Study On Fatigue Strength Of Welded Frame Of Suspension Monorail Bogie

With the continuous progress of society and the rapid development of economy,urban traffic congestion has become an important factor restricting the development of cities.Vigorously developing urban public rail transit can effectively relieve the pressure of urban traffic congestion.As a new type of medium and low volume urban rail transit system,suspended monorail system can basically realize zero distance transfer with the existing subway,bus,light rail,etc.,which is an excellent choice to solve the problem of urban traffic congestion.Suspension monorail system has a great development prospect in our country.As one of the most important parts of suspension monorail,bogie structure is related to the running quality and driving safety of the train.On the basis of fully studying the technical characteristics of advanced bogies at home and abroad,this paper designs a suspension monorail train bogie which uses a single motor to drive two axles at the same time.Firstly,the bogie’s overall structure is designed in detail by using the 3D modeling software CREO.Secondly,the standards or norms for fatigue strength evaluation of welded joints are introduced in detail,and their limitations and advantages and disadvantages are pointed out.Then,according to the European EN13749 standard and the International Union of Railways UIC615-4 standard,the static strength and fatigue strength of the bogie frame are evaluated.Finally,the welded joints at the lower beam of the frame and the stiffened plate of the end beam of the frame are taken as the research objects.The fatigue cumulative damage of the welded joints is evaluated by using the nominal stress method,the hot spot stress method,the structural stress method and the notch stress method respectively,and the rationality of the evaluation of different stress methods is discussed.After the strength calculation of the framework,the following conclusions are drawn:1.The maximum equivalent stress value of the frame is within the range of allowable stress under the condition of abnormal load.Under 10 kinds of abnormal load conditions,the maximum stress of the frame is 329.55 MPa,and the minimum safety factor is 1.08.The stress distribution of the frame is reasonable and the utilization degree of materials is high.2.Under normal operating load conditions,only 8 joints are not within the envelope of Smith-Goodman fatigue limit chart based on the maximum principal stress method.According to UIC615-4 standard and relevant regulations,the frame meets the fatigue strength requirements.3.The cumulative damage value of notch stress method is greater than the critical damage value given by the standard,and the fatigue evaluation result based on notch stress method is too conservative.The cumulative damage values based on the nominal stress method,the hot spot stress method and the structural stress method are all less than the critical damage values given by the relevant standards.4.When nominal stress method and hot spot stress method are used to evaluate the accumulated fatigue damage of welded joints,the S-N curve with low fatigue grade is recommended.The structural stress method is insensitive to the finite element mesh density and has more advantages than the nominal stress method and the hot spot stress method.With the accumulation of notch data and the corresponding prototype test,notch stress method can give play to its advantages in the future.