NUMERICAL SIMULATIONS OF ANNULAR EXTRUDATE SWELL OF POLYMER MELTS

Numerical viscoelastic simulations were carried out using a K-BKZ type of separable integral constitutive equation. Both reversible and irre versible models were tried for several types of damping functions to c alculate the annular extrudate behavior of high-density polyethylene ( HDPE). There are two aims in this study; first, to clarify the propert ies of these dumping functions, and second, to investigate the influen ce of rheological characteristics on annular extrudate swell. In these numerical simulations, relaxation spectrum and shear viscosity were f ixed, and the other characteristics were varied. The reversional respo nse of the damping function mainly has an effect on the magnitude of t he area swell even if the die is straight. The irreversible model expr esses the experimental results of annular extrudate swell better than the reversible model. The accurate fitting of N1 by the damping model is important for predicting it. The magnitude of N1 predicted from the Wagner exponential model is lower than that of the PSM model, and the area swell shows the same tendency as N1. A modified PSM model that a llows the N1 curve to shift can fit the magnitude of area swell. The r elationship between the diameter and thickness of the extrudate depend s on N2/N1, and it was estimated by simple linear elasticity of solids . The time-dependent viscosity varies with the type of damping functio n, and it influences the time-dependent swell.