Interplay of edge fracture and shear banding in complex fluids

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 nonmonotonic, 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 quasibulk) 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 by Hemingway and Fielding [Phys. Rev. Lett. 120, 138002 (2018)]: that precursors to edge fracture can induce quasibulk shear banding. We also appraise analytical predictions that shear banding can induce edge fracture [S. Skorski and P. D. Olmsted, J. Rheol., 55, 1219 (2011)]. Although a study of remarkable early insight, Skorski and Olmsted [J. Rheol., 55, 1219 (2011)] 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.