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

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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.