3-DIMENSIONAL PRESENTATION OF EXTENSIONAL FLOW DATA

A proposal has been made by Ferguson and Hudson (fur. Polym. J., 29 (1 993) 141-147; J. Non-Newtonian Fluid Mech., 52 (1994) 121-135) that th ree-dimensional representation of extensional flow data can be used to resolve apparent disagreements among the results from a variety of ex tensional flow experiments. A theoretical investigation of the procedu re, which involves plotting a transient extensional viscosity against strain and time is carried out in this paper. We then seek to draw som e conclusions about the validity and limitations of the approach. The method does not work for purely viscous non-newtonian liquids or for s imple (co-rotational and upper convected) Maxwell models. However, the failure of results to lie close to a unique surface (for any particul ar material) is most marked in situations where our theoretical models are least reliable. More work, both experimental and theoretical, is required. (C) 1997 Elsevier Science B.V.