Study of thermal effects associated with crack propagation during very high cycle fatigue tests

This paper studies the thermal effects associated with the propagation of a fatigue crack in a gigacycle fatigue regime. Ultrasonic fatigue tests were carried out on a high-strength steel. The temperature fields measured by infrared thermography show a significant and very local increase in the temperature just before fracture. In order to better understand these thermal effects and to make a connection with the initiation and the propagation of the fatigue crack, a thermomechanical model is developed. The fatigue crack is modeled by a circular ring heat source whose radius increases with time. The numerical resolution of the thermal problem allows determination of the time evolution of the temperature fields in specimens and shows a good correlation with experiment. These results provide experimental proof that in a very high cycle regime, the propagation stage of the crack constitutes a small part of the lifetime of the specimen.