# Evaluation of Structural Behavior and Fatigue Performance of a KR-Type Rail Clip
## 1 Introduction  
A rail fastening system clamps rails to railway sleepers or railway ties and is the main component of a railway track that delivers the trainload to the substructure. A rail clip (or rail clamp) is an essential part of a rail fastening system and provides a clamping force linking the rail and sleeper together to prevent tipping and the longitudinal and transverse displacement of the rail.  
A rail clip can be vulnerable to fatigue cracks because it is acted upon by high initial stresses during the assembly process and fluctuating stresses from repeated trainloads. Fatigue damages of rail clips have been reported in South Korea and other countries (see Figure 1 as an example) [1, 2]. If fatigue damage of multiple rail clips occurs simultaneously in a railway track, potential train derailment could occur, placing passenger comfort and riding safety at risk.  
Although the assessment of fatigue performance of rail clips plays such a vital role in terms of ensuring safety, limited research has been performed to investigate the exact cause of any fatigue damage on rail clips in the field. Past research has mainly focused on investigating the mechanical behavior and structural dynamics of rail fastening systems by employing numerical analyses, including understanding the interaction between track components [3, 4, 5]. There is a dearth of research evaluating the fatigue life of rail clips. A method to analyze the stress-based fatigue reliability of a rail clip under random train loading was also developed. The sensitivity analysis showed that the equivalent stress range had the largest influence on the fatigue reliability index. However, the fatigue evaluation technique proposed by the authors was based on crack propagation under the assumption of a small initial crack. The fatigue crack initiation life was not considered [6],Failure analysis of fatigue cracking was performed in the tension clamp SKL15 of the rail fastening system DFF-300. The fatigue performance of the tension clamps was determined based on both field measurements and finite element analyses (FEA). The authors evaluated the fatigue performance of the tension clamps, considering both the initial stress from the assembly process and the stress amplitude from repeated trainload, using the modified Goodman and Gerber diagrams to analyze the possibility of fatigue cracking [1].  
The KR-type rail fastening system has been developed in South Korea and used in some domestic railways. Figure 2 depicts the main components and assembled configuration of this rail fastening system. The fatigue performance of the rail clip has been assessed by conducting a simple fatigue test; however, a thorough fatigue performance investigation has not been conducted yet. In this study, both the structural behavior and fatigue performance of the KR-type rail fastening system were evaluated through laboratory tests and FEA. A laboratory assembly test was first performed to investigate the system's global response and local deformation pattern in an effort to identify potential fatigue vulnerabilities in the presence of stress concentration on the rail clip. The natural frequencies of the rail clip were also determined by performing a modal test in the laboratory. FEA was then conducted to supplement and compare the output with the experimental results. In FEA, the assembly process and the vertical rail movement of a train passage were simulated in two steps to capture the stress states from which one could assess any potential fatigue failure of the rail clip by using the modified Goodman diagram.  
Figure 1: Damaged rail clip.  
Figure 2: The KR-type rail fastening system: (**a**) components; (**b**) assembled configuration.