Research On Reliability Of A7N01Aluminum Alloy Welding Joints And Repair Welding

With the high-speed trains continuously improving the speed, security issueshave become increasingly prominent. Currently, in order to detect the security risks intime, it’s necessary to do regular testing. For the founded defects, what theengineering practice usually does with the detected surface defects of different types,different locations, and different sizes is to repair welding with uniform norms.However, the influence mechanism for repair welding to welding structure serviceperformation is complex due to repair welding often accompanied by jointperformance degradation, structure residual stress field changing, and it’s the hot topicin the structure safety research field. So it’s theoretically important and engineeringsignificant for improving service safety of high-speed train to establish a reasonableguideline for assessing defect repaired.This thesis takes A7N01aluminum alloy welded joints of the high-speed train asthe research object, by means of finite element simulation, as well as experimentalanalysis, and uses the BS7910method to do safety assessment for before and afterrepair welding joints. Besides, based on fracture mechanics theory, Paris formula isused to calculate its remaining life, and ultimately the paper put forward repairwelding norm of meeting the reliability requirements. Specific work and researchinclude the following aspects.The vehicle chassis stress distribution under service dynamic loads is obtainedby numerical simulation and experiment, and considering the work stress and residualstress of high-speed train chassis welded structure, high stress areas of before andafter repair welding are taken as three dangerous point for safety assessment position.Based on fracture mechanics theory, this paper utilizes finite element simulationcalculation for three typical butt joint of train chassis to get the crack shape factor as afunction of crack length for three typical joints before repair welding and joint afterrepair welding, which can provide the basis for assessing the reliability of high-speedtrain chassis.BS7910method is applied to do safety assessment for three dangerous points.The results of FAD show butt K-joint is the least secure. For welded joints with the actual existence crack, the results which assessing Brittle Crack separately forsemi-elliptical surface cracks and unilateral cracks show that three positions are bothassessed to meet safety requirements. Calculating the crack tolerance for the twotypes of cracks separately under the given conditions, the results show unilateral crackis more dangerous than semi-elliptical surface crack.Paris formula is used to calculate the residual fatigue life of three dangerouspositions for penetrating crack. The results show that, if the same initial crack lengthin the before-and-after repair welding joints, repair welding will bring in the reductionof joints bearing capacity. If the different initial crack length, the results show that theresidual fatigue life of after-repair welding joints is greatly improved, indicatingrepair welding is still an effective method to improve the carrying capacity of jointunder the presence of cracks. Finally, under the security conditions, based on theprinciple of the same remaining life for before and after repair welding, a defectoverhaul measure guidelines have been established and the guidelines can provide ascientific basis for the practical application.