Research On Node Area Corrosion Fatigue Remaining Life Assessment Of Steel Railway Bridge

In the course of manufacture and normal use,railway steel bridge could inevitably produce a variety of cracks because of various defects,and the corrosion fatigue crack developed by the corrosion pit is the most influential one.The railway steel bridges which serve for a long time in the natural environment are subjected to cooperative interaction of cyclic stress and corrosion environment by the action of the train running load,and the existing crack will rapidly expand,causing the sudden failure of the component and even corrosion fatigue failure of the structure.Evidently corrosion fatigue crack has become a major threat to the safe use of railway steel bridges.So the study on the remaining life of fatigue crack growth of railway steel bridge is useful to ensure the safety and normal use of railway steel bridges.Therefore,the finite element simulation,the dynamic stress analysis and the remaining life assessment of corrosion fatigue crack growth in the railway steel bridge node area by the action of the train running load were studied deeply and systematically in this paper taking a railway steel bridge as the engineering background and adopting the research way which combines the theory with the reality.According to the existing domestic and international research progresses and results of the remaining life of corrosion fatigue crack growth of railway steel bridge and combining with the engineering background,the research focuses on the following aspects:(1)Based on practical engineering background,the finite element simulation method of fatigue crack was researched,and the overall shell model of railway steel bridge and 29 groups entity sub-models of node were built respectively by the sub-model method which is one of the structural multi-scale analysis methods using ANSYS software.(2)According to actual engineering survey,train running load was calculated using MATLAB software.Then imposed to the overall model of the railway steel bridge,the load and boundary conditions of the entity sub-model of steel bridge node containing cracks were contained.Using rain flow cycle counting method,the stress amplitude of the node entity sub-model boundary region was extracted out.Appling the stress amplitude respectively to the entity sub-model of crack propagation,the stress and strain time history curve of crack tip region of the railway steel bridge node were achieved for dynamic stress analysis.(3)Based on fracture mechanics theory and displacement extrapolation method(a computational method of stress intensity factor on the basis of ANSYS program),stress intensity factor K of the 3D fatigue crack tip of the railway steel bridge node region was calculated and stress intensity factor database corresponding to crack propagation process was established by groups of crack growth models.(4)Using the corrosion fatigue crack propagation remaining life assessment theory of fracture mechanics and the crack propagation engineering model based on Pairs formula,the corrosion fatigue crack propagation remaining life calculative program was written by cumulative superposition method cycle by cycle,and the corrosion fatigue crack propagation remaining life of the railway steel bridge node region in different initial crack sizes and different train speeds were calculated to compared analysis.In summary,this research combined multi-scale finite element analysis method of structure based on sub-model method with corrosion fatigue crack propagation remaining life assessment theory based on fracture mechanics,which has certain applied value for the corrosion fatigue life assessment of complicated engineering structures.In this paper,the fatigue crack propagation life evaluation method for the complex engineering structures of large railway steel bridges was obtained.Therefore,service life of railway steel bridge components with corrosion crack under the action of train running load is determined and the safe use of steel bridge in the service life was ensured.So it is significant to the effective operation and maintenance of railway steel bridge and national rail travel safety.