Effect Of Mixing And Forming Processes On Fiber Length Of Carbon Fiber/silicone Rubber Composites

The fiber residual length and orientation are two important factors that affect the properties of fiber reinforced composites. The damage of carbon fiber during mixing and molding process was studied and series experiments were conducted in the paper. First, POLYFLOW was applied to simulate the flow characteristics and mixing characteristics in various mixers and processing conditions, including flow pressure, shear rate, velocity vector, streamline, mixing characteristics Mmix and modified Lyapunov index. The residual weight-average length Lw distribution of carbon fibers in silicon rubber was calculated by combination of theoretical model. Then, POLYFLOW was applied to simulate filling flow characteristics in the extruder, including flow pressure, velocity vector, shear rate, and Mmix. The molding flow characteristics in various wall slip coefficient were researched, and mixing flow characteristics were contrasted with filling flow characteristics. Finally, the fiber residual length was studied by mixing experiments in process conditions, the error between theoretical model predicted value and experiment value was analyzed, and the main factors affecting the fiber residual length were discussed. The main conclusions are made as follows:(1) The main impact factors on fiber residual length are mixer structure, rotation speed, and mixing time. The fiber breakage degree of ribbon rotor is bigger than stirring rotor because of the relative stronger shear mixing effect of ribbon rotor. Fiber breakage increases with the rotation speed and mixing time increasing.(2) The wall slip coefficient of the mold cavity has a great influence on the filling flow characteristics of carbon fiber/silicone rubber. The filling effect of composite molding is enhanced by lubricating or reducing the roughness of the mold cavity wall, and the damage of the fiber is reduced.(3) The shearing of the flow field in the mixing process is obviously stronger than that in the filling process, and the fracture of the carbon fiber occurs mainly in mixing process.(4) According to comparison between theoretical values and experimental values of fiber residual length, the computed weight-average length values fit well to experimental values, and the relative error is below 10%.