Influence of various DEM shape representation methods on packing and shearing of granular assemblies

Abstract Realistic yet efficient representation of particle shape is a major challenge for the Discrete Element Method. This paper uses angle-of-repose and direct-shear test simulations to describe the influence of several shape representation methods, and their parameters, on the bulk response of granular assemblies. Three rolling resistance models, with varying coefficient of rolling friction, are considered for spherical particles. For non-spherical particles, superquadrics with varying blockiness and multi-spheres with varying bumpiness are used to model cuboids and cylinders of several aspect ratios. We present extensive quantitative results showing how the various ways used to represent shape affect the bulk response, allowing comparisons between different approaches. Simulations of angle-of-repose tests show that all three rolling friction models can model the avalanching characteristics of cube/cuboid and cylindrical particles. Simulations of direct-shear tests suggest that both the shear strength and the dilative response of the considered non-spherical particles (but not their porosity) can only be predicted by the elasto-plastic rolling resistance model. The quantitative nature of the results allows identifying values of the shape-description parameters that can be used to obtain similar results when using alternative shape representation methods. Graphical abstract

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Sand- and Clay-Photocured-Geomembrane Interface Shear Characteristics Using Direct Shear Test

Sustainability ◽

10.3390/su13158201 ◽

2021 ◽

Vol 13 (15) ◽

pp. 8201

Author(s):

Lihua Li ◽

Han Yan ◽

Henglin Xiao ◽

Wentao Li ◽

Zhangshuai Geng

Keyword(s):

Soil Surface ◽

Friction Angle ◽

Direct Shear ◽

Tensile Crack ◽

Shear Tests ◽

Interface Shear ◽

Direct Shear Tests ◽

Carbon Black Powder ◽

Shear Characteristics ◽

Impermeable Layer

It is well known that geomembranes frequently and easily fail at the seams, which has been a ubiquitous problem in various applications. To avoid the failure of geomembrane at the seams, photocuring was carried out with 1~5% photoinitiator and 2% carbon black powder. This geomembrane can be sprayed and cured on the soil surface. The obtained geomembrane was then used as a barrier, separator, or reinforcement. In this study, the direct shear tests were carried out with the aim to investigate the interfacial characteristics of photocured geomembrane–clay/sand. The results show that a 2% photoinitiator has a significant effect on the impermeable layer for the photocured geomembrane–clay interface. As for the photocured geomembrane–sand interface, it is reasonable to choose a geomembrane made from a 4% photoinitiator at the boundary of the drainage layer and the impermeable layer in the landfill. In the cover system, it is reasonable to choose a 5% photoinitiator geomembrane. Moreover, as for the interface between the photocurable geomembrane and clay/sand, the friction coefficient increases initially and decreases afterward with the increase of normal stress. Furthermore, the friction angle of the interface between photocurable geomembrane and sand is larger than that of the photocurable geomembrane–clay interface. In other words, the interface between photocurable geomembrane and sand has better shear and tensile crack resistance.

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Mechanical Properties and Micro Mechanism of Nano-Clay-Modified Soil Cement Reinforced by Recycled Sand

Sustainability ◽

10.3390/su13147758 ◽

2021 ◽

Vol 13 (14) ◽

pp. 7758

Author(s):

Biao Qian ◽

Wenjie Yu ◽

Beifeng Lv ◽

Haibo Kang ◽

Longxin Shu ◽

...

Keyword(s):

Shear Strength ◽

Void Ratio ◽

Soil Mass ◽

Direct Shear ◽

Test Results ◽

The Sustainable Development ◽

Direct Shear Tests ◽

Soil Cement ◽

Nano Clay ◽

New Material

To observe the effect of recycled sand and nano-clay on the improvement of the early strength of soil-cement (7d), 0%, 10%, 15% and 20% recycled sand were added. While maintaining a fixed moisture content of 30%, the ratios of each material are specified in terms of soil mass percentage. The shear strength of CSR (recycled sand blended soil-cement) was investigated by direct shear test and four groups of specimens (CSR-1, CSR-2, CSR-3 and CSR-4) were obtained. In addition, 8% nano-clay was added to four CSR groups to obtain the four groups of CSRN-1, CSRN-2, CSRN-3 and CSRN-4 (soil-cement mixed with recycled sand and nano-clay), which were also subjected to direct shear tests. A detailed analysis of the modification mechanism of soil-cement by recycled sand and nano-clay was carried out in combination with scanning electron microscopy (SEM) and IPP (ImagePro-Plus) software. The test results showed that: (1) CSR-3 has the highest shear strength due to the “concrete-like” effect of the incorporation of recycled sand. With the addition of 8% nano-clay, the overall shear strength of the cement was improved, with CSRN-2 having the best shear strength, thanks to the filling effect of the nano-clay and its high volcanic ash content. (2) When recycled sand and nano-clay were added to soil-cement, the improvement in shear strength was manifested in a more reasonable macroscopic internal structure distribution of soil-cement. (3) SEM test results showed that the shear strength was negatively correlated with the void ratio of its microstructure. The smaller the void ratio, the greater the shear strength. This shows that the use of reclaimed sand can improve the sustainable development of the environment, and at the same time, the new material of nano-clay has potential application value.

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Extensive database of MSW shear strength parameters obtained from laboratorial direct shear tests: Proposal for data classification

Waste Management ◽

10.1016/j.wasman.2021.09.015 ◽

2021 ◽

Author(s):

Leonardo Vinícius Paixão Daciolo ◽

Natalia de Souza Correia ◽

Maria Eugenia Gimenez Boscov

Keyword(s):

Shear Strength ◽

Data Classification ◽

Direct Shear ◽

Shear Strength Parameters ◽

Shear Tests ◽

Strength Parameters ◽

Direct Shear Tests

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Experimental investigation of the system normal stiffness of a 5 MN direct shear test setup and the compensation of it in CNS direct shear tests

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/833/1/012011 ◽

2021 ◽

Vol 833 (1) ◽

pp. 012011

Author(s):

J Larsson

Keyword(s):

Experimental Investigation ◽

Direct Shear Test ◽

Shear Test ◽

Direct Shear ◽

Shear Tests ◽

Normal Stiffness ◽

Test Setup ◽

Direct Shear Tests

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THERMAL AND HYDRODYNAMIC PERFORMANCE OF A MICROCHANNEL HEAT SINK COOLED WITH CARBON NANOTUBES NANOFLUID

Jurnal Teknologi ◽

10.11113/jt.v78.9670 ◽

2016 ◽

Vol 78 (10-2) ◽

Author(s):

Nik Ahmad Faiz Nik Mazlam ◽

Normah Mohd-Ghazali ◽

Thierry Mare ◽

Patrice Estelle ◽

Salma Halelfadl

Keyword(s):

Thermal Resistance ◽

Heat Sink ◽

Operating Temperature ◽

Heat Removal ◽

Hydrodynamic Performance ◽

Spherical Particles ◽

Microchannel Heat Sink ◽

Pumping Power ◽

Rectangular Microchannel ◽

Aspect Ratios

The microchannel heat sink (MCHS) has been established as an effective heat removal system in electronic chip packaging. With increasing power demand, research has advanced beyond the conventional coolants of air and water towards nanofluids with their enhanced heat transfer capabilities. This research had been carried out on the optimization of the thermal and hydrodynamic performance of a rectangular microchannel heat sink (MCHS) cooled with carbon nanotube (CNT) nanofluid, a coolant that has recently been discovered with improved thermal conductivity. Unlike the common nanofluids with spherical particles, nanotubes generally come in cylindrical structure characterized with different aspect ratios. A volume concentration of 0.1% of the CNT nanofluid is used here; the nanotubes have an average diameter and length of 9.2 nm and 1.5 mm respectively. The nanofluid has a density of 1800 kg/m3 with carbon purity 90% by weight having lignin as the surfactant. The approach used for the optimization process is based on the thermal resistance model and it is analyzed by using the non-dominated sorting multi-objective genetic algorithm. Optimized outcomes include the channel aspect ratio and the channel wall ratio at the optimal values of thermal resistance and pumping power. The optimized results show that, at high operating temperature of 40°C the use of CNT nanofluid reduces the total thermal resistance by 3% compared to at 20°C and consequently improve the thermal performance of the fluid. In terms of the hydrodynamic performance, the pumping power is also being reduced significantly by 35% at 40°C compared to the lower operating temperature.

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