Influence of mean stress on contact wire fatigue

Abstract

When a pantograph passes underneath a contact wire, the upward force causes a bending stress in the contact wire. If this stress is high and occurs frequently, there is a possibility that the contact wire will suffer a fatigue fracture. To estimate the fatigue life of a contact wire, we have been using the S-N curve prepared for a mean stress of 88.2 MPa. In addition, a contact wire is gradually worn down by running contact strips so that the mean stress governing its fatigue life gradually increases. To estimate the fatigue life of a worn contact wire correctly, therefore, the influence of the mean stress on contact wire fatigue needs to be examined. For this paper, we carried out fatigue tests on GT110 hard-drawn copper contact wire at a mean stress of 154.2 MPa to obtain another S-N curve. Then, by using parameters that included the mean stress, we prepared a fatigue curve that integrates S-N curves for any mean stress. Finally, we estimated contact wire fatigue damage using this fatigue curve and proposed a new method to establish the allowable bending strain amplitude.