High Frequency Fatigue Crack Propagation Behavior of a Spheroidal Graphite Cast Iron 2001-01-0831
Owing to the combination of high strength and good ductility, spheroidal graphite cast iron (SGI) has been widely used in the automotive industry. The application of the damage-tolerance design approach to the mechanical parts subjected to high frequency vibration loading necessitates a more reliable determination of crack propagation threshold. In this study, the fatigue crack propagation behavior of a SGI (ferrite in matrix with about 5% pearlite) was investigated experimentally at a frequency of 20 kHz and the stress ratio of R=-1 and R=0.1. The propagation threshold was determined at a very slow rate of 10-11 m/cycle. The results of these tests have been compared with those of conventional fatigue test. Effects of cyclic loading frequency have been discussed. It is shown that the threshold stress intensity value is smaller at ultrasonic frequency. The observations of the fracture surface at SEM show that there is less oxidation at very high frequency in all propagation regimes.