Fatigue strength experiments of corroded small scale steel specimens

The objective of this work is to analyze the fatigue strength of small scale corroded steel specimens. The specimens were cut from a box girder, which was initially corroded in real sea water conditions. The surface of 11 corroded specimens was analyzed applying photogrammetry techniques and a description of an idealized corroded surface was established. The non-corroded specimens are identified as FAT 86 category but the fatigue test demonstrated that due to the severe corrosion degradation the experimental fatigue results of the corroded specimens are located above the fatigue design category FAT 50 and below FAT 100 referring to the nominal stress approach. The regression analysis of fatigue test results leads to m = 3.094 and Δσ97.7%,m=3=64.95MPa. Fatigue assessment of crack propagation on a pit like crack flow based on a failure assessment diagram was performed. The admissible initial idealized flow defect has been defined, which matches the fatigue life achieved by the fatigue test for different load categories and corrosion degradation level.