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)奖支持研究，以产生与一种新兴的独特材料相关的新知识，称为MAX阶段。这些混合金属-陶瓷材料在原子尺度上形成层，很像堆叠在一起的纸片，这使得层在局部扭曲，而不是在载荷下破裂。这种扭结行为最近才被发现，但如果被理解，就有可能为我们国家老化的能源、通信和交通系统提供更坚韧、更轻、更耐损坏的材料。因此，MAX相将在各种真实加载条件下以不同的堆叠顺序和层方向进行研究，包括冲击、动态疲劳和断裂。此外，还将执行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，能够提取比经典技术更多的材料行为信息。这些发现将为结构设计中利用MAX阶段的预测计算模型以及其他类似的先进材料提供有意义的输入。这项工作汇集了材料科学、应用力学和理论力学的多学科努力。通过舞蹈机械教育和推广计划，将能够以新的方式接触到所有年龄段的未开发的当地社区。研究和推广部分突出了两者所涉及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。这项研究的重点是一类新兴的材料，MAX相，一族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新分类的缺陷变形机制，称为涟漪，这是一种纳米尺度的屈曲现象，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，并在载荷下导致非线性类带(NKB)的形成。虽然材料科学界有相当一部分人在研究这些3D层状固体，但在介观到连续介质水平上研究它们的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。首先描述了变形行为随应变速率和应力状态的变化以及层位和堆积顺序的变化，利用非线性屈曲理论确定了NKB地层的驱动参数。第二项研究利用实验-数值混合方案对动态断裂中的裂尖能量进行了量化，并探索了冲击疲劳，扩展了经典的巴黎定律的时间效应。第三种是研究损伤行为，利用网格法和虚拟场法这一新兴的逆技术进行惯性碰撞实验。对MAX相的广泛研究将揭示在长度和时间尺度上相互竞争的延性、伪延性和脆性变形机制，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，并为特定纹理(缺陷工程)、功能分级和/或分层材料设计铺平道路。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.