Analysis of ball indentation on cohesive powder beds using distinct element modelling
Analysis of ball indentation on cohesive powder beds using distinct element modelling
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DOI：
10.1016/j.powtec.2012.08.017
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发表时间：
2013
影响因子：
5.2
通讯作者：
M. Pasha;C. Hare;A. Hassanpour;M. Ghadiri
中科院分区：
文献类型：
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作者：
M. Pasha;C. Hare;A. Hassanpour;M. Ghadiri
粘性粉末的流动性表征通常是粉末工艺可靠设计和一致操作所需的。这通常通过无侧限压缩试验或剪切试验来实现，但是这些技术需要相对大量的粉末并且限于大的预固结载荷。在许多工业情况下，必须处理和加工少量粉末，例如在胶囊中填充和定量少量粉末以及在干粉吸入器中分散。在其他情况下，测试粉末的可用性可能是一个限制性问题。Hassanpour和Ghadiri（2007年）已经表明，在某些情况下，用钝头压头在粘性粉末床上进行压痕可以测量与流动性相关的粉末流动阻力。然而，在压头尺寸和穿透深度方面的操作窗口的规格尚未得到充分分析。在目前的工作中，球压痕过程进行了分析，使用离散元法（DEM）的数值模拟。组件的流动阻力，通常称为硬度，是针对一系列样品量和操作变量进行评估的。它示出，为了实现可靠的硬度测量，需要20个颗粒直径的最小床高度。压头尺寸的灵敏度分析表明，直径小于16个颗粒直径的小压头在粉末流动应力测量中表现出波动，这并不代表剪切变形。较大的压头提供稳定的流动应力值，受到最低样品标准被满足。最大压头尺寸受模具尺寸限制。如果压头尺寸太接近模具尺寸，则壁提供限制并增加测量的硬度。
The characterisation of cohesive powders for flowability is often required for reliable design and consistent operation of powder processes. This is commonly achieved by the unconfined compression test or shear test, but these techniques require a relatively large amount of powder and are limited to large pre-consolidation loads. There are a number of industrial cases where small amounts of powders have to be handled and processed, such as filling and dosing of small quantities of powder in capsules and dispersion in dry powder inhalers. In other cases, the availability of testing powders could be a limiting issue. It has been shown by Hassanpour and Ghadiri (2007) that under certain circumstances, indentation on a cohesive powder bed by a blunt indenter can give a measure of the resistance to powder flow which is related to flowability. However, the specification of the operation window in terms of indenter size and penetration depth has yet to be fully analysed. In the present work, the ball indentation process is analysed by numerical simulations using the Distinct Element Method (DEM). The flow resistance of the assembly, commonly termed hardness, is evaluated for a range of sample quantities and operation variables. It is shown that a minimum bed height of 20 particle diameters is required in order to achieve reliable measurements of hardness. A sensitivity analysis of indenter size reveals that small indenters with diameters less than 16 particle diameters exhibit fluctuations in powder flow stress measurements, which do not represent shear deformation. Larger indenters provide stable values for flow stress, subjected to the minimum sample criteria being met. The maximum indenter size is limited by the die size. If the indenter size is too close to the die size the walls provide confinement and increase the measured hardness.