Study On Fatigue Behavior Of Oblique Cross Welded Joints Of Steel Bridge

The Cross welded joints are more and more widely used in long-span steel bridges,and they are prone to fatigue cracking under external action,which is related to the structural safety of steel box girders,so it is of great significance to study the fatigue performance of oblique cross welded joints.In this thesis,taking the actual engineering as the research background,based on the fatigue details of oblique cross penetration welded joints,a 60°angle is constructed to simulate the complex stress field under the combined action of normal stress and shear stress,and the test of oblique cross penetration welded joints is designed.the fatigue life of the welding detail was studied by fatigue test.On the basis of experiments,the finite element simulation of the fatigue details is carried out,and the hot spot normal stress and hot spot shear stress at the weld toe are obtained by linear extrapolation and quadratic extrapolation,and the fatigue life of skew cross penetration welded joints is predicted based on hot spot stress method.Finally,the crack propagation life is obtained by using the crack propagation analysis software FRANC3D,and the effects of crack depth,crack shape ratio and external load are analyzed.After the above exploration and analysis,the main conclusions of this paper are as follows:(1)As far as the experiment is concerned,the overall welding effect of the test pieces of group A and group C is better than that of group B.There is a big difference between the value and the theoretical value;Observing the fracture,it can be found that under the action of cyclic loading,the fatigue crack is formed from the weld toe of the obtuse angle and gradually expands laterally.(2)After the fatigue life evaluation of the specimen is carried out by using the equivalent force method and the interaction equation method of the hot spot stress method,it can be seen from the results that the theoretical value calculated according to Eurocode3 is the most conservative,which is speculated to be caused by the excessive tilt angle of the specimen.The theoretical value calculated according to the maximum principal stress is the largest,and it is speculated that this failure mode may be closer to the failure of the base metal.The actual value of the specimen is closest to the theoretical value calculated by the equivalent hot spot stress.(3)After the parametric analysis of the specimen,it can be found that:(1)the deeper the initial crack is,the larger the K_Ⅰand K_Ⅲare,but the smaller the K_Ⅱis;(2)when the shape ratio increases from 0.4 to 1.0,the stress intensity factor at the A end decreases gradually,and the stress intensity factor at the B end increases gradually,and the greater the eccentricity of the crack,the greater the difference between the A end and the B end.(3)the greater the external load,the greater the stress intensity factor.(4)The fatigue life of different specimens is predicted by FRANC3D,and after comparing the results with the actual values,it can be found that the results of A1 Magi B1and C1 are close to the theoretical values,and the actual values of B3 are much smaller than the theoretical values,which is speculated to be caused by the excessive offset of the sub-plate of specimen B3.In addition,from the fatigue life curve,it can be seen that the crack growth is relatively slow in the early stage,and the crack growth rate will increase sharply when the crack depth increases to a certain extent.