A Method For Predicting The Total Fatigue Life Of Steel Bridge Welded Structure Considering The Influence Of Residual Stress Is Presented

The study of fatigue life of welded steel bridge has important practical significance because of the repeated action of traffic load for a long time.As a new type of intelligent welding technology is widely used in steel bridge construction,welding initial defects are effectively eliminated,including crack initiation phase of the total life of welded structure fatigue assessment more accords with the demand of engineering,for this reason,the paper proposes a total bridge steel welded structure fatigue life prediction method combined with the critical distance method and fracture mechanics theory.At the same time,considering the significant influence of welding residual stress on fatigue crack initiation and propagation life,the influence of residual stress is included in the fatigue life prediction program based on the three-dimensional finite element analysis of residual stress distribution.The main research work and conclusions are as follows:(1)Taking the unequal plate butt weld joint and the non-load-carrying fillet weld joint as research objects,the distribution results of welding temperature field and stress field are obtained by dynamic simulation of welding process with 3d finite element.The availability of the simulation method is verified by relevant experimental test results,and the spatial distribution law of transverse welding residual stress is provided.(2)Proved that the critical distance are derived according to the fatigue failure criterion theory is applicable to fatigue crack initiation life analysis,based on the critical distance theory,a method for calculating the fatigue notch coefficient of crack initiation is presented and the effective stress concentration coefficient of crack initiation is calculated.The effective stress concentration coefficient of crack initiation considers the influence of residual stress,and the crack initiation life of two welded joints is predicted.The influence of residual stress on the initiation life was quantitatively analyzed by comparing the prediction results of the initiation life with and without residual stress.(3)Based on the theory of fracture mechanics,a method to modify the crack stress intensity factor according to the size of the transient crack was proposed,and the residual stress intensity factor was solved by using the weight function method.Then,the propagation life of two welded joints is predicted by using the crack propagation rate model.According to the distribution law of residual stress intensity factor along crack depth,the influence of residual stress on propagation life was studied.And the influence of transient crack size on fatigue crack propagation is discussed by analyzing the modified parameters.(4)The prediction results of initiation life and extended life were superimposed to obtain the predicted total fatigue life,and the accuracy of the method is verified by the results of fatigue test.According to the prediction results of the total fatigue life,the stress-total life curves of the two welded joints are given,and the applicability of the prediction method and the influence of residual stress on the total life are evaluated.By analyzing the proportion of the initiation life and the extended life in the total life,it is shown that the initiation life cannot be neglected in the fatigue life evaluation.