Distributed internal strain measurement of the fluid-solid state coefficients of thermal expansion below the glass transition temperature during a composite manufacturing process

Abstract

The total distributed strain produced during a vacuum-assisted resin infusion moulding composite manufacture process is measured in real time by using optical fibre sensors embedded in three different layers of a thin 5-harness satin weave flat plate cured with low-viscosity epoxy resin/cycloaliphatic polyamine epoxy resin polymer matrix. We present and discuss the chemical reaction of the epoxy resin polymer matrix adhesive to show that under manufacturing conditions, well below the glass transition point, substrates gradually come into contact with and become covered with epoxy resin polymer matrix strongly bonded to their surfaces. The fluid dynamics of the reaction system under such conditions reduces to a Cauchy equilibrium found in stressed solids, which leads to a strength of materials argument to show that the embedded, distributed optical fibres can accurately measure the motion of the surrounding epoxy resin polymer matrix before the gel point. The same argument is applied to the embedded 5-harness satin carbon fibre weave and leads immediately to an extension of the composite laminate theory for the thermodynamic liquid phase before the glass transition temperature. The predictions of the modified composite laminate theory framework are found to be consistent with experiment.