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

聚合物泡沫已被用于许多减轻影响的应用中，影响我们日常活动的各个方面，从步行和跑步到运动中的保护装备。尽管如此，其性能的缺陷导致严重的健康危害，例如，足球中的脑震荡，尽管试图通过层或强化来提高疗效。该奖项旨在利用一种新型的泡沫衍生物，称为拉胀泡沫，通过利用新的变形和能量耗散机制，有效地减轻对人类的影响危险。为了实现这一目标，该奖项致力于揭示材料和几何形状的不同方面如何有助于拉胀衬垫在能量耗散中的效率。该方法集成了计算和实验方法，以阐明跨越多个长度和时间尺度的结构-性质-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群体的学生。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。发泡泡沫及其密度分级衍生物，例如，拉胀聚脲泡沫可以同时激活几种能量耗散机制，使其成为理想的冲击缓解材料。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尺度下的内在能量耗散机制。集成框架的开发包括在宽范围的长度（分子到μm到mm）和时间（μs到ms）光谱上探测和建模材料。例如，在现场太赫兹时域光谱的变化，在分子间的振动模式在机械加载，高速数字图像相关的动态变形模式在多个尺度，扫描电子显微镜表征在微观尺度，和直接数值模拟使用有限元法。这一广阔的范围有望揭示细胞微观结构中捕获的材料与其分子排列变化、材料非线性、细胞的几何属性和不连续性、弹性不稳定性之间的复杂相互作用，以及它们在密度梯度拉胀材料的整体力学响应中的基本作用。该项目由材料与结构力学（MOMS）共同资助。该奖项反映了NSF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.