PSI - Issue 20

Valeriy Lepov et al. / Procedia Structural Integrity 20 (2019) 24–29 Valeriy Lepov et al / Structural Integrity Procedia 00 (2019) 000 – 000

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Thus, the dependence (4) considers the activation nature of fracture, and commonly with (1) and (3) can be used for numerical modeling of connected diffusion-elastoplasticity and damage accumulation problem for assessment of the reliability and a resource of structural elements for extreme environment and also for their weld joints. By means of the offered ratios the quantitative analysis of the phenomenon of cold brittleness is carried out. The analysis takes into account the low temperature and dissolved hydrogen influence on the process of damage accumulation. 5. Conclusion The activation model of the hydrogen embrittlement is developed for confirmation of the dislocation-phonon mechanism of low-temperature ductile-brittle transition. The cold brittleness is caused by fluctuation centers in the form of dislocations, shifts, micropores and microcracks, and their further growth. On the basis of the model the numerical analysis of an energy-phonon spectrum and forecasting of properties of microcrystalline and nanostructural materials with a high threshold of cold brittleness is possible. In particular, the ultrafine grains formation by intensive plastic deformation reduces a free path in a lattice, thereby reducing the inelastic dispersion of phonons responsible for a rupture of bonds under the influence of the external tension. It also allows the analyzing of parameters and frequencies of optimum energy effects (by neutron radiation, external voltage, etc.) on a structural integrity and design to lowering the range of ductile-brittle transition to the safe temperature range. As the recommendations about the increase of cold resistance of steels and their weld joints materials, the raise in energy of activation of plastic shear of steels and alloys, or a rupture of molecular bonds in polymers and composites is advisable. One of the most perspective technologies for metal materials is intensive plastic deformation which allows to create the equilibrium disperse structure of small grains with the compression stress (materials with submicrocrystalline structure), however for significant decrease the temperature range of DBT, especially for security operation of weld joints of such materials, the microalloying is recommended by rare-earth elements that will provide significant increase in energy of activation of plastic shear and inhibit the influence of lattice hydrogen to dislocation-phonon subsystem in bcc-metals. Acknowledgements The reported study was partially funded by RFBR, project number 18-48-140015, in theoretical research, and by Ministry of Science and Education of Russian Federation, Project III.28.1.1 in the frames of Program for Basic Research of the Siberian Branch of Russian Academy of sciences, in experimental study. Also the research was done using equipment of the Shared core facilities of the Federal Research Center of the Yakutsk Science Center of the Siberian Branch of the Russian Academy of Sciences. References Achikasova, V.S., Lepov, V.V., 2015. Ductile-brittle transition and internal friction at low-temperature. Science and Education 77, 75-77. Arkhangelskaya, E.A., Lepov, V.V., Larionov, V.P., 2001. Connected model of delayed destruction of the damaged medium, Physical mesomechanics 4, 81-87. Bartenev, G.M., 1984. Strength and mechanism of destruction of polymers. Khimia Publ., Moscow, pp. 280. (in Russian) Bartenev, G.M., Zuev, Yu.S., 1964. Strength and destruction of highly elastic materials. Khimia Publ., Moscow-Leningrad, pp. 388. (in Russian) Bolotin, V.V., 1990. A resource of machines and structures. Mashinostroenie, Moscow, pp. 448: (in Russian) Botvina, L.R., 2008. Fracture: Kinetics, Mechanisms, General Laws. Nauka Publishing House, Moscow, pp. 334. (in Russian) Broek, David, 1986. Elementary Engineering Fracture Mechanics. Forth revised edition. Kluwer Academic Publishers, Dordrecht, pp. 516. Chernov, V.M., Kardashev, B.K., Moroz, K.A., 2016. Low-temperature embrittlement and fracture of metals with different crystal lattices – dislocation mechanisms. Nuclear Materials and Energy 9, 496-501. Environment-Induced Cracking of Materials. 2008. Ed. S.A. Shipilov, R.H. Jones, ... R.B. Rebak, Elsevier science, pp. 1000. Freudenthal, A.M., 1975. Statistical approach to brittle fracture, Fracture, Vol. 2, Mathematical foundations of the theory of fracture. Ed. G. Libovits. Mir, Moscow, 616-645. Gonzáleza , P., Ciceroa, S., Álvareza , J.A., Arroyoa, B., 2018. Analysis of stress corrosion cracking in X80 pipeline steel: An approach from the Theory of Critical Distances, Procedia Structural Integrity 13, 3-10. Grigoriev, A.V., Lepov, V.V., 2015. Methods for assessing the life of railway equipment operated in the extreme conditions of the North, Zavodskaya Laboratory. Diagnostics of materials 81, 42-48.