Comparison of Fatigue Performances Based on Shape Change of Rail Fastening Spring

The fastening spring of a rail fastening system serves as an important connection in transferring the train load to the sleeper via rails on railway tracks. During initial fastening, a large tensile stress exceeding the yield stress can occur in the fastening spring structure, making it vulnerable to fatigue owing to stress fluctuations during train use. The damage caused by fatigue in the fastening springs have been reported for rail fastening systems on several domestic and international routes; however, research on this topic is limited. This study evaluates the fatigue performance of a fastening spring, SPS9 spring steel, developed in Korea based on shape change by performing a sensitivity analysis of various factors, including the heights at the end of the fastening spring and the spring arm, overall lateral width, and the diameter of the cross section of the fastening spring. The modified Goodman fatigue diagram was applied based on the tensile stress on initial fastening and the constant stress range due to a rail vertical displacement caused by train use through finite element analysis. The fatigue analysis showed that the lateral width and diameter factors of the fastening spring are found to be important variables for fatigue performance. Moreover, as the width and diameter increase, the fatigue performance improves significantly. The fatigue safety margin increased from 64% to 82% when the width increased from −20% to +20%, and increased from 54% to 81% with the diameter increase from 13 mm to 18 mm.