Gigacycle fatigue of ferrous alloys

• Published in: Fatigue & fracture of engineering materials & structures 1999-08, Vol.22 (8), p.667-672
• Main Authors: WANG, Q. Y, BERARD, J. Y, DUBARRE, A, BAUDRY, G, RATHERY, S, BATHIAS, C
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Fatigue; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy
• ISSN: 8756-758X; 1460-2695
• DOI: 10.1046/j.1460-2695.1999.00185.x

The objective of this paper is to determine the very long fatigue life of ferrous alloys up to 1x10 exp 10 cycles at an ultrasonic frequency of 20 kHz. A good agreement is found with the results from conventional tests at a frequency of 25 Hz by Renault between 10 exp 5 and 10 exp 7 cycles for a spheroidal graphite cast iron. The experimental results show that fatigue failure can occur over 10 exp 7 cycles, and the fatigue endurance stress S sub max continues to decrease with increasing number of cycles to failure between 10 exp 6 and 10 exp 9 cycles. The evolution of the temperature of the specimen caused by the absorption of ultrasonic energy is studied. The temperature increases rapidly with increasing stress amplitudes. There is a maximum temperature between 10 exp 6 and 10 exp 7 cycles which may be related to the crack nucleation phase. Observations of fracture surfaces were also made by scanning electron microscopy (SEM). Subsurface cracking has been established as the initiation mechanism in ultra-high-cycle fatigue ( > 10 exp 7 cycles). A surface-subsurface transition in crack initiation location is described for the four low-alloy high-strength steels (54SC6, 55SC7, 42Cr-Mo4 and 60CV2) and a SG cast iron.