Corrosion Fatigue Crack Initiation And Propagation Law And Life Prediction Of Bridge Cable

As the key component connecting the bridge deck system and the arch rib(or main cable,main tower),the cable transmits the dead and live loads of the bridge deck system to the main cable,arch rib or main tower,and is the lifeline of the long-span bridge based on the cable loadbearing system.However,during the service period of the bridge,the cable has a long service life and is exposed to the natural environment.Under the coupling effect of environmental erosion,external load,fatigue effect and sudden change effect and other disaster factors,the cumulative damage and fatigue resistance attenuation of the structure will be inevitable.Especially,corrosion and fatigue cause the reduction of durability and bearing capacity of cable,which has become the main factor affecting the service life and threatening the service safety of the bridge structure.In this paper,combining experimental research,numerical simulation and theoretical analysis,the systematic and in-depth study has been carried out on the initiation and propagation of corrosion fatigue cracks and the life prediction method of bridge cables.The main research work includes:(1)The stress corrosion test of steel wire of bridge cable was carried out,and the surface morphology of corroded steel wire was collected with the help of 3D scanner.The corrosion surface characteristics of cable steel wire under different corrosion ages and stress levels were studied,and the damage evaluation index of steel wire under stress corrosion and the extraction method of characteristic parameters of corrosion pit were proposed,revealing the distribution law of pit characteristic parameters under different corrosion ages and stress levels.The maximum pit depth of steel wire under stress corrosion was estimated by the analysis method of probability statistical extreme value.(2)The tensile tests of corroded steel wire under different corrosion ages and stress levels were carried out,the failure patterns,stress-strain curves and degradation laws of mechanical index of steel wire with different stress corrosion degrees were discussed.The finite element numerical method based on three-dimensional morphology was proposed,the whole failure process of steel wire under stress corrosion was revealed,and the functional relationship between different corrosion parameters and stress concentration coefficient,stress triaxiality and critical equivalent plastic strain was established.The damage constitutive model of steel wire under stress corrosion was proposed.(3)Through the fatigue test of steel wire with different stress corrosion degree,the influence of different corrosion age and stress level on the failure mode,fatigue life and S-N curve of steel wire were studied.The fatigue crack initiation mechanism,crack propagation behavior and the influence of stress corrosion degree on the initiation value and fracture toughness of fatigue crack propagation of steel wire with different stress corrosion degree were analyzed.(4)The numerical analysis method of fatigue crack initiation and propagation of cable steel wire considering stress corrosion surface was proposed,and the change law of stress in the crack tip during crack propagation was studied.The calculation method of stress intensity factor and fracture toughness in the crack tip was given,and the change law of initial stress intensity factor,fracture toughness and crack propagation rate of corroded steel wire under different pitting characteristic parameters and thickness loss were revealed.The theoretical calculation model of fatigue life of corroded steel wire was established.(5)The evolution mechanism of corrosion pits on the surface of steel wire under stress corrosion was revealed,and the whole process simulation method of series-parallel failure of cable body subjected to stress corrosion based on Monte Carlo method was also proposed.The degradation law of service life of cable body under different stress levels,fatigue load and wire breakage rate were analyzed,and the time-varying reliability evaluation of fatigue life of cable body under different stress corrosion degrees was also carried out.