Rheological characterization of commercial glass mat thermoplastics (GMTs) by squeeze flow testing

Abstract The flow behavior of commercial glass mat thermoplastics (GMTs) has been investigated by isothermal axisymmetric squeeze flow testing between parallel circular plates. Tests have been performed over a range of squeeze rates and the analysis is based on simple power law constitutive equations. A key part of the work is determining the relative contributions of shear and extensional flow to the overall squeezing force response. By developing a variational flow model, based on the upper bound theory, the behavior has been found to be predominantly extensional, with shear effects becoming important at very small plate separations. In addition, a predictive model for the radial pressure distribution during squeezing has been developed, based on fiber suspension rheology. Since fibers are generally long or continuous, treating the material as a statistically homogeneous fluid does not yield accurate results in this respect.