Study For Fatigue Life Assessment Of Welded Structures Considering Nonuniform Corrosion Damage

The complex welded structure of ship and ocean engineering suffer corrosion environment and wave load simultaneously during the service time, it can be found from the Class NK’s investigation for corrosion of welded joints in different area of ship structure that the welded joint suffered nonuniform corrosion damage severely, and the welded joint is liable to initiate crack due to its stress concentration, so the corrosion fatigue of welded joint is the key problem of ship and ocean engineering. The influence factors of corrosion fatigue is very complexThis paper studies the impact of external load on the corrosion reaction which is based on the theory of mechanochemical effect, and discusses the influence of external load on the corrosion potential and corrosion current by studying the variation of polarization curve under the external load. The effect of external load on the uniform corrosion and localized corrosion is also studied in this paper, and the synergistic effect between the applied elastic stress and chemical attack on the Q235steel was evaluated by the mechanochemical experiment. It can be concluded from the experimental results that the applied load accelerate the corrosion process of Q235steel in seawarter, and the variation trend of corrosion electrochemical properties is in accordance with the theoretical derivation.The effect of nonuniform corrosion on fatigue life of welded joint is discussed in this paper, which is considering the coupling effect between the mechanical factor and corrosion factor, and the effect of corrosion cell caused by stress distribution, this research is more closed to the engineering practice. The hot spot stress approach is adopted to calculate the corrosion fatigue damage of typical welded joints which is considering the synergistic effect between the load and corrosion, the iterative process of load and corrosion degeneration of plate thickness is used to simulate the coupling effect base on the results of experiment. The finite element model of nonuniform corrosion is built according to the results of mechanochemical experiment. The results of calculation reveal that corrosion fatigue damage which is considering the coupling effect is more severe than the single uniform corrosion fatigue damage, and the gap is becoming larger with the growth of the corrosion year.