Active Dynamic Granular Metamaterial through Controlled Jamming-Unjammming Transitions

University Of Illinois At Urbana-Champaign, Urbana IL

Investigators

Abstract

Granular media have a unique ability to transition from a free-flowing fluid-like response in the so-called unjammed state to a rigid solid-like response in the jammed state. Because of the importance of granular media in a variety of natural phenomena and industrial processes, the quasi-static (slow rate of deformation) response of granular media has been the focus of numerous studies, with emphasis on characterizing the transition between unjammed and jammed states. In this project, an integrated experimental and computational approach will be used to conduct research on a novel dynamic granular metamaterial (engineered materials system with hierarchy of structures) consisting of metallic spherical grains encapsulated in a flexible membrane. Jammed-unjammed switching in material response will be achieved with the help of a confining external pressure, to create an active metamaterial for impact protection applications that will combine the shape adaptivity of unjammed granular media with the rigid-like response of the jammed metallic grains. The successful development of the active dynamic metamaterial will lead to a range of applications, especially in the field of transportation, robotics, and manufacturing, that require both stiff and compliant behaviors, or shape adaptivity and morphing. Thus, the project will promote the progress of science related to granular mechanics and advance the national health, prosperity, and welfare through potential applications. Additionally, undergraduate researchers will be recruited and outreach to K-12 students will be performed to achieve broader impact. Underrepresented groups will be specifically targeted in these activities. This collaborative experimental and computational project will shed light on the fundamental understanding of the unjammed-to-jammed transition of granular media under dynamic loading conditions. In particular, it will focus on the two key energy dissipation mechanisms involved: friction and plasticity. In the first phase of the project, the effects of parameters such as packing fraction, particle constitutive response, and particle size distribution on the dynamic transition between unjammed and jammed states will be investigated. The second part of the project will focus on the ?passive? tailoring of this transition through pre-conditioning (i.e., pre-yielding) of the spheres or through the combination of stiff (elastic) and compliant (elasto-plastic) particles encapsulated in the deformable membrane, and on the ?active control? of the transition through the confining pressure applied on the encapsulated granular medium. The project will involve a combination of computational analysis based on a discrete element modeling of the impact response of the granular medium, and experiments involving a variety of 2D and 3D configurations of the confined and unconfined granular medium subjected to dynamic loading created with a Split Hopkinson pressure bar system. 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.