| The fatigue performance of heavy rail is required to be improved because of the high-speed heavy rail,and the fatigue life of heavy rail in service should be predicted according to the requirements of safe operation.In this paper,the fatigue performance and fatigue life of heavy rail are studied by means of contrastive analysis of experimental results,and the relationship between fatigue fracture and corresponding fatigue life becomes a key problem in this paper.The fatigue test of BGRE and U76 Cr heavy rail was carried out in this paper,and the fatigue performance of BGRE and U76 Cr heavy rail under different stress and different heat treatment mode was compared and studied.The high frequency fatigue testing machine was used to test the fatigue life of the heavy rail under the same stress ratio.The fatigue life of the heavy rail under different stress levels was measured between 335 MPa and 400 MPa.The S-N curve of the BGRE heavy rail was obtained.Compared with the same stress level,the fatigue performance of BGRE heat treatment state is better than that of rolling state,and the stress amplitude is calculated according to the micro fracture fatigue strip,the calculation error is about 8.05%,which can be used as a reference for fatigue life prediction.In order to study the effect of heat treatment on the change of fatigue performance of U76 Cr heavy rail,fatigue tests were carried out with U76 Cr heavy rail in different heat treatment states.The results showed that:the fatigue performance of rolling state,heat treatment state and 8 ?/S cold quenching state were significantly different.The fatigue life of U76 Cr 8 ?/S cold quenching state after heat treatment was 1.8 times longer than that of heat treatment state and 4.5 times longer than that of rolling state,and the fatigue performance of heat treatment state was significantly improved.The fracture performance is as follows : at the macro level,the fatigue source area,the fatigue extension area and the fatigue transient fracture area have obvious differences in the area proportion,while at the micro level,the fatigue extension area has greatdifferences,and the differences in fatigue crack,secondary crack,fatigue pattern and cleavage surface are all obvious.The results show that the fatigue life of rolled U76 Cr and BGRE heavy rail is 29,612 times and 56,496 times respectively,and the fatigue life of U76 Cr and BGRE after heat treatment is 75,160 times and 73,209 times respectively.In the microscopic fracture,fatigue cracks appeared in both of the two rolling heavy rails,but they were sparse and arranged in roughly parallel ways.However,there are river patterns on the surface of the fracture in the heat treatment state,no fatigue cracks are generated,and the secondary cracks are not obvious.Through the above experimental research,the fatigue properties of BGRE and U76 Cr rail are clarified.The fracture causes can be analyzed by fracture analysis.The analysis of fracture morphology of test pieces can provide reference for predicting rail fatigue life,which is of great significance for fatigue research in practical engineering. |
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