Squeeze flow characterisation of thermoplastic polymer

Abstract

New manufacturing concepts developed by the CRC-ACS involve co-curing a thermoplastic polymer layer onto the surface of a composite component. The layer can be reshaped to alter the dimensions of the laminate locally. A major physical phenomenon involved in these uses is squeeze flow of the thermoplastic polymer. In the present work, the squeeze flow of a selected thermoplastic at high temperature and under given pressure was studied. A power-law model for viscosity variation with shear rate was assumed to describe the non-Newtonian behaviour of the thermoplastic at high temperatures. Based on the viscosity model, a fluid mechanics model was derived for the squeeze flow between approaching parallel plates of infinite length. The model relates the plate approaching speed to the applied pressure, thermoplastic geometry (both thickness and width) and power-law viscosity model parameters. An experimental method and data analysis procedure were developed to determine the parameters of the power-law model that describes the viscosity of the thermoplastic material. Tests were conducted under isothermal conditions by squeezing composite laminates with integrated thermoplastic films. The transient thickness of the thermoplastic film was continuously measured and used to calculate the power-law model parameters for each test. A temperature range of 180–200 °C was investigated to establish the dependence of the power-law model parameters upon temperature. Using the squeeze flow model, and experimentally determined power-law viscosity model parameters, the effect of various process conditions on the thermoplastic thickness was investigated. Predictions were found to be valid for situations where the shear rate range matched that achieved during the power-law viscosity model parameters tests.