Fatigue strength of a clutch pedal made of reprocessed short glass fibre reinforced polyamide

The fatigue behaviour of a clutch pedal made of reprocessed short glass fibre reinforced polyamide 6,6 was experimentally investigated and results were compared with tests on the same part made of virgin material. The study concentrated on the differences between the fatigue behaviour of injection moulded parts and standard specimens made of the same reprocessed reinforced polyamide. The different types of loading than in standard specimens resulted into a different fatigue mechanism. Moreover the presence of sharp notches transformed the diffused damage observed in plain specimens into the formation of cracks at few critical locations. This investigation also allowed to evidence that in real parts the role of fibre shortening due to reprocessing is more pronounced because of the more complex shape of the mould cavity, causing a higher degree of fibre breakage during injection moulding, due to the longer and more tortuous path followed by the melt polymer filling the mould cavity. The use of reground material also caused the appearance of defects in pedals, i.e. voids, which diminished the fatigue strength. Nevertheless, the use of a 100% reprocessed material still ensured a high degree of safety and allowed for obtaining parts fully complying with safety specifications.