兰州大学机构库 >土木工程与力学学院
静态颗粒物质中的力传递机制及其力学响应特征的调控研究
Alternative TitleA study on force propagation and tuning mechanical response in static granular materials
杜微
Thesis Advisor王等明
2017-05-05
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Keyword颗粒物质 离散单元法 力学响应 复合模式 刚度比 均布压力 硬颗粒通道 调控机制
Abstract

由于离散性及粒子间相互作用的非线性耗散特性,使得颗粒物质很多宏观力学行为很难用传统的连续介质理论来描述。在这其中,系统对外界载荷的响应特征分析是颗粒物质力学研究中最为基础也是最为核心的问题之一。本学位论文系统研究了颗粒物质在外部集中载荷作用下的力学响应特征,详细讨论了各种材料参数和加载状态对系统内应力传递过程的影响规律,并将其与系统的宏观响应进行了有效关联,在此基础上尝试通过对不同材料粒子的空间构型变化来主动调控系统的宏观力学响应特征。主要工作如下:首先,建立了两种不同材料组分构成的层状复合颗粒模型,研究了系统在局部荷载作用下的宏观力学响应特征,给出了考虑不同刚度比、外载荷大小和摩擦系数下系统响应在单-双峰之间演变的相图。结果显示刚度比的减小会增加系统力学响应的线性范围和弹性,同时会导致系统的宏观力学响应从双峰向单峰演变。最后,基于系统内接触网络和接触力网络的变化,从机理上揭示了这种响应特征的变化对系统内接触力传递过程的依赖关系。其次,分析了复合模式和加载状态对系统宏观力学响应特征的影响。通过不同模式的复合颗粒模型在外加荷载作用下的主应力分布和底部响应特征,提出了刚度比的大小是影响复合颗粒系统力学响应特征的主要因素。通过刚度梯度递减模型给出了系统响应发生单-双峰转变时的临界刚度比。最后,分析了加载状态和系统无序度的变化对系统内力传递特征和宏观力学响应的影响规律。最后,基于接触力在不同属性颗粒材料交界面上传递特征的变化特征,对硬颗粒通道的模式和位置对系统宏观力学响应特征的调控机制进行了研究。通过在系统内不同位置处加入具有不同空间构型的硬颗粒通道,主动调控系统的弹性及其宏观力学响应特征。确定了颗粒通道的最优模型,在此基础上基于系统响应特性变化的相图,进一步讨论了颗粒通道的最优位置和可调控区域,给出了一种估算不同系统尺寸下颗粒通道最佳位置的方法。

本学位论文所开展的上述关于颗粒物质力学响应及调控方面的基础性研究工作,不仅系统揭示了复合颗粒物质在准静态加载下的力学行为特征,同时也可以为颗粒物质堆积和颗粒功能材料设计等相关基础性问题提供重要的理论依据和定量分析方法。

Other Abstract

Granular material usually exhibits some essential features, which present fundamental difficulties and great challenges in quantitatively modeling and simulating their macroscopic behaviors. Among these problems, the stress propagation in granular material under an external localized load has attracted much attention in recent years. In a granular material, the forces between internal particles, transmitted from one particle to the next via their contacts, may commonly form an inhomogeneous contact network at a meso-scopic scale, which carries most of external loads by way of force chains, while whole system may exhibit some localized deformation features at a macroscopic scale. This discrete nature commonly induces the occurrence of anisotropic force chains and spatially inhomogeneous stress distribution, which may lead to a difficult to describe mechanical properties of granular material using conventional continuum theories. The mechanical response of granular system under local external loading is a fundamental problem in researching field of granular materials. The macroscopic mechanical response of the particulate matter is mainly determined by contact force and contact network on the microscopic scale. Therefore, in order to understand the macroscopic mechanical response of granular material, it is a very important and effective approach to study and analyze the contact force propagation. In this paper, the discrete element method is used to study the stress transmission and mechanical response characteristics of granular material under the localized concentrated force.

   At first, a 2D composite granular layers composed by particles with variable stiffness is proposed, and the effect of stiffness ratio between component particles on mechanical response is mainly considered. The results show that the decrease of stiffness ratio broadens the linear range of mechanical response and enhances the elasticity of the response in a composite granular system, showing a role similar with the friction in a monodisperse granular packings. Furthermore, a phase diagram for the crossover between a single-peaked and a double-peaked response is proposed, in which the critical stiffness ratio corresponding to the occurrence of the crossover decreases with the magnitude of external loading and increases with the friction. Finally, the microscopic mechanism of the crossover of the response is further discussed based on changes in contact network and force network.Secondly, a variety of particle composite models were established on the basis of the two composite models. The main factors influencing the mechanical response in the composite model were the difference in the stiffness between the two kinds of particles. It meant the greater the difference in stiffness, the greater the impact of chain transfer. The influence of the disorder degree of the particles was also studied, and the disorder degree would be affected by the linear range and the critical load of the system. They were all decreased with the increasing of the degree of disorder.Finally, an new approach by adding hard particle channel to tune the mechanical response of granular slab applied by an external loading is put forward, and the dependence of tunable range for the external loading and effective region placing the channel on the channel mode, position and its comprising granular layers is mainly considered. From sets of numerical results, we find that the existence of hard particle channel can lead to a transition of the response into a single-peaked feature when the response of corresponding monodisperes system is double-peaked, but it works just when the position of this channel locates within a central small range of total layer depth. Outside this range, the variation of the response induced by the existence of the hard particle channel is not qualitative but just quantitative.

URL查看原文
Language中文
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/226203
Collection土木工程与力学学院
Recommended Citation
GB/T 7714
杜微. 静态颗粒物质中的力传递机制及其力学响应特征的调控研究[D]. 兰州. 兰州大学,2017.
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