Interplay of edge fracture and shear banding in complex fluids

TL;DR

This paper investigates how edge fracture and shear banding interact in complex fluids through simulations of two models, revealing conditions under which each phenomenon influences the other and modifying previous phase boundary predictions.

Contribution

It provides a detailed simulation-based analysis of the interplay between edge fracture and shear banding in complex fluids, extending and refining earlier theoretical predictions.

Findings

Precursors to edge fracture can induce shear banding.

Shear banding can cause edge fracture, with phase boundaries modified.

Phase diagrams depend on surface tension, wetting angle, and shear rate.

Abstract

We explore theoretically the interplay between shear banding and edge fracture in complex fluids, by performing a detailed simulation study within two constitutive models: the Johnson-Segalman model and the Giesekus model. We consider separately parameter regimes in which the underlying constitutive curve is monotonic and non-monotonic, such that the bulk flow (in the absence of any edge effects) is respectively homogeneous and shear banded. Phase diagrams of the levels of edge disturbance and of bulk (or quasi-bulk) shear banding are mapped as a function of the surface tension of the fluid-air interface, the wetting angle where this interface meets the walls of the flow cell, and the imposed shear rate. In particular, we explore in more detail the basic result recently announced in Hemingway et al. (2018): that precursors to edge fracture can induce quasi-bulk shear banding. We also appraise analytical predictions that shear banding can induce edge fracture, Skorski and Olmsted (2011). Although a study of remarkable early insight, that study made some strong assumptions about the nature of the "base state", which we examine using direct numerical simulation. The basic prediction that shear banding can cause edge fracture remains valid, but with qualitatively modified phase boundaries.