The dynamic strength of partially saturated powder compacts: the effect of liquid properties
The dynamic strength of partially saturated powder compacts: the effect of liquid properties
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DOI：
10.1016/s0032-5910(02)00118-3
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发表时间：
2002-10-16
影响因子：
5.2
通讯作者：
Page, NW
中科院分区：
文献类型：
--
作者：
Iveson, SM;Beathe, JA;Page, NW
在 0.01 至 150 mm/s 的变形速度下测量部分饱和颗粒的流动应力。这些颗粒直径为 20 毫米，高 25 毫米，由表面平均粒径 d(p) 为 35 克的玻璃 ballotini 制成。水、甘油和一系列硅油被用作液体粘合剂，其粘度μ和表面张力γ分别为0.001至60 Pa(.)s和0.025至0.072 N/m。结果发现，存在一个临界应变率（与粘合剂相关），低于该临界应变率时，峰值流动应力 sigma(pk) 与应变率 epsilon 无关。高于该临界应变率，流动应力随着应变率的增加而增加。当以两个无量纲组绘制时，结果折叠成一条曲线，其形式为：Str* = k(1) + k(2)Ca(n)，其中 Str*=sigma(pk)d(p)/gammacostheta 是无量纲峰值流动应力，Ca=muepsilond(p)/gammacostheta 是无量纲毛细管数，即粘性力与毛细管力的比率。 theta 是接触角（在本工作中假设为零）。参数的最佳拟合值为：k(1)=5.3+/-0.4、k(2)=280+/-40和n=0.58+/-0.04。这一结果表明，粘性力在低应变率下可以忽略不计，但在高应变率下变得占主导地位。 k(1) 与颗粒的静态峰值压缩强度有关，k(2) 确定粘性效应变得显着的临界 Ca，n 给出粘性力对应变率的幂律依赖性。这项工作对于造粒研究具有重要意义，因为它强调了这样一个事实，即在伪静态条件下测量的强度可能无法代表（甚至定性）材料在商业造粒机中遇到的较高应变率下的表现。(C) 2002 Elsevier Science B.V. 保留所有权利。
The flow stress of partially saturated pellets was measured at deformation velocities varying from 0.01 to 150 mm/s. The pellets, 20 mm in diameter and 25 mm high, were made with glass ballotini of a surface mean particle size, d(p), of 35 gm. Water, glycerol and a series of silicone oils were used as the liquid binder, covering viscosities, mu, and surface tensions, gamma, ranging from 0.001 to 60 Pa(.)s and 0.025 to 0.072 N/m, respectively. It was found that there was a critical strain rate (which was binder dependent) below which the peak flow stress, sigma(pk), was independent of the strain rate, epsilon. Above this critical strain rate, the flow stress increased with increasing strain rate. When plotted in terms of two dimensionless groups, the results collapsed onto one curve of the form:Str* = k(1) + k(2)Ca(n)where Str*=sigma(pk)d(p)/gammacostheta is the dimensionless peak flow stress and Ca=muepsilond(p)/gammacostheta is the dimensionless capillary number, the ratio of viscous to capillary forces. theta is the contact angle (assumed zero in this work). The best fit values of the parameters were: k(1)=5.3+/-0.4, k(2)=280+/-40 and n=0.58+/-0.04. This result suggests that viscous forces are negligible at low strain rates, but become dominant at high strain rates. k(1) is related to the static peak compressive strength of the pellets, k(2) determines the critical Ca at which viscous effects become significant and n gives the power law dependence of viscous forces on the strain rate. This work is significant for granulation research since it highlights the fact that strengths measured under pseudo-static conditions may not be representative, even qualitatively, of how materials behave at the higher strain rates encountered in commercial granulators.(C) 2002 Elsevier Science B.V. All rights reserved.