2023 Volume 79 Issue 11 Article ID: 22-00261
On the surface of the steel material (base material) undergoing repeated plastic deformation, a group of surface cracks in which multiple cracks are lined up in stripe patterns is often seen. This group of surface cracks is considered to be the source of ultra-low cycle fatigue cracks starting from the surface of steel material and has a great influence on the ultimate behavior of steel members. This paper clarifies the basic formation mechanism of surface cracks that appear in the process of generation of ultra-low cycle fatigue cracks from the viewpoint of bifurcation theory. Specifically, based on the results of repeated loading experiments and elasto-plastic analyses under large-amplitude strain, the generation and development of plastic wrinkles, caused by the surface instability mode, are microscopically related to the spatial periodicity of surface height. And, the spatial periodicity could already occur at the time of initial yielding of steel surface.
