Indentation-Induced Damage Initiation and Evolution in Single- and Poly-Crystalline Ceramics

为研究单晶和多晶陶瓷中裂纹的萌生和扩展以及断裂和塑性之间的相互作用，提出了一种联合实验和模拟工作。首先，将检验用于韧性测量的压痕-裂纹法的有效性，并将构建参数图来描述裂纹尺寸与接触半径之比与压头几何形状、外加载荷、韧性和硬度的关系。其次，通过实验检测几种碳化硅材料在载荷和深度传感球形压痕试验中的行为，并将其与基于晶体塑性的有限元模拟进行比较，该有限元模拟基于晶体塑性，具有沿晶和穿晶的耦合微断裂，使用内聚区方法，将得到耦合变形和微断裂过程的详细图像，由此可以预测如何定制微结构以优化其能量吸收。能够定量地预测断裂的萌生和扩展以及断裂和塑性之间的相互作用是从力学上理解陶瓷单晶和多晶的变形和破坏特性以及延性和增韧方法的关键一步。拟议的工作将为研究生和本科生提供一个很好的机会来参与实验/建模协同研究，其中包括细观力学建模和计算，以及先进的机械测试和微观结构表征。将通过两个研究生级别的班级编写和传播新的教育材料。PIs将参加他们研究所(由NSF和能源部支持)的现有教育/外联活动计划，这些活动旨在激发高中生和大学生对科学和工程职业的兴趣，以及从代表性不足的群体中招收学生。

A joint experimental and modeling effort is proposed to study the initiation and growth of crack and the interplay between fracture and plasticity in single- and poly-crystalline ceramics. First, the validity of indentation-cracking method for toughness measurement will be examined, and a parametric map will be constructed to delineate the dependence of the ratio of crack size and contact radius on indenter geometry, applied load, toughness, and hardness. Second, by experimentally examining the behavior of several SiC materials during load and depth sensing spherical indentation tests and comparing it to microstructurally based finite element simulations based on crystal plasticity with coupled intergranular and transgranular microfracture using a cohesive zone approach, a detailed picture of the coupled deformation and micro-fracture processes will be developed from which it will be possible to make predictions about how to tailor a microstructure to optimize its energy absorption. The ability to quantitatively predict the initiation and propagation of fracture and the interaction between fracture and plasticity is a critical step towards a mechanistic understanding of deformation and failure properties, as well as ductility and toughness enhancement methods, of ceramic single crystals and polycrystals. The proposed work will provide an excellent opportunity for the graduate and undergraduate students to participate in an experimental/modeling synergistic research that includes micromechanics modeling and computation, and advanced mechanical testing and microstructural characterization. New educational materials will be developed and disseminated through two graduate level classes. The PIs will participate in the existing programs at their institute (supported by NSF and Department of Energy) for education/outreach activities, which are designed to inspire interests of high school and college students in science and engineering careers, as well as for recruiting students from underrepresented groups.