Investigation of S275JR+AR structural steel fatigue performance in very high cycle domain

There is a limited data on VHCF for structural steels and their weldments for >107 cycles. Unalloyed low-carbon steel S275JR+AR (EN 10025) is a common structural material for the components made for the minerals and mining applications. The purpose of this research is an investigation of the gigacycle domain for S275JR+AR grade that is intended to work for years at normal frequencies (10-20 Hz) of loading with low stress amplitudes. The work focuses on ultrasonic fatigue testing of the steel in both as-manufactured and pre-corroded conditions. As the heating is a massive challenge for ultrasonic fatigue testing especially in the case of structural steels attributed with a pronounced frequency effect, temperature control arrangement is crucial for proper implementation of testing. The frequency effect is assessed by comparing the fatigue test data at 20kHz and conventional frequency of 15Hz. Its contribution is found to be significant because there is no overlap between the stress ranges of interest. The ultrasonic fatigue data is intended to be applied to the fatigue assessments of the equipment operating at normal frequency for 1010 cycles. Therefore, the effect of frequency sensitivity is quantified by calculating the difference in terms of stress amplitude between corresponding SN curves