Mechanics of Crystallization, Deformation and Phase Transformation in Granular Materials with Engineered Grain Geometries

这项拨款将集中于新型固体颗粒材料的工程、建模、制造和测试。像沙子这样的颗粒状材料看似简单，但它们的机制却非常丰富和复杂。在这个项目中，单个颗粒的几何形状将被操纵，以产生传统颗粒材料中看不到的结晶和变形机制，创造“设计的颗粒材料”。该项目将建立基于力学的颗粒材料结晶的基本理解，使大规模的操作和组装成为可能。该项目还将生成基于接触力学和几何硬化的颗粒晶体非弹性变形的力学模型。从这项工作中产生的新型颗粒材料将具有高强度，独特的组装/拆卸组合，强度和自我修复能力，使其成为具有吸引力的轻质材料和聚集体建筑。这些颗粒材料的可逆性质和大变形能力也将使它们作为形状变形材料、可编程“智能”材料、机器人和生物医学材料具有吸引力。该项目将开展积极的外展活动，包括科罗拉多大学的课程开发，本科生的研究项目，高中生的主动学习模块，以及促进和改善STEM的多样性。该项目的一个主要科学目标是创建一个统一的、基于力学的框架，以捕获工程颗粒材料的组装、相变、变形和失效。具有特殊意义和关键科学问题的颗粒系统包括：(1)“颗粒晶体”的高度堆积和空间填充，其刚度和强度比传统颗粒材料高几个数量级；（ii）利用机械刺激引导晶粒通过非晶转变；（iii）限制和无限制变形的效果，以创造和控制有吸引力的功能，如形状变形、愈合、刚度和强度调整；（iv）分支颗粒的联锁机制，在拉伸中产生高强度和韧性。方法包括使用几何敏感接触算法的离散元建模，颗粒的3D打印以及原位3D成像（折射率匹配扫描）的力学实验。对这些新的“工程”颗粒材料的基本理解将导致颗粒材料和结构的制造和力学的新范式，并产生先进的功能，如适应性，形状变形或自我修复。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。

This grant will focus on the engineering, modeling, fabrication and testing of new types of solid granular materials. Granular materials like sand are seemingly simple, but their mechanics is remarkably rich and complex. In this project, the geometry of individual grains will be manipulated to generate crystallization and deformation mechanisms not seen in traditional granular materials, creating “granular materials by design”. This project will establish a mechanics-based fundamental understanding of crystallization in granular materials, enabling manipulation and assembly at large scales. This project will also generate mechanics-based models for the inelastic deformation of granular crystals based on contact mechanics and geometrical hardening. The new granular materials that will emerge from this work will have high strength, unique combinations of assembly / disassembly, strength and self-healing, making them attractive as lightweight materials and aggregate architectures. The reversible nature and the large deformation capabilities of these granular materials will also make them attractive as shape morphing materials, programmable “smart” matter, robotics and biomedical materials. Vigorous outreach activities will be developed in this project including curriculum development at the University of Colorado, research projects for undergraduate students, active learning module for high school students, as well as promotion and improvement of diversity in STEM. A major scientific objective for this project is to create a unified and mechanics-based framework that captures the assembly, phase transformations, deformation and failure of engineered granular materials. Granular systems of specific interest and critical scientific questions include: (i) high packing and space filling in “granular crystals” with stiffness and strength orders of magnitude higher than traditional granular materials; (ii) steering of grains through amorphous-crystalline transitions using mechanical stimuli; (iii) effects of confinement and unlimited deformations to create and control attractive functionalities such as shape morphing, healing, tuning of stiffness and strength; (iv) mechanics of interlocking in branched particles to generate high strength and toughness in tension. Methods include discrete element modeling using geometry-sensitive contact algorithms, 3D printing of grains, and mechanical experiments with in-situ 3D imaging (refractive index matching scanning). A fundamental understanding of these new “engineered” granular materials will lead to new paradigms for the manufacturing and mechanics of granular materials and structures, and for the generation of advanced functionalities such as adaptability, shape morphing or self-healing.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.