| As the main stressed component of cable-supported bridge,the health of cables during the service period will directly affect the operation safety of bridge.Corrosion fatigue failure under the combined action of corrosion medium and fatigue load is one of the typical failure modes of cable-supported bridge,which seriously affects its safety and durability.The essence of corrosion fatigue failure is the interaction of electrochemical process and mechanical process,which is far more than the simple superposition of alternating stress and corrosion medium.In order to study the damage evolution process of cable system under corrosion medium and fatigue load and predict its service life,this paper firstly sets out from the electrochemical nature of metal corrosion and establishes the numerical model of corroded cables by using cellular automata technology.Then,the user material subroutine(UMAT)is written based on the material damage constitutive relationship,and the contact friction between wires in the cables is considered to visualize the damage evolution process of corroded cable under fatigue load and obtain its fatigue life.On the basis of the above research,the Gutman model is used to further study the acceleration effect of mechanics on corrosion and its influence on the initial corrosion morphology,so as to realize the analysis of mechanical-chemical coupling process and study the influence of the coupling effect on the fatigue life of the cables.Based on the above research process,the main work and research results of this paper are as follows:(1)Aiming at the friction problem between cable wires,the normal contact is defined as hard contact,and the tangential contact is defined as penalty function method.PYTHON language is used to decompose the analysis step into multiple incremental substeps to effectively solve the non-convergence problem caused by contact friction.The cyclic loading process of fatigue load is realized based on the "cyclic block" method,which greatly improves the calculation efficiency.(2)Based on the material damage constitutive equation,the user material subroutine(UMAT)is written and the friction between cable wires is considered,which realizes the visualization of damage evolution process of health cables under fatigue load,quantifies the deterioration rate and obtains fatigue life.(3)With the help of MATLAB program of cellular automata,AutoCAD and commercial software RHINO,the point coordinates,mesh model and 3D solid model of cables were obtained respectively.The cable 3D finite element model was obtained by importing commercial software ABAQUS,and the cyclic loading of fatigue load was realized by using PYTHON language.Based on the verified UMAT program,the damage evolution process of cables with random corrosion pits was visualized,the fatigue life of corroded cables was calculated,and the influence of pit morphology on the damage evolution rate and life was analyzed.The results show that the life of cables with random pits is lower than that of cables with regular semi-ellipsoidal pits,which indicates that the regular semi-ellipsoidal defects widely used in engineering to simulate the corrosion defects on the surface of engineering components will make the predicted life unsafe.Compared with the pit width,the pit depth has a more significant effect on the cables life.(4)The MATLAB program of cellular automata is modified based on Gutman model to realize the corrosion evolution process assisted by fatigue load,and the equivalent plastic strain is obtained by writing UMAT program to update the "corrosion probability matrix" in the cellular automata program,so as to realize the coupling between fatigue load and corrosion medium,study the damage evolution process under the coupling action of the both,and predict the cables life.The results show that,compared with pre corroded cables,the corrosion fatigue coupling effect can accelerate the corrosion fatigue failure process of cables.When the loading stress range is small,the fatigue life is basically unchanged.With the increase of the stress range,the fatigue life is reduced by 30% to 40% compared with the pre corroded cable structure.The research method in this paper can fully consider the friction effect between the wires of the cable,which makes up for the existing research.In order to simplify the calculation,the contact of the steel wire bundle or steel strand is treated simply as "node coupling".In addition,this paper investigates and realizes the promotion and acceleration of mechanics to chemistry,fully studies the influence of fatigue load on the initial corrosion morphology of cables,and further studies the influence of corrosion morphology on the damage evolution and life of cables,which provides reference for studying the coupling effect of corrosion medium and fatigue load.The conclusion of this paper has theoretical support and practical significance for cable performance degradation and accurate life assessment in engineering. |
PDF Full Text Request