Frequency effects in ultrasonic fatigue testing (UFT) of Q355B structural steel

Ultrasonic Fatigue Testing (UFT) is an accelerated fatigue testing method, capable of running at 20 kHz. This increased test frequency can have significant influence on the results produced for ferritic steels due to the strain rate sensitivity of the deformation mechanisms and internal heat dissipation. The aim of this investigation was to evaluate the frequency effect for the structural steel Q355B. To achieve this, the fatigue performance of the material was evaluated at 20 Hz and at 20 kHz using a test method designed to reduce the variables between the tests to just the load frequency. The discrepancy between the SN curves produced at the two frequencies was evaluated and found to match well with similar steels in literature. The effect of the ferrite content on the frequency sensitivity was evaluated, and the heat generation and fracture origin within the samples was discussed. The observations for each of these matched similar observations in literature.