High Temperature Fracture of Ceramic Matrix Composites: A Micromechanics Experimental Approach

陶瓷基复合材料是一种新型的高温工程用先进材料。由于扩展裂纹与第二相增强材料的相互作用，它们表现出比整体陶瓷更高的强度和断裂韧性。基于裂纹桥联和断裂过程区的脆性基复合材料增韧机理的理论在过去几年中得到了发展。虽然对连续纤维和晶须增强陶瓷的这些机制在室温下都进行了详细的研究，但它们在高温下的断裂行为还没有得到很好的描述。这项研究的第一个目标是开发一种新的实验方法，它将提供高温下断裂过程的定量测量。该方法包括一种简单的实验技术，它允许同时测量裂纹扩展阻力曲线，并在20-17500℃的温度范围内直接观察受控加载期间的微观断裂过程。第二个目标是研究三种重要的、表征良好的材料的行为，它们代表了一系列性能：碳化硅晶须增强氧化铝、尼卡隆纤维/LAS玻璃陶瓷和碳/碳复合材料。研究的主要意义在于，它将为确定陶瓷在高温下断裂和变形的基本机制提供工具。有了这些工具，材料开发人员可以设计具有改进断裂行为的陶瓷基复合材料，应用设计人员将能够预测其结构组件在高温条件下的可靠性。

Ceramic matrix composites ar a new class of advanced materials intended for high temperature engineering applications. They exhibit enhanced strength and fracture toughness over monolithic ceramics due to the interaction of a propagating crack with the second phase reinforcing material. Theories for the mechanisms of toughening in brittle matrix composites, based on crack bridging and a fracture process zone, have been developed over the past few years. While these mechanisms have been studied in detail for both continuous fiber and whisker reinforced ceramics at room temperature, their fracture behaviors at elevated temperature are not well characterized. The first goal of this research is the development of a new experimental approach which will provide a quantitative measure of fracture processes at high temperature. The approach involves a simple experimental technique which permits simultaneous measurement of crack growth resistance curves and direct observation of microscopic fracture processes during controlled loading over a temperature range of 20-1,7500C. The second goal is to study the behaviors of three important and well characterized materials, representing a range of properties: SiC whisker reinforced alumina, Nicalon fiber/LAS glass ceramic, and carbon/carbon composite. The primary significance of the research is that it will provide the tools to determine the fundamental mechanisms of fracture and deformation of ceramics at high temperature. With these tools, materials developers can design ceramic matrix composites with improved fracture behavior and application designers will be able to predict the reliability of their structural components under high temperature conditions.