Selection of loading schemes for assessing the fatigue resistance of frame elements of flat cars

Purpose: traffic safety is a priority goal for the railway industry. The existing problem of cracks periodically detected during operation in the structures of flat cars requires new approaches to the theoretical and practical assessment of the fatigue resistance and crack resistance of their structures. The problem of crack formation under low temperature conditions is of particular relevance. Methods: an experimental method has been developed for determining the spectrum of vertical loading of platform cars for transporting containers and the spectrum of longitudinal loads for cars operating in areas with low temperatures has been substantiated; a method for assessing crack resistance based on stress extrema determined experimentally has been proposed. The method is based on the principles of fracture mechanics, which take into account the influence of negative temperatures. Results: based on the stress extremes in the design of extendedlength platform cars, determined on the basis of the proposed method, it was established that it is possible to use one well-founded scheme that maximally loads all zones of the car as a test scheme for experimental assessment of fatigue resistance indicators under vertical and longitudinal loads. Using the proposed method, it is possible to determine the size of an acceptable crack-like defect based on the conditions of the initial crack growth. Stress intensity factors obtained on the basis of experimentally determined stress extrema showed that in the design of flatcars of increased length for transporting containers, crack growth is possible at subzero temperatures, which is not consistent with the methodology for assessing fatigue strength of the GOST 33211-2014 standard. Practical significance: the proposed method for assessing the spectrum of vertical loading of flatcars of increased length for the transportation of containers allows, from a variety of options for car loading schemes, to select one scheme for testing, which maximally loads all its potentially dangerous zones. Some research results were used to develop a standard test method for fatigue resistance of extended-length flat cars.