Papers by Keyword: Granular Material

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Authors: Shu Kui Zheng, Ming Fang Tang, Zhen Jing Yang
Abstract: For insulation, green roof has been widely applied and researched in recent years. The effective thermal conductivity (ETC) of planting soil of green roof plays an important role to insulation. The ETC of six kinds of compound planting soil, usually used in green roof,were measured with different water content. The results show that the ETC of compound planting soils has linear relationship with weight humidity. A sensible, albeit simplified mathematical model, with weight humidity and dry apparent density as variables, was established for the dynamic ETC of compound planting soil. To verify model accuracy, the calculation data of ETC of compound planting soil, which under natural climatic conditions for 2 years, were compared with experimental data, and the results indicate that the model have high accuracy in a wide range of weight humidity. In additional, the ETC proper range of compound planting soil was derived.
2065
Authors: Hui Yan, Jian Qun Yu, Xing Xing Kou
Abstract: This paper presents a new method that use the library function offered by Pro/TOOLKIT and on account of Visual C++ development platform to achieve the recognition of Pro/ENGINEER solid model of mechanical components and extraction of geometry information. Motion attribute is set according to requirements, and analytical mode of three-dimensional discrete element method is built, therefore, Pro/ENGINEER software and the performance analysis software of three-dimensional discrete element method developed autonomously are integrated. A kind of new method and new tool is offered to three-dimensional discrete element method performance analysis and optimization design, and three-dimensional discrete element method belongs to relevant mechanical components contacted and acted with granular materials. What’s more, the correctness and effectiveness of boundary modeling method of three-dimensional discrete element method and developed software are tested and verified through real examples.
2069
Authors: De An Sun, Wen Xiong Huang, Dai Chao Sheng, Haruyuki Yamamoto
Abstract: A practical elastoplastic constitutive model for granular materials is presented. And the model is suitable for description of the material behaviour for a wide range of stresses, including those sufficient to cause particle crushing. With a limited number of model parameters, the model can predict the confining-pressure dependent stress-strain relation and shear strength of granular materials in three-dimensional stresses, especially of variation of shear strength and dilatancy characteristics due to particle crushing under high confining pressure. The model parameters, which have clear physical meanings, can be determined from the results of isotropic compression test and conventional triaxial compression tests. The model performance is demonstrated for triaxial compression tests of a sand for a wide range of the confining-pressure from 0.2MPa to 8.0MPa.
1273
Authors: Lj. Budinski-Petković, M. Petković, Z.M. Jakšić, S.B. Vrhovac
Abstract: We perform numerical simulation of a lattice model for the compaction of a granular material based on the idea of reversible random sequential adsorption. Reversible random sequential adsorption of objects of various shapes on a two−dimensional triangular lattice is studied numerically by means of Monte Carlo simulations. The growth of the coverage ρ(t) above the jamming limit to its steady−state value ρ∞ is described by a pattern ρ (t) = ρ∞ − ρEβ[−(t/τ)β], where Eβ denotes the Mittag−Leffler function of order β ∈ (0, 1). For the first time, the parameter τ is found to decay with the desorption probability P− according to a power law τ = A P− −γ. Exponent γ is the same for all shapes, γ = 1.29 ± 0.01, but parameter A depends only on the order of symmetry axis of the shape. Finally, we present the possible relevance of the model to the compaction of granular objects of various shapes.
355
Authors: Martin Grüner, Marion Merklein
Abstract: The use of high and ultra high strength steels in modern bodies in white raises steadily since the 1980’s. This trend is caused by the consumers’ wish of low fuel consuming cars with an increased passenger’s safety. The processing of these steels brings new challenges e.g. high flow stresses and a low formability at room temperature or high tool loads. These challenges can be resolved by warm forming at temperatures up to 600 °C reducing the flow stresses and increasing formability. For the production of complex parts that can not be produced by deep drawing hydroforming is an appropriate technology which can also help to reduce the number of parts and thus the weight of the body in white. Nowadays typical fluids used for hydroforming are only temperature stable up to about 330 °C so that it is not possible to combine the benefits of warm forming and hydroforming. Media like gases and fluids tend to leakage during the process which can only be avoided by a sealing or high blank holder forces. A new approach is the use of ceramic beads as medium for hydroforming at elevated temperatures. Building up a heatable tool for hydroforming with granular material used as medium makes it necessary to consider thermal conductivity so that there is a need of thick insulation plates. These insulation plates show high elastic deformations affecting the blank holder forces during the forming process. Measurements of the compressibility of these plates and implementation in numerical simulation allow a significant increase of the prediction accuracy of the model. A comparison of real part geometry and numerical results from models with and without consideration of elastic deformation will be given.
707
Authors: Hong Xiang Tang, Xing Zhang, Xi Hua Chu
Abstract: Three different numerical tests, i.e. no rolling test, free rolling test and rolling resistance test, in the framework of discrete element method (DEM) are carried out to simulate the micro-structure development in shear bands. The rotational angles and effective strain in the specimen under different conditions are given out. By contrast, it can be concluded that the development of shear bands in granular material can be simulated well when the rolling resistance is taken into account in DEM.
246
Authors: Bo Zhou, Ji Wei Li, Peng Shuai
Abstract: Abstract. The regular grain orientation of granular materials is a common phenomenon in nature. Based on the research of grain shape effect on mechanical property of granular materials, two kinds of idealized shape grain (kind of long rod and square) assemblies with different grain orientation were studied by simulated biaxial compression test using Discrete Element Method. The significant orientation which can be computed as the mean value of all grain orientation is introduced to represent the orientation regularity of granular materials. In order to study the anisotropy, the mobilized friction angle and volumetric strain of assemblies with different significant orientation were obtained under both vertical and horizontal loading. The results show that the regular orientation of grains influences the movement such as motion and rotation obviously; with the increasing of significant orientation, peak mobilized friction angle of long rod grain assembly gradually increases under horizontal loading, and decreasing under vertical loading.
24
Authors: Alessandro L. Sellerio, Daniele Mari, Gérard Gremaud
Abstract: We investigate the jamming transition observed in vibrated granular systems composed of millimeter size glass beads. When a granular system is submitted to vibrations with decreasing intensity, it evolves in a way similar to glass-forming liquids: from a low viscosity, liquid-like state, it evolves into an amorphous jammed state. This evolution is observed by the means of an immersed oscillator acting as a torsion pendulum in forced mode. The complex susceptibility of the oscillator is measured as a function of the probe forcing frequency and of the vibration intensity. Focusing on the strongly vibrated states, we observe that there are two different dynamic regions. The first is a high fluidization regime, where the internal friction is found to be proportional to the ratio between the pulsation and the vibration intensity: . In this region, the system shows an apparent viscous friction . In the second, low fluidization, regime, we observe a more complex behavior, and the measured internal friction appears to be well described by a relation of the form: . In this second case, the key role is played by a critical breakaway stress, σcr, needed to break the network of chains of forces that form between the grains. Finally, if vibration intensities are still reduced, we also observe that onset of jamming is clearly distinguishable: we observe a sharp increase in the apparent dynamic modulus together with a peak in internal friction. This transition presents important similarities to those observed in glasses, and it leads to the second (low vibrations) regime, where the key role is played by the square root of the vibration intensity.
422
Authors: Darya Sandulyak, Vera Ershova, Anna Sandulyak, Alexander Sandulyak
Abstract: The paper analyses the data on measuring the packaging density γ and porosity ω of the medium-loading of balls with d diameter and the loading tank of D diameter, as well as the compound of balls of diameters d1 and d2d1. The stabilization of γ and ω was observed with D/d≥4-5: γ=0.61-0.63, ω=0.37-0.39, which allows evaluating the medium-loading of the commensurable granules as a conditionally orderly structure with cells, on average close to square-rhombic ones. As to the compound of the granule-balls in the range of d2/d1=1-0.5, judging by the data on γ and ω variance with d2/d1<0.4-0.5 (up to γ=0.85-0.87 and ω=0.13-0.15 with d2/d1→0), the media-loadings of multi-dimensional granules with characteristic γ and ω values can be considered as provisionally ordered structures with corresponding cells. We provide the expression for defining averaged values of the coordination number of the granule.
382
Authors: Maxim Esin, Arcady V. Dyskin, Elena Pasternak
Abstract: Modelling of large-scale deformation patterning in geomaterials is important for predicting instabilities and failures in the Earths crust. Shear band formation and the evolution of the bands is a predominant mechanism of deformation patterning. Independent rotations of separate grains/particles can affect the pattern formation by adding the effect of rotational degrees of freedom to the mechanism of instability. To model this mechanism we use a special experimental technique based on digital image correlation in order to recover both displacement and independent rotation fields in 2D physical models of granular material. In the physical model the particles are represented by smooth steel monodispersed disks with speckles painted on them to enable the rotation reconstruction. During the loading the deformation pattern undergoes stages of shear band formation followed by its dissolution due to re-compaction and particle rearrangement with the subsequent formation of multiple shear bands merging into a single one and the final dissolution. Also, patterns of rotations are observed at an intermediate scale between the scale of the particles and the scale of the shear band.
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