Investigation of fatigue fracture features in elastic clamps of railway fastening systems

Introduction. In this article, a study was conducted focusing on the investigation of fatigue fracture characteristics of elastic clamps used in railway fastening systems, which were subjected to fatigue tests following standard and accelerated methodologies. The problem of improving the quality and extending the service life of rail fasteners, particularly elastic clamps, has become the most acute at the present time. The reason is the development of high-speed and heavy train traffic. In operation, the elastic clamp perceives preloading by mounting force and dynamic loading by cycles of preloading and partial unloading due to the impact of rolling stock. Fatigue life is the most important parameter determining clamps reliability and train safety. The purpose of this study is to analyse the main mechanisms of fatigue fracture of three clamps tested under various cyclic loading modes (according to standard and accelerated test methods) by examining fatigue fracture surfaces.

Materials and methods. The elastic clamp CP 369.102 (clamp ZhBR-65) was chosen as the object of the study. The tests were performed using both the standard method that meets the requirements of GOST 33186–2014 and the accelerated Locati method. Fractographic method was used in the analysis of clamps fatigue fracture surfaces.

Results. The similarity of processes leading to fatigue fracture has been established for clamps tested using standard and accelerated methods. A fractographic analysis was conducted on the fatigue fracture surfaces of three elastic clamps. An analysis of the fatigue fracture mechanism is provided for each clamp. For the clamp tested by the standard method, a non-metallic inclusion was found at the crack initiation site.

Discussion and conclusion. In all studied cases, the fracture of the clamps was accompanied by the initiation of fatigue microcracks originating from inclusions or defects on the lateral surface (the rod surface of the clamp). Current standard does not normalise contamination with non-metallic inclusions intended for the manufacture of clamps. It is reasonable to conduct additional studies in order to assess the influence of non-metallic inclusions in the steel on the fatigue durability of the clamps.

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