Active Dynamic Granular Metamaterial through Controlled Jamming-Unjammming Transitions

颗粒介质具有从所谓的未堵塞状态下的自由流动的流体状响应转变为堵塞状态下的刚性固体状响应的独特能力。由于颗粒介质在各种自然现象和工业过程中的重要性，颗粒介质的准静态（缓慢的变形速率）响应一直是众多研究的焦点，重点是表征未堵塞和堵塞状态之间的过渡。在这个项目中，一个综合的实验和计算的方法将被用来进行研究的一种新型的动态颗粒超材料（工程材料系统与层次结构）的金属球形颗粒封装在一个灵活的膜。材料响应中的堵塞-未堵塞切换将借助于限制外部压力来实现，以产生用于冲击保护应用的有源超材料，其将联合收割机结合未堵塞的颗粒介质的形状适应性与堵塞的金属颗粒的刚性样响应。主动动态超材料的成功开发将导致一系列应用，特别是在运输，机器人和制造领域，这些应用需要刚性和柔性行为，或形状自适应和变形。因此，该项目将促进与颗粒力学相关的科学进步，并通过潜在的应用促进国民健康，繁荣和福利。此外，将招募本科研究人员，并与K-12学生进行外联，以实现更广泛的影响。这些活动将特别针对任职人数不足的群体。这个合作的实验和计算项目将阐明动态加载条件下颗粒介质的未堵塞到堵塞过渡的基本理解。特别是，它将集中在两个关键的能量耗散机制：摩擦和塑性。在该项目的第一阶段，将研究参数的影响，如包装分数，颗粒本构响应，和颗粒尺寸分布之间的动态过渡未堵塞和堵塞状态。该项目的第二部分将集中在？被动？通过预调节来调整这种转变（即，预屈服）的球体或通过组合的刚性（弹性）和顺应性（弹塑性）颗粒封装在可变形膜，并在？主动控制？的过渡通过围压施加在封装的粒状介质。该项目将涉及基于颗粒介质冲击响应的离散元建模的计算分析，和实验，涉及各种二维和三维配置的受限和非受限颗粒介质受到动态载荷与分离霍普金森压杆系统创建。该奖项反映了NSF的法定使命，并已被认为是值得支持，通过评估使用基金会的学术价值和更广泛的影响审查标准。

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.