Micromechanisms of Mechanically-Induced Cyclic Crack Growth in Brittle Solids

该计划旨在研究几种陶瓷和陶瓷基复合材料，代表具有不同增韧机制的材料。目的是发现疲劳裂纹在整体陶瓷中的原因和方式，其中韧化是由裂纹挠曲和/或晶粒桥接引起的，例如粗晶和细晶Al2O3和晶粒拉长的Si3N4。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 -晶须增强氧化铝，以及韧性相增韧陶瓷基复合材料，如al增韧氧化铝。疲劳试验，以及裂纹尖端后的裂纹尖端屏蔽（增韧）机制退化的显微组织表征和尖端前累积的显微组织损伤，将用于研究这些材料中循环裂纹扩展的微观机制。%%%%本研究旨在寻求对陶瓷遭受循环疲劳破坏的机制的基本理解。许多具有不同增韧机制的陶瓷材料将用于本研究。通过显微组织表征和疲劳试验，研究了这些材料循环裂纹扩展的微观机制。

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.