Fatigue testing and fatigue life prediction of injection molded carbon-fibre reinforced plastics for automotive oil-pan application

Fatigue testing and fatigue life prediction of two injection molded carbon-fibre reinforced plastics are presented and discussed in the present paper. These two materials are being considered for automotive oil-pan application, namely PA66 LCF40, i.e. long carbon fibre-reinforced polyamide 66 pellets with 40 wt.% fibre concentration and PA66 SCF40, i.e. short carbon fibre-reinforced granules with 40 wt.% fibre concentration. Stress-controlled fatigue tests were carried out at room temperature under stress ratio, R= -1 and service temperature, 120 °C under stress ratio, R= -1, 0.1 and 10. The results showed that the fatigue behavior of LCF40 and SCF40 was similar at room temperature irrespective of the significantly higher ultimate tensile strength of LCF40 compared with SCF40. However, the fatigue performance of LCF40 was better than SCF40 at 120°C under R=-1 and 0.1while no apparent difference was observed under stress ratio, R=10 except the relatively higher fatigue strength at 2 million cycles for LCF40. Based on the fact that the measured fracture strains are statistically similar from fatigue and tensile testing, the Hwang & Han model was used to predict the fatigue performance, and the results are in good agreement with the experimental ones.