Study on the influences on fiber micro-structure variations and the connection to final shrinkage/warpage on long fiber reinforced thermoplastics (FRT) parts

Because of its great potential and capability, the fiber-reinforced thermoplastics (FRT) material and technology have been widely utilized into industry recently. However, due to the microstructures of fiber inside plastic matrix are very complex, they are not easy to be visualized. The connection from microstructures to the final shrinkage/warpage is still not fully understood yet. In this study, we have performed a benchmark with three standard specimens based on ISO 527 where those specimens have different gate designs. Due to the geometrical effect, the warpage behaviors are quite different for those three specimens. Specifically, it pushes one specimen warped downward and bended inward, another warped upward, and the other slightly upward at the same time. The difference might be due to the interaction of the entrance effect of molten plastic with fiber content to cause high asymmetrical fiber orientation distribution (FOD). Moreover, the experimental study is also performed to validate the simulation results. From short shot testing to the warpage and bending measurement for each individual model, overall, the tendency for both numerical simulation and experimental results is in a reasonable agreement. However, to get better understand between the microstructures of the fibers and the final shrinkage/warpage, it still needs for further more study.