Study on Torsional Fretting Fatigue Behavior and Its Damage Mechanism for Train Axle Safety Service

Jinfang Peng, Zhibiao Xu, Yanping Ren, Jianhua Liu, Minhao Zhu^*[1]

Traction Power State Key Laboratory, Southwest Jiaotong University, Chengdu 610031

ABSTRACT: With the rapid development of global economy, it is urgent to develop transportation toward high speed and heavy load. After the import, digestion, absorption and re-innovation of high-speed railway in China, railway development has entered into the stage of stable operation. Service safety, quality and efficiency improvement have become the important development direction. The service safety is the cornerstone of the whole industry, among which the reliability of axle service is one of the core problems. As one of the main fretting fatigue modes, torsional fretting fatigue has few been reported. So, the overall study of torsional fretting fatigue behavior is necessary, its failure mechanism not only has important scientific significance for understanding fretting fatigue damage mechanism and improving tribology theory, but also can provide theoretical guidance for resisting torsional fretting fatigue damage.

In this study, a pneumatic device is designed based on multi-axis fatigue testing machine which can provied normal loading. The damage mechanisms of torsional fretting fatigue for the two materials of Different Crystal Structures have been investigated systematically, which is using micro-analysis metohods of optical microscope(OM), scanning electron microscope(SEM), electron energy disperse spectroscopy(EDX), X- ray photoelectron spectrometer(XPS), electron probe microscope(EPMA), transmission electron microscope(TEM) and white light interference surface profile-meter with high-flux test method. The S~N curves database of torsional fretting fatigue on two materials was established, the torsional fretting fatigue life was much shorter than the plain fatigue due to the fretting actions, which might decrease to 20%~80%, or even lower. With torque stress increasing, the fretting fatigue life of materials showed decreasing firstly, and then abnormally increasing, finally decreased again. Based on the theory of fretting maps, the S-N curve can be divided into three areas: the partial slip zone (PSR), the mixed zone (MFR) and the slip zone (SR). The microstructure evolution in the contact zone of torsional fretting fatigue was closely related to the crystal structure of materials. The TEM analysis results showed: for the austenitic stainless steel with FCC structure, the evolution of dislocation configuration changes from the twinning to dislocation cell deformation mechanism with the torsional stress increasing. But for the carbon steel with BCC structure, the evolution of dislocation configuration was mainly in the tangles, accumulation and climb of dislocation, and finally it was in the mechanism of dislocation cell deformation.

Keywords: fretting damage；torsional fretting fatigue；high-flux test method；microstructure