| The fatigue life of the load bearing structure determines the safe operating life of the equipment,fatigue analysis of structural is an essential part of equipment design and manufacturing and service maintenance.However,the fatigue analysis of structural is different from the material specimens,that their fatigue characteristics are different.The fatigue life of the structure is not only affected by the load,but also closely related to the structure's characteristics and its load carrying capacity characteristics.In order to obtain a fatigue life prediction method closer to the actual situation,the cast aluminum beam that a bearing structure of the CRH5 EMU is taken as an example in this paper,and the characteristics of the structure itself and its carrying capacity characteristics is taken into consideration to analysis.Details are as follows:(1)The fatigue test of the cast aluminum beam is carried out to investigate the stress response under the actual load of the structure.The accuracy of the finite element model of cast aluminum beam is verified by comparison with finite element stress analysis.The high stress areas and the dangerous locations of the structure is determined by structural stress analysis.(2)A rigid-flexible multi-body dynamics model of CRH5 intermediate vehicle with undercarriage transmission system is established.The simulation based on the track irregularity spectrum and actual line conditions of the Beijing-Tianjin line,which obtain the random running load of the cast aluminum beam.And then the random load is analyzed from the perspective of time domain and frequency domain.Combined with finite element transient analysis,the stress-time history of cast aluminum beam under running load is obtained.And using the statistical analysis of the rain flow counting method,an eight-level stress spectrum is prepared.(3)Analyzed the influence factors of stress concentration,size effect and surface processing quality of the structural characteristics.The structure's S-N curve is obtained by modifying the S-N curve of the material with the influence factors.Among them,the stress concentration factor is obtained by defining the stress integral path at the most dangerous position section and calculate the nominal stress.The size factor is obtained by the stress field intensity approach.According to the obtained stress concentration factor,elliptical and U-shaped two kinds of notched flat specimens are designed to obtain the damage field diameter,and the calculation results are mutually verified.The size factor is obtained by taken the field strength of the cast aluminum beam and the small notch specimen as intermediate parameter.The result shows that:The damage field diameter in the stress field strength method is related to the material properties and the stress concentration factor,and is independent of the shape of the notch that causes the stress concentration.(4)In order to analyze the influence of residual strength degradation on damage accumulation,based on the existing Corten-Dolan model considering residual strength degradation,the exponential parameter d in the model is redefined as an exponential function related to the residual strength degradation coefficient,which is introduced into Corten-Dolan model analysis.The multi-step load test data analysis shows that the Corten-Dolan cumulative damage model with the exponential parameter d considering the residual strength degradation has a certain improvement compared with the traditional model.Based on the structural S-N curve and two cumulative damage models,the equivalent damage analysis of the test damage is carried out.The results show that the Corten-Dolan model with the exponential parameter d considering the influence of residual strength degradation considers the influence of residual intensity degradation compared with the traditional model.The predicted mileage is smaller and more conservative. |
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