The effect of surface tension on tow impregnation of unidirectional fibrous preform in resin transfer molding

Resin transfer molding (RTM) is an efficient technique for fabrication of large polymer composite parts with complicated shapes. The process consists of injecting liquid resin into a mold cavity with preplaced fiber preform. Voids trapped in the composite during the filling stage were believed to be the consequences of the non-uniform micro- and macro-flaws in the pore spaces. A two-dimensional flow model is developed to study the impregnation flow in both the micro- and macro-regions during the mold filling process. The capillary force is included in the model to investigate its effect on the micro- and macro-flows. The capillary force is the major cause that results in the leading of the micro-flow for a low filling rate, that cannot be ignored if the analysis of the void formation is to be performed. It is found that mold filling process with capillary number near the value of the critical capillary number is an adequate condition to result in a uniform filling pattern in RTM.