Résumé
In the Low Cycle and High Cycle Fatigue regime, the first visible signs under an optical microscope of fatigue crack initiation are the occurrence of Persistent Slips Bands followed by the extrusion/intrusion formation on the specimen surface. In this study, the first signs of fatigue crack initiation were studied in the HCF domain on a body centred cubic Armco iron (with 80ppm of carbon content).The tests were performed on a piezoelectric fatigue machine on plate specimens. During the tests, the microstructure evolution was observed by optical microscope, and the temperature recording on the specimen surface was achieved by an infrared focal plane array camera. From the temperature recording, the intrinsic dissipation profile along the specimen gage part was calculated using a local expression of the heat diffusion equation. The results showed that above a stress level, Slips Marks can be clearly observed on the surface specimen, and related to the intrinsic dissipation distribution. Observations under a Scanning Electron Microscope on the specimen surface and the fracture surface are related to stage I and stage II of fatigue damage.