Research On Fatigue Failure Causes And Reliability Of Weld Joints Of Bogie Traction Rod Bracket Of HDX2 Locomotive

With the rapid expansion of China’s high-speed railway network,the demand for high-speed railway locomotives to operate in complex terrain and extreme road conditions is rapidly increasing,and the safety and reliability of locomotives are facing stricter tests.As an important structural component of railway vehicles,locomotive bogies transmit complex loads during locomotive operation and ensure smooth operation of the locomotive,which is a key component to ensure the safe service of the vehicle.In this paper,the failure mechanism analysis is carried out for the phenomenon that multiple cracks appear on the fillet weld of the bogie traction rod bracket when the service mileage of HDX2 electric locomotive running on a line crossing the Qinling Mountains does not reach the design value,and the failure reason and improvement method are simulated according to UIC615-4 standard load conditions and Goodman fatigue limit diagram,Perform fatigue tests on failed and optimized traction rod bracket welds based on line load data.The research results of this article are as follows:1.Failure analysis was conducted on the weld seam of the frame pull rod seat where cracks occurred.It was determined that the main reasons for the cracks in the weld seam were the locally large gap between the pull rod seat and the substrate,defects such as incomplete penetration and air holes at the root of the pull rod seat fillet weld,and the calculated thickness of the weld seam at the local position of the pull rod seat was too low.This resulted in excessive stress concentration at the root of the pull rod seat fillet weld seam,leading to the initiation of cracks and the continuous expansion of cracks during locomotive operation,the microstructure and mechanical properties of the material have little effect on weld failure.2.Based on the failure reasons and improvement methods of the fillet weld of the bogie pull rod seat of this type of locomotive,simulation calculations were conducted to study its fatigue reliability.The results showed that the static and fatigue strength of the two types of pull rod seats in the original design scheme(A6)of the frame pull rod seat weld met the requirements under UIC standard working conditions.When there were standard allowable maximum root gaps,side wall incomplete fusion,root incomplete fusion,porosity defects,and crack defects in the fillet weld of the pull rod seat,Except for the maximum crack defect,all other model calculation results meet the fatigue strength requirements.3.The calculation results of the reinforcement plan(A8)for the weld seam of the pull rod seat meet the static and fatigue strength requirements under standard working conditions.When there is the maximum allowable defect in the fillet weld seam of the pull rod seat,the A8 weld seam has better tolerance for defects.After repairing the welding seam of the in-service construction to A8,in order to reduce the impact of welding residual stress,stress relief treatment must be carried out on the welding area.4.Combined with the test line data processing,the three stage fatigue test under the equivalent load of the test line was carried out on the existing welded structure,the repair plan of the existing welded structure weld defects and the welded structure with increased weld thickness.The results proved the reliability of the repair of the existing welded structural join connection weld defects of the locomotive B-type pull rod seat and the safety of optimizing the fatigue performance of the welded structure.