EAGER: Optical Measurement and Analysis of Dynamic Large Deformations of Mechanical Metamaterials

这个早期概念探索性研究（EAGER）项目将进行基础实验和数值研究，以阐明超材料中的波方向性、应变局部化和破坏载荷路径等特性。结构晶格为具有引导、转向和衰减机械波能力的机械超材料的设计提供了框架，这与隔振、噪声吸收和应力波缓解等应用相关。这些特性是设计用于波浪管理和冲击保护的新型机械超材料的关键。项目目标的成功实现将为广泛的工程材料以及多孔的、自然发生的或生物启发的建筑材料的表征提供许多可能性。该项目的研究结果将影响防弹衣设计的能量吸收结构的设计方法，车辆保护，以及用于运输，体育和军事用途的头盔保护层。因此，该项目支持基础调查，这些调查将有利于致力于减轻头部受伤和脑震荡影响或爆炸影响的研究。此外，部分项目发现将直接转移到本科实验课程的教育模块中，这将使学生接触到最先进的机械表征方法。通过基于数字图像相关的新型全场测量技术，以及波浪特性、动力不稳定性和坍塌机制的数值分析，研究结构晶格在大变形时的动力行为。目前可用的数字图像相关技术不适合估计高度多孔结构中的位移和应变，即孔隙体积大大超过材料占用的体积。此外，这些技术在动态事件中跟踪大运动的能力方面受到限制。该项目将通过制定利用网格连通性的图像跟踪程序和拉格朗日运动跟踪框架来解决这些挑战，该框架的灵感来自实验流体动力学中使用的粒子图像测速。实验技术的制定和实施将使波浪运动的研究成为可能，最值得注意的是，不稳定，非均匀变形和潜在崩溃的开始。实验测量将告知和验证数值模型，然后将用于估计波浪运动方向，应变局部化和不稳定性。

This EArly-concept Grant for Exploratory Research (EAGER) project will perform a fundamental experimental and numerical study to elucidate properties such as wave directionality, strain localization and failure load paths in metamaterials. Structural lattices provide the framework for the design of mechanical metamaterials with the ability to guide, steer and attenuate mechanical waves, which is relevant to applications such as vibration isolation, noise absorption, and stress wave mitigation. These properties are key to the design of novel mechanical metamaterials for wave management and impact protection. Successful achievement of the project objectives will open numerous possibilities for the characterization of a broad class of engineered materials as well as of porous, naturally occurring, or bio-inspired architected materials. The findings of the project will impact design methodologies for energy absorbing structures for body armor design, vehicle protection, and protective layers for helmets for transportation, sport and military use. Thus, the project supports fundamental investigations that will benefit research devoted to the mitigation of the effect of head injuries and concussions, or the effect of blasts. In addition, part of the project findings will be directly transferred to an educational module for an undergraduate laboratory course that will expose students to state-of-the-art mechanical characterization methodologies.The dynamic behavior of structural lattices undergoing large deformations will be investigated through novel full-field measurement techniques based on digital image correlation, along with the numerical analysis of wave properties, dynamic instabilities and collapse mechanisms. Currently available digital image correlation techniques are not suitable for the estimation of displacements and strains in structures that are highly porous, i.e. with volume of voids significantly exceeding the volume occupied by material. Furthermore, these techniques are limited in their ability to track large motion during dynamic events. The project will address these challenges through the formulation of image tracking procedures that exploit the connectivity of lattices, and of a Lagrangian framework for motion tracking that takes inspiration from particle image velocimetry used in experimental fluid dynamics. The formulation and implementation of the experimental technique will enable the study of wave motion and, most notably, of the onset of instabilities, non-uniform deformations and potentially collapse. Experimental measurements will inform and validate numerical models that will then be used to estimate directions of wave motion, strain localizations and instabilities.