Anisotropic air permeability in out-of-autoclave prepregs: Effect on honeycomb panel evacuation prior to cure

An experimental technique to characterize interply void formation in unidirectional prepregs

“…These voids generally decrease to zero during processing, which is attributed to air evacuation through gaps created by the interlaced structure. The same phenomena cannot be transferred to unidirectional prepregs, due to smoother surfaces compared to woven prepregs, as well as lower out-ofplane air permeability [16]. In-situ experimental techniques to characterise interply void formation are currently limited.…”

A stochastic approach to model material variation determining tow impregnation in out-of-autoclave prepreg consolidation

“…The model's results are in compliance with expectations. However, results cannot be directly compared to experimental While air flow in thickness direction is negligible according to [25], in-plane air evacuation transversal to the fibres has to be resolved for a more realistic representation of void formation in unidirectional OoA prepregs. Capillary forces have to be considered to achieve a more detailed description of the infiltration process for higher fibre volume fractions.…”

Effects of debulk temperature on air evacuation during vacuum bag-only prepreg processing

“…Permeability describes gas (and liquid) transport through a porous medium, and is thus an important process variable affecting air evacuation. The intrinsic permeability of a material is determined solely by the solid matrix, and is independent of the fluid properties and flow mechanisms, while the effective gas permeability of composites is affected by both material and process parameters [10]. In-plane permeability of prepregs has been studied extensively [11][12][13][14], albeit mostly at room temperature.…”

“…However, the initial in-plane permeability values for typical VBO prepregs are on the order of 10 À14 m 2 [11,12]. In contrast, the through-thickness permeability is generally 3 and 4 orders of magnitude less than the in-plane permeability [10,12]. Kratz et al [10] and Tavares et al [15] both investigated the through-thickness permeability during cure and reported an increase in through-thickness permeability at high temperature due to the decrease in resin viscosity.…”

“…In contrast, the through-thickness permeability is generally 3 and 4 orders of magnitude less than the in-plane permeability [10,12]. Kratz et al [10] and Tavares et al [15] both investigated the through-thickness permeability during cure and reported an increase in through-thickness permeability at high temperature due to the decrease in resin viscosity. However, no observations have been reported on the effects of debulk temperature on air evacuation, and no comparison is available to identify which air evacuation pathway (in-plane or transverse) is more effective during this period.…”