The Multiaxial Stretching of Polypropylene at High Temperatures

It has recently been shown that the crosslink-sliplink model of Ball, Doi Edwards and Warner has the property of predicting necking of the polymer network, and that it can be used to model the high-temperature drawing behaviour of polypropylene. The main features of the polymer behaviour - the onset of necking, the existence of a natural draw ratio and strain hardening - are inherent properties of the theory. In this paper we introduce a modification of the model which allows for more accurate representation of observed stress-strain curves. The modified model is incorporated into a finite element package and applied to uniaxial necking and the drawing of a hollow tube over a conical mandrel. Good predictions of shapes and drawing forces are obtained.