Rheology of glass mat thermoplastics and sheet moulding compounds

The rheological behaviour of glass mat thermoplastics and sheet moulding co mpounds has been investigated by isothermal axisymmetric squeeze flow betwe en circular plates. Squeezing force and plate separation, as well as radial pressure distribution, were measured continuously throughout the test for a wide range of rates. The analysis is based on power law constitutive equa tions. A key parr. of the work is the determination of the relative contrib utions of shear and extensional flow to the overall squeezing force respons e. A variational approach has been adopted, which predicts predominantly ex tensional flow behaviour, with shear effects becoming important at small pl ate separations. A predictive model, based on fibre suspension rheology for the radial pressure distribution during squeezing has also been developed, which agrees well with the experimental results. (C) 1998 The Institute of Materials.