Christian Burtin

Simple modelling of impregnation in pultrusion process of thermoplastic composites

Pultrusion is a continuous process with application in the manufacture of fibre–reinforced composites. This work reports the impregnation process which is one of the major concerns in pultrusion. We set out to develop a model that describes the flow advancement for a thermoplastic matrix when the reinforcements pass through the die. Therefore, the influence of several processing conditions on the impregnation state has been assessed. An analytical model based upon the Darcys law and Stokes equation was applied to describe the progression of the radial flow front through porous medium. In this investigation, a unidirectional fibrous medium is adopted and the injected fluid is considered to be Newtonian and incompressible. Results show that the geometry of the die, pulling velocity and obviously the fibres permeability are the major factors influencing the degree of wetting. This analytical methodology is a useful tool to control the matrix impregnation.

Thermoplastic pultrusion process: Modeling and optimal conditions for fibers impregnation

Pultrusion is a crucial method for continuous production of fiber-reinforced composites. It was developed several years ago for thermosetting polymer matrices, but the challenge is now to extend it to thermoplastic matrices, with a much higher viscosity. In this paper, we propose an analysis of the parameters influencing fiber impregnation in the conditions of this process. A semi-analytical one-dimensional axisymmetric model based on Darcy’s law and Stokes equations is developed to predict the impregnation profile inside the fibrous phase in the case of a natural impregnation governed by capillary forces. Thanks to a dimensional analysis, it enables to quantify the influence of all the material and testing parameters under the assumption of a slow variation of the geometry of the impregnation die. The cases of a straight and conical dies are discussed. For the first case, an exhaustive numerical study enables to define the optimal processing conditions for a perfect impregnation. Those results are shown to be useful tools for finding an optimal pulling velocity and die length for a given fluid/fibers pair. For the second case, we show that section reductions do not improve impregnation.

Investigation of capillary impregnation for permeability prediction of fibrous reinforcements

In thermoplastic pultrusion process, unidirectional glass fibre bundles are very often used as reinforcement. This study was motivated by the industrial requirement to evolve from low viscosity thermoset resin processes to high viscosity thermoplastic polymers. The key parameters to control the impregnation process are the permeability of the fibrous reinforcement and the capillary pressure. The current studys objectives are threefold: (1) study the fibres arrangement by X-ray tomography, (2) determine the longitudinal and transversal permeabilities as well as capillary pressure to use them as input parameters of impregnation process in pultrusion and (3) carry out sensitivity analyses of the permeability measurements to the perturbation of fibre structure. To reach these purposes, two theoretical models were used to determine both axial and transversal tow permeability. The axial impregnation of aligned fibres was described by Washburn equation applied to 1D infiltration into the bundles. The in-plane impregnation was described by Darcys law. The elliptical equation for highly anisotropic medium was resolved. Results show that permeability measurements are subjected to large variations, caused by perturbation of the fibre architecture during experiments. Besides, it was shown that the tensile force applied on fibres during pultrusion has a great effect on impregnation. Indeed, the permeability increases with the applied tension.

Prediction of mechanical property loss in polyamide during immersion in sea water

It is well known that the water absorption in polyamide leads to a large reduction in the mechanical properties of the polymer, which is induced by the plasticization of the amorphous phase. However, predicting such a loss in a marine environment is not straightforward, especially when thick samples are considered. This study presents a modeling study of the water absorption in polyamide 6 based on the free volume theory. Using this modeling coupled with a description of the stress yield changes with Tg, it is possible to predict the long term behavior of thick samples when immersed in sea water. Reliability of the prediction is checked by a comparison with experimental results.