Fatigue Crack Propagation Analysis And Life Prediction Of Q690 High-strength Steel Joint Plate

The joint plate of a long-span steel bridge is an important connecting member,It is subject to complex forces and is prone to fatigue failure.Thanks to the excellent performance of high-strength steel,Q690 high-strength steel has begun to be used in the construction of long-span bridges.Therefore,it is necessary to analyze the Q690 highstrength steel joint plate fatigue crack propagation of long-span steel bridge.The S-N fatigue strength curve fatigue analysis method has been widely used in various national codes.This method has the disadvantages of high test cost and difficulty to analyze initial cracks.Based on the fracture mechanics method,fatigue crack propagation rate tests were carried out on Q690 high-strength steel base material and butt welds.Using the interaction of Abaqus and Franc3 D,fatigue crack propagation analysis and life prediction were performed on the Q690 high-strength steel joint plate of long-span steel truss arch bridges.The main research results of this thesis are as follows:(1)As the stress ratio R increases,the fatigue crack propagation rate of both Q690 base material specimens and weld specimens increases.The Paris parameters C and m of Q690 high-strength steel base material and welds were obtained,and a Paris correction formula for Q690 high-strength steel base material concerning stress ratio R was proposed.The fatigue resistance of Q690 high-strength steel is significantly higher than that of ordinary steel such as Q345 q D.(2)Introduced a numerical analysis method for simulating fatigue crack propagation using Abaqus and Franc3 D,and compare experimental data with simulation data.The results show that this method can accurately simulate fatigue crack propagation with high precision.(3)By establishing a Midas/civil full-bridge model for the overall analysis of a longspan steel truss arch bridge,the dangerous nodes were determined and the load spectrum analysis was carried out on the dangerous nodes.A refined Abaqus model was established for the joint plate to analyze the fatigue crack propagation performance.The results show that the stress intensity factor at the crack tip of the joint plate and the fatigue crack propagation rate increase with the crack length increase.After the crack propagates to a certain extent,the crack propagation rate exponentially increases and the structure fails rapidly.(4)The joint plate fatigue crack propagation life of the base metal and weld were analyzed respectively.Analyzed the impact of initial crack location,material,and initial crack on the residual life of fatigue crack propagation.The results show that Q690 highstrength steel can significantly improve fatigue life,and the weld life of Q690 highstrength steel is longer than that of the base metal.The initial crack size has a significant effect on the residual life of fatigue crack propagation.This thesis carries out fatigue crack propagation rate tests on Q690 high-strength steel base material and welds,filling the gap in fatigue crack propagation parameters for Q690 high-strength steel base material and welds.And proposes a numerical analysis method for fatigue crack propagation,which can be accurately and efficiently applied to the evaluation of the residual life of fatigue crack propagation in actual engineering projects.Fatigue crack propagation analysis and life prediction were performed on the Q690 high-strength steel joint plate of a large-span steel truss arch bridge.