PSI - Issue 13

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

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a) b) Fig. 3 a) SEM image of the fatigue crack propagation area showing the mostly transcrystalline manner of the fatigue crack propagation with large amount of secondary cracks. b) Area of the final fracture – transcrystalline cleavage fracture with a small fraction of intercrystalline facets. 2.3. The FEM analysis To reveal the effect of the small transition radius and the additional bending loading on the stress distribution, the finite element analysis (FEM) was carried out. Two cases were examined, the first one with the transition radius of the correct value and the pure tension loading and the second one, with the real transition radius and with the applied bending loading. The result of FEM analysis showed significant increase of the stress maxima in the second examined case. While for the optimal combination of the correct radius and a pure tension loading maximum stress in the radius was 291.28 MPa, for the case with the real value of the radius and a real loading in the bending mode the maximum values of the stresses were 449.18 MPa. The position of the stress maxima in the FEM model fully corresponds with the observed fatigue cracks initiation places.

a) b) Fig. 4 a) Draw hook in the assembled position. b) The linear casing of the examined draw hook, with heavy worn upper part of the linear casing.

3. Discussion

The analysis of mechanical properties and chemical composition revealed that the material fulfills all the requirements prescribed in the TNŽ 28 2612 standard. On the other hand, it should be stated that the TNŽ 28 2612 standard was established in the 1979 and is still in use without any major changes. Properties prescribed in the standard are not entirely satisfactory when taking into account the current requirements for the operation of the railway