東華大學圖書館 |

Characterization and Mechanism of Rigidity in Columns of Star-Shaped Granular Particles = = 对星状颗粒材料堆积体互锁结构稳定性机制的研究.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Characterization and Mechanism of Rigidity in Columns of Star-Shaped Granular Particles =/
Reminder of title:	对星状颗粒材料堆积体互锁结构稳定性机制的研究.
Author:	Zhao, Yuchen.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
Description:	104 p.
Notes:	Source: Dissertations Abstracts International, Volume: 82-03, Section: B.
Contained By:	Dissertations Abstracts International82-03B.
Subject:	Physics. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28001831
ISBN:	9798672148182

Characterization and Mechanism of Rigidity in Columns of Star-Shaped Granular Particles = = 对星状颗粒材料堆积体互锁结构稳定性机制的研究.
Zhao, Yuchen.

Characterization and Mechanism of Rigidity in Columns of Star-Shaped Granular Particles =对星状颗粒材料堆积体互锁结构稳定性机制的研究. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 104 p.

Source: Dissertations Abstracts International, Volume: 82-03, Section: B.

Thesis (Ph.D.)--Duke University, 2020.

This item must not be sold to any third party vendors.

An important challenge in the science of granular materials is to understand the connection between the shapes of individual grains and the macroscopic response of the aggregate. Granular packings of concave or elongated particles can form free-standing structures like walls or arches, in sharp contrast to the behaviors of spherical grains. For some particle shapes, such as staples, the rigidity arises from interlocking of pairs of particles, but the origins of rigidity for non-interlocking particles remains unclear. In addition to their intrinsic interest, these packings are relevant to lightweight and reconfigurable structures in civil, geotechnical and material engineering applications.In this thesis, we report on experiments and numerical simulations of packings of star-shaped particles consisting of three mutually orthogonal sphero-cylinders whose centers coincide. The first set of experiments studies the chance of obtaining a free-standing column when the confining tube of the column is removed, which we will call it as "intrinsic stability''. We prepare monodisperse packings of star-shaped particles with different length-to-arm diameter aspect ratio α, interparticle friction and particle-base friction. We also vary packing density by vibrating the packings when they are in the tube. We find that the intrinsic stability depends on packing dimension: columns of greater diameter or shorter height are more stable. Both arm length and interparticle friction can greatly increase the intrinsic stability, while the packing density and basal friction have limited effects on the intrinsic stability.The second set of experiments involves stability of free-standing columns (prepared from the first set of experiments) under three different external perturbations: (1) base tilting; (2) static axial loading; and (3) vertical vibration. For the base tilting test, we gradually tilt the base of the column and observe column collapse as a function of tilt angle. We find that columns of low friction particles are more fragile than those of high friction particles. For the axial loading test, we gradually increase the loading on a column until it collapses. We find that tall columns are more fragile. For the vibration test, we apply vertical sinusoidal vibration from the base to destabilize the column. Both interparticle and basal friction improve packing stability in terms of increasing relaxation time under vibration. We also find that tall columns are more sensitive to the vibration in the sense that they collapse faster than short ones under the same vibration.In the third set of experiments, we vary α and subject the packings to quasistatic direct shear. For small α, we observe a finite yield stress. For large α, however, the packings become rigid when sheared, supporting stresses that increase sharply with increasing strain. Analysis of x-ray micro-computed tomography data collected during the shear reveals that the stiffening is associated with a tilted, oblate cluster of particles near the nominal shear plane in which particle deformation and average contact number both increase.Molecular dynamics simulations that closely match the third experiments are used to investigate the finite yield stress and the stiffening. In simulation, interparticle contact forces are known to us. For yield packings (small α), simulations suggest no apparent cohesion. For stiffening packings (large α), simulation results show that the particles are collectively under tension along one direction even though they do not interlock pairwise. These tensions come from contact forces with large associated torques, and they are perpendicular to the compressive stresses in the packing. They counteract the tendency to dilate, thus stabilizing the particle cluster.

ISBN: 9798672148182Subjects--Topical Terms:

516296
Physics.
Subjects--Index Terms:

Geometric cohesion

Characterization and Mechanism of Rigidity in Columns of Star-Shaped Granular Particles = = 对星状颗粒材料堆积体互锁结构稳定性机制的研究.
LDR:08811nmm a2200397 4500 001 2275789
005 20210401103738.5
008 220723s2020 ||||||||||||||||| ||eng d
020 $a 9798672148182
035 $a (MiAaPQ)AAI28001831
035 $a AAI28001831
040 $a MiAaPQ $c MiAaPQ
100 1 $a Zhao, Yuchen. $3 2099748
245 1 0 $a Characterization and Mechanism of Rigidity in Columns of Star-Shaped Granular Particles = $b 对星状颗粒材料堆积体互锁结构稳定性机制的研究.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2020
300 $a 104 p.
500 $a Source: Dissertations Abstracts International, Volume: 82-03, Section: B.
500 $a Advisor: Socolar, Joshua E. S.
502 $a Thesis (Ph.D.)--Duke University, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a An important challenge in the science of granular materials is to understand the connection between the shapes of individual grains and the macroscopic response of the aggregate. Granular packings of concave or elongated particles can form free-standing structures like walls or arches, in sharp contrast to the behaviors of spherical grains. For some particle shapes, such as staples, the rigidity arises from interlocking of pairs of particles, but the origins of rigidity for non-interlocking particles remains unclear. In addition to their intrinsic interest, these packings are relevant to lightweight and reconfigurable structures in civil, geotechnical and material engineering applications.In this thesis, we report on experiments and numerical simulations of packings of star-shaped particles consisting of three mutually orthogonal sphero-cylinders whose centers coincide. The first set of experiments studies the chance of obtaining a free-standing column when the confining tube of the column is removed, which we will call it as "intrinsic stability''. We prepare monodisperse packings of star-shaped particles with different length-to-arm diameter aspect ratio α, interparticle friction and particle-base friction. We also vary packing density by vibrating the packings when they are in the tube. We find that the intrinsic stability depends on packing dimension: columns of greater diameter or shorter height are more stable. Both arm length and interparticle friction can greatly increase the intrinsic stability, while the packing density and basal friction have limited effects on the intrinsic stability.The second set of experiments involves stability of free-standing columns (prepared from the first set of experiments) under three different external perturbations: (1) base tilting; (2) static axial loading; and (3) vertical vibration. For the base tilting test, we gradually tilt the base of the column and observe column collapse as a function of tilt angle. We find that columns of low friction particles are more fragile than those of high friction particles. For the axial loading test, we gradually increase the loading on a column until it collapses. We find that tall columns are more fragile. For the vibration test, we apply vertical sinusoidal vibration from the base to destabilize the column. Both interparticle and basal friction improve packing stability in terms of increasing relaxation time under vibration. We also find that tall columns are more sensitive to the vibration in the sense that they collapse faster than short ones under the same vibration.In the third set of experiments, we vary α and subject the packings to quasistatic direct shear. For small α, we observe a finite yield stress. For large α, however, the packings become rigid when sheared, supporting stresses that increase sharply with increasing strain. Analysis of x-ray micro-computed tomography data collected during the shear reveals that the stiffening is associated with a tilted, oblate cluster of particles near the nominal shear plane in which particle deformation and average contact number both increase.Molecular dynamics simulations that closely match the third experiments are used to investigate the finite yield stress and the stiffening. In simulation, interparticle contact forces are known to us. For yield packings (small α), simulations suggest no apparent cohesion. For stiffening packings (large α), simulation results show that the particles are collectively under tension along one direction even though they do not interlock pairwise. These tensions come from contact forces with large associated torques, and they are perpendicular to the compressive stresses in the packing. They counteract the tendency to dilate, thus stabilizing the particle cluster.
520 $a 在关于颗粒材料物理性质的研究当中，理解颗粒形状对材料整体性质的影响是一个具有挑战性的课题。与普通颗粒材料形成鲜明对比的是，凹多面体或者是长条形的颗粒可以通过互锁来形成各种无需边界支撑的结构，比如柱体、桥拱。举个例子：订书钉形状的颗粒可以堆砌成无需边界支撑柱体，其原理可以简单地理解为订书钉之间可以互相勾连。然而，对于无法互相勾连且也能形成以上稳定结构的颗粒堆积体（比如长棍子或者星状颗粒），其中的物理机制尚不清楚。对以上问题的研究，不仅可以增进人们对互锁结构基本物理机制的了解，还可以为轻质和可重复利用的功能建筑材料的设计和应用提供新思路。在这篇博士论文中，我用物理实验和数值仿真模拟来研究星状颗粒材料中互锁结构的物理性质。本论文第一个实验系列研究当柱体侧面边界被移除后柱体的稳定性，我称之为"内在稳定性"。我采用不同长宽比或摩擦系数的星状颗粒来制备各种颗粒的圆柱体堆积。这些圆柱体有不同的长和高。我们发现圆柱堆积体的内在稳定性与圆柱的尺寸有关。短或者宽的圆柱更加容易被制备，即有更大的内在稳定性。增加颗粒长宽比或者颗粒间摩擦系数都可以极大地增加内在稳定性。提高堆积体体积分数或者是颗粒与地面的摩擦系数对内在稳定性的提升相对较弱。本论文第二个实验系列涉及那些已经具有内在稳定性的圆柱体。它们处于无边界支撑的站立状态。我研究三种不同外界扰动对其稳定性的影响。扰动包括：（1）底部倾斜。（2）垂直加压。（3）垂直震动。在底部倾斜扰动实验中，我通过缓慢增加圆柱体地面倾斜角来使圆柱体倒塌，并观察其倒塌过程。我发现由低摩擦系数颗粒组成的圆柱体比高摩擦系数的更加脆弱。在垂直加压的实验中，我通过缓慢增加圆柱体横截面上的压力来破坏圆柱体，并发现高的圆柱体比更加脆弱。在垂直震动实验中，我通过驱动地面正弦震动来影响圆柱体，并观察其倒塌过程。颗粒间和颗粒-地面间的摩擦系数均可大幅提高倒塌过程所需的时间。我还发现高圆柱体在受到震动倒塌的初期过程较快。本论文第三个实验系列涉及对不同长宽比α的星状颗粒组成的圆柱体的准静态剪切力学实验和数值仿真模拟。对于α较小的颗粒，我发现屈服剪应力大小有限。对于α较大的颗粒，圆柱体在剪切的作用下更加牢固，剪应力随着应变不断上升。我通过分析实验的X光断层扫描数据，发现剪应力上升是由于一个横在剪切平面的颗粒团簇所导致的。这个颗粒团簇承受了巨大的剪应力，星状颗粒的胳膊显著弯曲且颗粒间的接触点数目也随着应变的增加而增加。我用分子动力学数值方法模拟了上述剪切实验来研究颗粒堆积体内部的受力状态。对于发生屈服的堆积体（α较小），数值模拟显示该堆积体不存在宏观粘性，与实验结论一致。对于剪应力不断增加的堆积体（α较大），我发现星状颗粒可以集体地支撑着外部的一个方向上的拉应力，尽管两个颗粒之间无法承受拉应力。拉应力来自于那些对单个颗粒施加大力矩的接触点，且其方向总是垂直于压应力的方向。这些拉应力的方向与颗粒的剪胀方向一致，因此拉应力稳固了这个颗粒团簇，使其具有稳定性。.
590 $a School code: 0066.
650 4 $a Physics. $3 516296
650 4 $a Statistical physics. $3 536281
650 4 $a Civil engineering. $3 860360
653 $a Geometric cohesion
653 $a Granular material
653 $a Interlocking
653 $a Particle shape effect
653 $a Rigidity transition
653 $a X-ray computed tomography
690 $a 0605
690 $a 0217
690 $a 0543
710 2 $a Duke University. $b Physics. $3 1035984
773 0 $t Dissertations Abstracts International $g 82-03B.
790 $a 0066
791 $a Ph.D.
792 $a 2020
793 $a English
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28001831