Transient rheological behavior of a long discontinuous fibermelt system

The transient elongational behavior of a highly-aligned 60% fiber volume fraction long-discontinuous-fiber filled poly-ether-ketone-ketone (PEKK) melt system was investigated with a computer controlled extensional rheometer at 370C. Long discontinuous graphite fibers, 7 m in diameter, and PEKK thermoplastic constituted the melt system. Experiments conducted under conditions to approximate controlled strain rate and controlled stress produced +E(t,) and -(t,E) similar to a shear dominated flow of a non-linear viscoelastic fluid. Increasing strain rate resulted in an increasing peak stress and in an increasing ratio between peak stress and plateau stress. Increasing controlled stress level resulted in decreasing elongational viscosity and increasing post-elastic-step strain rate. The ratio of apparent E/PEKK was 3.67x108 to 3.94x1010 for average strain rates from 6.81x10-7 to 1.49x10-3 s-1. A variable taper shear cell analysis provided the range of expected E/, which agreed well at high strain rates with the experimetal data. 1996 Society of Rheology.

Transient rheological behavior of a long discontinuous fibermelt system Academic Article