Criteria for extensional necking instability in complex fluids and soft solids. Part II imposed tensile stress and force protocols
Criteria for extensional necking instability in complex fluids and soft solids. Part II imposed tensile stress and force protocols
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复杂流体和软固体中拉伸颈缩不稳定性的标准。
DOI：
10.1122/1.4965037
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
S. Fielding
中科院分区：
文献类型：
--
作者：
D. M. Hoyle;S. Fielding
通过线性稳定性分析和非线性模拟，研究了在恒定应力和力作用下，复杂流体或软固体细丝受单向拉伸时的颈缩问题。我们证明颈缩是一种流动不稳定性，这是一个不可避免的后果，基本上任何粘弹性材料的本构行为。我们推导出的颈缩，可以报告的实验测量的材料功能的形状的特征签名方面的发病标准，因此，应该普遍适用于所有材料。为了确认他们的一般性，我们显示他们在六个本构模型举行数值。在恒定应力的条件下，我们发现两个不同的动力学制度作为时间的函数。在第一个政权的应变率迅速达到规定的流体的基本均匀的本构曲线的值，在给定的应力。在这第一个政权，没有明显的颈缩出现。第二个制度，然后englomeration中的均匀流不稳定，形成一个颈部。这种颈缩不稳定性可以通过两种不同的模式发生。第一模式是相对温和的，并出现在本构曲线的斜率为正的任何制度。它具有由本构曲线的斜率的倒数设定的每累积应变单位的颈缩速率。当张力的一个仔细定义的“弹性导数”首先作为时间的函数向下倾斜时，第二种模式开始。我们讨论的方式，这些模式的不稳定性表现在纠缠的聚合物流体，展示了四个不同的制度的颈缩行为作为应力的函数。在恒定施加力的条件下，典型地，流动扫过所讨论的流体的基本本构曲线，在该曲线正倾斜的任何状态下不稳定地颈缩。
We study the necking of a filament of complex fluid or soft solid subject to uniaxial tensile stretching, under conditions of constant imposed stress and force, by means of linear stability analysis and nonlinear simulations. We demonstrate necking to be a flow instability that is an unavoidable consequence of the constitutive behaviour of essentially any viscoelastic material. We derive criteria for the onset of necking that can be reported in terms of characteristic signatures in the shapes of the experimentally measured material functions, and that should therefore apply universally to all materials. To confirm their generality, we show them to hold numerically in six constitutive models. Under conditions of constant stress, we find two distinct dynamical regimes as a function of time. In the first regime the strain rate quickly attains a value prescribed by the fluid's underlying homogeneous constitutive curve, at the given stress. In this first regime, no appreciable necking arises. A second regime then ensues in which the homogeneous flow destabilises to form a neck. This necking instability can occur via two distinct modes. The first mode is relatively gentle and arises in any regime where the slope of the constitutive curve is positive. It has a rate of necking per accumulated strain unit set by the inverse of the slope of the constitutive curve. The second mode sets in when a carefully defined `elastic derivative' of the tensile force first slopes down as a function of the time. We discuss the way in which these modes of instability manifest themselves in entangled polymeric fluids, demonstrating four distinct regimes of necking behaviour as a function of stress. Under conditions of constant imposed force, typically the flow sweeps up the underlying constitutive curve of the fluid in question, with instability to necking in any regime where that curve is positively sloping.
影响因子：
16.6
作者：
Smith, M. I.;Besseling, R.;Bertola, V.
通讯作者：
Bertola, V.
聚合物熔体的恒力拉伸流动：实验和建模
影响因子：
3.3
作者：
M.H. Wagner;V.H. Rolón-Garrido
通讯作者：
V.H. Rolón-Garrido