Analysis of the dynamic radial compaction of granular media

The previously developed continual approximation is used to analyze the radial axisymmetric compaction of a granular medium in the presence of a rigid undeformable rod on the symmetry axis. It is shown that, during pulsed loading, high densities close to those corresponding to the nonporous state can be attained due to inertia effects. The influence of the initial radial dimensions of the rod-powder-medium system on the compaction process is analyzed. The problem is found to be scale invariant under various constraints imposed on the ratio of the characteristic dimensions. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 6, pp. 181–189, November–December, 2008     

DEM simulations of die filling during pharmaceutical tabletting

The flow behaviour of powders from a stationary shoe into a moving die, which mimics the die filling process in a rotary tablet press, was analysed using a discrete element method （DEM）, in which 2D irregular shaped particles were considered. The influence of the particle shape, size and size distribution, the number of particles used in the simulation, the initial height of powder bed in the shoe, and the filling speed on the average mass flow rate and the critical filling speed （the highest speed at which the die can be completely filled） were explored. It has been found that a maximum flow rate is obtained at the critical filling speed for all systems investigated and poly-disperse systems have higher mass flow rates and higher critical filling speeds than mono-disperse systems. In addition, the powder with particles which can tessellate generally has a lower filling rate and a lower critical titling speed.     

Rate of creation of the contacts between grains in a loose array of particles submitted to an uniaxial pressure

Macroscopic resistivity measurements have been performed on TiC/Al₂O₃ random mixtures submitted to uniaxial compression (0-95 kN). Such a random mixture exhibits an insulator-conductor transition which appears at increasing force while decreasing the conductive composition of the TiC/Al₂O₃ mixture. It is demonstrated that the conductivity behavior may be understood in the framework of a site percolation model. Finally, the rate of creation of the contacts between conductive grains is extracted from the macroscopic resistivity measurements. Received 6 December 2000 and Received in final form 30 March 2001     

Robust propagation direction of stresses in a minimal granular packing

By employing the adaptive network simulation method, we demonstrate that the ensemble-averaged stress caused by a local force for packings of frictionless rigid beads is concentrated along rays whose slope is consistent with unity: forces propagate along lines at 45 degrees to the horizontal or vertical. This slope is shown to be independent of polydispersity or the degree to which the system is sheared. Further confirmation of this result comes from fitting the components of the stress tensor to the null stress “constitutive equation”. The magnitude of the response is also shown to fall off with the -1/2 power of distance. We argue that our findings are a natural consequence of a system that preserves its volume under small perturbations. Received 30 April 2001 and Received in final form 16 August 2001     

Particle morphology and packing effects on the shock loading of powders

A physically based model for the shock Hugoniot of a powdered material is described which allows separate identification of the cold and thermal contributions to pressure and specific internal energy. Special features of this model are provision for the effects of porosity on the stress state and an empirically determined cold loading contribution to pressure. The model was tested against published Hugoniot data for iron and gave excellent agreement for shock pressures ranging from low to high values.This shock Hugoniot was used to explore the shocked state of 4 samples of iron powder derived from commercially available material. The purpose of this study was to investigate the effect of powder particle characteristics and initial starting densities on the shocked state.The powder samples investigated had a range of morphologies and sizes. Powders with either a large shape factor or high internal friction, as determined in shear cell experiments, exhibited a higher stiffness in the cold loading curve. In the shocked state, this translated into a higher cold component of pressure and energy than found in the other powders.The effect of initial powder density was studied by applying the Hugoniot model to two impact initiated shock loadings, one for a stainless steel flyer impacting at 0.5 km/s and one at the higher velocity of 2.0 km/s. Both were applied to iron powder targets preloaded to a range of initial densities. For a given impact event, the proportion of shock energy in the thermal mode was found to decrease with increasing initial density. This decrease was more pronounced at higher shock strengths. As a result of the decreasing component of thermal energy with higher initial density, there was a reduction in the continuum temperature behind the shock. However, the corresponding increase in the component of cold energy with the falling relative contribution from the thermal energy lead to increasing density behind the shock suggesting that there is a trade off in terms of temperature and density achievable with a given impact event.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

岩土介质中局部化变形研究的一些新进展

岩土中的剪切带产生通常是断裂和失稳的前兆, 常引起滑坡等地 质灾害, 对油气或水合物等矿藏的开采容易导致压实带形成. 压实带的产生使岩土孔隙减小, 颗粒破碎, 从而导致沉陷、对油气的挤压等.本文重点对剪切带的宽度和压实带的研究现状作综述, 阐述在该问题的研究上从微观 观测到宏观表述的重要性. 通过分析, 认为还有如下问题值得研究: 怎样 准确得出局部化变形带的宽度和方向?局部化变形带形成后孔隙水和油气的渗流会发生什么 变化?颗粒层次的微结构特性是通过什么方式影响宏观表现的等等.     

某填方土基粉土冲击压实处理试验研究

冲击压实是一种新型的土体处理方法,它具有效率高、综合成本低等优点,其影响深度特别符合公路、场道土基对有效加固深度的要求。本文以某大型填方土基工程为例,介绍了冲击压实技术在填方土基中的应用。在对粉土填料性状分析试验的基础上进行冲压施工,同时进行了沉降观测、压实度试验、载荷试验、回弹模量试验,通过试验结果分析确定了合理的施工参数,并根据检测取得了良好的冲击压实效果。以此次试验确定的施工参数在该工程取得了良好的压密效果和经济效益。     

UNDERSTANDING THE MECHANICAL PROPERTIES OF SINGLE MICRO-PARTICLES AND THEIR COMPACTION BEHAVIOUR

The compaction of particulate materials to form tablets is increasingly employed as a final dosage form for functional products due to its simplicity and low cost. However, the functionality of some products may be impaired due to the high compression pressures required. The general aim of the current study is to understand the relationship between the mechanical properties of single feed particles （〈 100μm） and their compaction behaviour in order to produce tablets at low compression pressure with acceptable strength. The materials studied were pharmaceutical excipients, comprising three enteric polymer particles and three different powders in the form of agglomerates. The mechanical properties of the individual particles or agglomerates were determined by a micromanipulation technique. The samples were also compacted in cylindrical tableting dies. It was observed that there was a strong correlation between the forces required to cause the fracture of the single particles and those derived from the compaction measurements as determined using an existing analysis.     

The effect of roller pressure and share of plant matter in mulching soil cultivation on its density and water content

The aim of this study was to assess the impact of the roller load (with cultivating tools) and doses of plant matter (straw and charlock) mixed with soil on the air and humidity conditions of such soil. The innovation of the research consisted in abandoning the use of Kopecky’s cylinders: the bulk density of mulched soil was determined by measuring its mass and volume, which it obtained in vases before and after the roller work. Capillary infiltration was also carried out for soil in vases.Variable research factors characterizing the roller working conditions in the mulching tillage, were: source/type of plant material cut into 10 cm chopped straw, its share in soil, three ranges of soil water content and vertical unit load on the roller.Increasing the straw dose to 30 Mg^.ha⁻¹ reduces the bulk density from 1.17 to 0.76 g^.cm⁻³, while increasing the dose of charlock to 60 Mg^.ha⁻¹ under these conditions, it reduces the density to 1.03 g^.cm⁻³. At the same time, humidity conditions change: volumetric water content decreases in case of straw from 13.9% to 8.5% and increases in case of charlock to 17.4%. Changes occur also in case of full water capacity.