Micromechanisms of Mechanically-Induced Cyclic Crack Growth in Brittle Solids

该计划旨在研究陶瓷的几个类别， 陶瓷基复合材料，代表具有不同 增韧机制 目的是找出原因和方法 疲劳裂纹在整体陶瓷中生长， 由裂纹偏转和/或晶粒桥接引起，例如 粗、细粒Al 2 O 3和晶粒拉长的Si 3 N 4。 其他 材料包括相变和微裂纹增韧 陶瓷如PSZ和ZTA，脆性纤维或晶须 增强陶瓷基复合材料，如SiC晶须增强的 氧化铝和韧性相增韧陶瓷基复合材料 例如Al增韧氧化铝。 疲劳试验，以及 降解的微观结构表征 裂纹尖端后面的裂纹尖端屏蔽（增韧）机制 以及尖端前方累积的微结构损伤， 用于研究循环裂纹扩展的微观机制， 材料. %%%% 这项研究旨在寻求对以下问题的基本理解： 陶瓷遭受循环疲劳破坏的机制。 一 陶瓷材料的数量，代表不同的材料 增韧机制，将用于这项研究。 显微组织特征与疲劳试验一起， 用于研究循环裂纹扩展的微观机制， 材料.

This proposed program aims to study several classes of ceramics and ceramic matrix composites, representing materials with different mechanisms of toughening. The objective is to discover why and how fatigue cracks grow in monolithic ceramics where toughening is induced by crack deflection and/or grain bridging, such as in coarse and fine grained Al2O3 and grain-elongated Si3N4. Other materials include the transformation and microcrack toughened ceramics such as PSZ and ZTA, the brittle fiber or whisker reinforced ceramic matrix composites such as SiC-whisker reinforced alumina, and the ductile-phase toughened ceramic matrix composites such as Al-toughened alumina. Fatigue tests, together with microstructural characterization of the degradation of the crack-tip shielding (toughening) mechanisms behind the crack tip and accumulated microstructural damage ahead of the tip, will be used to study the micromechanism of cyclic crack-growth in these materials. %%%% This research is designed to seek a fundamental understanding of the mechanisms by which ceramics suffer cyclic fatigue failure. A number of ceramic materials, representing materials with different mechanisms of toughening, will be used for this study. Microstructural characterizations together with fatigue tests are used to study the micromechanisms of cyclic crack-growth in these materials.