Abstract
Ultrasonic fatigue testing is an increasingly used method to study the high cycle fatigue (HCF) and very high cycle fatigue (VHCF) properties of materials. Specimens are cycled at an ultrasonic frequency, which leads to a drastic reduction of testing times. This work focused on summarising the current understanding, based on literature data and original work, whether and how fatigue properties measured with ultrasonic and conventional equipment are comparable. Aluminium alloys are not strain-rate sensitive. A weaker influence of air humidity at ultrasonic frequencies may lead to prolonged lifetimes in some alloys, and tests in high humidity or distilled water can better approximate environmental conditions at low frequencies. High-strength steels are insensitive to the cycling frequency. Strain rate sensitivity of ferrite causes prolonged lifetimes in those steels that show crack initiation in the ferritic phase. Austenitic stainless steels are less prone to frequency effects. Fatigue properties of titanium alloys and nickel alloys are insensitive to testing frequency. Limited data for magnesium alloys and graphite suggest no frequency influence. Ultrasonic fatigue tests of a glass fibre-reinforced polymer delivered comparable lifetimes to servo-hydraulic tests, suggesting that high-frequency testing is, in principle, applicable to fibre-reinforced polymer composites. The use of equipment with closed-loop control of vibration amplitude and resonance frequency is strongly advised since this guarantees high accuracy and reproducibility of ultrasonic tests. Pulsed loading and appropriate cooling serve to avoid specimen heating.
Highlights
Ultrasonic fatigue testing is a powerful method to investigate the fatigue properties of materials in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regimes.Specimens are stimulated by resonance vibrations at a frequency close to 20,000 Hz rather than being stressed by external forces as in conventional fatigue tests
Original fatigue data generated by the authors on Ti6Al4V and 2024-T351 aluminium alloys were used in this study
Together with a similar fractographic appearance, the authors interpret this as an indication that there is no appreciable frequency effect on fatigue lifetime between testing frequencies of 20 kHz and 20 Hz in the investigated Ti6Al2Sn4Zr6Mo alloy. These results show that titanium alloys may be considered insensitive to frequency effects
Summary
Ultrasonic fatigue testing is a powerful method to investigate the fatigue properties of materials in high cycle fatigue (HCF) and very high cycle fatigue (VHCF) regimes. Testing apparatus or rotating bending equipment are typically performed at cycling frequencies below 100 Hz. technical components are typically stressed at cycling frequencies far below the ultrasonic range, so that cycling frequencies in conventional tests are much more comparable to those prevailing in actual applications. Technical components are typically stressed at cycling frequencies far below the ultrasonic range, so that cycling frequencies in conventional tests are much more comparable to those prevailing in actual applications It is important for high-frequency testing to consider possible frequency effects on the progress of fatigue damage and the measured fatigue lifetimes. The present work aims to review and compare ultrasonic and conventional fatigue data, discuss the potential variations between these results, and offer insights into how these data correlate for each material
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