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

这个早期概念探索性研究资助（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、应变局部化和失效载荷路径等特性。结构晶格为机械超材料的设计提供了框架，具有引导、操纵和衰减机械波的能力，这与振动隔离、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、天然或生物灵感建筑材料的表征提供多种可能性。该项目的研究结果将影响防弹衣设计、车辆保护和运输、体育和军事用途头盔保护层的能量吸收结构的设计方法。因此，该项目支持基础研究，这将有利于致力于减轻头部受伤和脑震荡或爆炸影响的研究。此外，部分研究成果将直接转化为本科生实验课程的教学模块，让学生了解最先进的力学表征方法。通过基于数字图像相关的新型全场测量技术，沿着波浪特性的数值分析，动态不稳定性和崩溃机制。目前可用的数字图像相关技术不适合于高度多孔结构中的位移和应变的估计，即空隙的体积显著超过材料所占据的体积。此外，这些技术在动态事件期间跟踪大运动的能力方面受到限制。该项目将通过制定图像跟踪程序来应对这些挑战，该程序利用了晶格的连通性，并采用拉格朗日运动跟踪框架，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法。实验技术的制定和实施将使波动的研究，最值得注意的是，不稳定性，不均匀变形和潜在的崩溃的发病。实验测量将为数值模型提供信息和验证，然后将其用于估计波动方向、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.