Verification of fiber orientation mechanism by resin flow behavior in the flow front confluence region

Injection-molded fiber-reinforced resins exhibit anisotropic mechanical properties due to the orientation of the fibers caused by resin flow. Therefore, the prediction of fiber orientation is important for predicting the function of injection-molded fiber-reinforced resin products. In previous reports, fiber orientation behavior has been observed in simple resin flow specimens such as flat plates. In this paper, fiber orientation was observed in the flat and rib parts of a ribbed two-point gate flat plate. As a result, the fiber in the center of the wall thickness was oriented in the flow direction in the rib section after flow-front meet, confirming a five-layer orientation different from that previously reported. To verify the fiber orientation mechanism, the velocity distribution and velocity history of the resin were measured. It was found that the fibers near the wall surface were oriented by shear forces, while the fibers in the center of the rib wall thickness were oriented by a combination of elongation flow and shear forces.