Flow-induced Orientations of Fibers and Their Influences on Warpage and Mechanical Property in Injection Fiber Reinforced Plastic (FRP) Parts

During the past two centuries, due to too fast growth of the human population, the pollution made by human has seriously impacts on our environment, particularly, for the CO₂ emission. To diminish the CO₂ emission problem, one of the effective solutions is applying lightweight material, such as the fiber-reinforced plastics (FRP), to replace metal in the manufacturing of transportation vehicles. However, since the reinforced function of the fibers inside plastic matrix is very complex, it is not easy to be visualized and managed. Specifically, the connection from microstructures of the fibers to the physical properties of the final product is far from our understanding. In this study, we have proposed a benchmark with three standard specimens based on ASTM D638 with different gate designs. This system is used to study the fiber microstructures and associated mechanical properties using numerical simulation and experimental studies. Results showed that the tensile properties (including tensile modulus and tensile stress) of all three ASTM standard specimens can be improved significantly in the appearance of the fibers. Moreover, the tensile properties variation of the finished parts associated with the microstructures of the short fibers based on the gate design have been also investigated. Specifically, the tensile modulus and the strength of the Model I are greater than that of Model II, while Model III is much less than others because of its double gate effect. The reason why the tensile modulus and the strength of the Model I is greater than that of Model II is due to some entrance effect. That entrance effect will further provide flow-induced fiber orientation to melt and then enhance the tensile properties of Model I. To confirm the observation, a series simulation and experimental studies have been performed. Specifically, the fiber orientation distribution is predicted using CAE, and verified using micro-CT scan and image analysis by Avizo software. Hence, the correlation from fiber microstructure feature (particularly in fiber orientation) to tensile modulus and tensile stress for fiber reinforced thermoplastic (FRP) in injection molding process can be validated.