The use of extensional rheometry to establish operating parameters for stretching processes

Abstract

This work describes a method of determining the limits of uniform extensibility, in terms of failure and fracture, from rheological tests in extensional flow. The limit of uniform stretching can be expressed in terms of the Weissenberg number for the process, as demonstrated by data for three chemically diverse polymers, polystyrene, poly(methyl methacrylate), and a polyester. The BKZ‐K model can be used to predict necking failure, as determined by the Considére criterion, and an empirical correlation can be derived for fracture.

Influence of long-chain branching on the rheological behavior of polyethylene in shear and extensional flow

“…7. As can be seen, despite a relatively large experimental scatter, the general trend is of increasing values for the strain at maximum axial force, with increasing We, which is in general agreement with previous observations by other authors [32,35,36]. However, there seems to be a lower dependency of strain at failure on We for PE-D, i.e., the copolymer with the broader dispersion of molecular weight.…”

“…One criterion for failure (necking) that was first applied and used for solids is the Considère criterion [34]. This criterion predicts the beginning of necking to occur when a maximum is observed in the force-extension curve, and other authors have used this simple criterion to discuss failure for different stretching conditions (see, for example, Pearson and Connelly [35] and McKinley and Hassager [36]). However, Joshi and Denn [33] recently showed that this criterion is not directly applicable when there is a substantial viscous component to the flow, and that its applicability is likely to be limited only to situations in which high Weissenberg numbers are found.…”

On modes and criteria of ABS melt failure in extension

“…This also occurred due to the lower elongational viscosity as investigated by Yao et al (1998Yao et al ( , 2000. However, our results of the temperature and strain rate dependence of Hencky strains at ductile failure do not agree with the experimental results of White (1977, 1978) and the simulation of Hassager et al (1998), but are consistent with the experimental and simulation results of Pearson and Connelly (1982).…”

Time dependent effects on the rupture of molten linear polymers in extension

“…On the other hand, the other materials referred above did not show any marked dependence with the strain rate. Pearson and Connelly [11] have also performed experiments in extension with PS, PMMA and POCH (a co-polyester), and found that the Hencky strain to break was also almost independent of strain rate.…”