PSI - Issue 13

Ulewicz R. et al. / Procedia Structural Integrity 13 (2018) 2164–2169 Ulewicz R., Nov ý F., Novák P., Palček P. / Structural Integrity Procedia 00 (2018) 000 – 000

2168

5

transport. Especially the prescribed values of the impact toughness are not sufficient and the material exhibits the brittle behavior. In the case of the fatigue crack initiation, this crack subsequently propagates at very high rates through the brittle material, resulting in the fatal failure in very short time, thus no defectoscopy control could reveal the initiated fatigue cracks, Bathiass and Bonis (1998) , Bokůvka et al. (2014), Holzman and Klesnil (1972). Failure to provide the prescribed transition radius resulted in the significant stress concentration in the area of transition radius and this could be the most significant factor that contributed to the examined fatal failure. To avoid similar failures in the future, the prescribed value of the transition radius has to be strictly respected and controlled, together with the surface quality in these most exposed parts. The heavily worn upper part of the linear casing suggests specific operating condition. This rarely found type of linear casing damage was explained by the difference of the wheel diameters of the neighboring cars. It is a common situation in the railway transport, but in the case when it encounters two extreme values (984 mm and 1050 mm) it can result in an unusual wear of the linear casing part and creation of the additional bending loading on the draw hook assembly. These suggestions were supported by the FEM analysis showing the significant increase in the stress values in the most exposed parts. The places with the stress maxima fully correspond to the places of the fatigue crack initiation. The maximum stress value in the case of the real radius and additional bending loading is of 449 MPa and it is very close to the experimentally found value of the yield strength of the examined draw hook (YS  477 ± 5 MPa).

a)

b) Fig. 5 Results of the FEM analysis: a) the case of pure tension loading with the correct value of the transition radius. b) the real case, with the bending loading and the real value of the transition radius.