Corrosion effect on ultra-low cycle fatigue capacity: A laboratory and numerical study

Abstract

This article investigates the effect of corrosion on the ultra-low cycle fatigue capacity of Q235 steel. The study focuses on atmospheric corrosion with a corrosion rate of 11.28 %. For this purpose, 25 grooved samples with groove sizes of 1.2 mm, 3.2 mm, and 6.4 mm were prepared. Over 7 months, the samples were exposed to accelerated atmospheric corrosion using the ASTM G60–01 standard method to reach the specified corrosion rate. Monotonic and cyclic loading were applied to the corroded samples to determine the ultra-low cycle fatigue parameters (η and λ), considering the effects of corrosion. The parameter η, related to monotonic loading, was calculated as 2.2, while the parameter λ, related to cyclic loading, was determined to be 1.75. Using these parameters, the capacity of a full-scale steel connection subjected to uniform corrosion of 11.28 % was calculated with finite element software and compared with experimental results. During the 5 % drift angle cycle of the SAC loading protocol, the corroded modeled connection exhibited the onset of ultra-low cycle fatigue failure near the column, consistent with crack initiation in the experimental connection. Due to the proximity of the crack to the column and the potential for crack propagation into the column, the R-RBS1 drilling method was applied. This retrofitting method moved the crack initiation location away from the column to the safe zone in the beam. However, it reduced the energy dissipation in the corroded connection by 17 %; therefore, the method of drilling for retrofitting in corroded connections should be done carefully.