Fracture properties of corroded steel under monotonic tension load

Corrosion caused component rupture and structural collapse accidents occur frequently. Therefore, it is important to assess the fracture risk of corroded in-service steel structures. Corrosion morphology is found to be a significant factor deteriorating the ductility of the steel. Therefore, fracture properties of a tensile corroded Q235structural steel, which has been in-service in the outdoor environment in Beijing for 25 years with protection from the original anti-corrosion coating, are investigated in the paper. To this end, a series of experiments on the steel, including monotonic tension and surface scanning tests on raw samples, tension and shear tests on non-corrosion samples fabricated with the core material of the rusted steel, as well as electronic microscope scanning (EMS) on fracture surfaces of samples, are conducted. Sensitivity analyses of morphology parameters on fracture properties of raw samples are performed. Further, Finite element (FE) models are developed to replicate the experimental results. Additionally, in order to predict the probability of crack failure and assess the residual performance of corroded steel components, both Void Growth Model (VGM) and Stress-Weighted Damage Model (SWDM) and a micromechanical fracture model (known as LOU) which are more suitable for complex stress states, are employed to evaluate the accuracy through comparisons with test and FE results. Finally, fracture modes of corroded steel samples are analyzed. Research results in this study indicate that, although the aggressiveness level of the Q235 steel with only initial coating and served outdoor for 25 years in Beijing is roughly mild, the ductility of the tensile sample could be reduced by up to about 36.811 %. Several fractures may initiate almost simultaneously at both the rough surface and core of seriously rusted samples. Fracture mechanism of the sample is mixed microvoid coalescence and quasi cleavage. It can also be concluded that, compared to VGM micromechanical fracture model, SWDM and LOU model are more appropriate for fracture prediction of corroded steel components.