Properties Of Granular Materials Research Articles

Discrete element simulation of mechanical characteristics of sands under principal stress axes rotation

The mechanical behavior of sands and other granular materials subjected to rotation of principal stress axes is significantly dependent on the micro fabric properties and their evolution. The discrete element simulation for sands under cyclic rotation of principal stress axes was validated by comparing the numerical simulation and laboratory test results on the development of two normal strains,the relationship between shear stress and shear strain,the evolution of the volumetric strain,and the effects of initial void ratio and stress ratio. Four variables characterized by the spatial distribution features of particle major axis orientation and interparticle contact normal directions were used to describe the fabric properties of granular materials. The evolution of the four fabric variables in a single cycle was studied for granular materials subjected to cyclic rotation of principal stress axes. The effects of initial void ratio and stress ratio on the evolution of fabric variables were also investigated in detail.

Characterisation of unbound aggregate materials considering physical and morphological properties

The objective of this paper is to evaluate the factors affecting resilient and permanent deformation behaviour of unbound granular materials, with a focus on the aggregate physical and morphological characteristics. To evaluate the behaviour of base course, repeated load triaxial testing is commonly used to establish the stress-dependent resilient modulus properties of unbound aggregate base and subbase materials. Although resilient modulus of aggregates is a critical input into mechanistic-empirical pavement design methods, the resilient modulus of unbound base material is often estimated from empirical correlations with index properties in the AASHTOWare Pavement ME design procedure for its simplicity. Since actual field stress conditions and resilient modulus stress states are generally quite different from those generated in the empirical test methods, use of an empirical correlation could lead to an unreliable prediction of resilient modulus and permanent deformation. In order to properly assess the stability of an unbound aggregate layer, it is necessary to establish a proper process to understand the factors affecting fundamental and performance-related properties of unbound granular materials. In this study, aggregate samples from four different sources were tested for resilient modulus and Poisson’s ratio measurements using the Precision Unbound Material Analyzer equipment. Morphological or shape properties of aggregate samples were also measured using an image analysis device. The results demonstrate that aggregate physical and morphological properties affect aggregate resilient and permanent deformation. Further, it is suggested that the resilient modulus of the aggregate should not be used as the sole indicator of rutting performance of aggregate base.

Impact of Subgrade and Granular Layer Material Properties on Rutting

Material properties play avital role to determine the structural and functional performance of pavement layers during its service life. Pavement deformation or rutting is one of the key distress that affects the pavement performance. The strength parameters of subgrade and granular layer are correlated with the permanent deformations characteristics. Theindividualeffect in addition to combined effectof various combinations are considered to estimate rutting using multi linear regression (MLR) and artificial neural network (ANN) techniques. The data was collected in staggered position at every kilometer of a national highway stretch. The characteristic deflection, field dry density, modified liquid limit, California bearing ratio (CBR) were correlated individually with the rutting measurement and sensitivity analysis also performed. The impact of fines and dynamic behavior of soil response are considered in four possible combinations and correlated with rutting. The result shows that characteristic deflection, field dry density, modified liquid limit and modulus of elasticity of subgrade, and granular layer individually consists good relation with rutting except liquid limit. A good correlation was obtained supporting the validity of R2 values of ANN for subgrade and granular layer 0.84 and 0.86 respectively for combinations of parameters. Likewise, results of R2 values for MLR models obtained are 0.70 and 0.79, for the given layers subsequently comparing the R2 values of MLR and ANN it is concluded that ANN models are more efficient than MLR.

Properties of granular materials as heat transfer and storage medium in CSP application

A selection of granular natural and ceramic materials has been experimentally characterized with regard to their application as heat transfer and storage media in concentrating solar power plants. Thermophysical, thermomechanical, tribological and rheological measurements have been conducted in order to identify the most suitable candidates for this dynamic high temperature operation. Ceramic materials are found to comprise some advantages, but natural products offer a considerably more economic solution. Thermal bulk conductivity is found to be only marginally affected by the solid's thermal conductivity, while specific heat is the same for all solids. Ceramics entirely withstand thermal cycling, while quartz-containing materials are prone to severe degradation. Most materials are found to attain a saturated state of attrition while being sheared under load, wherein quartz sand offers the lowest mass fraction of debris at saturation level. In the investigated grain size range, all materials show good flowability. The generation of debris requires consideration in the design of the CSP storage components.

Discrete element modelling and cavity expansion analysis of cone penetration testing

This paper uses the discrete element method (DEM) in three dimensions to simulate cone penetration testing (CPT) of granular materials in a calibration chamber. Several researchers have used different numerical techniques such as strain path methods and finite element methods to study CPT problems. The DEM is a useful alternative tool for studying cone penetration problems because of its ability to provide micro mechanical insight into the behaviour of granular materials and cone penetration resistance. A 30° chamber segment and a particle refinement method were used for the simulations. Giving constant mass to each particle in the sample was found to reduce computational time significantly, without significantly affecting tip resistance. The effects of initial sample conditions and particle friction coefficient on tip resistance are investigated and found to have an important effect on the tip resistance. Biaxial test simulations using DEM are conducted to obtain the basic granular material properties for obtaining CPT analytical solutions based on continuum mechanics. Macro properties of the samples for different input micro parameters are presented and used to obtain the analytical CPT results. Comparison between the numerical simulations and analytical solutions show good agreement.

Moisture influence on the resilient deformation behaviour of unbound granular materials

The influence of moisture on the resilient deformation properties of unbound granular materials was investigated based on repeated load triaxial tests. Results showed that the resilient modulus (MR) decreased with increasing moisture for a relatively low number of load cycles (N) where the deformation behaviour was mostly resilient with a negligible amount of associated accumulated permanent deformation (PD). Modelling attempts on this behaviour were quite satisfactory. Furthermore, the MR showed an increasing trend with increasing moisture, up to the optimum, when the N was relatively large with a significant amount of accumulated PD. Above the optimum, the MR generally decreased. Further investigation suggested that moisture aided the post-compaction (PC) and possible particle rearrangement that resulted in the increased PD and increased MR. The existing model did not work in this case indicating that the effect of PC on MR should be considered in modelling.

Granular media-based tube press hardening

Press hardening process can benefit the formability of 22MnB5 in high temperature and high strength as a final product. It is widely used for weight reduction of car body without sacrifice of its crashworthiness. Nevertheless, not only strength but also stiffness is important for some vehicle components. Press hardening of tube using granular media is the possible technology to realize the press hardening process for tubular components, which have much higher stiffness as compared to sheet metal parts. To choose appropriate granular media, instrumented die compaction test and high pressure direct shear test were established to characterize the material property of granular material. A hot tensile test was used to determine the formability of 22MnB5 tube material. Interaction between granular media and tube material including friction coefficient and heat transfer coefficient was measured by shear test and heat transfer test. Based on these works, a thermal–mechanical coupled finite element model was used to analyses the process. In validation experiment, a T-shape specimen was formed and quenched. Process parameters such as loading force, interfacial friction, and tube geometry were also investigated via numerical and experimental research for a better understanding of the process. The interfacial friction between granular media and tube showed significant effects to the forming result. These effects were represented by process parameters such as friction coefficient, tube length, types of granular media. A multi-type granular media brought out higher pressure transfer effect and also reduced interfacial friction force, which showed better formability.

Effects of shape and size polydispersity on strength properties of granular materials.

By means of extensive contact dynamics simulations, we analyze the combined effects of polydispersity both in particle size and in particle shape, defined as the degree of shape irregularity, on the shear strength and microstructure of sheared granular materials composed of pentagonal particles. We find that the shear strength is independent of the size span, but unexpectedly, it declines with increasing shape polydispersity. At the same time, the solid fraction is an increasing function of both the size span and the shape polydispersity. Hence, the densest and loosest packings have the same shear strength. At the scale of the particles and their contacts, we analyze the connectivity of particles, force transmission, and friction mobilization as well as their anisotropies. We show that stronger forces are carried by larger particles and propped by an increasing number of small particles. The independence of shear strength with regard to size span is shown to be a consequence of contact network self-organization, with the falloff of contact anisotropy compensated by increasing force anisotropy.

Mechanical Properties of Granular Materials and Their Impact on Load Distribution in Silo: A Review

Abstract Mechanical properties of granular materials and their impact on load distribution in storage silo were discussed with special focus on materials of biological origin. Granular materials classification was briefly outlined. The evolution of constitutive models of granular materials developed in the frame of mechanics of continuum was addressed. Analytical methods, Finite Element Methods (FEM), and Discrete Element Methods (DEM) of estimation of silo pressure were discussed. Special attention was paid to the following issues: dynamic pressure switch in the first moment of silo discharge, asymmetry of loads due to eccentric discharge, and impact of uncontrolled increase of moisture content of grain on silo pressures.

A novel liquid bridge model for estimating SWCC and permeability of granular material

As traditional liquid bridge model based on Yang–Laplace theory fails to model behaviors of unsaturated granular materials when liquid bridges fuse with each other in funicular and capillary regimes, a method called “Redistribution of Air Volume and Reduction of Liquid Bridge Force” is proposed, and incorporated into the original discrete element method to resolve this issue. Both soil water characteristic curve and suction stress characteristic curve are worked out by the modified discrete element method, the results of which coincide with theoretical solutions for simple cubic packing and tetrahedral packing of granular materials. Furthermore, parameter study shows that soil water characteristic curve depends on effective particle diameter, particle size distribution and packing density. Typical soil water characteristic curves of sand and silt are obtained using the modified method, with a trend similar to that of experiment qualitatively. With the help of Mualem model and Kozeny–Carman equation, permeability is also predicated for granular materials. In particular, the air entry value coincides with or close to those of typical sand and silt in magnitude. Finally, a case study of SWCC prediction for sandy soil is implemented with acceptable results. We may conclude that the modified discrete element method is capable of predicting hydraulic properties of granular materials qualitatively and semi-quantitatively.

Foams in a rotating drum: An analogy with granular materials

Abstract Rotating drums are usually used to study the flowing properties of granular materials. Here, we report experiments performed in a drum made of a circular Hele–Shaw cell filled with a monodisperse foam and its surfactant solution. The cell is placed vertically and rotated around its center with an angular velocity ω. The rotation of the cell modifies the foam properties and therefore influences its response to the external strain. The observed foam behavior is similar to granular media in several aspects. Using tools developed for granular materials, we characterize the foam evolution in terms of a dimensionless viscous number If and we compare the foam rheology to the theory developed for the immersed granular material rheology.

READ-As and GEH sorption materials for the removal of antimony from water

The objective of this work was to verify the sorption properties of granular filter materials (GEH, READ-As) during the process of removing antimony from water. The pilot tests showed that the use of sorption materials could possibly decrease the antimony content in water to the values limited for drinking water (5 μg/L Sb). A more suitable adsorbent for removing antimony was READ-As. At a concentration of antimony in raw water ranging from 21.5 to 31.1 μg/L, a filtration rate of 5.58 m/h, the value of the bed volume of 3,967, and the adsorption capacity of 128.4 μg/g, which was achieved at a breakthrough concentration of 5 μg Sb/L, were determined. The surface characteristics of the sorption materials used through the physical adsorption of nitrogen, mercury porosimetry, X-ray microanalysis, and scanning electron microscopy (SEM) were studied.

Influence of Nonlinear Resilient Models of Unbound Aggregates on Analysis and Performance of Road Pavements

800x600 Proper characterisation of the mechanical properties of unbound granular materials (UGM) is an essential issue in the analysis and design of flexible pavements. In particular, the resilient modulus of aggregates is a key input parameter in UGM characterization and prediction of pavement structural performance. In the present work, three UGM constitutive models are implemented within an axi-symmetric finite element code developed to simulate the nonlinear behaviour of pavement structures including two local aggregates of different mineralogical nature, typically used in Algerian pavements. The performance of these mechanical models is examined with regards to their capability of representing adequately, under various conditions, the granular material non-linearity in pavement analysis. In addition, deflection data collected by falling weight deflectometer (FWD) are incorporated into the analysis in order to assess the sensitivity of critical pavement design criteria and pavement design life to the three constitutive models. Finally, conclusions of engineering significance are formulated. Normal 0 21 false false false FR X-NONE X-NONE MicrosoftInternetExplorer4

Introduction to barodesy

Barodesy is a frame for constitutive modelling of soils based on their asymptotic properties. This frame allows the constitutive relation to be derived by reasoning on the general properties of granular materials. The constitutive relation obtained in this way is a single tensorial equation of outstanding simplicity that expresses the evolution of stress in dependence of the deformation. More than a mere equation, barodesy is rather a constitutive theory to provide a frame for understanding the intricate mechanical behaviour of condensed granular matter. As compared with previous publications on barodesy, the present paper contains considerable improvements in terms of conceptual rigour, simplicity and performance.

Invited review: Clogging of granular materials in bottlenecks

During the past decades, notable improvements have been achieved in the understanding of static and dynamic properties of granular materials, giving rise to appealing new concepts like jamming, force chains, non-local rheology or the inertial number. The 'saltcellar' can be seen as a canonical example of the characteristic features displayed by granular materials: an apparently smooth flow is interrupted by the formation of a mesoscopic structure (arch) above the outlet that causes a quick dissipation of all the kinetic energy within the system. In this manuscript, I will give an overview of this field paying special attention to the features of statistical distributions appearing in the clogging and unclogging processes. These distributions are essential to understand the problem and allow subsequent study of topics such as the influence of particle shape, the structure of the clogging arches and the possible existence of a critical outlet size above which the outpouring will never stop. I shall finally offer some hints about general ideas that can be explored in the next few years. Received: 21 November 2014, Accepted: 5 December 2014; Reviewed by: K. To, Institute of Physics, Academia Sinica, Taipei, Taiwan; Edited by: L. A. Pugnaloni; DOI: http://dx.doi.org/10.4279/PIP.060014Cite as: I Zuriguel, Papers in Physics 6, 060014 (2014)

Pushing on a Nonlinear Material

Understanding how materials bend, stretch, or compress under an applied force (or “load”) is essential in the design of buildings, vehicles, and machines. These deformations can be straightforwardly calculated for materials like aluminum, glass, or carbon fiber, which tend to deform little and can therefore, to a good approximation, be treated as linear: doubling the load doubles the effect, like pulling on a spring. In contrast, scientists are still looking for the right way to perform the equivalent calculations on stretchy materials like rubbers and foams, and disconnected “granular” materials, such as soil, sand, and cereals. All of these materials share a common property that they are easy to deform by large amounts, and therefore, the linear approximation no longer applies. Corentin Coulais, now at the University of Leiden, the Netherlands, and his colleagues report experiments on a model “soil” in which they carefully tracked the soil’s elastic response to a force exerted on it via a series of very gradual steps [1]. By comparing their results to predictions of an idealized theory of granular materials, they were able to identify the theory’s strengths and limitations. The work could therefore help researchers develop more reliable methods for predicting the behavior of granular materials. Physicists have been working on a number of models to understand how granular materials cross the boundary between being able to support a load to failing completely—a problem of considerable importance for engineers who need to know if a soil can serve as a foundation for a house or bridge. A promising route is to describe this boundary as a “jamming transition” [2, 3]. In this picture, particles are collectively “jammed” into place by their neighbors. However, under an applied stress, they can dislodge from those cages and give way—an “unjamming” transition that is analogous to the melting of an ordinary solid. Similar to the thermodynamic equations of state, where compressibility is a known function of state variables like pressure or temperature, the theory behind jamming can predict material properties of granular materials, such as how they stiffen as a function of particle packing density. But, so far, most of these predictions assume that the particles are frictionless, leaving it unclear which aspects of the theory apply to real situations in which friction is present. Coulais and his colleagues focused their study on two key predictions from the jamming framework [2, 3] that had not been tested for real, frictional particles. The first is the values of the critical exponents that describe how elasticity and dilatancy (the tendency to decrease packing density under shear [4]) vary as the material is sheared near the jamming transition. The second is to measure how characteristic lengths, in this case the one that characterizes the onset of nonlinearity as a function of distance from a disturbance, depend on the proximity of the material to the jamming/unjamming transition. To test these predictions, they used an experimental technique that allowed them to measure the force on each particle as they pushed grains in a jammed state outward from the center of the material. Instead of actual grains of sand, they used 5-millimeter-diameter polymer disks, laying 8000 of these disks in a single, densely packed layer. The polymer disks are photoelastic, meaning they rotate the polarization of light passing through them by an amount that depends on how much stress they experience. When properly calibrated [5, 6], these patterns of birefringence (Fig. 1) can measure the force at each individual contact. To generate shear within the layer of disks, Coulais and his colleagues slowly inflated a 26-millimeter “balloon” at the center of the packed layer. They then observed the progressive changes in the particle-scale stress, strain, dilation, and pressure resulting from each inflation step. For the tiniest steps possible, the researchers observed that the grain-scale stresses (forces between particles) were a nonlinear function of the local strain (the amount the aggregate deformed). But with each subsequent step, the packing experienced a dilatancy-associated pressure rise and a decreased in stiffness. This dilatancy softening

Sound Absorption Measurements and Numerical Estimation of Non Acoustical Parameters of some Moroccan Raw Green Materials

Knowledge of acoustical properties of granular and fibrous sustainable materials has been stimulated thanks to their rather easy handling and durability. In this work direct measurements of the normal incidence sound absorption coefficient of three non consolidated materials (esparto fibers, cork and perlite) have been carried out using the so-called transfer function method. These materials are plentiful in Morocco and they require low amounts of energy for processing, which makes them attractive as either thermal insulating or sound absorbing materials. Results show that the acoustical efficiency of studied materials is comparable to traditional materials. In addition, an inverse estimation of non acoustical parameters (flow resistivity, tortuosity and porosity) of these materials has been performed introducing a new predictability approach. This is based on Global Sensitivity Analysis combined with Global Numerical Optimization Techniques, regarding most usual mathematical models.

Micro–macro properties of quartz sand: Experimental investigation and DEM simulation

The ability to accurately simulate the realistic behavior of granular materials is one of the challenging issues of the numerical techniques. The first purpose of this study is to calibrate the microscopic properties of granular materials by Discrete Element Method (DEM). Coefficients of rolling and sliding friction as two main microscopic properties of granular material have a significant effect on the amount of macroscopic properties like Angle of Repose (AoR). Earlier studies indicated that the same AoR can be demonstrated by different combinations of the microscopic properties of materials. Therefore the AoR cannot singly be considered as a reliable criterion for DEM calibration, hence time as the second macroscopic property was considered along with the AoR for the calibration of microscopic properties. Furthermore, the need for further study in the field of fine particles led to the use of quartz sand with the diameter in the range of 300 to 600μm in this study. It was assumed that the sand grains are spherical particles and dry material (non-cohesive).In the first step of the calibration process, the Sandglass test was performed to measure the macroscopic properties of quartz sand. Then the Sandglass was simulated by DEM for a varied range of coefficients of rolling and sliding friction. A comparison between the AoR and discharging time of materials and DEM results indicated that the coefficients of rolling and sliding friction of sand particles are 0.3 and 0.52 respectively. The calibrated model was verified by performing a comparison between the experimental and simulation results of the conical pile test.The second purpose of this research is to decrease the computational time of DEM simulation through utilizing a slice of a domain instead of the whole domain where the material slice represents the realistic mechanical behavior of materials. Therefore, a rectangular container was experimentally tested and numerically simulated at different thicknesses of the container. Both experimental and numerical results indicated that the critical thickness of the cabin is 32 times of the particle diameter at which the front and rear walls of the cabin do not restrict the mobility of particles in the median plane. In addition, when the wall boundary condition was replaced by periodic boundary condition, the critical thickness decreased to 4 times of particle diameter which significantly improved the computational speed.

STUDY ON EXCESS PORE WATER PRESSURE CHANGES OF SATURATED SOFT CLAY SUBJECTED TO UNDRAINED UNI-DIRECTIONAL AND MULTI-DIRECTIONAL CYCLIC SIMPLE SHEARS

In this paper, normally consolidated specimens of kaolinite clay were tested under undrained uni-directional and multi-directional cyclic simple shears. It is shown from the test results that shear strain amplitude (γ), cyclic shear direction (phase difference (θ)) and the number of cycles (n) have significant effects on the changes of excess pore water pressure during cyclic shearing. However, the effect of cyclic shear direction on the excess pore water pressure can be eliminated by using a new parameter - cumulative shear strain (G*). Conventional estimation method of excess ore water pressure can not be used for the case of multi-directional cyclic shear with the number of cycles larger than 50 (n > 50). Consequently, a new estimation method, which is a function of cumulative shear strain was proposed. This method can be applied to various experimental conditions including uni-directional and multi-directional cyclic simples shear with different shear strain amplitudes and number of cycles.ReferencesAnsal, A., Iyisan, R. and Yildirim, H., 2001. “The cyclic behavior of soils and effects of geotechnical factors in microzonation”, Soil Dynamics and Earthquake Engineering, Vol. 21, No. 5, pp. 445-452.DeGroot, D. J., Ladd, C. C. and Germaine, J. T., 1996. Undrained multidirectional direct simple shear behavior of cohesive soil, J. Geotechnical Eng., ASCE, Vol. 122, No. 2, pp.91-98.Fukutake, K. and Matsuoka, H. A., 1989. “Unified law for dilatancy under multi-directional simple shearing”, Journal of JSCE Division C, JSCE, Vol. (412/III-1), pp. 143-151 (tiếng Nhật).Hyodo, M., Yamamoto, Y. and Sugiyama, M., 1994. “Undrained cyclic shear behaviour of normally consolidated clay subjected to initial static shear stress”, Soils and Foundations, Vol. 34, No. 4, pp.1-11.Matsuda, H., 1997. “Estimation of postearthquake settlement-time relations of clay layers”, Journal of JSCE Division C, JSCE, Vol. 568(III-39), pp. 41-48 (tiếng Nhật).Matsuda, H. and Ohara, S., 1989. “Threshold strain of clay for pore pressure buildup”, Proc. of 12h World Conf. on Soil Mechanics and Foundation Engineering, Rio De Janeiro, pp. 127-130.Matsuda, H. and Nagira, H., 2000. “Decrease in effective stress and reconsolidation of saturated clay induced by cyclic shear”, Journal of JSCE Division C, JSCE, Vol. 659(III-52), pp. 63- 75 (tiếng Nhật).Matsuda, H., Shinozaki, H., Okada, N., Takamiya, K. and Shinyama, K., 2004. “Effects of multi-directional cyclic shear on the postearthquake settlement of ground”, Proc. of 13th World Conf. on Earthquake Engineering, Vancouver, B.C., Canada, Paper No. 2890.Matsuda, H., Andre, P. H., Ishikura, R. and Kawahara, S., 2011. “Effective stress change and post-earthquake settlement properties of granular materials subjected to multi-directional cyclic simple shear”, Soils and Foundations, Vol. 51, No. 5, pp. 873-884.Ohara, S., Matsuda, H. and Kondo, Y., 1984. “Cyclic simple shear tests on saturated clay with drainage”, Journal of JSCE Division C, JSCE, Vol. (352/III-2), pp. 149-158 (tiếng Nhật).Ohara, S. and Matsuda, H., 1988. “Study on the settlement of saturated clay layer induced by cyclic shear”, Soils and Foundations, Vol. 28, No. 3, pp. 103-113.Ohmachi, T., Kawamura, M., Yasuda, S., 159 Mimura, C. and Nakamura, Y., 1988. “Damage due to the 1985 Mexico Earthquake and the ground conditions”, Soils and Foundations, Vol. 28, No. 3, pp. 149-159.Yasuhara, K. and Andersen, K. H., 1991. “Recompression of normally consolidated clay after cyclic loading”, Soils and Foundations, Vol. 31, No. 1, pp. 83-94.Yildirim, H. and Ersan, H., 2007. “Settlements under consecutive series of cyclic loading”, Soil Dynamics and Earthquake Engineering, Vol. 27, No. 6, pp. 577-585.

Influence of the sulphate content of recycled aggregates on the properties of cement-treated granular materials using Sulphate-Resistant Portland Cement

The present work discusses the results of an experimental study investigating the performance of cement-treated granular materials, which were prepared from natural aggregates, recycled concrete aggregates, crushed clay bricks and gypsum. Recycled aggregates can potentially contain large amounts of acid-soluble sulphates. High sulphate contents can lead to the formation of ettringite, which causes dimensional instability in cement-treated materials. The tested samples were manufactured with different types of cement (CEM II and Sulphate-Resistant Portland Cement) and different compositions of the recycled materials to observe the effects of the sulphate content on the mechanical behaviour and the dimensional stability. As a result, the influence of the amount of sulphates on the deformation was determined, which is an aspect that must be considered in applications of this recycled product in road layers.