Shear Fracture in Cone‐Plate Rheometry
Shear Fracture in Cone‐Plate Rheometry
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锥板流变测定中的剪切断裂
DOI：
10.1122/1.549698
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发表时间：
1983
影响因子：
3.3
通讯作者：
M. Keentok
中科院分区：
文献类型：
--
作者：
R. Tanner;M. Keentok
当在锥形板和平行板流变仪中受到中等剪切速率时，粘弹性样品倾向于在样品边缘断裂，从而阻止在高剪切速率下测量粘度和法向应力。Hutton用临界弹性应变能解释了这种行为，我们提供了一种基于断裂力学的替代解释。由图可知，当|N2|>2Γ/3a时发生裂缝，其中N2为第二法向应力差，Γ为表面张力系数，a为裂缝尺寸。本文给出的实验数据表明，该方程正确地预测了剪切断裂的发生及其发生的剪切速率。在高剪切速率下，由于离心力的作用，牛顿液体和一些粘弹性液体从锥板和平行板流变仪中喷射出来。对于牛顿液体，简单地考虑样品边缘的离心力和表面张力。
When subject to moderate shear rates in a cone‐plate and parallel plate rheometer, viscoelastic samples tend to fracture at the edge of the sample thus preventing the measurement of viscosity and normal stresses at high shear rates. An explanation of this behavior has been given in terms of a critical elastic strain energy by Hutton and we offer an alternative explanation based on fracture mechanics. It is shown here that fracture occurs if |N2|>2Γ/3a, where N2 is the second normal stress difference, Γ is the surface tension coefficient, and a is the size of the fracture. The experimental data presented here show that this equation correctly predicts the occurrence of shear fracture and also the shear rate at which it occurs. At high shear rates, Newtonian liquids and some viscoelastic liquids are ejected from the cone‐plate and parallel plate rheometer due to the effect of centrifugal forces. For a Newtonian liquid a simple consideration of the centrifugal and surface tension forces at the sample edge pr...