PSI - Issue 4

Pavel Hutař et al. / Procedia Structural Integrity 4 (2017) 42 – 47 Author name / Structural Integrity Procedia 00 (2017) 000 – 000

3

44

Fig. 1. Scheme of the railway wheelset considered.

It is visible that the highest value of residual stress is close to the surface of the axle and compressive stress field is in the depth between 0-8 mm from the axle surface. This area is very important for RFL prediction (the time of fatigue crack grow up to length 8 mm is higher than the time of fatigue crack grow from the length 8 mm to the critical crack length). Therefore, the residual stresses can significantly influence the RFL of the railway axle and should be considered in the procedure of RFL estimation.

Fig.2. Considered distribution of the axial residual stresses from the outer axle surface to the inner one.

The distribution of residual stresses shown in the Fig. 2 is implemented to the finite element model of the axle. The stress intensity factors are determined according to the methodology described in the paper Náhlík et al. (2017). The stress intensity factors are evaluated using optimised crack front shape obtained by the special procedure described in the mentioned paper (Náhlík et al. (2017)). Fig. 3a shows values of the stress intensity factor as function of the crack length ( K - a dependence), which are determined only for the bending load and load caused by the press-fitted wheel. The total stress intensity factor is given by superposition of each stress intensity factor component. Consideration of residual stresses leads to the decrease of total stress intensity factor (compressive residual stresses close to the axle surface reduce the total load), see Fig. 3b. The railway axles are subjected to variable amplitude loading (trains go on straight track, to curved track, over switches, crossovers, etc.). These events commonly increase the basic bending load level caused by weight of the vehicle (Beretta et al. (2016), Pokorný et al. (2016) and Traupe et al. (2004)). Variable amplitude loading is represented by the load spectrum (load block), see histogram of load amplitudes in Fig. 4. Each load amplitude is described by dynamic coefficient k . The static load (caused by weight of the train only) corresponds to k = 1,