Life Prediction And Realization Of Low Cycle Fatigue Welded Joints Based On Structural Strain Method

Welding technology is a commonly used connection method for rail vehicles.Welded joints are locations where vehicle fatigue damage often occurs.Fatigue damage is divided into high-cycle fatigue and low-cycle fatigue.The methods for evaluating the high-cycle fatigue life of structures currently include nominal stress method,hot spot stress method,and structural stress method.At present,the research methods for the prediction of low cycle fatigue life of welded joints are mainly from the aspects of strain-stress and initial failure cracks.There is not much development of software for low cycle fatigue life prediction.In order to solve this problem,this paper studies the principles of elastoplastic mechanics and low-cycle fatigue structure strain method,designs and develops a visual software system suitable for the prediction of low-cycle fatigue life of welded joints,and finally verifies the software system with examples,Indicating the practicability and effectiveness of the software.The specific research contents of this article are as follows:(1)Study the theory of structural strain method and realize its calculation module.This article first studies the basic concept of low-cycle fatigue,and then learns the principle of the structural strain method.After obtaining the pseudo-structure stress data similar to the structural stress method,the equivalent structural stress parameter method is used to solve the fatigue life,the structural strain method evaluation process is programmed,and the low-cycle fatigue calculation module of the structural strain method is implemented.(2)Researched visualization theory and implemented fatigue visualization module.In order to facilitate designers to modify and communicate with each other,this article based on OSG three-dimensional platform to visually develop fatigue life data of welded structures,through the visualization platform to improve the process of fatigue life assessment.(3)Design and implement a life prediction system based on the structural strain method.Based on the theory of structural strain method,a visualized low-cycle fatigue life prediction system was designed and developed.The system consists of 6 modules: finite element interface module,load spectrum module,structural strain calculation module,pseudo-structure stress calculation module,and post-processing module.(4)An example is used to verify the effectiveness of the evaluation system.By evaluatingthe examples of closed circular welds and non-closed straight welds,comparing the life results obtained by the structural strain method and the structural stress method,the life evaluation of the welded joint is finally carried out.The low-cycle fatigue life prediction system developed in this paper provides computer software support for low-cycle fatigue life prediction and also has a visualization function.Redistribute the stress of the welding material and predict the low cycle fatigue life.The results show that the evaluation software has good practicability and effectiveness,and at the same time,the stress concentration location can be observed through the life cloud image.Compared with the fatigue life calculated by the structural stress method,the life prediction data of the structural strain method at the weak position of the weld is more cautious.