Improvement of Mechanical Properties of Discontinuous Carbon Fiber Reinforced Thermoplastic Induced by the Fiber Unbundling

Abstract

The purpose of this study is to investigate the effects of the fiber unbundling on the mechanical properties of carbon fiber reinforced thermoplastic (CFRTP) fabricated using discontinuous carbon fibers and polypropylene. Tensile test and puncture impact test were performed using CFRTP of which the volume fractions (V_f) were 10, 20, and 30 %. The wet type of unbundling treatments, which applied the water flow with shearing forces, were given to carbon fiber bundles with 5 and 10 mm lengths. Tensile strength and puncture energy of CFRTP were improved by the effects of fiber unbundling in spite of the same V_f. The amount of strain at the maximum tensile stress also increased with the progress of fiber unbundling. The effects of fibers unbundling on mechanical properties were obtained even in the small-scale of unbundling treatments which still remained a certain amount of fiber bundles in CFRTP. However, it was difficult to obtain the effects of improving mechanical properties in the condition of high V_f using long fibers (10 mm) due to the occurrence of the deviation of fiber direction.