Hydrostatic consolidation of commingled fibre composites

A molten hybrid-yarn composite is modelled as a continuum. Constitutive equations governing hydrostatic consolidation are formulated, based on a two-phase continuum mechanical framework developed in a recent paper [Larsson R, Wysocki M, Toll S. Process-modelling of composites using two-phase porous media theory. European Journal of Mechanics-A 2004;23:15-36]. The fibre bundles are assumed to be completely surrounded by resin, thus subjected to hydrostatic pressure. To model the infiltration of resin into the fibre bundles, we introduce a compressible solid phase consisting of fibres plus intra-fibre void. The compression of the solid phase is caused by a combination of infiltration and elastic compression of the fibre bundles. The models are micromechanical, and all parameters have a clear physical meaning and are measurable in principle. Using parameter values out of the literature and estimated from micrographs, the number of adjustable parameters may be brought down to one: a spring constant for the fibre bundle elasticity. Consolidation experiments are performed, where a tool is closed to a prescribed compression and then held fixed, while the pressure is monitored over time. The predicted and measured pressure traces are in good agreement.