Numerical Simulation And Experimental Study On Double Fatigue Crack Propagation Of Steel Bridge Deck Welds

Orthotropic steel bridge deck is the primary structural form of long-span steel bridge deck.However,due to its complex structure,many welds and high residual stress,cracks are easy to initiate and expand rapidly at the welding defects under the action of vehicle.With the aging of bridges,the size and density of fatigue cracks in existing steel bridge decks increase,which leads to the enhancement of the interaction between near source multi cracks.The multi crack communication and fusion is the main crack and continues to expand,resulting in the sharp decline of local stiffness of steel bridge decks,which greatly affects the fatigue life of steel bridge decks.This paper is supported by the National Natural Science Foundation of China,"Fatigue reliability evaluation for welded joints in steel bridge decks considering coupled propagation of multiple cracks(51908068)",aiming at the characteristics of collinear double fatigue crack coupling growth of steel bridge deck,the influence of Double Crack coupling sensitive parameters on crack growth is revealed by using finite element numerical simulation and fatigue test analysis methods,and the dynamic growth behavior of single crack and multi crack at the weld toe is compared,The fatigue life of collinear double cracks is evaluated,and the finite element results are verified by full-scale segmental test model.The main research contents are as follows:(1)Based on linear elastic fracture mechanics and finite element analysis method,the coupled propagation behavior of double cracks at the joint of steel deck top plate and U-rib weld is analyzed.The results show that when the collinear double crack coupling propagation occurs,the spacing between the two cracks has a significant effect on the stress intensity factor at the near point of the crack,and the maximum interaction factor can reach 1.26,while the far end and depth points are less affected by the crack spacing,but the interaction factor is always greater than 1,which proves that there is amplification effect between near source multiple cracks;(2)The sensitive parameter analysis of Double Crack coupling propagation in weld is carried out,and the influence law of parameters such as basic crack shape,interference crack position and shape on crack coupling propagation is revealed.When the shape ratio of collinear double cracks is 0.5 and the crack spacing is half of the crack semi major axis,it can be taken as the effective distance of collinear double crack coupling propagation,and the basic crack shape ratio has a positive correlation with the effective distance of coupling propagation.When the basic crack shape is relatively large,the interference crack will also have a great impact on the crack depth point and distal point.(3)The crack propagation and fusion process of collinear double cracks are simulated,and the fatigue life of the crack is evaluated.The equivalent crack front criterion is selected to simulate the fusion of collinear double cracks at the weld of steel bridge deck.During the fusion process,the main crack propagation direction will change to the depth direction until the end of the fusion.The influence of coupled propagation on crack fatigue life is mainly reflected in that the early fusion of the initial crack increases the crack size and causes the acceleration of crack propagation.However,after the crack reaches the fatigue life,it does not stop growing,and the crack will continue to expand in the length direction,and it is very easy to fuse to form an ultra long crack.(4)The fatigue test of full-scale segment model of steel bridge deck is carried out,and the reliability of numerical simulation analysis results is verified.when a crack is initiated at the weld,its stress will decrease rapidly and cause local stress redistribution,and the stress at the near point of the crack is greater than that at the far point of the crack.The crack propagation behavior and propagation law are basically consistent with the theoretical simulation,which proves that there is collinear double crack coupling propagation effect under the effective spacing.