On the rectilinear flow of a second-order fluid and the role of the second normal stress difference in edge fracture in rheometry (Q1321587)

The authors consider the rectilinear flow of a second-order fluid between two parallel plates and investigate the consequences of two restrictions which arise from the vanishing of the shear stress on a free surface. The free surface has a small semi-circular indentation, and the edge crack in it is almost parallel to the plates. The above mentioned restrictions are: (i) the velocity gradient being normal to the free surface, and (ii) the velocity gradient being parallel to it. It is shown that under the first restriction the cause of initiation of fracture is a tensile normal stress on the free surface. When the crack has developed, it is maintained in an equilibrium position under the second restriction. Furthermore, it is shown that the initiation and arrest of fracture are caused by the second normal stress difference and not by the first normal stress difference. This is a well-written paper with interesting results. Possible extensions of the work are mentioned by the authors.