Dr. Bing Yang, Associate Professor, Vice Dean of State Key Laboratory of Traction Power, Southwest Jiaotong University, China

Title: Influence of Loading Frequency on Short Fatigue Crack Behavior for LZ50 Axle Steel

Abstract: Loading frequency is one of the possible factors which could affect the short fatigue crack behavior of materials. In this study, the replica tests on surface short fatigue cracks of smooth hourglass shaped specimens for railway LZ50 axle steel at totally 4 different loading frequencies, i.e., 15Hz, 140Hz, 160Hz and 180Hz, were carried out. Some aided tests were also performed. The comparison analysis results show that: (1) In the low frequency, normal frequency and high frequency range mentioned above, the influence of loading frequency on the initiation and propagation behavior of short fatigue crack is very limited. Therefore, the loading frequency effect is negligible; (2) The propagation behavior of short fatigue crack can be well described by a crack growth rate model with a driving force of the size of dominant effective short fatigue crack (DESFC) which can reflect the influence of multi-microstructural barriers; (3) Though loading frequency has only very limited effects on the short fatigue crack behavior, the growth rate and the micro hardness are relatively high in low loading frequency tests before the DESFC breaks the first obstacle of grain boundary and the growth decelerates significantly for the first time; (4) While performing the safety assessment of axle, the choice of crack growth curve can be carried out without considering the influence of loading frequency.

Keywords: fatigue, short crack, loading frequency, axle steel