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

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, its 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.

Full article: Guan et al, Extreme Mechanics Letters, 2022 https://doi.org/10.1016/j.eml.2022.101784