An in situ investigation of the draw resonance phenomenon in film casting of a polypropylene melt
An in situ investigation of the draw resonance phenomenon in film casting of a polypropylene melt
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DOI：
10.1016/j.jnnfm.2012.02.006
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发表时间：
2012-04-01
影响因子：
3.1
通讯作者：
Muenstedt, Helmut
中科院分区：
文献类型：
--
作者：
Burghelea, Teodor I.;Griess, Hans Juergen;Muenstedt, Helmut
对聚丙烯薄膜流延过程的稳定性进行了实验研究。通过结合原位测量的流延薄膜的宽度和数字粒子图像测速（DPIV）测量的聚合物膜内的速度分布，几个现在的制度被确定：稳定，振荡和混乱。测量的速度分布沿着和整个挤出薄膜对应于每个拉伸制度。本文用轴向速度分量的高轴向梯度的“V”形区域的出现解释了在混沌拉伸状态下观察到的薄膜边缘的间歇性物理破裂，该区域表明拉伸应力的高度不均匀分布。通过测量薄膜宽度和速度的波动统计，我们得到了一个连续的在到达混沌区之前获得的涨落数据可以用定态的Landau-Ginsburg方程拟合。观察到一个稳定的极限环在分叉的发病确定它作为一个超临界Hopf分叉。实验发现的缩放的发病率和振幅的分叉与韦森伯格数表明，弹性不稳定的绘图过程。这可以用材料在剪切和拉伸两种情况下的减薄行为来解释。对膜宽和点速度波动的谱分析提供了对分叉点以外激发的谐波的定量描述。混沌状态的过渡是伴随着一个重大的重组的功率谱与一个稳定的极限环的周期加倍分叉。(C)2012爱思唯尔有限公司版权所有。
An experimental investigation of the stability of the casting process of a polypropylene film is presented. By combined in situ measurements of the width of the cast film and Digital Particle Image Velocimetry (DPIV) measurements of the velocity distributions within the polymer film, several now regimes are identified: stable, oscillatory and chaotic. Measurements of the velocity distribution along and across the extruded film corresponding to each drawing regime are presented. The intermittent physical rupture of the film's edges observed within the chaotic drawing regime is explained by the emergence of a "V-shaped" region of high axial gradients of the axial velocity component which indicates a highly inhomogeneous distribution of tensile stresses.By measurements of the statistics of the fluctuations of both the film's width and velocity a continuous (second order) imperfect bifurcation towards oscillatory states is found. The fluctuation data acquired before the chaotic regime is reached can be fitted by the stationary Landau-Ginsburg equation. The observation of a stable limit cycle at the onset of the bifurcation identifies it as a supercritical Hopf bifurcation. The experimentally found scaling of the onset and amplitude of the bifurcation with the Weissenberg number indicates that elasticity destabilizes the drawing process. This can be explained by the thinning behavior of the material in both shear and extension.The spectral analysis of the fluctuations of both film's width and point-wise velocity provides a quantitative description of the harmonics excited beyond the bifurcation point. The transition to chaotic states is accompanied by a major reorganization of the power spectra consistent with a period doubling bifurcation of a stable limit cycle. (C) 2012 Elsevier B.V. All rights reserved.