Fracture and Orientation of Long-Glass-Fiber-Reinforced Polypropylene During Injection Molding

Injection processing parameters directly influence the final fiber length and may have a negative effect on the mechanical properties of a part. The aim of the work is to investigate and quantify the effects of the injection rate (2/10/50 cm³/s) on the fiber length, the distribution, and orientation during injection molding and the mechanical properties of long-glass-fiber-reinforced polypropylene (LGF/PP) by experimental and simulated methods. When the injection rate increases from 2 to 10 cm³/s, the fiber length sharply decreases from the original 11 mm to 3.43 mm at the nozzle and 1.30 mm at the filling end, and almost 88% of the fibers are less than 3 mm when the injection rate is 50 cm³/s. A distinct hierarchical orientation (skin-shear-core) for the fiber distribution in the thickness is obtained via a metallographic microscope, which shows that the shear layer (here the shear stress is larger and the fiber is more inclined to oriented along the flow direction) decreases with increasing injection rate. Moreover, the numerical results of the residual fiber length and orientation at different injection rates are in accord with the trend of the measured results. POLYM. ENG. SCI., 60:13–21, 2020. © 2019 Society of Plastics Engineers