Edge fracture in non-colloidal suspensions

•An analysis of edge fracture for non-colloidal suspensions is given.•Comparison is made with experiments.•Agreement with experiment is satisfactory. The phenomenon of edge fracture interferes with measurement in cone-plate and parallel plate rheometers. The instability is due to the effect of the second normal stress difference (N2) at the free edge. With non-colloidal suspensions, even in suspensions with Newtonian matrix fluids, N2 is dominant and the flows are more stable than the viscoelastic flows. There are no guidelines for the onset of fracture in these materials. In this Note we discuss the stability of non-colloidal suspensions and suggest that a useful guide to the onset of instability can be made if the ‘flaw’ size at the edge is assumed to be about 10% of the gap size, as found previously.