Failure analysis of the conductive slide support rod of section insulator applied in urban rail transport system

Abstract

The support rod of conductive slide of a section insulator which was applied in urban rail transport system fractured after operation for about 4 years. The failed section insulator was installed at the turning of the train route. Multiple failure causes had been analyzed utilizing a combination methods of chemical composition analysis, mechanical property test, metallographic examination, macro morphology and microstructure observation. The support rod is made of AISI-304/L/C stainless steel. No obvious microstructure defects are detected in crack origins or the matrix material. The mechanical properties and the chemical composition satisfy the requirement. The failure mechanism of the support rod is proved to be high cycle fatigue fracture (HCF). The main fatigue crack origin locates at the right-angle edge of the arc-shaped transition region of the support rod where stress concentration can be generated easily. In addition, arc discharge-induced cracks can be observed on the local burned surface of the support rod, and they contribute a lot to the fatigue crack initiation. Finally, the alternating load mainly results from the change of train operation direction at the turning position and this change further leads to the direction change of the contact force between pantograph and insulator section. Besides, the impact, vibration and unsmooth contact caused by pantograph also contribute to the alternating load.