Resin flow in porous preform during VARTM: A theoretical and experimental investigation

Abstract

In recent times, fiber reinforced polymer (FRP) composites have received enormous attention due to their exhibited improved mechanical properties, lightweight and design flexibility to manufacture large structures as an attractive alternative structural material compared to conventional metals for marine, aerospace, automobile, and civil industries. FRP manufacturing technology strives to completely saturate the dry fiber phase with thermoplastic or thermoset resins to yield a heterogeneous material with enhanced capabilities. This work focuses on the physics of resin impregnation in dry fiber preform during vacuum assisted resin transfer molding (VARTM). Vacuum infusion (VI) of porous dry preform is modelled as incompressible fluid flow through homogeneous porous media by means of Darcy’s law coupled with continuity equation. During infusion, as the flow front progresses, the net compaction pressure is shared by the liquid resin and compacted air; thus, VI becomes a two-phase fluid flow problem. Moreover, in VARTM as the flow front advances, the flexible vacuum bag (on top of the preform) causes the porous preform to relax resulting in a transient spatially varying fibre volume fraction (Vf ). This, in turn, causes the permeability and thickness of the preform to vary spatially and temporally. To capture this physics of a moving boundary two-phase incompressible flow in porous media, VI model has been coupled with the level set front tracking method to visualise the location of flow front, predict the instantaneous change in thickness, the complete impregnation time, and distribution of Vf . In addition, to manufacture large structures and lower the fill times, high permeability medium (HPM) is placed on top of the preform to enhance the flow velocity. This results in varying flow fronts in HPM layer and the underlying dry preform. A depth-averaged control volume technique has been used to modify the aforementioned VI model in the presence of HPM. Additionally, VI inclusive of geometry effects in the presence or absence of HPM and gravity has also been investigated. Finally, a novel experimental setup has been developed that captures the in-situ transient fluid pressure profiles, out-of-plane displacements of the preform during VI and evolving flow fronts. The model predictions show a close match with experimentally measured flow fronts and fill times.