Measurement and modelling of dynamic fluid saturation in carbon reinforcements

LCM of thermoset-based fiber reinforced composites for large-scale applications: are process kinetics and structural properties antagonistic?

“…( 4) is called the superficial velocity, or filtration velocity, which was initially defined by Darcy as the ratio of the volumetric flow rate Q out of a porous medium, over the cross-section of this porous medium, A. Integration of these equations for multiphase flow with the relevant boundary conditions leads to a description of the flow kinetics, and progressive saturation, provided that the hydraulic functions describing pressure and relative permeability versus saturation are identified [20].…”

“…(5) As a result, for unidirectional saturated flow (kr=1) under constant applied fluid pressure at the mold inlet, impregnation time for in plane flow along a given distance L is: (6) where is the pressure difference between outlet and inlet, which in case of a saturated flow assumption, should also include the capillary pressure drop acting at the flow front [20][21][22]. To minimize the impregnation time, while keeping the viscosity of the resin and the fiber volume fraction similar, strategies will include increasing the pressure gradient (but this requires heavier equipment and molds, and may lead to fiber movement), decreasing the impregnation length, for example by optimizing the presence of inlet points [23] and favoring through thickness impregnation, as performed in vacuum infusion thanks to high permeability flow grids placed on top of the textile.…”

“…However, some general trends can be highlighted. First, as indicated above, increasing permeability by increasing the separation of scales between tightly packed tows and larger channels, leads to a larger unsaturated region during impregnation, which may increase the risk of porosity in the tow region, if the overall resin velocity is such that viscous flow dominates [20]. This can be minimized by a careful control of the processing conditions, with sufficient resin bleeding, or the presence of less permeable regions towards the resin outlet, to fully saturate the part.…”