基于界面连续逾渗模型的复杂颗粒材料弹性性能研究

Granular materials have been broadly applied in a variety of national economic systems. Elastic properties of granular materials can significantly affect their bearing capacities and service life in practical engineering applications. Meanwhile, percolation of interfaces interacted by particles plays an important role in the prediction of elastic properties of granular materials. However, it is a huge challenge to characterize quantitatively percolation of interfaces around complex convex particles through the existing experimental technologies and analytical methods. Also, there is no a multi-scale correlative scheme explicitly incorporating interfacial percolation characteristics and components into the prediction of elastic properties of granular materials with complex convex reinforced particles. The ambition of this proposal is to firstly develop a three-phase composite structure of granular materials that is composed of complex convex particles of a high packing density, interfaces with a constant dimension surrounding particles and homogeneous matrix, on the basis of an optimized discrete element method and a relaxation iteration scheme. By virtue of some relevant theories like statistical mechanics and numerical simulations, the interfacial excluded volume and the interfacial percolation characteristics such as the percolation threshold, percolation transition width and correlation-length critical exponent are quantitatively characterized, respectively. Then, a multi-scale correlative framework that incorporates the derived interfacial percolation characteristics and components to accurately predict the elastic moduli of granular materials is proposed by using some technological means like mesomechanics of composites, the coupling model of the discrete element method and the finite element model, and the random walk scheme. Moreover, in order to test the reliability of the proposed multi-scale framework, normal concrete compression experiments and its microstructure measurement are further investigated. It is expected that this project will provide an efficient analytical model and method for custom designing granular materials and evaluating their service life by optimizing components of materials to regulate interfacial microstructures so that to enhancing the elastic properties of granular materials.

颗粒材料弹性性能关系到其在工程应用中的承载能力和服役寿命，颗粒间相互作用引起的界面逾渗对颗粒材料弹性性能具有重要影响。然而现有的试验手段和分析方法难以定量表征复杂凸形颗粒周围界面逾渗，且尚未阐明界面逾渗特征与颗粒材料弹性性能之间的定量关联机制。本项目拟通过离散元和松弛迭代方法发展高密度复杂凸形颗粒及其周围界面组成的颗粒材料三相复合结构模型；借助统计力学等相关理论和数值模拟手段定量表征复杂凸形颗粒周围界面排斥体积、界面逾渗阈值、逾渗相变宽度和逾渗相关长度指数；采用复合材料细观力学、离散元与有限元耦合、以及随机游走机制等方法构建颗粒材料弹性模量与界面逾渗特征及其组成关联的多尺度模型；并开展混凝土受压试验与微观测试，分析关联模型的有效性。研究目标是通过优化材料组成来调控界面微结构，达到改善颗粒材料弹性性能的目的，为颗粒材料的“定制设计”及其在工程应用中服役寿命的预测提供有效的分析模型和方法。

随着一带一路、海洋强国等国家重大战略的实施，颗粒材料空前规模地应用于各种环境条件下的结构工程中，颗粒材料的宏观弹性性能决定了工程的服役寿命。在微观尺度上，颗粒材料是由复杂形状的多分散颗粒随机堆积组成。但由于实验测量和球形颗粒堆积结构的局限性，无法定量表征具有复杂颗粒形状的微观结构与弹性性能之间的关联机制。本项目通过数值模拟、理论分析和试验研究相结合的技术方案，自主开发了单粒径和多粒径的两相和三相椭球、复杂凸多面体颗粒随机有序堆积模型、离散元模型、松弛迭代紧密堆积模型，提出了复杂形状颗粒周围界面的数值方法和理论模型，明确了颗粒组成与界面体积分数之间的关联机制；建立了圆柱形硬核-软壳三相结构的排斥体积模型，准确的预测了多面体和椭球形软化颗粒逾渗阈值、逾渗相变宽度和逾渗相关长度指数，揭示了颗粒材料有效弹性性能与微结构的定量关联机制。项目负责人在四年的执行周期内以第一作者(含通讯作者)共计发表25 篇学术论文、其中被SCI 检索25 篇(JCR 一区22 篇)，包括业内国际权威期刊：Carbon、Composites Part B: Engineering、 International Journal of Engineering Science、Composites Science and Technology、Materials & Design、Cement and Concrete Composites、Computer Methods in Applied Mechanics and Engineering、Soft Matter、Physical Review E、Computers and Structures 等，一篇论文被编辑入选为Soft Matter主封面文章。参加国内外学术会议11 次、其中邀请报告4 次；申请发明专利10项、授权6 项。获中国建筑材料联合会•中国硅酸盐学会建筑材料科学技术奖一等奖(2020年)、二等奖(2019年)各一项、获中国水利水电科学研究院科学技术奖二等奖(2021年)、获中国公路学会科学技术奖一等奖(2021年)、获江苏省研究生教育改革成果奖、河海大学教学成果奖、大禹水利科学奖各一项。