The Influence Of Cast Pore On The Local Cyclic Stress And Strain Of High Manganese Steel For Crossing

Rail transport plays an important role in national economy,and the railway frog made of high manganese steel accounts for 90% of railroad frogs.Under its practical service conditions,the railway frogs are often subjected to repeated rolling and impact from the wheel.Therefore,the concentrations of stress and strain near the cast pore are inevitably existent,which tend to result in damage and failure and decrease the service life of frogs.Consequently,the research into the local cyclic stress and strain behavior around cast pore is significant for protecting the safety of people's lives and property and contributes to preventing and avoiding fatigue and damage problems in engineering components.Low-cycle fatigue(LCF)tests were performed and the Chaboche's material parameters were obtained via math software MATLAB using the LCF data.The Chaboche's model incorporates both the Bauschinger effect and cyclic hardening under fatigue loading.Three-dimensional(3D)image-based numerical simulation was performed,which considers the 3D shape of actual irregular pore visualized via high-resolution synchrotron X-ray computed tomography and 3D visualization software VGstudio.The local cyclic stress/strain behaviors around a single actual pore was investigated,and compared with those around an idealized ellipsoidal and a spherical pore.Afterwards,models,containing multiple pores or two actual pores,were also created.The local cyclic stress/strain behaviors around multiple pores and also the interactions between stress/strain fields of adjacent pores were investigated.Finally,the stress/strain distribution in an actual frog and as well the influence of a single pore were studied.The results show that stress and strain are all concentrated near the pore at different loading stages in the first cycle for either the single-pore,double-pore,or multi-pore models.Even if the externally-applied strain is fully unloaded,the local residual stress and strain are still largely concentrated around pores.Such residual stress and strain gradually increase with the increase of externally-applied strain.Furthermore,the local stress and strain near a certain pore in the case of multi-pore models is obviously smaller than in the case of single pore only at various cyclic loading stages.This result indicates that the stress and strain around the object pore under investigation shielded or sheared by other pores in the multi-pore model.According to the results of double-pore models,with the increase of pore size or the decrease of pore-pore distance,the stress/strain fields between two adjacent pores are overlapped and mutually enhanced.It is suggested that a pore has an amplification effect on the stress and strain fields around a closely-adjacent pore under investigation.The simulation results,from the frog model containing a single pore,show that the pore shape,orientation,and depth all have influences on the local stress/strain distribution in the railway frog.The concentrations of stress and strain near the actual pore are significantly larger than those near the idealized spherical pore in the frog.The concentrations of stress and strain in the frog with an elongated,horizontally oriented irregular pore are larger than when the pore is slanted or even much larger than when the pore is vertically oriented.Furthermore,it is demonstrated that the stress and strain concentrations decrease gradually with the increase of pore depth below the tread of the frog.