Stress relaxation and reversed flow of low-density polyethylene melts following uniaxial extension

Abstract

SynopsisThe extensional dynamics of two low-density polyethylene melts Lupolen 3020D and Lupolen 1840D, both showing a stress overshoot in start-up of uniaxial extension [Rasmussen, H. K., J. K. Nielsen, A. Bach, and O. Hassager, "Viscosity overshoot in the start-up of uniaxial elongation of low density polyethylene melts," J. Rheol. 49(2), 369-381 (2005)], have been further investigated in stress relaxation and reversed flow. After the overshoot, the stress relaxation has a remarkably faster decrease of the transient stress than when the relaxation is initiated before the overshoot. The measurements from the reversed flow also show that the melts appear less elastic after the overshoot. Multi mode versions of the pom-pom and interchain pressure model fit the data quantitatively up to the stress maximum, but neither model captures the qualitative behavior after the maximum. V C 2012 The Society of Rheology. [http://dx

Modifying the pom-pom model for extensional viscosity overshoots

“…This processing splits the raw data set into two parts, approximation and details (noise), and the former part is then selected to represent the result. It is possible to retrieve the raw data set by adding the noise part to the approximation part; details of wavelet processing and an example of comparison between the raw and the denoised data can be found in Huang et al (2012). The experimental error was not reported in Hoyle et al (2013).…”

“…1 shows the results of the stress relaxation measurements for DOW 150 R at 160 C. The presented data are the denoised data after wavelet processing [Huang et al (2012)]. With the strain rate _ 0 ¼ 0:1s À1 , the stress relaxation measurement at 0 ¼ 4:5 (after the overshoot-AO case) shows a remarkably faster decrease in the tensile stress decay coefficient compared with the measurement at 0 ¼ 3 (before the overshoot-BO case), which is in agreement with the observations by Huang et al (2012) for another two LDPE melts. At this rate, strong crossing between the AO and BO curves ensues.…”

“…The nonlinear rheology in extensional flow has been reported by Hoyle et al (2013) using three different rheometers including the FSR [Bach et al (2003)]. In Hoyle et al (2013),the transient stress of DOW 150 R from the FSR was measured two to three times for each stretching rate, and the reported data are the denoised data after wavelet processing [Huang et al (2012)]. This processing splits the raw data set into two parts, approximation and details (noise), and the former part is then selected to represent the result.…”

“…Such measurements for LDPE melts [Huang et al (2012)] imply that the stress relaxes faster when the flow is ceased after the overshoot (AO case) than before the overshoot (BO case).…”

Uncertainty Analysis of 2d Vector Fields Through the Helmholtz-Hodge Decomposition

“…In some applications like blow molding and fiber spinning, to verify that extensional flow is the dominant type of deformation is important (Huang et al, 2013). …”