AbstractSizings significantly affect the processing and final performance characteristics of resin transfer molded (RTM) parts. Manufacturers often use sizings to enhance compatability between the resin and reinforcement and to assist processing. In particular, such coatings can affect the microscopic flow characteristics of resins during the infusion stages of the RTM process. To understand the mechanisms by which sizings affect preform wet‐out and the extent of such effects, the influence of fiber sizings and fiber loadings on the flow of a vinyl‐ester resin system, through axially aligned carbon fibers, have been measured. The results and analysis of the experiments reported herein form the basis for a phenomenological model that describes the effect of sizings on micro‐flow in RTM. Furthermore, the work provides insight into the relationships among micro‐flow, macro‐flow, and preform infiltration. It is seen that sizings dramatically influence micro‐impregnation and, for the flow configuration studied, radial micro‐flow into fiber bundles was the rate limiting process for complete fiber bu
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