Ratcheting behaviour of Stellite 21 as laser cladding material for flange tip lift crossings repair

Abstract

Laser cladding holds the promise to repair damaged rails, including flange tip lift crossings (FTLC) in tram rails. In order to further understand the effectiveness of laser cladding against rail damage, this study investigated the ratcheting behaviour of the laser cladding alloy Stellite 21, used in FTLC repairs, in comparison to the currently used rail steel grade R260. Experimental studies were conducted under uniaxial and biaxial stress-controlled cyclic loads. The study found that under identical uniaxial stress conditions, Stellite 21 exhibits superior ratcheting behaviour compared to R260 steel. Various mean stresses and stress amplitudes were also studied, revealing that increases in mean stresses or stress amplitudes resulted in higher ratcheting strains and ratcheting strain rates. Additionally, biaxial compression-torsion cyclic loading tests were performed on the R260 to replicate real-life stress conditions. The results indicated that the direction of plastic strain accumulation depended on the direction of the applied non-zero mean stress. The findings from this study are essential for calibration of parameters of cyclic plasticity models, which can be used to simulate ratcheting performance of laser-cladded FTLCs under in-service conditions for the prediction of fatigue crack initiation life and maintenance requirements of flange tip lift crossings.