Extensional and shearing flow of a glass-mat-reinforced thermoplastics (GMT) material as a non-Newtonian viscous fluid

The isothermal squeezing flow of glass-mat-reinforced thermoplastics (GMT) has previously been confirmed to behave anisotropically, and a transversely isotropic Newtonian fluid model was applied to fit the experimental data. The model was used to calculate the extensional viscosities, and was compared to the viscosity calculated from an isotropic model, showing a difference up to 20% between the two models. In this work the GMT squeezing flow has been modelled as a transversely isotropic power-law fluid. The equations of motion were solved for the three power law viscosity parameters, which were found from the geometrical shape of the elliptically deformed specimens, the applied force and the strain rates in the three directions. Good agreement between the experimental applied stress and the predicted curves from the model was achieved. The influence of shear on the compression moulding was also investigated with a special model being developed for the case of non-lubricated mould-plate surfaces. An expression for the shear force at the walls has been derived. The GMT compression moulding was modelled as a combination of extensional and shearing flows. Non-Newtonian anisotropic extensional and shear viscosities were determined for the GMT isothermal compression moulding. (C) 1999 Elsevier Science Ltd. All rights reserved.