Effect of laminate structure on flow induced deformation of fiber preform in resin transfer molding

Laminate structure of fiber preform is an important factor in determining the processing conditions of liquid composite molding as well as mechanical properties of fiber reinforced composite product. In resin transfer molding process, fiber preform deforms undesirably by the flow pressure of resin, which causes defectives in size, properties and appearance of the final composite products. Therefore, process condition should be strictly controlled in order to prevent preform deformation in the molding process. Several types of fiber deformation such as slip, wrinkle, and contraction are observed by structural and process related factors. In this study, structural factors of fiber preform affecting the flow induced fiber deformation in resin transfer molding are investigated, which include fiber volume fraction and laminate structure of fiber preform. Effects of laminate structure are investigated by measuring two important factors which are hydrodynamic friction coefficient between fiber and mold surface and bulk stiffness of fiber preform in the mold. The former is related to slip and the latter is related wrinkle and contraction of fiber preform. Several kinds of fiber mat such as unidirectional and woven fabrics are tested and the resulting flow induced deformations are predicted and compared with the observed deformations in resin transfer molding. Woven structure of the most outer layer was an important factor in friction related deformation and the overall structure of the fiber preform affected the local deformations such as wrinkle and compaction. It is expected that the unexpected fiber deformation can be prevented by optimum design of laminate structure considering fiber deformation as well as mechanical properties of composite.