，开展了对CMCs复杂应力状态下损伤演化规律的研究。开发了基于剪滞模型、宏细观统一本构模型以及纤维随机断裂模型的CMCs复杂应力状态计算程序，实现了细观失效过程的模拟。开展了纳米压痕试验，计算得到了CMCs中碳化硅基体的原位弹性模量。.然后针对带基体纤维束CMCs试样，开展了拉伸加卸载试验，提出了基于应力-应变响应的界面摩擦模型的参数识别方法。该方法可识别界面脱粘应力和界面摩擦力，并可预测材料的拉伸应力-应变曲线。对带基体纤维束中碳纤维的原位弹性模量和强度分布进行了研究，提出了等效弹性模量和等效强度分布的概念，并模拟了碳纤维的原位性能。考虑基体开裂、界面脱粘、界面摩擦和纤维断裂四种失效模式，建立了带基体纤维束的宏细观统一本构模型。将带基体纤维束视为横观各向同性材料，计算出复杂应力状态下带基体纤维束的应力-应变曲线。考虑材料内部损伤萌生及演化的方向性，初步建立了包含拉伸剪切损伤的各向异性损伤本构模型。.最后将平纹编织CMCs看作是带基体纤维束以及SiC基体单元的集合体，基于XCT技术，建立了平纹编织CMCs的细观几何模型，通过多尺度方法，模拟了平纹编织CMCs的损伤演化过程和应力-应变关系。