Analysis of the scatter in fatigue life testing of thick thermal cut plate edges

Structural elements of ships are subjected to a high number of cyclic loads, which are critical to fatigue life. Especially for ultra-large container ships the cutting of thick steel plates with high finishing quality and good fatigue life is important, e.g. located at openings in walls and decks of ships. This study presents a series of fatigue tests with 50 mm thick S355 specimens that are thermally gas cut on different shipyards. The obtained stress-life (S-N) curve contains significant horizontal scatter which often occurs for specimens that spend a high number of cycles on crack initiation. However, it is found that both the local stress concentrations and the origin of failure affect the number of load cycles significantly. Accounting for local stress concentrations provides an explanation for the initially encountered scatter in the S-N curves and indicates possible limitations of the nominal stress approach for thermal cut edges.