Measuring techniques for the very high cycle fatigue behaviour of high strength steel at ultrasonic frequencies

To analyse the fatigue behaviour of steels in the very high cycle fatigue regime, an ultrasonic testing facility was developed that allows describing the cyclic deformation behaviour at ultrasonic frequencies by measuring characteristic fatigue data at a sufficiently high frequency. In correlation with scanning electron micrographs, fatigue tests prove that the sensitive measuring techniques indicate fatigue induced microstructural changes by a significant rise in the process parameters more than 10(6) cycles before final failure occurs. By further analysis of the attenuation behaviour of the ultrasonic resonance system, the logarithmic decrement can be used as a reasonable physical value to indicate changes in the microstructure with a very high sensitivity. This allows an improved understanding of the fatigue mechanisms in the very high cycle fatigue regime.