The influence of fiber wetting in resin transfer molding: Scale effects

Abstract

Resin transfer molding (KIM) has become a popular technique for fabrication of composite parts. During the mold filling stage, the resin is forced to flow into pore spaces between tow filaments and the between the tows themselves. Voids trapped in the composite during the filling stage are believed to be the consequence of the non-uniform micro-flows inside fiber bundles and macro-flows between them. Thus, to minimize the void formation, the processing parameters should be determined to generate a uniform front. In this case, the flow inside tows is driven by both the injection pressure and the capillarity forces and matches the flow outside the tows, which is driven only by pressure. To control such a flow, both viscous and capillarity flows have to be known at all scales of the fibrous structure. For this purpose, the wetting effects at the different scales (ranging from the individual tow to the multi-layers reinforcements) are investigated. Original experiments are carried out to visualize micro-flows and to measure the capillarity flow rates. Wicking effects are quantified in terms of the overall and local effective permeabilities. A new parameter that accounts for interactions between flows splitting in macro-and micro-flows is introduced. Practical ways to reduce voids entrapment are also discussed.

Capillary wicking in a fibrous reinforcement – Orthotropic issues to determine the capillary pressure components

“…This is due to the lower permeability in transverse direction. This is also consistent with the fact that capillary effects are more important than viscous effects in porous media with low permeability [5].…”

“…These studies, mostly on RTM process, aim to determine optimal process parameters, controlling velocity of resin flow or modulating injection pressure [4][5][6][7]1,8,9]. Studies simulating the resin flow in a porous medium during VARTM were also carried out [10][11][12][13][14][15], showing the importance of capillary effects during the process and the necessity to integrate them in physical and numerical models for an accurate prediction of voids formation.…”

Three‐dimensional flow simulation of resin transfer molding utilizing multilayered fiber preform

“…Although the transparent mold experiments allow flow observation only for surface and edge of preforms, it has been known that they offer satisfactory results for validation of simulation results. 23,29 In this study, three-dimensional mold filling simulation of RTM was used to investigate the flow pattern in multi-layered and cylindrical braided fiber preforms since the flow pattern could not be observed by experimental method precisely. To validate the simulation results, experimental observation was also conducted in both radial and transverse directions.…”

Free boundary viscous flows at micro and mesolevel during liquid composites moulding process

“…This di culty arises because as seen from Figure 2, the ÿbre preform consists of dual scale pores. The larger pores between the woven ÿbre tows (inter-tow spaces) are of the order of the tow diameter which is usually few millimetres, whereas the pores between every ÿbre ÿlament within a tow (intra-tow spaces) are of the order of the ÿbre diameter which is few micrometres [2][3][4][5][6][7][8][9]. Therefore, in the terminology of homogenization techniques, except a characteristic dimension of the mould identifying the macroscale, two other characteristic dimensions of di erent orders can be found, corresponding then to the meso and the microscale (Figure 2).…”