PSI - Issue 13

Nový F. et al. / Procedia Structural Integrity 13 (2018) 2170–2173 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

2173

4

Fractography analysis (Fig. 4) revealed the brittle character of the fracture at all testing temperatures. Fig. 4a shows the mostly transcrystalline fracture with cleavage facets (specimen broken at +20 °C). At lower temperatures (Fig. 4b - 20 °C) more intercrystalline facets can be observed on the fracture surface.

Fig. 4 Fractography analysis of the impact toughness; specimens broken at +20 °C (a) and -20 °C (b).

4. Conclusions

Based on carried out experiments and analysis, it could be concluded that the fracture of locomotive draw hook was caused by the insufficient impact toughness of the draw hook material. As it is usual in the similar cases, during the examination several factors causing brittle behavior were identified. • The results of the impact toughness tests revealed insufficient toughness over the whole range of testing temperatures. At the temperature of 0 °C (the draw hook failure occurred at ambient temperature of -2 °C) the impact toughness K U was only 6.5 J, what is not sufficient for any engineering application, when the dynamic loading is assumed. • The observed brittle behavior was caused by the low toughness of the material itself and together with no appropriate microstructure resulted in very low values of impact toughness. • The tensile tests revealed lower values of the UTS than prescribed in the TNŽ 28 2612 standard, but with regard to character of the fracture, this was not the cause of the examined failure. • The deeper analysis of the material requirements prescribed in the TNŽ 28 2612 standard revealed serious shortcomings in the testing methods and conditions in the standard itself. • To avoid similar failure in the future, it is necessary change the material used for the manufacturing of the locomotives draw hooks and to change the testing procedures prescribed in the relevant standard, as well.

References

Sirong Y. Principles of railway Location and Design. Academic Press, New York, 2018. Holzman M. Klesnil M. Brittle and fatigue fracture of materials and structures. SNTL Praha, (in Czech), 1972. Gomes M. et al. Effect of microstructural parameters on the mechanical properties of eutectoid rail steels. Materials Characteri zation, 39 (1), pp. 1 - 14, 1997. Qiu H., Hanamura T., Torizuka S. Influence of Grain size on the ductile fracture toughness of ferritic steel. ISIJ International, 54 (8), pp. 1958 1964, 2014. Skočovký P. et al. Structural materials. EDIS Žilina (In Slovak), 2000.