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1
Hall, S. A., i J. Wright. "Three-dimensional experimental granular mechanics". Géotechnique Letters 5, nr 4 (grudzień 2015): 236–42. http://dx.doi.org/10.1680/jgele.15.00094.
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Goldshtein, Alexander, Michael Shapiro, Leonid Moldavsky i Mati Fichman. "Mechanics of collisional motion of granular materials. Part 2. Wave propagation through vibrofluidized granular layers". Journal of Fluid Mechanics 287 (25.03.1995): 349–82. http://dx.doi.org/10.1017/s002211209500098x.
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According to numerous experimental observations and theoretical models vibrated layers composed of large granules behave like a solid plastic body. In contrast, in this study experimental data are presented that reveal that, for constant vibration amplitudes A ≥ 1 cm with the frequency ω increasing from zero, all layers pass through three vibrational states, with the respective behaviours being as of (i) a solid plastic body, (ii) a liquid, (iii) a gas. In the liquid-like vibrational state transverse waves propagating along the layer width were observed. These waves were shown to be gravitational resonance waves, with the corresponding frequencies well correlated by the known formula for incompressible liquids. In the gas-like vibrational state compression (shock) and expansion waves propagating across the layer height, were observed.A theoretical model for time-periodic collisional vibrational regimes was developed on the basis of the Euler-like equations of a granular gas composed of inelastic spheres. The model shows that the vibrational granular state (bed porosity, shock wave speed, granular pressure and kinetic energy) is inter alia governed by the dimensionless parameter V = (Aω)/(hmg)1/2, with g, hm being the gravitational acceleration and the height of the resting layer, respectively. This is in contrast with the previous studies, where the behaviour of vibrated granular layers was interpreted in terms of the dimensionless acceleration Δ = (Aω2)/g. The proposed model was tested by processing the data obtained from photographs of the particle distribution within vibrated layers. Theoretical predictions of the particle average concentration compared favourably with the experimental data.Other phenomena observed in vibrated granular layers include the formation of caverns, circulatory motion of granules and synchronized periodic motion of two adjacent vibrated layers of different widths. The importance of the observed phenomena in relation to various technological processes involving bulk materials (vibromixing, vibroseparation, etc.) is discussed.
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Rusinek, R. "Experimental method for determination of the pressure distribution in granular solids". Research in Agricultural Engineering 49, No. 2 (8.02.2012): 61–64. http://dx.doi.org/10.17221/4954-rae.
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This paper presents two methods of determination of pressure distribution in rape seeds. The study utilized hydraulic pressure sensors with active rubber face and stress state transducer with six duralumin face sensors. This project utilized methodology well known from soil mechanics for determination stress in plant granular material. The hydraulic pressure sensors has been design to measure normal pressure in granular material. The stress transducer has been designed to measure pressure in six different directions, which orientation enable to calculate the stress state from the pressure measurements. The project enclose to design calibrations procedure. Calibration of each of sensors of stress transducer was performed both under air pressure and inside the bedding of rapeseeds. The preliminary tests of both pressure sensors developed for the direct in-bulk measurement within granular material allowed to determinations pressure distribution in granular materials. Experiments were performed inside bedding of rapeseeds of 6% moisture content.
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Hurley, R. C., S. A. Hall i J. P. Wright. "Multi-scale mechanics of granular solids from grain-resolved X-ray measurements". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, nr 2207 (listopad 2017): 20170491. http://dx.doi.org/10.1098/rspa.2017.0491.
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This work discusses an experimental technique for studying the mechanics of three-dimensional (3D) granular solids. The approach combines 3D X-ray diffraction and X-ray computed tomography to measure grain-resolved strains, kinematics and contact fabric in the bulk of a granular solid, from which continuum strains, grain stresses, interparticle forces and coarse-grained elasto-plastic moduli can be determined. We demonstrate the experimental approach and analysis of selected results on a sample of 1099 stiff, frictional grains undergoing multiple uniaxial compression cycles. We investigate the inter-particle force network, elasto-plastic moduli and associated length scales, reversibility of mechanical responses during cyclic loading, the statistics of microscopic responses and microstructure–property relationships. This work serves to highlight both the fundamental insight into granular mechanics that is furnished by combined X-ray measurements and describes future directions in the field of granular materials that can be pursued with such approaches.
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Abdul Qadir Rahimoon. ""ABOUT STRESS TRANSMISSION THROUGH DISORDERED MEDIA CONFINED IN SILO GEOMETRY "". Bulletin of Toraighyrov University. Physics & Mathematics series, nr 1.2022 (28.03.2022): 48–57. http://dx.doi.org/10.48081/wnvy4031.
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"Granular materials are found everywhere around us. A fundamental understanding of the behaviour of these materials is bound to have profound economic benefits. To understand the macroscopic behaviour of granular media and its relationship with the microscopic properties are major objectives of granular mechanics. However, presently macroscopic equations are empiric because of the complexities at the microscopic level. Granular media exhibit properties that are different from those of solids, liquids and gas and much of their behavior has not been fully understood. In this paper a brief survey of Physics of confined granular media has been presented. This is accomplished by reviewing the experimental and theoretical work done to determine the properties of static granular media and concerning theories presented to explain the properties. The apparent mass measurement at the bottom of a granular pile confined in a vertical tube decreases for denser granular packing. The denser granular packing comprising of two different diameters of granules augment the apparent mass instead. This anomalous behavior occurs when small granules are stacked on the large ones. In the case of anomalous increase, a percolation effect is found and correlated with the augment of apparent mass at the bottom of granular column. "
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CIAMARRA, MASSIMO PICA, ANTONIO DE CANDIA, ANNALISA FIERRO, MARIO NICODEMI i ANTONIO CONIGLIO. "STATISTICAL MECHANICS OF STATIC GRANULAR PACKINGS UNDER GRAVITY". International Journal of Modern Physics B 23, nr 28n29 (20.11.2009): 5345–58. http://dx.doi.org/10.1142/s0217979209063675.
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Despite the large use of granular materials in the industry, and the large number of natural phenomena where granular materials are involved, a comprehensive theoretical framework of their physics is still missing. An important perspective was proposed almost 20 years ago by S.Edwards, which suggested the possibility of a statistical mechanics description of granular materials at rest in their mechanically stable states. This article focuses on the theoretical foundations and current understanding of a statistical mechanics approach of granular materials under gravity. Experimental and numerical results discussing such an approach and clarifying its limit of validity are described as well.
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Shukla, A., C. Y. Zhu i M. Sadd. "Angular dependence of dynamic load transfer due to explosive loading in granular aggregate chains". Journal of Strain Analysis for Engineering Design 23, nr 3 (1.07.1988): 121–27. http://dx.doi.org/10.1243/03093247v233121.
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An experimental investigation was conducted to study the dependence of packing geometry on the dynamic load transfer in two dimensional granular aggregate chains. The granular media was simulated by circular discs made of photoelastic material. The experimental method utilizes the combination of high speed photography and photoelasticity to visualize the dynamic load transfer phenomenon in two dimensional model chains subjected to explosive loading. The photographs thus obtained were analysed to get the normal and tangential loads at the contact points as a function of time. The results indicate that the load transfer is strongly dependent on the angle between the vectors drawn from the mass centres of the contacting granules.
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Aleksandrov, A. S., A. V. Smirnov i T. V. Semenova. "Stress Investigation in Pavement Layers and a New Nalculation Model". Materials Science Forum 945 (luty 2019): 813–20. http://dx.doi.org/10.4028/www.scientific.net/msf.945.813.
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The paper is devoted to the comparison results of experimental data and theoretical stress calculations (arising in pavement layers made from granular materials). The formulas of continuum mechanics and mechanics for granular materials and mathematical dependences, got in accordance with engineering calculation method, were taken as a calculation model. The experimental stress values, measured by Steven B.D. using ring stand (University of Canterbury), were applied as a standard. The ring stand ley us employ moving loads to the stand segments with pavement constructed over the ring stand. It was discovered that the best match of values of experimental and calculation data is got by stress computing based on formulas of mechanics for granular materials (M.E. Harr or I.I. Kandaurov) or continuum mechanics, but with O.C. Frohlich parameter added to С.R. Foster, R.G. Ahlvin and H.H. Ulery’s formula. This Frohlich parameter can be taken as a material parameter. In the conclusion the authors show the way of modification of the well-known approaches in mechanics for granular materials. This new way makes possible to calculate minimum principal stress σ3.The modified mathematical relationships of principal stress calculation can be used in models for elastic, plastic, elastic-plastic deformation calculations and in conditions of plasticity.
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Sornette, A., D. Sornette i P. Evesque. "Frustration and disorder in granular media and tectonic blocks: implications for earthquake complexity". Nonlinear Processes in Geophysics 1, nr 4 (31.12.1994): 209–18. http://dx.doi.org/10.5194/npg-1-209-1994.
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Abstract. We present exploratory analogies and speculations on the mechanisms underlying the organization of faulting and earthquake in the earth crust. The mechanical properties of the brittle lithosphere at scales of the order or larger than a few kilometers are proposed to be analogous to those of non-cohesive granular media, since both systems present stress amplitudes controlled by gravity, and shear band (faulting) localization is determined by a type of friction Mohr-Coulomb rupture criterion. here, we explore the implications of this correspondence with respect to the origin of tectonic and earthquake complexity, on the basis of the existing experimental data on granular media available in the mechanical literature. An important observation is that motions and deformations of non-cohesive granular media are characterized by important fluctuations both in time (sudden breaks, avalanches, which are analogous to earthquakes) and space (strain localizations, yield surfaces forming sometimes complex patterns). This is in apparent contradiction with the conventional wisdom in mechanics, based on the standard tendency to homogenize, which has led to dismiss fluctuations as experimental noise. On the basis of a second analogy with spinglasses and neural networks, based on the existence of block and grain packing disorder and block rotation "frustration", we suggest that these fluctuations observed both at large scales and at the block scale constitute an intrinsic signature of the mechanics of granular media. The space-time complexity observed in faulting and earthquake phenomenology is thus proposed to result form the special properties of the mechanics of granular media, dominated by the "frustration" of the kinematic deformations of its constitutive blocks.
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Elkholy, Karim N., i M. M. Khonsari. "Granular Collision Lubrication: Experimental Investigation and Comparison to Theory". Journal of Tribology 129, nr 4 (25.05.2007): 923–32. http://dx.doi.org/10.1115/1.2768613.
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An experimental investigation of the friction and lift characteristics of granular lubrication is presented. Experiments are carried out to demonstrate the vertical displacement (lift) observed in an annular shear cell apparatus. Results are presented for the friction coefficient as a function of the rotational speed and the applied load for several surface roughness combinations. Simulations of the kinetic theory for the granular material are performed and compared to the experimental results. The experiments provide an evidence for the formation of granular lift between two disks undergoing sliding motion.
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Lu, Feng, Chenxi Zhang i Fei Wei. "Compressibility of granular fluids". Physics of Fluids 34, nr 3 (marzec 2022): 033307. http://dx.doi.org/10.1063/5.0084196.
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The effect of granular pressure on the fluctuation of the granular volume fraction is investigated experimentally in a gas–solid flow system. Granular compressibility, defined by the response of granular volume fractions in granular pressure, is also measured. It is found that there exists a critical granular pressure beyond which the transition from the coexistence of a liquid-like granular phase and a gas-like granular phase to homogenous granular fluids takes place. The transition from a heterogenous to homogenous granular phase is characterized by an abrupt change in the granular compressibility. To describe the characteristic change in compressibility, a granular hydrostatic model is formulated by considering both collisional and non-collisional interactions. The model predictions agree well with experimental results.
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Jung, Yeonsu, Sohyun Jung, Sang-im Lee, Wonjung Kim i Ho-Young Kim. "Avian mud nest architecture by self-secreted saliva". Proceedings of the National Academy of Sciences 118, nr 3 (11.01.2021): e2018509118. http://dx.doi.org/10.1073/pnas.2018509118.
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Mud nests built by swallows (Hirundinidae) and phoebes (Sayornis) are stable granular piles attached to cliffs, walls, or ceilings. Although these birds have been observed to mix saliva with incohesive mud granules, how such biopolymer solutions provide the nest with sufficient strength to support the weight of the residents as well as its own remains elusive. Here, we elucidate the mechanism of strong granular cohesion by the viscoelastic paste of bird saliva through a combination of theoretical analysis and experimental measurements in both natural and artificial nests. Our mathematical model considering the mechanics of mud nest construction allows us to explain the biological observation that all mud-nesting bird species should be lightweight.
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Mykulyak, S. V., V. O. Polyakovskyi i S. I. Skurativskyi. "Experimental study of shear deformation of the medium formed by the massif of ribbed grains". Geofizicheskiy Zhurnal 43, nr 2 (3.06.2021): 178–88. http://dx.doi.org/10.24028/gzh.v43i2.230197.
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The approach to the study of the seismically active zone as an open system that is in a state of self-organized criticality is becoming increasingly used in modern research. The models used in this approach should reflect the most characteristic features of such media: discreteness, nonequilibrium, nonlinear and nonlocal nature of interactions. In this paper, the medium is modeled by a granular massif with ribbed grains. Three different massifs are used in the research. Within one massif, all grains are identical, while grains from different massifs differ in shape (cubic or irregular ribbed) and characteristic size.
A number of experiments of shear deformation of such granular massifs were carried out in order to study the influence of the shape and size of grains on the statistical charac-teristics of the process. The influence of the stress state on the deformation properties of these media was also studied. The experiments proved the qualitative similarity of the behavior of different granular media. Obtained experimentally force jumps, represen-ting the reaction of the granular medium to shear deformation, obey the distributions in the form of power dependencies. However, the magnitudes of the forces arising in the massifs depend on the grain shape and size as well as the stress state in the massifs. The experiments with shear deformation of the granular media under the external action of small impulse stresses have shown that such action causes a smoother, devoid of sharp jumps, deformation. External perturbations shift the distribution of the force jumps towards smaller values, leaving their exponents unchanged.
The analysis of experimental results using nonadditive statistical mechanics confirmed the presence of long-range correlations in the massif of ribbed granules during its shear deformation.
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Miryuk, O. A. "Influence of Fillers on Silicate Compositions Porization". Key Engineering Materials 887 (maj 2021): 521–27. http://dx.doi.org/10.4028/www.scientific.net/kem.887.521.
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The article is devoted to the problem of raw material base expanding and improving construction and technical properties of porous granular materials. The results of experimental studies of silicate compositions based on liquid glass and technogenic fillers containing burnable or gas-forming components are presented. Influence of molding mixtures’ composition on thermal expansion nature of granular compositions was established. Preference of a filler combined, containing glass cullet, silica clay and mineral additives was revealed. Multicomponent composition of a filler helps to intensify composition’s expansion. Electron microscopy studies of porous silicate granules have confirmed the advantages of combined fillers using. Effectiveness of sodium additive introduction to regulate technological properties of the raw material and the process of pores formation has been proven. Expediency of mechanical activation of a raw mixture to reduce the temperature of expansion and obtain granules with a bulk density of not more than 300 kg/m3 has been determined.
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Yang, Jie, Zhen-Yu Yin, Farid Laouafa i Pierre-Yves Hicher. "Hydromechanical modeling of granular soils considering internal erosion". Canadian Geotechnical Journal 57, nr 2 (luty 2020): 157–72. http://dx.doi.org/10.1139/cgj-2018-0653.
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This paper attempts to formulate a coupled practical model in the framework of continuum mechanics to evaluate the phenomenon of internal erosion and its consequences on the mechanical behavior of soils. For this purpose, a four-constituent numerical approach has been developed to describe the internal erosion process. The detachment and transport of the fine particles have been described by a mass exchange formulation between the solid and fluid phases. The stress–strain relationship of the soil is represented by a nonlinear incremental model. Based on experimental data, this constitutive model has been enhanced by the introduction of a fines content–dependent critical state, which allows accounting for the influence of fines on soil deformation and strength. The applicability of the practical approach to capture the main features of the internal erosion process and its impact on the mechanical behavior of the eroded soil have been validated by comparing numerical and experimental results of internal erosion tests on Hong Kong completely decomposed granite (HK-CDG) mixtures, which demonstrated that the practical model was able to reproduce, with reasonable success, the experimental data. Furthermore, the influence of the stress state, the initial soil density, and the initial fraction of fines have been analyzed through numerical simulations using the proposed model.
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Milatz, Marius. "Application of single-board computers in experimental research on unsaturated soils". E3S Web of Conferences 195 (2020): 02022. http://dx.doi.org/10.1051/e3sconf/202019502022.
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In this contribution, the application of single-board computers for the investigation of the hydro-mechanical behaviour of unsaturated granular soils is presented. Single-board computers, such as the Raspberry Pi or Arduino, have recently experienced a hype of applications in school and university teaching, in the maker scene, amongst hobbyists, but also in research. In combination with easy to learn and open programming languages, such as Python, individual experimental set-ups for research in unsaturated soil mechanics, using actuators and sensors can be easily developed with the help of different programmable hardware, such as stepper motors, analog-to-digital converters and other controller boards. For the experimental application in imaging of unsaturated granular soils by computed tomography (CT), we present a miniaturized uniaxial compression device for the measurement of unsaturated shear strength and capillary cohesion in CT-experiments. The device has already been applied for CT-imaging of the development of water distribution and capillary bridges in between different shear steps. Furthermore, a new fully programmable hydraulic experimental set-up for the automated investigation of transient hydraulic paths of the water retention curve of granular media is presented. Both devices have been developed in the framework of the Raspberry Pi single-board computer and Python programming language with simple and relatively inexpensive hardware components. In addition to the technical development of the testing devices, experimental results of the hydro-mechanical behaviour of unsaturated sand and glass beads, derived from uniaxial compression tests and water retention tests, will be presented.
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Viswanath, P., i Arghya Das. "Exploring chemo-mechanics of granular material using DEM". EPJ Web of Conferences 249 (2021): 14013. http://dx.doi.org/10.1051/epjconf/202124914013.
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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 and grain rearrangement as the guiding element for the granular media response.
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Darban, Reza, Emilia Damiano, Aldo Minardo, Lucio Olivares, Luciano Picarelli i Luigi Zeni. "An Experimental Investigation on the Progressive Failure of Unsaturated Granular Slopes". Geosciences 9, nr 2 (29.01.2019): 63. http://dx.doi.org/10.3390/geosciences9020063.
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Slope failure is a complex process which depends on several factors concerning nature and properties of soil, slope morphology and structure, past stress history, groundwater regime, boundary conditions, and their changes. As a consequence, the mechanism of slope failure is typically characterized by the development of a highly non-uniform strain field, which does not allow an easy prediction of the failure conditions. Usually, the process which will bring the slope to final collapse starts with local soil failure, which then leads to formation and propagation of a shear zone, and finally to general slope failure. This mechanical process is called progressive failure. However, in spite of the progresses in the knowledge of the slope behavior, a complete framework about the progressive failure is still missing; in particular, information about the response of granular unsaturated sloping soils is very poor. This paper reports the results of a couple of small-scale experiments on slopes reconstituted with unsaturated pyroclastic soils and subjected to continuous rainfall. The use of miniaturized sensors and optical fibers provided useful data to read some aspects of the mechanics of failure.
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Shukla, A., M. H. Sadd i H. Mei. "Experimental and computational modeling of wave propagation in granular materials". Experimental Mechanics 30, nr 4 (grudzień 1990): 377–81. http://dx.doi.org/10.1007/bf02321508.
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VISWANATHAN, H., N. A. SHEIKH, R. D. WILDMAN i J. M. HUNTLEY. "Convection in three-dimensional vibrofluidized granular beds". Journal of Fluid Mechanics 682 (1.08.2011): 185–212. http://dx.doi.org/10.1017/jfm.2011.209.
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We study convective motion in vertically vibrated three-dimensional granular beds by comparing the predictions of a model based on a hydrodynamic description to Navier–Stokes order with experimental results obtained using positron emission particle tracking (PEPT). The three-dimensional conservation equations relating mass, momentum and energy are solved using the finite element (FE) method for a viscous vibrofluidized bed by using only observable system parameters such as particle number, size, mass and coefficients of restitution. The mean velocity profiles from the viscous model show reasonable agreement with the experimental results at relatively low altitudes for the range of experimental values studied, though the velocity fields at higher altitudes were systematically underestimated by the model. We confirm that the convection rolls are influenced by the sidewall coefficient of restitution and demonstrate the scaling relationships that operate, where increasing amplitude of vibration leads to a reduction in the angular velocity of the rolls.
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Zhu, C. Y., A. Shukla i M. H. Sadd. "Prediction of Dynamic Contact Loads in Granular Assemblies". Journal of Applied Mechanics 58, nr 2 (1.06.1991): 341–46. http://dx.doi.org/10.1115/1.2897191.
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An experimental-numerical hybrid technique has been developed to predict the intergranular contact load transfer in granular media subjected to explosive loading. The granular media were simulated by assemblies of circular disks in contact. The peak contact load transfer coefficients (i. e., the ratio of the maximum output contact load to the input contact load as a function of the contact angles) of a given particle were obtained through controlled experimental studies. These coefficients, along with the principle of superposition, were then used to predict the peak contact loads in several regular as well as irregular assemblies of disks. The predicted results compared favorably with the experimental data for several different assemblies.
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Hsiau, S. S., i M. L. Hunt. "Kinetic Theory Analysis of Flow-Induced Particle Diffusion and Thermal Conduction in Granular Material Flows". Journal of Heat Transfer 115, nr 3 (1.08.1993): 541–48. http://dx.doi.org/10.1115/1.2910720.
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The present study on granular material flows develops analytical relations for the flow-induced particle diffusivity and thermal conductivity based on the kinetic theory of dense gases. The kinetic theory model assumes that the particles are smooth, identical, and nearly elastic spheres, and that the binary collisions between the particles are isotropically distributed throughout the flow. The particle diffusivity and effective thermal conductivity are found to increase with the square root of the granular temperature, a term that quantifies the kinetic energy of the flow. The theoretical particle diffusivity is used to predict diffusion in a granular-flow mixing layer, and to compare qualitatively with recent experimental measurements. The analytical expression for the effective thermal conductivity is used to define an apparent Prandtl number for a simple-shear flow; this result is also qualitatively compared with experimental measurements. The differences between the predictions and the measurements suggest limitations in applying kinetic theory concepts to actual granular material flows, and the need for more detailed experimental measurements.
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Xu, Weipan, Haiyang Zeng, Peng Yang i Mengyan Zang. "Numerical analysis on tractive performance of off-road tire on gravel road using a calibrated finite element method–discrete element method model and experimental validation". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 234, nr 14 (15.06.2020): 3440–57. http://dx.doi.org/10.1177/0954407020930175.
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The interaction between off-road tires and granular terrain has a great influence on the tractive performance of off-road vehicles. However, the finite element method or the discrete element method cannot effectively study the interaction between off-road tires and granular terrain. The three-dimensional combined finite element and discrete element method is applied to handle this problem. In this study, a calibrated finite element method–discrete element method model is established, in which the finite element model of off-road tire is validated by stiffness tests, while the discrete element model of gravel particles is validated by triaxial compression tests. The calibrated finite element method–discrete element method model can describe the structural mechanics of the off-road tire and the macroscopic mechanical properties of the gravel road. Tractive performance simulations of the off-road tire on gravel road under different slip conditions are performed with the commercial software LS-DYNA. The simulation results are basically corresponded with the soil-bin test results in terms of granular terrain deformation and tractive performance parameters versus the slip rates. Finally, the effects of tread pattern, wheel load, and tire inflation pressure on tractive performance of off-road tire on granular terrain are investigated. It indicates that the calibrated finite element method–discrete element method can be an effective tool for studying the tire–granular terrain interaction and predicting the tractive performance of off-road tire on granular terrain.
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TATSUMI, SOICHI, YOSHIHIRO MURAYAMA, HISAO HAYAKAWA i MASAKI SANO. "Experimental study on the kinetics of granular gases under microgravity". Journal of Fluid Mechanics 641 (10.12.2009): 521–39. http://dx.doi.org/10.1017/s002211200999231x.
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The kinetics of granular gases, including both freely cooling and steadily driven systems, is studied experimentally in quasi-two-dimensional cells. Under microgravity conditions achieved inside an aircraft flying parabolic trajectories, the frictional force is reduced. In both the freely cooling and steadily driven systems, we confirm that the velocity distribution function has the form exp(−α|v|β). The value of exponent β is close to 1.5 for the driven system in a highly excited case, which is consistent with theory derived under the assumption of the existence of the white-noise thermostat (van Noije & Ernst, Gran. Mat., vol. 1, 1998, p. 5764). In the freely cooling system, the value of β evolves from 1.5 to 1 as the cooling proceeds, and the system's energy decays algebraically (Tg = T0(1 + t/τ)−2), agreeing with Haff's law (Haff, J. Fluid Mech., vol. 134, 1983, p. 401430).
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A. Alshibli, Khalid, i Lynne E. Roussel. "Experimental investigation of slip-stick behaviour in granular materials". International Journal for Numerical and Analytical Methods in Geomechanics 30, nr 14 (2006): 1391–407. http://dx.doi.org/10.1002/nag.517.
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Sawicki, Andrzej, Jacek Mierczyński, Agata Mikos i Justyna Sławińska. "Liquefaction Resistance of a Granular Soil Containing Some Admixtures of Fines". Archives of Hydro-Engineering and Environmental Mechanics 62, nr 1-2 (1.06.2015): 53–64. http://dx.doi.org/10.1515/heem-2015-0019.
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AbstractThe paper deals with the mechanics of sand with some admixtures of fines. The basic question is whether such admixtures are liquefiable or not. Experimental results show that admixtures of fines do not essentially influence the liquefaction susceptibility of granular soils. The original experimental investigations support this conclusion.
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He, Kang, Huabin Shi i Xiping Yu. "An experimental study on aquatic collapses of bidisperse granular deposits". Physics of Fluids 33, nr 10 (październik 2021): 103311. http://dx.doi.org/10.1063/5.0065346.
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MERUANE, C., A. TAMBURRINO i O. ROCHE. "On the role of the ambient fluid on gravitational granular flow dynamics". Journal of Fluid Mechanics 648 (7.04.2010): 381–404. http://dx.doi.org/10.1017/s0022112009993181.
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The effects of the ambient fluid on granular flow dynamics are poorly understood and commonly ignored in analyses. In this article, we characterize and quantify these effects by combining theoretical and experimental analyses. Starting with the mixture theory, we derive a set of two-phase continuum equations for studying a compressible granular flow composed of homogenous solid particles and a Newtonian ambient fluid. The role of the ambient fluid is then investigated by studying the collapse and spreading of two-dimensional granular columns in air or water, for different solid particle sizes and column aspect (height to length) ratios, in which the front speed is used to describe the flow. The combined analysis of experimental measurements and numerical solutions shows that the dynamics of the solid phase cannot be explained if the hydrodynamic fluid pressure and the drag interactions are not included in the analysis. For instance, hydrodynamic fluid pressure can hold the reduced weight of the solids, thus inducing a transition from dense-compacted to dense-suspended granular flows, whereas drag forces counteract the solids movement, especially within the near-wall viscous layer. We conclude that in order to obtain a realistic representation of gravitational granular flow dynamics, the ambient fluid cannot be neglected.
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Suiker, Akke S. J., i Norman A. Fleck. "Frictional Collapse of Granular Assemblies". Journal of Applied Mechanics 71, nr 3 (1.05.2004): 350–58. http://dx.doi.org/10.1115/1.1753266.
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The frictional collapse of an assembly of equisized spheres is studied by a discrete element model. The macroscopic constitutive response is determined as a function of the level of Coulomb friction between particles. It is found that the level of Coulomb friction has a strong effect upon the relative proportion of sliding and rolling between particles, and consequently upon the macroscopic strength of the granular assembly. The discrete element predictions are shown to be in good agreement with experimental results obtained from triaxial tests on an aggregate of steel spheres. It is demonstrated that the shape of the collapse surface can be adequately represented by the Lade-Duncan continuum model.
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Herbert, Eric, Cyprien Morize, Aurélie Louis-Napoléon, Christophe Goupil, Pierre Jop i Yves D’Angelo. "Buoyancy-driven destabilization of an immersed granular bed". Journal of Fluid Mechanics 843 (26.03.2018): 778–809. http://dx.doi.org/10.1017/jfm.2018.141.
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Under suitable conditions, an immersed granular bed can be destabilized by local thermal forcing and the induced buoyant force. The destabilization is evident from the triggering and establishment of a dense fluid-like granular plume. Varying the initial granular layer average height $h$, a time series of the free layer surface is extracted, allowing us to dynamically compute the underlying volume of the granular layer. Different observed phenomena, namely the initial interface deformation, the lowering of the average granular interface (i.e. decrease of the granular layer volume) and the emission of a plume, are analysed. We show that the phenomenon is mainly driven by heat transfer, for large $h$ and also involves a variable height thermal boundary condition and Darcy flow triggering, for small $h$. Simple modelling with no adjustable parameters not only allows us to capture the observed scaling power laws but is also in quantitative agreement with the obtained experimental data.
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Aziz, M., I. Towhata, S. Yamada, M. U. Qureshi i K. Kawano. "Water-induced granular decomposition and its effects on geotechnical properties of crushed soft rocks". Natural Hazards and Earth System Sciences 10, nr 6 (17.06.2010): 1229–38. http://dx.doi.org/10.5194/nhess-10-1229-2010.
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Abstract. The widespread availability of soft rocks and their increasing use as cheap rockfill material is adding more to geotechnical hazards because time-dependent granular decomposition causes significant damage to their mechanical properties. An experimental study was conducted through monotonic torsional shear tests on crushed soft rocks under fully saturated and dry conditions and compared with analogous tests on standard Toyoura sand. Due to the sensitivity of material to disintegration upon submergence, saturated conditions accelerated granular decomposition and, hence, simulated loss of strength with time, whereas, dry test condition represented the response of the soil with intact grains. A degradation index, in relation to gradation analyses after each test, was defined to quantify the degree of granular decomposition. Possible correlations of this index, with strength and deformation characteristics of granular soils, were explored. Enormous volumetric compression during consolidation and monotonic loading of saturated specimens and drastic loss of strength parameters upon submergence were revealed. It is revealed that the observed soil behaviour can be critical for embankments constructed with such rockfill materials. Moreover, the enhanced ability of existing soil mechanics models to predict time-dependent behaviour by incorporating water-induced granular decomposition can simplify several in situ geotechnical problems.
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Avagyan, Arik, David Chiao, Nathan Dostart, Kaiyuan Zhu, Shinhu Cho, Kevin Remick, Alexander F. Vakakis, D. Michael McFarland i Waltraud M. Kriven. "Experimental study of embedded and non-embedded ordered granular chains under impulsive excitation". Acta Mechanica 227, nr 9 (10.05.2016): 2511–27. http://dx.doi.org/10.1007/s00707-016-1564-y.
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RIBEIRO, G. O., P. C. GUETTI i P. SERNA. "Experimental study of the mechanical behavior of self-compacting concrete based on fracture mechanics". Revista IBRACON de Estruturas e Materiais 10, nr 3 (czerwiec 2017): 744–59. http://dx.doi.org/10.1590/s1983-41952017000300010.
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ABSTRACT Considering the physical nonlinearity of concrete and the fundamentals of fracture mechanics for quasi-brittle materials, the objective of this study was to determine the fracture energy and the length of the fracture process zone (FPZ) as well as the modulus of elasticity, the tensile strength and the compressive strength of self-compacting concrete (SCC) to characterize its mechanical behavior. A series of tests, including a three-point bending test of SCC and conventional vibrated concrete (CVC) specimens, with a notch at mid-span, and tensile and compressive tests were performed. The mechanical parameters obtained from the CVC specimens were considered as a comparative reference. The effect of the following variables was evaluated and considered at two levels: compressive strength (30 and 50 MPa), granular composition (fine and coarse particle size) and maximum diameter of the aggregate (12 and 20 mm). The effect of these variables on the mechanical behaviors of the SCC specimens was evaluated based on the test results of specimens of four types of concrete, which were obtained from the combination of the variables. The bending tests were performed according to the RILEM TC 89-FMT recommendations, which are based on the size-effect method.
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ARMANINI, ARONNE, HERVÉ CAPART, LUIGI FRACCAROLLO i MICHELE LARCHER. "Rheological stratification in experimental free-surface flows of granular–liquid mixtures". Journal of Fluid Mechanics 532 (10.06.2005): 269–319. http://dx.doi.org/10.1017/s0022112005004283.
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Sun, Yunhui, Wentao Zhang, Yi An, Qingquan Liu i Xiaoliang Wang. "Experimental investigation of immersed granular collapse in viscous and inertial regimes". Physics of Fluids 33, nr 10 (październik 2021): 103317. http://dx.doi.org/10.1063/5.0067485.
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Tsang, Jonathan Michael Foonlan, Stuart B. Dalziel i N. M. Vriend. "The granular Blasius problem". Journal of Fluid Mechanics 872 (14.06.2019): 784–817. http://dx.doi.org/10.1017/jfm.2019.357.
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We consider the steady flow of a granular current over a uniformly sloped surface that is smooth upstream (allowing slip for $x<0$) but rough downstream (imposing a no-slip condition on $x>0$), with a sharp transition at $x=0$. This problem is similar to the classical Blasius problem, which considers the growth of a boundary layer over a flat plate in a Newtonian fluid that is subject to a similar step change in boundary conditions. Our discrete particle model simulations show that a comparable boundary-layer phenomenon occurs for the granular problem: the effects of basal roughness are initially localised at the base but gradually spread throughout the depth of the current. A rheological model can be used to investigate the changing internal velocity profile. The boundary layer is a region of high shear rate and therefore high inertial number $I$; its dynamics is governed by the asymptotic behaviour of the granular rheology for high values of the inertial number. The $\unicode[STIX]{x1D707}(I)$ rheology (Jop et al., Nature, vol. 441 (7094), 2006, pp. 727–730) asserts that $\text{d}\unicode[STIX]{x1D707}/\text{d}I=O(1/I^{2})$ as $I\rightarrow \infty$, but current experimental evidence is insufficient to confirm this. We show that this rheology does not admit a self-similar boundary layer, but that there exist generalisations of the $\unicode[STIX]{x1D707}(I)$ rheology, with different dependencies of $\unicode[STIX]{x1D707}(I)$ on $I$, for which such self-similar solutions do exist. These solutions show good quantitative agreement with the results of our discrete particle model simulations.
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Hurley, Ryan C. "Stress and force measurement uncertainties in 3D granular materials". EPJ Web of Conferences 249 (2021): 02009. http://dx.doi.org/10.1051/epjconf/202124902009.
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We have developed and employed a 3D particle stress tensor and contact force inference technique that employs synchrotron X-ray tomography and diffraction with an optimization algorithm. We have used this technique to study stress and force heterogeneity, particle fracture mechanics, contact-level energy dissipation, and the origin of wave phenomena in 3D granular media for the past five years. Here, we review the technique, describe experimental and numerical sources of uncertainty, and use experimental data and discrete element method simulations to study the method’s accuracy. We find that inferred forces in the strong force network of a 3D granular material are accurately determined even in the presence of noisy stress measurements.
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Patton, J. S., C. E. Brennen i R. H. Sabersky. "Shear Flows of Rapidly Flowing Granular Materials". Journal of Applied Mechanics 54, nr 4 (1.12.1987): 801–5. http://dx.doi.org/10.1115/1.3173120.
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Shear flows of granular materials are studied in an open channel. The wall shear is calculated from an open channel momentum equation which includes the density variations in the flow. An experimental technique was developed that allowed the measurement of the average density of the flow at different longitudinal locations in the channel. Two sizes of glass beads are examined and results show the variations in the wall shear as a function of various dimensionless parameters.
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Hassan, Suhad Majed, i Bushra Suhale Albusoda. "Mitigation of collapse characteristics of gypseous soils by activated carbon, sodium metasilicate, and cement dust: An experimental study". Journal of the Mechanical Behavior of Materials 31, nr 1 (1.01.2022): 631–38. http://dx.doi.org/10.1515/jmbm-2022-0065.
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Abstract This study includes adding chemicals to gypseous soil to improve its collapse characteristics. The collapse behavior of gypseous soil brought from the north of Iraq (Salah El-Deen governorate) with a gypsum content of 59% was investigated using five types of additions (cement dust, powder sodium meta-silicate, powder activated carbon, sodium silicate solution, and granular activated carbon). The soil was mixed by weight with cement dust (10, 20, and 30%), powder sodium meta-silicate (6%), powder activated carbon (10%), sodium silicate solution (3, 6, and 9%), and granular activated carbon (5, 10, and 15%). The collapse potential is reduced by 86, 71, 43, 37, and 35% when 30% cement dust, 6% powder sodium meta-silicate, 10% powder activated carbon, 6% sodium silicate solution, and 10% granular activated carbon are used, respectively.
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WILDMAN, R. D., T. W. MARTIN, J. M. HUNTLEY, J. T. JENKINS, H. VISWANATHAN, X. FEN i D. J. PARKER. "Experimental investigation and kinetic-theory-based model of a rapid granular shear flow". Journal of Fluid Mechanics 602 (25.04.2008): 63–79. http://dx.doi.org/10.1017/s0022112008000700.
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An experimental investigation of an idealized rapidly sheared granular flow was performed to test the predictions of a model based on the kinetic theory of dry granular media. Glass ballotini beads were placed in an annular shear cell and the lower boundary rotated to induce a shearing motion in the bed. A single particle was tracked using the positron emission particle tracking (PEPT) technique, a method that determines the location of a particle through the triangulation of gamma photons emitted by a radioactive tracer particle. The packing fraction and velocity fields within the three-dimensional flow were measured and compared to the predictions of a model developed using the conservation and balance equations applicable to dissipative systems, and solved incorporating constitutive relations derived from kinetic theory. The comparison showed that kinetic theory is able to capture the general features of a rapid shear flow reasonably well over a wide range of shear rates and confining pressures.
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Ahn, Hojin, Christopher E. Brennen i Rolf H. Sabersky. "Analysis of the Fully Developed Chute Flow of Granular Materials". Journal of Applied Mechanics 59, nr 1 (1.03.1992): 109–19. http://dx.doi.org/10.1115/1.2899415.
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Existing constitutive relations and governing equations have been used to solve for fully developed chute flows of granular materials. In particular, the results of Lun et al. (1984) have been employed and the boundary value problem has been formulated with two parameters (the coefficient of restitution between particles, and the chute inclination), and three boundary values at the chute base wall, namely the values of solid fraction, granular temperature, and mean velocity at the wall. The boundary value problem has been numerically solved by the “shooting method.” The results show the significant role played by granular conduction in determining the profiles of granular temperature, solid fraction, and mean velocity in chute flows. These analytical results are also compared with experimental measurements of velocity fluctuation, solid fraction, and mean velocity made by Ahn et al. (1989), and with the computer simulations by Campbell and Brennen (1985b).
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Vilquin, Alexandre, Hamid Kellay i Jean-François Boudet. "Shock waves induced by a planar obstacle in a vibrated granular gas". Journal of Fluid Mechanics 842 (7.03.2018): 163–87. http://dx.doi.org/10.1017/jfm.2018.128.
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The low value of the speed of sound in dilute granular media permits the study of the properties of supersonic flows for a wide range of Mach numbers. In this paper, we report the experimental observation of a subsonic–supersonic transition in a vibrated granular gas. The shock fronts studied are obtained by simply pushing a rectangular obstacle into the granular gas for different obstacle velocities. The supersonic regime is characterized by the formation of normal shock waves whose width increases when the Mach number decreases to values close to 1. The bimodal model proposed by Mott-Smith in the 1950s provides a good description for the velocity distributions as well as the macroscopic quantities for shock waves in molecular gases but remains inadequate for dissipative media like granular gases and plasmas. Here by examining the shock front structure for a wide range of Mach numbers, we adapt the Mott-Smith bimodal description to a dissipative medium. By using balance equations from granular kinetic theory and taking into account different dissipation sources, the proposed model allows us to understand how this dissipation modifies temperature, mean velocity and volume fraction profiles through the shock front.
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Brennen, C. E., S. Ghosh i C. R. Wassgren. "Vertical Oscillation of a Bed of Granular Material". Journal of Applied Mechanics 63, nr 1 (1.03.1996): 156–61. http://dx.doi.org/10.1115/1.2787191.
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A bed of granular material which is subjected to vertical vibration will exhibit at least one sudden expansion at a critical acceleration amplitude. This sudden expansion corresponds to a bifurcation similar to that exhibited by a single ball bouncing on a vibrating plate. Theoretical analysis based on this model yields results which are in accord with the experimental observations. Other bifurcations may occur at higher vibration levels.
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Daouadji, A., H. AlGali, F. Darve i A. Zeghloul. "Instability in Granular Materials: Experimental Evidence of Diffuse Mode of Failure for Loose Sands". Journal of Engineering Mechanics 136, nr 5 (maj 2010): 575–88. http://dx.doi.org/10.1061/(asce)em.1943-7889.0000101.
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Monsorno, D., C. Varsakelis i M. V. Papalexandris. "A two-phase thermomechanical theory for granular suspensions". Journal of Fluid Mechanics 808 (2.11.2016): 410–40. http://dx.doi.org/10.1017/jfm.2016.649.
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In this paper, a two-phase thermomechanical theory for granular suspensions is presented. Our approach is based on a mixture-theoretic formalism and is coupled with a nonlinear representation for the granular viscous stresses so as to capture the complex non-Newtonian behaviour of the suspensions of interest. This representation has a number of interesting properties: it is thermodynamically consistent, it is non-singular and vanishes at equilibrium and it predicts non-zero granular bulk viscosity and shear-rate-dependent normal viscous stresses. Another feature of the theory is that the resulting model incorporates a rate equation for the evolution of the volume fraction of the granular phase. As a result, the velocity fields of both the granular material and the carrier fluid are divergent even for constant-density flows. Further, in this article we present the incompressible limit of our model which is derived via low-Mach-number asymptotics. The reduced equations for the important special case of constant-density flows are also presented and discussed. Finally, we apply the proposed model to two test cases, namely, steady shear flow of a homogeneous suspension and fully developed pressure-driven channel flow, and compare its predictions with available experimental and numerical results.
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Nguyen, Trung-Kien, Thanh-Trung Vo i Nhu-Hoang Nguyen. "DEM investigation on strain localization in a dense periodic granular assembly with high coordination number". Frattura ed Integrità Strutturale 16, nr 59 (22.12.2021): 188–97. http://dx.doi.org/10.3221/igf-esis.59.14.
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Strain localization is one of key phenomena which have been studied extensively in geomaterials and for different kinds of materials including metals and polymers. This well-known phenomenon appears when structure/material is closed to failure. Theoretical, experimental, and numerical research have been dedicated to this subject for a long while. In the numerical aspects, strain localization inside the periodic granular assembly has not been well studied in the literature. In this paper, we investigate the occurrence and development of strain localization within a dense cohesive-frictional granular assembly with high coordination number under bi-periodic boundary conditions by Discrete Element Modeling (DEM). The granular assembly is composed of 2D circular disks and subjected to biaxial loading with constant lateral pressure. The results show that the formation of shear bands is of periodic type, consistent with the boundary conditions. This formation has the origins of the irreversible losing of cohesive contacts, viewed as micro-crackings which strongly concentrated in the periodic shear zones. This micromechanical feature is therefore strongly related to the strain localization observed at the sample scale. Finally, we also show that the strain localization is in perfect agreement with the sample’s displacement fluctuation fields.
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Sain, Ratnanabha, Tapan Mukerji i Gary Mavko. "On microscale heterogeneity in granular media and its impact on elastic property estimation". GEOPHYSICS 81, nr 6 (listopad 2016): D561—D571. http://dx.doi.org/10.1190/geo2016-0152.1.
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We emphasize the existence of stress-dependent microscopic heterogeneities in granular media and their influence on macroscopic property estimation using numerical simulations. Although numerical simulations based on contact mechanics successfully reproduce experimental stress-dependent acoustic response of granular media, most contact-mechanics-based effective medium theories (EMTs) fail. We have determined that the main reason for this discrepancy is an inadequate theoretical treatment of micro-heterogeneities in structure, force, and stress. Under infinitesimal perturbations used for estimating elastic moduli, microheterogeneities lead to displacements or relaxations — typically ignored in EMT. These infinitesimal granular relaxations are necessary to comply with detailed force balance, but do not involve grain slip and hence do not depend on friction. Furthermore, we have found that these relaxations primarily depend on the “amount” of heterogeneity, which to a first order are dependent on stress only and are independent of mineralogy. In the absence of an effective medium framework to estimate such relaxation corrections, we have provided simulation-based corrections to account for the impact of heterogeneity on elastic moduli calculations in EMT.
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Zharov, M. V. "Investigation of the features of crystallization of granules of high-strength aluminum alloys of the Al-Zn-Mg-Cu system at ultra-high cooling rates". PNRPU Mechanics Bulletin, nr 4 (15.12.2021): 71–82. http://dx.doi.org/10.15593/perm.mech/2021.4.08.
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The article presents the results of studies of the process of obtaining granular materials from high-strength aluminum alloys of the Al - Zn - Mg - Cu system by centrifugation of the melt with ultra-high cooling rates of granules. The concept of a «steam jacket» is introduced, namely, a steam layer that occurs between the granule body and the cooling liquid, which prevents the intensity of heat removal and is an obstacle to increasing the crystallization rate due to the lower thermal conductivity of water vapor. It is established that the formation of a vapor layer always occurs due to the heating of the cooling liquid in contact with the melt drop to boiling temperatures and the transition of the cooler from the liquid phase to steam. The technology of increasing the rate of crystallization of granules due to the constant removal of the vapor layer is proposed. The removal (knocking down) of the vapor shell that occurs around the drop occurs due to the high speed of the drop movement in the cooling medium. Fundamentally important in the industrial implementation of this technology is not so much the design of the device for obtaining pellets by centrifugation of the melt, namely, the high required rotation speed of the spraying crucible of the device under consideration. The results of experimental data are presented to determine the necessary rotation speed of the perforated cup, which ensures the creation of a sufficient initial velocity of the drop movement, leading to a constant churning of the «steam jacket». It is determined that an increase in the rates of heat removal from the crystallized granules and, as a result, an increase in the crystallization rate leads to an increase in the strength characteristics of granular aluminum alloys of the Al-Zn-Mg-Cu system. In particular, in the production of pressed semi-finished products from alloys of the Al-Zn-Mg-Cu system, such as B95, B96c. the increase in the strength characteristics of the material of the press products is up to 15 % compared to the same granular materials obtained by traditional methods with industrial crystallization rates of melt droplets. It is established that this method, based on the removal of the vapor layer around the formed granule, is the only possible one for further increasing the cooling rate and, as a result, the crystallization rate. Reducing the size of granules to the size of powders leads to serious technological problems in the further consolidation of granules and, in fact, is a dead end branch of the further development of granulation methods.
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Zhao, Xue Liang. "Numerical Modeling of Granular Assembly Using Discrete Element Method". Advanced Materials Research 146-147 (październik 2010): 738–42. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.738.
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Discrete element method (DEM) is a powerful tool for the study of granular materials. Some issues in numerical modeling of DEM including parameter selection and mass/density scaling method are discussed. A new method to simulate the resin membrane in the laboratory which is more accurate and simpler is proposed. Using DEM, microscale behavior of soil including particle rotation and mesoscale void ratio distribution are analyzed. Failure modes and stain localization are revealed from the particle scale analysis. Configurations of the shear band are investigated. It shows that microstructure and micromechanics is the underlying mechanics of the macroscale behavior of the granular soil. Being a simpler, faster, and cheaper method compared with traditional experimental method, DEM can capture the discrete characteristics and provide deeper insight of the granular materials.
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Kim, Tae-Hyung, i Stein Sture. "Capillary-induced tensile strength in unsaturated sands". Canadian Geotechnical Journal 45, nr 5 (maj 2008): 726–37. http://dx.doi.org/10.1139/t08-017.
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While a majority of the studies related to unsaturated soils have focused on volume change, flow, and shear strength behavior, investigations of tensile strength of unsaturated soils, especially granular soils, have not received much attention except for those on cemented and clayey soils. This paper focuses on fundamental studies of tensile strength properties of granular soils in the unsaturated state, which were examined experimentally and theoretically. Experimental studies have shown that it is possible to accurately measure the tensile strength of sands at water contents in the range of 0.5%–17% by means of simple techniques. The method of specimen preparation has proved important, and the use of relatively large specimens has made development of homogeneous specimens and measurements relatively straightforward. The magnitude of the tensile strength of moist and relatively clean sands varies with water content, density, and soil type. The experimental data are also compared with mechanics-based models developed for monosized spheres, and their application for a real granular soil with a variety of particles is discussed in the unsaturated state, which includes the pendular, funicular, and capillary regions.