Font Size: 

In gigacycle fatigue regime (Very High Cycle Regime, Nf >107cycles), thecracks can nucleate on inclusions, “supergrains”, pores ...which leads to a fish-eyepropagation around the defect. The initiation from an inclusion or other defect is closedto the total life, perhaps much more than 99% of the life in many cases. The integrationof the Paris law allows one to predict the number of cycles at crack initiation. As thecrack initiation appears, a short crack around the defect propagates followed by a longcrack. In all cases, a cyclic plastic zone around the crack exists, and the recording ofthe surface temperature of the sample during the test must allow to follow the crackpropagation and to determine the number of cycles at the crack initiation. A thermo-mechanical model was developed. It allows the determination of the temperature fieldevolution in the specimen and shows a good correlation with the experiments.In this study, several fish-eyes from various materials (normalized steels, quenched andtempered steels, aluminium alloys) are observed by Scanning Electron Microscope, andthe fractographic results are analyzed in accordance with the mechanical and thermo-mechanical model. These analysis suggest a mechanism for fisheyes formation.