Fracture surface topography analysis of in-beam fatigue behavior for 20% cold-worked 316 stainless steel

Topography on the fatigue fracture surface was examined by using a confocal laser microscope for the side-notched small specimens of 20% cold-worked 316 stainless steel fractured in stress-controlled fatigue tests under the in-beam (dynamic), post-irradiation (static) and unirradiation conditions with 17 MeV protons at 60 °C. A technique of the fracture surface topography analysis (FRASTA) was adopted to extract the information of plastic deformation at the crack tip for the in-beam, post-irradiation and unirradiated specimens. The progress in plastic deformation at the crack tip was significantly delayed in the dynamic irradiation condition while not so much as in the static irradiation condition. The present results of FRASTA would not only support the superiority of dynamic irradiation effect to the static irradiation effect on fatigue behavior but also provide good evidence for the mechanism of the dynamic irradiation effect based on the interaction between continuously induced defect clusters and mobile dislocations.