COMPARISON OF FATIGUE LIFE EXTENSION RESULTS IN RAILWAY COUPLINGS OF CAST STEEL ASTM 148 90-60 USED IN FREIGHT TRAINS

In this paper, fatigue life extension results from pre-existing surface defects in cast steel ASTM A148 90-60 of railway couplings used in service in Portugal for coal transportation are presented using two crack growth relationships (Paris equation and modified Paris equation). Fatigue lives were obtained and the results were discussed in terms of the threshold value for non-propagation cracks (modified Paris law) the initial value of the starting crack. It was found that for both crack growth relationships significant crack extension lives can be assumed. Therefore for these components and in this application damage tolerant procedure can be used with safety and this component can be kept in service provided appropriate inspection procedures are applied to detect and measure fatigue cracks. This will avoid early retirement from service of these components.