Publication details for Prof Tom McLeishHoyle, David M., Huang, Q., Auhl, D., Hassell, D., Rasmussen, H. K., Skov, A. L., Harlen, O. G., Hassager, O. & McLeish, T. C. B. (2013). Transient overshoot extensional rheology of long-chain branched polyethylenes: Experimental and numerical comparisons between filament stretching and cross-slot flow. Journal of rheology 57(1): 293-313.
- Publication type: Journal Article
- ISSN/ISBN: 0148-6055, 1520-8516
- DOI: 10.1122/1.4767982
- Further publication details on publisher web site
- Durham Research Online (DRO) - may include full text
Author(s) from Durham
This work analyses the high-strain extensional behavior of long-chain branched polyethylenes, employing two novel extensional rheometer devices, the filament stretching rheometer and the cross-slot extensional rheometer. The filament stretching rheometer uses an active feedback loop to control the imposed strain rate on a filament, allowing Hencky strains of around 7 to be reached. The cross-slot extensional rheometer uses optical birefringence patterns to determine the steady-state extensional viscosity from planar stagnation point flow. The two methods probe different strain-rate regimes and in this paper we demonstrate the agreement when the operating regimes overlap and explore the steady-state extensional viscosity in the full strain-rate regime that these two complimentary techniques offer. For long-chain branched materials, the cross-slot birefringence images show a double cusp pattern around the outflow centre line (named W-cusps). Using constitutive modeling of the observed transient overshoot in extension seen in the filament stretching rheometer and using finite element simulations we show that the overshoot explains the W-cusps seen in the cross-slot extensional rheometer, further confirming the agreement between the two experimental techniques.