Author(s): Petrie CJS,
Abstract: A proposal has been made by Ferguson and Hudson that three-dimensional representation of extensional flow data can be used to resolve apparent disagreements among the results from a variety of extensional flow experiments. This paper carries out a theoretical investigation of the procedure, which involves plotting a transient extensional viscosity against strain and time. We then seek to draw some conclusions about the validity and limitations of the approach. The method does not work for purely viscous non-Newtonian liquids nor for simple (co-rotational and upper convected) Maxwell models. However the failure of results to lie close to a unique surface (for any particular material) is most marked in situations where our theoretical models are least reliable. More work, both experimental and theoretical, is required.