International audienceThis paper presents an experimental device developed to detect and estimate dissipated energy during very high cycle fatigue tests (VHCF) at high loading frequency (20 kHz) and low stress (i.e. far below the yield stress). Intrinsic dissipation is computed using local expressions of the heat diffusion equation and thermal data fields provided by an infrared focal plane array camera. The results obtained from tests performed on pure copper specimens show that dissipated energy exists whatever the attainable stress range and show that the dissipated energy rate is not constant throughout the test. Both findings are respectively incompatible with the concepts of fatigue limit based on elastic shakedown or on stabilized cyclic state associated with the mechanical hysteresis loop (viscoplastic shakedown)
International audienceIn 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
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.