Microstructural Engineering of SiC-Si3N4 Nanocomposites Using a Combination of Classical Molecular Dynamics and Cohesive Finite Element Methods

碳化硅(SiC)-氮化硅(Si3N4)纳米复合材料体系是一种重要的材料体系，在高温结构体系中具有广阔的应用前景。在进一步尝试通过不同的形态变化来改善这些复合材料的性能之前，需要对纳米级碳化硅增强体对复合材料行为的影响有一个基本的理论了解。在这项研究中，这种提高断裂强度的计算和理论微观结构工程分析将使用内聚力有限元方法(CFEM)，显式地考虑与第二相(碳化硅颗粒)、初生相(Si3N4基质)和晶界(GBs)相关的多个长度尺度。由于第二阶段和GBS涉及纳米尺度，分析还将侧重于将现有的实验信息与相应的经典分子动力学(MD)模拟相结合，以探索当实验得出的内聚力-分离关系被原子推导的关系取代时，各种SiCSi3N4形貌在预测断裂抗力方面的差异。鉴于先进的民用和机械系统(如先进的化石燃料能源转换系统)对新材料的巨大需求，开发的分析工具和分析结果将是一个重要的科学和工程里程碑。这项研究将与K-12、本科生和研究生教育的强化、RET和REU项目的发展、少数群体和代表性不足的群体参与、新课程开发和课堂教学经验的增强相结合。研究成果将纳入正在教授的研究生和本科生固体力学课程以及正在开发的微/纳米力学课程。新课程的讲稿和研究计算机代码将在万维网上张贴，界面友好。正在崛起的初中和高中女性以及来自代表性不足社区的学生将有机会在暑期大学校园参观期间通过动手学习来探索技术、数学和科学概念。

Silicon Carbide (SiC)-Silicon Nitride (Si3N4) nanocomposite material system consisting of nano-sized SiC reinforcements in a Si3N4 matrix is an important material system with excellent promise for use in high temperature structural systems. A fundamental theoretical understanding of the effect of nano-sized SiC reinforcements on the behavior of the composites is required before further attempting to improve the properties of these composites by varied morphological alterations. In this research such computational and theoretical microstructural engineering analyses for improved fracture strength will be performed with an explicit account of the multiple length scales associated with the second phase (SiC particles), the primary phase (Si3N4 matrix) and the grain boundaries (GBs), using the cohesive finite element method (CFEM). Since the second phase and the GBs involve nanoscopic lengthscales, the analyses will also focus on combining available experimental information with the corresponding classical molecular dynamics (MD) simulations for exploring differences in the fracture resistance prediction of various SiC-Si3N4 morphologies when the experimentally derived cohesive traction-separation relations are replaced by the atomistically derived ones. In view of the significant demand for new materials in advanced civil and mechanical systems such as advanced fossil fuel energy conversion systems, the developed analysis tool and analyses outcomes will represent a significant scientific and engineering milestone. The research will be integrated with K-12, undergraduate, and graduate educational enhancements, RET and REU program development, minority and underrepresented group involvement, new course development, and in-classroom teaching experience enhancement. The results of the research will be incorporated in the graduate and undergraduate solid mechanics courses being taught and in the micro-/nano-mechanics courses being developed. Lecture notes of the new courses taught and the research computer codes will be posted on the World Wide Web with user-friendly interfaces. Rising junior and senior high school women and students from underrepresented communities will be provided opportunities to explore technology, math, and science concepts using hands-on learning during summer time University campus visits.