Dislocation Mechanisms and Local Strength with a View towards Sleeper Screw Failures

Dislocation structures can be directly related to the fatigue properties of metals, such as fatigue strength, including the fatigue limit and saturation stress. We present an indirect dislocation-structure-based method to evaluate the local stresses for an in-depth analysis of sleeper screw failures, as there is little knowledge about the load and local stresses related to these failures. The sleeper screw, fastening baseplates of rails to sleepers, is a small but critical component in the railway. High loads from passing trains are transferred to the screws, leading to cyclic straining. In the present study, three stress-level tension fatigue experiments are designed in the constant stress mode at a stress ratio R = 0 and a testing frequency of 10 Hz. The microstructures in the failed specimens are characterized and compared with those close to the fracture surface of screws that failed in the field. The dislocation structure similarities and differences are analyzed, and the potential of the proposed methodology is discussed.