Dissipative and microstructural effects associated with fatigue crack initiation on an Armco iron

In this study, the first signs of fatigue crack initiation are studied in the HCF domain on a body centered cubic Armco iron (with 80 ppm of carbon content). Some tests are performed on plate specimens through a piezoelectric fatigue machine. During fatigue tests, the deformation evolution is observed by optical microscope, and the temperature recording on the specimen surface is achieved by an infrared focal plane array camera. From the temperature recording, the intrinsic dissipation field is calculated using a local expression of the heat diffusion equation. The results show that above a given stress level, Slips Marks can be clearly observed on the surface specimen, and related to the intrinsic dissipation distribution. Observations through a Scanning Electron Microscope on the specimen surface and the fracture surface are related to stage I and stage II of fatigue damage.