scholarly journals An Experimental Study of the Effect of Particle Shape on Force Transmission and Mobilized Strength of Granular Materials

2021 ◽  
pp. 1-12
Author(s):  
Eloïse Marteau ◽  
Jose Andrade
Keyword(s):  
Shear Strength ◽  
Granular Materials ◽  
Particle Shape ◽  
Quantitative Description ◽  
Contact Forces ◽  
Force Chains ◽  
Sand Sample ◽  
Force Transmission ◽  
Statistical Characterization ◽  
Granular Assemblies

Abstract Force chains have been regarded as an important hallmark of granular materials. Numerous studies have examined their evolution, properties, and statistics in highly idealized, often circular-shaped, granular assemblies. However, particles found in nature and handled in industries come in a wide variety of shapes. In this paper, we experimentally investigate the robustness of force chains with respect to particle shape. We present a detailed analysis on the particle- to continuum-scale response of granular materials affected by particle shape, that includes the force transmission and mobilized shear strength. The effect of shape is studied by comparing experimental results collected from shear tests performed on 2D analogue circular- and arbitrarily-shaped granular assemblies. Particle shapes are directly discretized from X-Ray CT images of a real sand sample. By inferring individual contact forces using the Granular Element Method (GEM), we provide a direct visualization of the force network, a statistical characterization of the force transmission and a quantitative description of the shear strength in terms of rolling, sliding and interlocking contact mechanisms. We report that force chains are less prevalent in assemblies of arbitrarily-shaped particles than in circular-shaped samples. Furthermore, interlocking is identified as the essential contact mechanism that (1) furnishes a stable structure for force chains to emerge and (2) explains the enhanced shear strength observed in the arbitrarily-shaped samples. These findings highlight the importance of accounting for particle shape to capture and predict the complex mechanical behavior of granular materials across scales.

Effect of Interparticle Friction on the Micromechanical Strength Characteristics of Three Dimensional Granular Media

2015 ◽  
Vol 16 ◽  
pp. 79-89
Author(s):  
Karinate Valentine Okiy
Keyword(s):  
Shear Strength ◽  
Principal Stress ◽  
Coordination Number ◽  
Granular Media ◽  
Three Dimensional ◽  
Contact Forces ◽  
Strength Characteristics ◽  
Fabric Anisotropy ◽  
Granular Assemblies ◽  
Interparticle Friction

The role of interparticle friction on the micromechanical strength characteristics of granular assembly subjected to gradual shearing was analyzed. Three dimensional discrete element method (DEM) was applied in the simulation of quasi-static shearing of granular assemblies with varying interparticle frictional coefficients [µ= 0.10, 0.25, 0.50]. From the reported simulation results, analysis of the following was performed for varying interparticle frictional capacities.i. The normal and tangential stress contributions of weak and strong contacts to principal stress components.ii. Contribution of strong and weak contacts to principal and deviator stress.iii. Evolution of mechanical coordination number and fabric anisotropy of strong contact forces.From this analysis, it is safe to conclude that interparticle friction has a direct effect on the major and minor principal stress components in sheared granular assemblies. Consequently, increasing interparticle friction capacity enhances macroscopic shear strength in sheared granular assemblies. Likewise, at the peak shear strength of the sheared granular media, there exists a maximum fabric anisotropy of strong contact forces and this corresponds to a minimum value of mechanical coordination number (minimum possible number of load bearing contacts per particle).

scholarly journals Impact of sample scaling on shear strength: coupled effects of grains size and shape

2021 ◽  
Vol 249 ◽  
pp. 06011
Author(s):  
Sandra Linero-Molina ◽  
Emilien Azéma ◽  
Nicolas Estrada ◽  
Stephen Fityus ◽  
John Simmons ◽  
...  
Keyword(s):  
Particle Size ◽  
Shear Strength ◽  
Granular Materials ◽  
Particle Shape ◽  
Contact Dynamics ◽  
Material Strength ◽  
Particle Sizes ◽  
Size And Shape ◽  
Particle Size And Shape ◽  
Geotechnical Testing

Size limitations of geotechnical testing equipment often require that samples of coarse granular materials have to be scaled in order to be tested in the laboratory. Scaling implies a convenient modification of the particle size distribution (PSD) to reduce particle sizes. However, it is well known that particle size and shape may be correlated in nature, due to geological factors (as an example). By means of two-dimensional contact dynamics simulations, we analyzed the effect of altering the size span on the shear strength of granular materials when particle size and shape are correlated. Two different systems were considered: one made of only circular particles, and the second made of size-shape correlated particles. By varying systematically the size span we observed that the resulting alteration of material strength is not due to the change in particle sizes. It results instead from the variation of the particle shapes induced by the modification of the PSD, when particle size and particle shape are correlated. This finding suggests that particle shape distribution is a higher order factor than PSD for the shear strength of granular materials. It also highlights the importance of particle shape quantification in soil classification and the case for its consideration in activities such as sampling, subsampling, and scaling of coarse materials for geotechnical testing

Neutron Diffraction Techniques in Granular Mechanics

2017 ◽  
Vol 905 ◽  
pp. 190-195
Author(s):  
Christopher M. Wensrich ◽  
Erich H. Kisi ◽  
Vladimir Luzin ◽  
Oliver Kirstein ◽  
Alexander L. Smith ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Granular Materials ◽  
Plastic Anisotropy ◽  
Continuum Theory ◽  
Neutron Imaging ◽  
Three Dimensions ◽  
Force Transmission ◽  
Complex Behaviour ◽  
Granular Assemblies ◽  
Particle Level

Granular materials demonstrate unique mechanical properties stemming from their discrete nature. At large length scales granular assemblies are often viewed from the perspective of continuum theory where they show complex behaviour such as elastic and plastic anisotropy related to the load and deformation history. This complex behaviour is inextricably linked to the micromechanics of load sharing and force transmission at the particle level. At these scales, bulk stress is not shared homogeneously between particles, but rather by a network of `force chains' that form a skeleton supporting the vast majority of the applied load. The formation and failure of these structures govern much of the bulk behaviour of these materials. Neutron diffraction techniques are now providing a window into the mechanics of granular materials at both bulk and particle scales. Through a combination of tomographic neutron imaging and diffraction based strain measurement it is now possible to directly examine the stress within individual particles in granular assemblies. Results of these experiments in two and three dimensions are presented and the outlook for this approach to studying the mechanics of granular materials is discussed.

scholarly journals Estimating Contact Force Chains Using Artificial Neural Network

2021 ◽  
Vol 11 (14) ◽  
pp. 6278
Author(s):  
Mengmeng Wu ◽  
Jianfeng Wang
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Particle Size ◽  
Granular Materials ◽  
Coordination Number ◽  
Contact Force ◽  
Force Chains ◽  
Granular System ◽  
Biaxial Test ◽  
Artificial Neural

The inhomogeneous distribution of contact force chains (CFC) in quasi-statically sheared granular materials dominates their bulk mechanical properties. Although previous micromechanical investigations have gained significant insights into the statistical and spatial distribution of CFC, they still lack the capacity to quantitatively estimate CFC evolution in a sheared granular system. In this paper, an artificial neural network (ANN) based on discrete element method (DEM) simulation data is developed and applied to predict the anisotropy of CFC in an assembly of spherical grains undergoing a biaxial test. Five particle-scale features including particle size, coordination number, x- and y-velocity (i.e., x and y-components of the particle velocity), and spin, which all contain predictive information about the CFC, are used to establish the ANN. The results of the model prediction show that the combined features of particle size and coordination number have a dominating influence on the CFC’s estimation. An excellent model performance manifested in a close match between the rose diagrams of the CFC from the ANN predictions and DEM simulations is obtained with a mean accuracy of about 0.85. This study has shown that machine learning is a promising tool for studying the complex mechanical behaviors of granular materials.

scholarly journals Comparative 3D DEM simulations of sand–structure interfaces with similarly shaped clumps versus spheres with contact moments

2021 ◽  
Author(s):  
A. Grabowski ◽  
M. Nitka ◽  
J. Tejchman
Keyword(s):  
Particle Shape ◽  
Friction Angle ◽  
Rigid Wall ◽  
Numerical Results ◽  
Contact Forces ◽  
Interface Roughness ◽  
Interface Shear ◽  
Dem Simulations ◽  
Micropolar Continua ◽  
Interface Behaviour

AbstractThree-dimensional simulations of a monotonic quasi-static interface behaviour between initially dense cohesionless sand and a rigid wall of different roughness during tests in a parallelly guided direct shear test under constant normal stress are presented. Numerical modelling was carried out by the discrete element method (DEM) using clumps in the form of convex non-symmetric irregularly shaped grains. The clumps had an aspect ratio of 1.5. A regular grid of triangular grooves (asperities) along the wall with a different height at the same distance was assumed. The numerical results with clumps were directly compared under the same conditions with our earlier DEM simulations using pure spheres with contact moments with respect to the peak and residual interface friction angle, width of the interface shear zone, ratio between grain slips and grain rotations, distribution of contact forces and stresses. The difference between the behaviour of clumps and pure spheres with contact moments proved to be noticeable in the post-peak regime due to a different particle shape. The rolling resistance model with pure spheres was proved to be limited for capturing particle shape effects. Three different boundary conditions along the interface were proposed for micropolar continua, considering grain rotations and grain slips, wall grain moments and wall grain forces, and normalized interface roughness. The numerical results in this paper offer a better understanding of the interface behaviour of granular bodies in DEM and FEM simulations.

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