Compression in the processing of polymer composites 2. Modelling of the viscoelastic compression of resin-impregnated fibre networks

This paper presents a study of the viscoelastic compression of resin-impreg nated fibre cloths. The experiments included a type of plain-weave cloth an d two types of resin, an epoxy behaving approximately as a Newtonian fluid and a polyester following power-law, non-Newtonian behaviour. The experimen tal studies of viscoelastic compression included a review of compression te sts at two different compression speeds, and also compression hysteresis te sts and pressure relaxation tests. The mathematical analysis covered the de velopment of a viscoelastic model in which the total applied pressure durin g compression was split between the pressure to compress the assembly of fi bre cloths and the pressure required for the resin flow through the deforma ble, porous medium. It considers elastic and viscoelastic effects from the fibre medium, and viscous and elastic effects from flowing resin. Regarding the type of resin, it includes modelling of both a Newtonian and a non-New tonian fluid. The model was fitted to the experimental data for wet compres sion for both types of resin and yielded best-fit values for parameters fro m the Carman-Kozeny equation and the non-Newtonian type of Darcy's law, for the plain-weave fabric used. (C) 1999 Elsevier Science Ltd. All rights res erved.