A More Comprehensive Modeling of Contact Force During Shear Testing Using Dem (original) (raw)
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A Simple Device for Testing Dynamic Material Properties of Granular Materials
A simple testing device was designed for the purpose of experimental and numerical investigation of soil protective properties. Two types of soil mixtures: gravel and dry sand were tested in this device. The device was numerically modeled using the commercial code Ls-Dyna. The constitutive model used for the sand consists of an equation of state and, a pressure dependent yield variant of the Drucker-Prager strength law. The experimental and computational results demonstrate that a key factor of the strength of soil is penetration of pressurized air into the soil mixture. When the soil is exposed to pressurized air, the testing devise fails. This results from soil fluidization due to air penetration into the soil. A soil composed of sand-gravel mixture prevents this exposure and, is more resistant to pressure loads. This resistance is maintained for limited time duration. However, this time duration is considerably longer than the duration applied by a blast load.
A SIMPLE DEVICE FOR TESTING DYNAMIC MECHANICAL PROPERTIES OF GRANULAR MATERIALS
A simple testing device was designed for the purpose of experimental and numerical investigation of soil protective properties. Two types of soil mixtures: gravel and dry sand were tested in this device. The device was numerically modeled using the commercial code Ls-Dyna. The constitutive model used for the sand consists of an equation of state and, a pressure dependent yield variant of the Drucker–Prager strength law. The experimental and computational results demonstrate that a key factor of the strength of soil is penetration of pressurized air into the soil mixture. When the soil is exposed to pressurized air, the testing devise fails. This results from soil fluidization due to air penetration into the soil. A soil composed of sand-gravel mixture prevents this exposure and, is more resistant to pressure loads. This resistance is maintained for limited time duration. However, this time duration is considerably longer than the duration applied by a blast load.
Computational Particle Mechanics, 2018
Collapsing soil structure caused by mineral dissolution is a challenge to geoenvironmental projects. Although the parameters affecting the macro-response of collapsible soil have been addressed experimentally, the micromechanical behavior of soluble soil is unclear. The aim of this study was to simulate the dissolution behavior of a granular assembly at the particle level. A DEM code was developed that considers both localized and random dissolution as well as the particle size distribution and stress level. The effect of particle dissolution was simulated by considering the role of particle size in the load-bearing skeleton. The results show that mechanical behavior of a granular assembly is strongly influenced by the location and percentage of dissolution of particles. The loss of the soluble particles decreases physical contact and transfers to neighboring particles due to the arching forces around the voids, as in a honeycomb structure. However, if the soluble areas cut across the load-bearing force chains, a honeycomb fabric cannot form because of the lack of an arching effect, leading to the collapse of the structure and large volume change. Particle loss of up to 3% will not have a serious impact on the mechanical behavior of the granular assembly. After fine particle dissolution of a binary mixture, the arching effect around them decreases the volumetric strain in comparison with the dissolution of coarse particles. Also, during dissolution, the high stress level will decrease the peak friction angle, but the opposite is true for the post-dissolution behavior above 12% strain.
Physical test of a particle simulation model in a sheared granular system
Physical Review E, 2009
We report a detailed comparison of a slow gravity-driven sheared granular flow with a discrete-element simulation performed in the same geometry. In the experiments, grains flow inside a silo with a rectangular cross section and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index-matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The simulations use a Cundall-Strack contact model between the grains using contact parameters that have been used in many other previous studies and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. We then perform a detailed comparison of the particle fluctuation properties as measured by the displacement probability distribution function and the mean square displacement. All in all, our study suggests a high level of quantitative agreement between the simulations and experiments.
Mechanics of Materials, 2009
In this study, we report a direct comparison between a physical test and a computer simulation of rapidly sheared granular materials. An annular shear cell experiment was conducted. All parameters were kept the same between the physical and the computational systems to the extent possible. Artificially softened particles were used in the simulation to reduce the computational time to a manageable level. Sensitivity study on the particle stiffness ensured such artificial modification was acceptable. In the experiment, a range of normal stress was applied to a given amount of particles sheared in an annular trough with a range of controlled shear speed. Two types of particles, glass and Delrin, were used in the experiment. Qualitatively, the required torque to shear the materials under different rotational speed compared well with those in the physical experiments for both the glass and the Delrin particles. However, the quantitative discrepancies between the measured and simulated shear stresses were nearly a factor of two. Boundary conditions, particle size distribution, particle damping and friction, including a sliding and rolling, contact force model, were examined to determine their effects on the computational results. It was found that of the above, the rolling friction between particles had the most significant effect on the macro stress level. This study shows that discrete element simulation is a viable method for engineering design for granular material systems. Particle level information is needed to properly conduct these simulations. However, not all particle level information is equally important in the study regime. Rolling friction, which is not commonly considered in many discrete element models, appears to play an important role.
YADE-OPEN DEM: an open-source software using a discrete element method to simulate granular material
Engineering Computations, 2009
Purpose -YADE-OPEN DEM is an open source software based on the Discrete Element Method which uses object oriented programming techniques. The paper describes the software architecture. Design/methodology/approach -The DEM chosen uses position, orientation, velocity and angular velocity as independent variables of simulated particles which are subject to explicit leapfrog time-integration scheme (Lagrangian method). The three-dimensional dynamics equations based on the classical Newtonian approach for the second law of motion are used. The track of forces and moments acting on each particle is kept at every time-step. Contact forces depend on the particle geometry overlap and material properties. The normal, tangential and moment components of interaction force are included. Findings -An effort has been undertaken to extract the underlying object oriented abstractions in the Discrete Element Method. These abstractions were implemented in C++, conform to object oriented design principles and use design patterns. Based on that, a software framework was developed in which the abstractions provide the interface where the modelling methods can be plugged-in. Originality/value -The resulting YADE-OPEN DEM framework is designed in a generic way which provides great flexibility when adding new scientific simulation code. Some of the advantages are that numerous simulation methods can be coupled within the same framework while plug-ins can import data from other software. In addition, this promotes code improvement through open source development and allows feedback from the community. However implementing such models requires that one adheres to the framework design and the YADE framework is a new emerging software. To download the software see http://yade.wikia.com webpage.
Rock Mechanics and Rock Engineering, 2008
The paper presents the results of a numerical analysis, carried out by using the Discrete Element Method (DEM) and aimed at reproducing a series of tests on a small-scale laboratory model of a slope. Particular attention is devoted to the validation of DEM when used for the prediction of the run-out distance and of the impact force on obstacles. The soil used for the small-scale model is a mono-granular medium sand, which revealed to be particularly suitable to simulate flows like debris or rock avalanches. The experimental set-up comprises a flume equipped with a system of differently sized instrumented obstacles. The numerical model of the granular flow has been calibrated on the basis of the displacement measurements, obtained through a photogrammetric technique.
Exploring chemo-mechanics of granular material using DEM
EPJ Web of Conferences, 2021
Particle Size Distribution (PSD) is one of the prime guiding factors of granular media response. Degradation via weathering is a process, which brings about a gradual shift in the PSD. In nature, chemically sensitive material like calcite undergoes chemo-mechanical degradation bringing about variations in their behaviour. In the present study, an experimental investigation is carried out to get insight into the mechanical response during the coupled chemo-mechanical process. The experiments were carried out at two different rates of dissolutions in a custom made 1D compression mould. From the experiments, it is clear that the higher rate of dissolution reduces the lateral earth pressure more than the lower rate. Discrete Element Method (DEM) analyses the micromechanical process behind the observed response from experiments. The results showed a reduction in lateral stress as soon as the dissolution starts. DEM analysis confirms the competing mechanism between grain size reduction an...
An interpretation of the influence of particle shape on the mechanical behavior of granular material
Granular Matter, 2019
An earthquake refers to volcanic or magmatic activity or any other sudden stress changes in the earth which can result in instability, liquefaction and ground settlement. Past studies show that liquefaction and instability of granular soils are not the only consequence of earthquakes. Significant advances have been made in the past few decades to understand the effect of various soil characteristics (e.g. size, mineralogy, fines content) and boundary conditions on their role on the instability and liquefaction susceptibility of geomaterials. However, studies on the impact of particle shape on the mechanical characteristics of granular material has been relatively less documented and is therefore, unclear. The current experimental study deals with the above problem, where, three materials having different shapes (crushed glass, Rhein sand and round glass beads) but possessing the same uniformity coefficient and mean grain size were used. The materials were thoroughly washed in a 0.063 mm sieve to eliminate fines. Experiments were conducted using the monotonic triaxial (both drained and undrained) and direct shear devices available at the Ruhr-Universität Bochum. No significant particle breakage was observed throughout the entire test program for the three materials. The results of our experiments showed the significant influence of the grain shape on the mechanical characteristics of sands (e.g. shear strength, peak friction and dilation angle). The analysis of results showed a possible correlation between the mechanical and intrinsic characteristics of granular material and the particle shapes.
Interface behavior of granular materials: discrete numerical simulation of a ring simple shear test
The paper aims at analyzing the interface behavior of granular material with a particular interest on the grain size distribution and the contact law (linear or non-linear elastic). The effect of these parameters on the initial state (density and arrangement) and the global behavior is studied by the simulation of a ring simple shear test using the Discrete Element Method and compared with theoretical developments. The global behavior characterized by the initial shear modulus is compared with the results of an homogenization approach explicitly accounting for the particle size distribution and the linear or non linear elasticity of the contact law.