| dc.description.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. | en_US |
