Paper Number
IN10 

Session
Flow-induced Instabilities in Non-Newtonian Fluids

Title
Viscoelastic creasing: Free-surface instability of a viscoelastic liquid under compression

Presentation Date and Time
October 12, 2022 (Wednesday) 10:50

Track / Room
Track 5 / Sheraton 2

Authors (Click on name to view author profile)

  1. Guan, Xianheng (University of Pittsburgh, Mechanical Engineering and Materials Science)
  2. Reddipalli, Likhitha (Sastra University, Chemical Engineering Dept)
  3. Butler, Dylan (University of Pittsburgh)
  4. Liu, Qihan (University of Pittsburgh, Mechanical Engineering and Materials Science)
  5. Velankar, Sachin (University of Pittsburgh, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Xianheng Guan1, Likhitha Reddipalli2, Dylan Butler3, Qihan Liu1 and Sachin Velankar3
1Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261; 2Chemical Engineering Dept, Sastra University, Thanjavur, India; 3Chemical Engineering, University of Pittsburgh, Pittsburgh, PA 15261

Speaker / Presenter 
Velankar, Sachin

Keywords
experimental methods; theoretical methods; flow-induced instabilities; polymer melts

Text of Abstract
It has been known for many decades that when the free surface of an elastic material such as a block of rubber experiences severe compression, it surface develops sharp cusp-like creases. We show that a viscoelastic liquid undergoes a similar, but rate-dependent, surface-creasing instability. Experiments on a well-entangled molten polymer compressed at a controlled rate show that the strain required for creasing increases as rate decreases. A model is developed wherein the creasing criterion known previously for neo-Hookean elastic solids is applied to the elastic portion of the deformation of a viscoelastic liquid. Using the upper-convected Maxwell model, we derive an analytical criterion for viscoelastic creasing which is in good agreement with experiments. It predicts that the strain for creasing increases with decreasing Weissenberg number, and creasing is not possible below a critical Weissenberg number.