Collaborative Research: Design of Negative Stiffness Metamaterials

工程师经常面临在结构刚度高的材料和阻尼性能优异的材料之间进行选择的关键决策。现有材料不能同时提供这两种能力。该奖项支持通过设计负刚度（NS）超材料来打破这种权衡的基础研究。这些材料的特性来自于它们的内部结构，其中包括微尺度结构，这种结构可以前后弹跳以吸收能量，这种现象被称为负刚度。在这个项目中开发的新颖的自上而下的设计策略将使工程师能够快速确定尽可能接近性能目标的材料设计。负刚度超材料将有利于社会的各种应用，如刚性，低振动的风力涡轮机叶片和转子以及潜艇的声纳支架。这项研究涉及研究生和本科生，教育推广活动，以及一个少数民族服务机构，这将有助于扩大代表性不足群体的参与，并对工程教育产生积极影响。研究团队将采用一种新颖的、自上而下的设计探索策略来设计这些材料，以便快速有效地将特定应用的系统级性能要求反向传播到微观尺度材料结构的特征中。这种自上而下的策略与试错、自下而上的策略形成鲜明对比，后者在多种材料结构中循环，以寻找令人满意的系统级性能。自顶向下的设计探索策略利用贝叶斯网络分类器在多层次设计问题的每个层次上映射结构-属性关系，这样映射可以跨层次相交，以识别良好的多层次设计，并有效地指导寻找更好的设计。设计探索策略与三个级别的材料模型相结合，从(a)微观层面，必须设计卡通内含物的几何形状和制造路线，以提供负刚度行为；(b)中观层面，必须设计延性基体中内含物的分布，以提供目标有效材料性能；(c)部件的宏观层面。它必须与超材料一起设计，以提供目标的结构刚度和阻尼。材料设计和建模工作将通过使用微立体光刻技术增材制造微尺度夹杂物，将其嵌入基体材料中，并测试所得复合材料以确定整体动态结构刚度和损耗特性来验证。与工业伙伴的合作将为NS超材料在具有挑战性的军事和商业应用中的应用铺平道路。

Engineers frequently face a critical selection decision between materials with high structural stiffness and materials with superior damping capabilities. Existing materials cannot provide both capabilities simultaneously. This award supports fundamental research to break this tradeoff by designing negative stiffness (NS) metamaterials. These materials gain their properties from their internal structure, which includes micro-scale structures that snap back and forth to absorb energy - a phenomenon called negative stiffness. Novel top-down design strategies developed in this project will allow engineers to quickly identify the material designs that meet performance goals as closely as possible. Negative stiffness metamaterials will benefit a variety of applications of great interest to society, such as stiff, low-vibration wind turbine blades and rotors and sonar mounts for submarines. The research involves graduate and undergraduate students, educational outreach activities, and a minority-serving institution, which will help broaden the participation of underrepresented groups and positively impact engineering education. The research team will design these materials with a novel, top-down design exploration strategy for quickly and efficiently back-propagating application-specific, system-level performance requirements to the characteristics of the micro-scale material structure. This top-down strategy contrasts with trial-and-error, bottom-up strategies that cycle through multiple material structures in search of satisfactory system-level performance. The top-down design exploration strategy utilizes Bayesian network classifiers for mapping structure-property relationships at each level of the multi-level design problem in such a way that the maps can be intersected across levels to identify good multi-level designs and also efficiently guide the search for better designs. The design exploration strategy is coupled with three levels of material models, ranging from (a) the micro-scale level on which the geometry and fabrication route for the snap-through inclusions must be designed to provide negative stiffness behavior to (b) the meso-scale level on which the distribution of inclusions in a ductile matrix must be designed to provide targeted effective material properties to (c) the macro-scale level of a component, which must be designed along with the metamaterial to provide targeted structural stiffness and damping. Materials design and modeling efforts will be validated by additively manufacturing micro-scale inclusions using microstereolithography, embedding them in a matrix material, and testing the resulting composite to determine the overall dynamic structural stiffness and loss characteristics. A collaboration with an industrial partner will pave the way for applications of the NS metamaterials in challenging military and commercial applications.