Rheological model for the forming of fabric-reinforced thermoplastic sheets

The paper investigates the suitability of the idealized fibre-reinforced fluid (IFRF) model for the thermoforming of fabric-reinforced thermoplastic sheets, and a strategy is proposed for determining the materials parameters required to characterize the sheet theological behaviour. The IFRF theory for a viscous fluid with two inextensible directions is developed for modelling fabric sheets and specific forms of the constitutive equation are derived. Some simple flows are analysed and it is shown that in throughthickness shear flows, as for example in a torsion rheometer experiment, the fabric angle ϖ remains constant, whereas in in-plane flows ϖ is a function of the strain rate. Trellis deformations are investigated by considering the in-plane stretching flow of a fabric with fibres inclined to the load direction. The torsion rheometer test is analysed for a fabric pre-deformed to a fabric angle ϖ. In this case, tests on rectangular specimens with different aspect ratios and fabric angles are proposed which enable the three viscosities in the model to be determined.