Collaborative Research: Investigations of Density-graded Auxetic Foams at Multiple Scales

聚合物泡沫已用于许多减轻冲击的应用，影响我们日常活动的各个方面，从步行和跑步到动作运动中的保护装备。然而，尽管试图通过分层或加固来提高功效，但它们在性能上的缺陷导致了严重的健康危害，例如足球中的脑震荡。该奖项旨在开发一种新型的泡沫衍生物，即所谓的消长泡沫，通过利用新的变形和能量耗散机制，有效减轻对人类的影响带来的危险。为了达到这一目标，该奖项努力揭示材料和几何形状的不同方面如何有助于消声填充物在能量消耗方面的效率。该方法结合了计算和实验方法来阐明跨越多个长度和时间尺度的结构-性能-性能关系。拟议的合作活动的成功实施将导致新的耐冲击材料。这项研究的跨学科性质将促进下一代科学家和工程师的参与和培训，重点是来自代表性不足和服务不足的少数民族的学生。来自不同学术水平的学生将被招募并参与研究的不同方面。生长型泡沫及其密度梯度衍生物，如生长型聚脲泡沫，可以同时激活几种能量耗散机制，使其成为理想的减震材料。该奖项旨在开发一个全面的实验计算框架，以阐明这些材料在多个尺度上的内在能量耗散机制。集成框架的开发包括在广泛的长度（分子到μm到mm）和时间（μs到ms）光谱范围内探测和建模材料。例如，机械加载过程中分子间振动模式变化的原位太赫兹时域光谱，多尺度动态变形模式的高速数字图像相关，微尺度表征的扫描电子显微镜，以及使用有限元方法的直接数值模拟。这一广阔的范围有望揭示被包裹在细胞微观结构中的材料与其分子排列变化之间的复杂相互作用，材料非线性，细胞的几何属性和不连续，弹性不稳定性，以及它们在密度梯度增减材料的整体力学响应中的基本作用。该项目由材料和结构力学（mom）以及民用、机械和制造创新部门的动力学、控制和系统诊断（DCSD）项目共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Polymeric foams have been used in many impact mitigation applications, affecting various aspects of our daily activities ranging from walking and running to protection gears in action sports. Nonetheless, shortcomings in their performance results in serious health hazards, e.g., concussions in football, despite attempts to increase efficacy through layers or reinforcement. This award seeks to exploit a novel derivative of foams, known as auxetic foams, to effectively mitigate the danger from impacts to humans by leveraging new deformation and energy dissipation mechanisms. To reach this goal, this award strives to uncover how different aspects of the material and geometry contribute to the efficiency of the auxetic padding in energy dissipation. The approach integrates computational and experimental methods to elucidate the structure-property-performance relations spanning multiple lengths and time scales. The successful implementation of the proposed collaborative activities will lead to novel impact-tolerant materials. The interdisciplinary nature of this research will facilitate the engagement and training of the next generation of scientists and engineers, with emphasis on students from underrepresented and underserved minorities. Students from different academic levels will be recruited and involved in different aspects of the research.Auxetic foams and their density-graded derivatives, e.g., auxetic polyurea foams, can simultaneously activate several energy dissipation mechanisms, making them ideal impact mitigating materials. The award aims to develop a comprehensive experimental-computational framework to elucidate the intrinsic energy dissipation mechanisms operative in these materials at multiple scales. The development of the integrated framework includes probing and modeling the material over a broad range of length (molecular to μm to mm) and time (μs to ms) spectra. For example, in-situ terahertz time-domain spectroscopy for changes in the intermolecular vibrational modes during mechanical loading, high-speed digital image correlation for dynamic deformation modes at multiple scales, scanning electron microscopy for characterization at the microscale, and direct numerical simulations using the finite element method. This expansive scope is expected to reveal the complex interplay between the material entrapped in the cellular microstructure and the change in their molecular arrangement, material nonlinearities, the geometrical attributes and discontinuities of the cells, elastic instabilities, and their fundamental role in the overall mechanical response of density-graded auxetic materials.This project is co-funded by the Mechanics of Materials and Structures (MOMS) and the Dynamics, Control, and Systems Diagnostics (DCSD) programs in the Civil, Mechanical and Manufacturing Innovation Division.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.