Fracture resistance of short-glass-fiber-reinforced and short-carbon-fiber-reinforced polypropylene under Charpy impact load and its dependence on processing

In this paper, short-glass-fiber-reinforced and short-carbon-fiber-reinforced polypropylene composites were investigated with respect to the work of fracture (WOF), here viz the notched Charpy impact energy. Short glass fibers and short carbon fibers were incorporated into polypropylene with a twin-screw extruder and all of the specimens were injection molded into dumbbell-shaped tensile bars in a twin-screw injection-molding machine. Rectangular impact bars were obtained from tensile bars by removing the two clamping parts. Charpy impact tests were performed with a Charpy impact tester on specimens with V-notches. The values of the notched Charpy impact energy were obtained from each group of eight specimens. The effects of glass and carbon fiber volume fractions on their lengths in single and hybrid short fiber composites were investigated. The composite WOF was studied qualitatively by taking into account the effects of fiber volume fraction and fiber length distributions using the total WOF theory. Fiber length distributions have been previously shown to depend on the processing conditions. On the other hand, the composite impact resistance was shown to depend on fiber length and hence on processing. The dependence of the composite impact energy on processing is discussed.