Toughness, Strength, and R-Curve Behavior of Microcracking Materials (Materials Research)

本研究是对陶瓷材料韧性和应力致微裂纹的研究工作（DMR-8305800）的延续。调查重点关注以下主题：1)结合重要物理材料参数的陶瓷裂纹扩展的计算机计算和建模；2)利用小角中子散射表征陶瓷-玻璃复合材料系统的应力诱发微裂纹；3)陶瓷和陶瓷-玻璃复合材料的强度-韧性关系研究。在多相陶瓷材料中，微裂纹是常见的，特别是当材料中存在的几个相之间的热膨胀系数存在明显差异时。这种现象可以用来调整材料的力学性能，通过适当选择各种相，消除微裂纹或在规则裂纹附近引入微裂纹。微裂纹的存在往往可以降低规则裂纹尖端的应力强度，从而使规则裂纹停止扩展。这种现象导致陶瓷在使用中更坚韧，并且在压力下不易发生灾难性故障。目前的研究旨在增加对这一现象的理解，并允许设计更坚韧的陶瓷。

This research is continuation of work (previous research under DMR-8305800) on understanding the toughness and stress- induced microcracking of ceramic materials. The investigation emphasizes the following topics: 1) computer computation and modelling of the growth of cracks in ceramics which incorporates the important physical materials parameters, 2) characterization of ceramic-glass composites systems which demonstrate stress- induced microcracking using small angle neutron scattering, 3) study of the strength-toughness relationships for ceramics and ceramic-glass composites. In multiphase ceramic materials, microcracking is common, especially when there is a pronounced difference in the coefficient of thermal expansion between the several phases present in the material. This phenomenon can be used to tailor the mechanical behavior of the material, by proper selection of the various phases, to allow elimination of the microcracks or introduction of the microcracks in the vicinity of regular cracks as desired. The presence of microcracks can often reduce the stress intensity at the tips of regular cracks, and thereby cause the regular cracks to stop propagating. This phenomenon causes the ceramic to be tougher in service, and less susceptible to catastropic failure under stress. The present research is designed to increase understanding of the phenomenon, and allow design of tougher ceramics.