CAREER: Integrated Research and Education on the Dynamic Behavior of Metal-ceramic Layered Solids

该学院早期职业发展计划（Career）奖支持与新兴独特材料（称为MAX阶段）相关的新知识的研究。这些混合金属-陶瓷材料在原子尺度上形成层，就像叠在一起的纸一样，这使得层在载荷下局部扭结而不是破裂。这种扭结行为直到最近才被发现，但如果被理解，就有可能为我们国家日益老化的能源、通信和运输系统提供更坚固、更轻、更耐损伤的材料。因此，在各种真实载荷条件下（包括冲击、动态疲劳和断裂），将通过不同的堆叠顺序和层向来研究MAX相。此外，在这些复杂加载场景下，利用尖端高速成像和表面加速度映射的实验技术将被执行，能够提取比经典技术更多的材料行为信息。这些发现将为利用MAX相以及其他类似先进材料进行结构设计的预测计算模型提供有意义的输入。这项工作汇集了材料科学、应用力学和理论力学等多学科的努力。通过舞蹈机械教育和外展计划，将以新颖的方式接触未开发的各个年龄段的当地社区。研究和拓展部分突出了两者的内在创造力和相关性，旨在激励下一代STEAM（科学、技术、工程、艺术和数学）爱好者。本研究的重点是一类新兴的材料，MAX相，一类层状六方早期过渡金属碳化物和氮化物。这些材料表现出一种被称为波纹的新分类缺陷变形机制，这是一种纳米级屈曲现象，它以不同于塑性中的位错运动或断裂中的键断裂的方式适应应变，并导致在载荷下形成非线性类带（NKB）。虽然材料科学界正在研究这些3D层状固体的显著部分，但在中观到连续体水平上追求其行为的研究相对较少。这一努力旨在通过三个高度整合的实验研究重点来填补这一空白。首先，利用非线性屈曲理论确定NKB地层的驱动参数，表征了变形行为随应变速率和应力状态、层向和堆叠顺序的变化。第二部分利用混合实验-数值方法量化了动态断裂中的裂纹尖端能量学，并探索了冲击疲劳，扩展了经典的巴黎定律的时间效应。第三部分研究损伤行为，利用网格法和虚拟场法进行惯性冲击实验。对MAX相的广泛研究将揭示在长度和时间尺度上竞争的韧性、伪韧性和脆性变形机制，从而为系统地捕获、理解和优化这些独特的层状固体做出重大贡献。更广泛地说，这些发现将有助于理解各向异性材料如何在复杂的加载条件下适应应变，并为特定的纹理（缺陷工程）、功能梯度和/或分层材料设计铺平道路。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development Program (CAREER) award supports research to generate new knowledge related to an emerging class of unique materials, known as MAX phases. These hybrid metal-ceramic materials form layers on the atomistic scale, much like pieces of paper stacked together, which allows the layers to locally kink instead of crack under load. This kinking behavior has only recently been discovered, yet if understood, has the potential to provide tougher, lighter and more damage-tolerant materials for our nation's aging energy, communication and transportation systems. As a result, MAX phases will be investigated with varying stacking sequences and layer orientations across a variety of real-world loading conditions, including impact, and dynamic fatigue and fracture. In addition, experimental techniques utilizing cutting edge high-speed imaging coupled with surface acceleration mapping under these complex-loading scenarios will be performed, that are able to extract more material behavior information than classical techniques. These findings will provide meaningful input for predictive computational models in structural design leveraging MAX phases, as well as other similar advanced materials. This work brings together multidisciplinary efforts in materials science, and applied and theoretical mechanics. Novel means to reach untapped local communities at all ages will be enabled through a dance-mechanics education and outreach program. The research and outreach components highlight the innate creativity and correlations involved in both, and aims to inspire the next generation of STEAM (science, technology, engineering, arts and mathematics) enthusiasts. This research focuses on an emerging class of materials, MAX phases, a family of layered hexagonal early transition-metal carbides and nitrides. These materials exhibit a newly classified defect deformation mechanism termed ripplocations, a nanoscale buckling phenomena, which accommodates strain in a different manner than dislocation motion in plasticity or bond rupture in fracture, and leads to the formation of nonlinear kind bands (NKB) under load. While a notable portion of the materials science community is examining these 3D layered solids, relatively little research exists pursuing their behavior on the meso- to continuum level. This effort aims to fill that gap through three highly integrated experimental research foci. The first characterizes deformation behavior varying strain rate and stress states, as well as layer orientation and stacking sequences, utilizing nonlinear buckling theory to determine the driving parameters in NKB formation. The second quantifies crack tip energetics in dynamic fracture leveraging a hybrid experimental-numerical scheme, as well as explores impact fatigue, extending the classic Paris Law for temporal effects. The third pursues damage behavior, conducting inertial impact experiments exploiting the Grid Method and the Virtual Fields Method, an emerging inverse technique. The extensive investigations on MAX phases will shed light on competing ductile, pseudo-ductile and brittle deformation mechanisms across length and time scales, thus making a significant contribution towards systemically capturing, understanding and optimizing these unique layered solids. More broadly, the findings will help understand how anisotropic materials accommodate strain under complex loading conditions, and paves the way for specifically textured (defect engineered), functionally graded, and/or hierarchical material design.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.