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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4. Conclusions

The performed analysis examined that the fatigue failure of the draw hook was caused by the synergy effect of three main factors – material, manufacturing technology and the operating conditions.  Material defined in the standard concerning the train draw hook does not possess the sufficient impact toughness and is very sensitive to the presence of notches in the construction elements. As a result, there is a high probability of the fatigue crack initiation and these cracks propagate quickly through the brittle material.  Transition radius, in the most exposed part, where the shape is changing from the rectangular cross-section to cylindrical, has very low value and did not fulfill requirements prescribed in the TNŽ 28 2612 standard. This resulted in the stress concentration in the transition area, which served as a preferred site for the fatigue crack initiation.  Additional bending loading, resulting from the specific operating conditions, contributed to the increased loading in the most exposed parts and significantly decreased the total lifetime of the examined draw hook.  The FEM analysis compared two cases, the first one with the correct transition radius with just pure tension loading and the second one with the real (smaller) transition radius and additional bending load. The results showed significantly higher stresses in the case of the real radius and additional bending loading (449 MPa) compared to the case of pure tension with correct radius (291 MPa).  Combination of all the three aforementioned facts resulted in the initiation of the fatigue cracks and their rapid propagation resulting in the fatal failure.

References

Sirong Y. Prin ciples of railway Location and Design. Academic Press, New York, 2018 . Petrenko V. Simulation of Railway Vehicle Dynamics in Universal Mechanism Software. Procedia Engineering 134, pp. 23 - 29, 2016. Bathiass C. Bonis J. Fracture from Defects, 1, 321. Procedia of ECF12, 1998. Bokůvka O. et al. Fatigue of Materials at Low and High Frequency Loading. EDIS ŽU Žilina, 2014. Holzman M. Klesnil M. Brittle and fatigue fracture of materials and structures. SNTL Praha, (in Czech), 1972.