PSI - Issue 30

S.P. Yakovleva et al. / Procedia Structural Integrity 30 (2020) 193–200 Yakovleva S. P. et al. / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 6. Fracture surfaces of zone I (a) and zone II (b, c) specimens tested at -60 °  С . The long arrow shows the union of secondary cracks by cracking the jumper between them, the short arrow shows the union of pores by cracking the jumpers 4. Conclusions It was found that the fatigue failure of mass spring steel during operation in the cryolithozone was preceded by the formation of a system of scattered damages to the structure of various scaling levels – from micro-damages at the substructure level to meso-damages in the form of small and large pores ranging in size from a few to ≈ 40 micrometers. The results of the structural and statistical analysis of microhardness and the estimation of the porosity of the metal in different spring zones showed that the prefracture zone with intermediate values of the accumulation coefficient of microdamage and the volume fraction of porosity is characterized by a lower microhardness value (due to the process of softening); deviation of the microhardness distribution from the Gaussian law; significant prevalence of fine pores number (pore diameter not more than 20 microns). Under the considered operating conditions, the combination of substructural damage with multiple fine pores was a critical type of defect with a more adverse effect on the resistance of the material under study to fatigue failure compared to the factor of the presence of large pores. The fatigue damage accumulated in the spring steel studied did not lead to its embrittlement: the impact toughness values indicate satisfactory resistance of the steel to brittle fracture at climatic cold temperatures. Wherein, the resistance to brittle destruction is a significant degree determined by mesoscale damages (porosity). Mechanism of the effect of porosity on brittle fracture resistance is associated with the occurrence of deformation processes in the vicinity of pores, as well as during growth and coalescence of pores. The possibility of micro deformations and raising a complexity of the fracture surfaces topography increase the energy intensity of destruction. The research results can be used to develop methods for obtaining and information processing on the structural damage of materials and to extend the service life of elastic elements of vehicles operating in the cryolithozone. References Bhat, S., Patibandla R., 2011. Metal Fatigue and Basic Theoretical Models: A Review. Alloy Steel – Properties and Use, Dr. Morales, E.V. (Ed.). INTECH Open Access Publisher. 203–236. Botvina, L.R., 2008. Destruction: Kinetics, Mechanisms, Common Pattern. Nauka, Moscow, pp. 334. Dodds, R. H., Anderson, T. L., Kirk, M. T., 1991. A Framework to Correlate a/W Effects on Elastic-Plastic Fracture Toughness. Int. J. of Fracture. 48 (1), 1–22. Ermakov, B. S., Tsupka, S. A., Makeeva, Yu. K., 2017. Evaluation of the causes of the destruction of elastic elements in the Far North. Welding and Safety, Proc. 2nd All-Russia Conf. Tsumori Press, Yakutsk, pp. 443. Fractography of Modern Engineering Materials: Composites and Metals, 1993, vol. 2, Masters, J. E. and Gilbertson, L. N. (Eds). Philadelphia, Pittsburgh, pp. 217. Ishkov A. M., Kuz’minov, M. A., Zudov, G. Yu., 2004. Theory and Practice of Reliability of Equipment in the North, Larionov, V. P. (Ed). YaF GU SO RAN. Yakutsk. pp. 313. Karzov,G.P., Margolin,B.Z., Shvetsova, V.A., 1993. Physical and Mechanical Modeling of Fracture Processes. Politekhnika, Saint Petersburg, pp. 391.