Study on fatigue properties of unequal-thickness butt welds of high-strength steel under salt spray and dry-wet cycles

Abstract

With the development of engineering technology, the application of high-strength steel (HSS) in large-span bridges is becoming more and more widespread. However, due to long-term service in the ocean, salt spray, humidity and heat and other corrosive environments, HSS bridge structures are often difficult to avoid the occurrence of corrosion and fatigue damage and other problems. In view of the unique environmental characteristics of the marine atmospheric zone, this paper is targeted to carry out indoor salt spray, dry and wet cyclic accelerated corrosion testing of Q690D HSS. A prediction model for the correlation between indoor accelerated corrosion and marine atmospheric exposure corrosion was established. The fatigue performance of unequal thickness butt welds (UTBW) of HSS with different levels of corrosion damage was investigated. The fatigue damage mechanism of corroded HSS welded joints was investigated based on the fatigue fracture of UTBW specimens. Based on the surface corrosion morphology, a fatigue life assessment method for HSS welded joints with different corrosion degrees was established. The results show that the fatigue strength of the HSS UTBW specimens without corrosion is 219.25 MPa. When the corrosion cycle is 60 days, its fatigue strength decreases by 17.85 %. When the corrosion cycle increases from 60 days to 150 days, its fatigue strength decreases by 7.47 %. When the deepest corrosion pit is equivalent to a semi-elliptical surface crack with the same depth and surface width as that of the corrosion pit, the S-N curve obtained through numerical calculation can evaluate the fatigue life of the UTBW of corroded HSS.