Research On Corrosion Fatigue Failure Mechanism And Life Prediction Methods Of The Steel Bridge

Steel bridges play an important role in the transportation network.Fatigue and corrosion are two important factors that affect the safety and durability of steel bridges.Corrosion fatigue is a process in which materials deteriorate to fracture under the combined action of cyclic loading and corrosive medium.It involves multidisciplinary content and is a very complex subject.In this thesis,theoretical and experimental researches are carried out on the corrosion fatigue problem of steel bridges.The main contents and results are as follows:(1)A set of temperature-controlled,corrosion-controlled liquid circulation system was developed to introduce a corrosive environment into the fatigue test system and relevant corrosion fatigue tests were carried out.The system can adjust and control the temperature,concentration and p H value of the corrosive liquid in real time.(2)A series of fatigue and corrosion fatigue tests of T-welded joint specimens of steel bridges were designed and carried out,and the evolution process of corrosion fatigue damage was clarified.The test results show that the introduction of the corrosive environment greatly changes the crosssection morphology of the crack propagation zone and seriously reduces the fatigue life of the specimen.(3)Based on damage mechanics,combined with metal corrosion damage mechanism and metal mechanics electrochemical principle,an improved corrosion fatigue damage evolution model(ICFDEM)was proposed,and a corresponding calculation and analysis program was developed.The model can consider the coupling effects of corrosion environment and cyclic loads.ICFDEM was used to predict the corrosion fatigue life of various steels and welds in different corrosive environments,which verifies the rationality and versatility of ICFDEM.(4)The improved Paris model was proposed by introducing corrosion damage variable into the Paris model,which takes into account the influence of mechanical factors on the evolution of corrosion damage and the promotion effect of corrosion damage on crack growth.The improved Paris model can be used to calculate corrosion fatigue crack growth rate and crack propagation length.The predicted crack length of steel specimens is in good agreement with the experimental results,which verifies the accuracy and rationality of the model.The improved Paris model was used to predict the corrosion fatigue life of the T-welded specimens,and the prediction results were analyzed with the test results.(5)Based on the ICFDEM and the improved Paris model,the methods for predicting the corrosion fatigue life of steel bridges were established respectively.The methods can consider the coupling effect of corrosion and fatigue,can be used to analyze the effect of load sequence on the corrosion fatigue life of steel bridges.The method established based on ICFDEM reflects the influence of the early damage accumulation on the later damage evolution,and the method established based on the improved Paris model reflects the effect of corrosion damage on the crack growth rate.(6)Based on the corrosion fatigue life prediction method of steel bridges,the fatigue and corrosion fatigue life of a real bridge were systematically evaluated,and the influence of different methods and parameters on the predicted life was analyzed.