斜冲颗粒介质的离散单元模型及其多尺度动力特性的基础研究

As a fundamental issue in granular material dynamics, the process of granular media under impact has aroused attention for nearly a decade in crater scaling laws and inversion problem of the dynamics process for planets bombarded by celestial bodies, which have practical application prospects in both natural environment and national defense. Under the effect of impact, yield will occur in granular materials, and solid phase will be transformed into liquid-gaseous phase due to localized strain field. Thus this dissipative system exhibits multi-scale features for the coexistence of grain scale, meso-scale and macro-scale. As the most common impact process, it is very valuable for oblique impact to be examined thoroughly. However, the complexity of the process has seriously constrained the development on this question. Considering these mechanisms, the multi-scale dynamic characteristics of granular media under oblique impact will be obtained by developing a three-dimensional elastic-plastic discrete element model based on the theoretical model of collision between soft-spheres. The research is to reveal the microscopic movement of the particle, the evolution of the mesoscopic contact force chains, and the macroscopic dynamic properties of particle swarms; investigate the dependence post-impact motions of projectile and crater scaling on initial conditions and system variables; develop a statistical method and a theoretical model to describe the dynamic process of granular media under impact, which will be validated and improved through experimental study.

作为颗粒动力学研究中的基础性课题，颗粒介质在冲击作用下的动力过程于近十年来在冲击坑尺度关系及星球冲击动力过程反演中受到高度重视，在自然环境和国防上均有重要的应用前景。颗粒介质受冲击作用时，局部化的应变场使其由固态向液态和气态演化，且该耗散系统呈现颗粒尺度、细观尺度和宏观尺度共存的现象。复杂的相变过程和多尺度特征使得该系统的动力学特性的研究极为困难。斜冲击过程与垂直冲击过程相比更为复杂，目前该领域的研究尚无重大进展。本项目拟针对颗粒介质受斜冲击作用下的多尺度动力特性进行研究。基于软球正碰模型，建立冲击颗粒介质的三维弹塑性离散单元模型；揭示斜冲颗粒系统中颗粒的运动规律，细观接触力链演化特征以及群体颗粒宏观动力特性；探讨初始条件和物理变量对冲击颗粒的运动形式及冲击坑尺度关系的影响；发展一套能够描述冲击颗粒介质动力学过程的理论模型和统计方法，并通过实验研究对宏观运动特性和理论模型进行验证和完善。

物体冲击颗粒介质这一动力过程在探月车的着陆、冲击坑的形成、土木工程中混凝土的桩基检测以及地质工程中岩土的强度测试中广泛存在。目前已有研究主要针对物体垂直冲击颗粒的受力特征及动力特征进行研究，然而冲击角度的变化对物体的运动形式、受力特征以及颗粒介质的溅射特征有极大的影响。本项目综合考虑冲击角度和体积分数对物体冲击颗粒介质的动力学过程的影响，并取得了如下重要进展：（1）建立了斜冲击颗粒介质的三维弹塑性离散单元模型，该理想弹塑性模型首先应用超导股线在循环加载情形下的受力分析。（2）建立了颗粒介质受冲击情形下，力链的演化、体积分数的变化以及能量耗散的统计方法。（3）基于搭建的颗粒介质受冲击的实验平台，设计制造了一种既能够控制速度和角度，可变冲击粒径且能有效消除颗粒旋转的冲击装置。（4）首次对物体斜冲击颗粒介质时的运动轨迹进行实验测试，并跟踪了颗粒介质受斜冲后的溅射特征。 本项目开展过程中，研究团队已发表SCI论文4篇，EI论文1篇，实用新型专利1个，目前3篇论文在整理过程中，发明专利授权中。