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

碳化硅-氮化硅纳米复合材料体系是一种在氮化硅基体中添加纳米SiC增强剂的重要材料体系，在高温结构体系中具有良好的应用前景。在进一步尝试通过不同的形态改变来改善这些复合材料的性能之前，需要对纳米SiC增强剂对复合材料行为的影响有一个基本的理论理解。在本研究中，将使用内聚有限元法（CFEM）对与第二相（SiC颗粒）、初级相（Si3N4基体）和晶界（GBs）相关的多个长度尺度进行明确的计算和理论微观结构工程分析，以提高断裂强度。由于第二阶段和GBs涉及纳米尺度的长度，因此分析还将集中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，以探索当实验推导的内聚拉伸-分离关系被原子推导的关系取代时，不同SiC-Si3N4形态的抗断裂预测的差异。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代表一个重要的科学和工程里程碑。这项研究将与K-12、本科和研究生教育加强、RET和REU计划发展、少数民族和代表性不足的群体参与、新课程开发和课堂教学经验加强相结合。研究结果将被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/纳米力学课程中。新课程的课堂讲稿和研究的计算机代码将以用户友好的界面发布在万维网上。初高中女生和来自代表性不足社区的学生将有机会在暑假期间通过实践学习探索技术、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.