High Cycle Fatigue of Cast Aluminum Alloys at Ultrasonic Frequency

Ultrasonic fatigue testing machines working at approximately 20 kHz allow extending the number of testing cycles to the 10⁸-10¹⁰ range, which would be prohibitive using conventional servo-hydraulic machines (up to 100 Hz). One of the questions that arise, however, is if the results from these very high frequency tests are comparable to the ones obtained from conventional tests performed at lower frequencies. This paper compares the high cycle fatigue (HCF) behavior of four cast aluminum alloys under two test frequencies (75 Hz and 20 kHz). It is shown that the S-N curve for some alloys is very sensitive to the testing frequency.