The mechanism of low-temperature ductile-to-brittle transition in damaged polycrystalline materials with bcc lattice undergoing phase transition of II or higher order has been clarified from the viewpoint of modern physics and thermodynamics of phase transitions, when at submicroscopic level the processes of dislocations piling up in separate slip planes, both at large-angle grain boundaries and at inclusions, micropores, stress fields, leads to the appearance of a germinal microcrack. The microcracks formed in this way further grow in the stress field and merge with each other, forming a main crack at the macro level, which reaches a critical size and provokes fracture (strength loss and fragmentation). The realization of such a mechanism for various materials is confirmed by experimental data and implemented as a stochastic algorithm of crack growth in a field of randomly distributed microdefects of random orientation and a given size spread. The kinetics of brittle fracture at the phase transition is described by introducing an order parameter in the form of the amplitude of the dislocation plasticity rate, and solving the Verhulst equation for the activation dynamics of dislocation and non-dislocation defects at different structural levels. In this way, the rate of damage accumulation and the probability of reaching the limit state with subsequent failure are determined. A multilevel numerical simulation approach has been applied to crack growth and fracture in composite materials. It is shown that the introduction of graphene oxide and flash-graphene into concrete mixtures improve the thermal and mechanical characteristics of concrete composite. Graphene and its derivatives can significantly improve the energy efficiency and performance of modern concrete materials. Nevertheless, to build more correct physical and mathematical models of the phenomenon of low-temperature ductile-to-brittle transition and to confirm its nature as a phase transition of II or higher order, it is necessary to perform an additional experimental study to identify jumps in the thermal and electrical conductivity of the material at low temperature tests under the dynamic loading conditions, for example, under the ultrasonic impact.

This work was funded by the Russian Science Foundation (No. 24-21-20122). The research was carried out using the equipment of the CSU FRC YaSC SB RAS.

Lepov Valery Valeryevich, born on 10.11.1964 in the Yakutsk city. After graduating from high school No.8 in 1981, he entered the Bauman’s Moscow State Technical School (Moscow),on Faculty of Power Engineering, where graduated as a mechanical engineer with a specialization in aircraft engines in 1987, having a Certificate of technical English translator. From 1986 to 1989 he worked as an engineer on Diploma practice and on Assignment at the Research Institute of Chemical Technology at the NPO “Soyuz” (Moscow District, General Director Academician B.P. Zhukov), and organized a temporary youth work team to achieve an advanced performance. From 1987 to 1989 he was also a freelance English translator of the All-Union Translation Center. In 1989 he transited to Welding Laboratory of the Institute of Physical-Technical Problems of the North of the Siberian Branch of Academy of Sciences of USSR (Yakutsk). In 1995, upon completion of correspondence postgraduate studies at the A.A. Blagonravov’s Institute of Mechanical Engineering of the Russian Academy of Sciences (Moscow), he defended Ph.D. thesis “Synergetic approach to the assessment of resistance to delayed fracture of elements of welded structures”, on specialty 01.02.06 “Dynamics and Strength of Machines, Devices and Equipment” (supervised by Academician of RAS Larionov V.P. and Prof. Alymov V.T.). In 2006 he defended his Dr. Sc. thesis “Structural models of damage accumulation and crack resistance of structural materials”. Author and co-author more of 330 scientific papers, including 5 monographs, patents, algorithms, know-hows, and more than 50 popular science articles.  Since 1995, he is the Head of the Laboratory of Physicochemistry, Technology and Mechanics of Materials (since 2000, Physicochemistry and mechanics of ductile-brittle transition), from 2006 to 2016 Head of the Fracture Processes Modeling Department, since 2010 the Research Director, Acting Director, Head of Scientific Direction, since 2019 Director of IFTPS SB RAS. Project leader of the priority direction 2.3.2 “Mechanical Engineering” of the Russian Federation FNI Program for the long-term period up to 2030, fundamental research of the Presidium and specialized departments of the Russian Academy of Sciences, projects of the Federal Program “Industry of Nanosystems”, RFBR, International STC. He is the Chairman of the Organizing Committees of a number of international and All-Russian conferences, including the Eurasian Symposium on Strength and Service Life at Low Temperatures (EURASTRENCOLD), and many others. From 1996 to 2000, Chairman of the Council of Young Scientists and Specialists of YSC SB RAS, organizer and expert of Youth Conferences and Forums in Yakutsk. Since 2004 an expert of the Small Innovative Foundation in Science and Technology (Bortnik's START), Ministry Science and Higher Education of Russian Federation (since 2011), RAS, RFBR, eCOST (European Program for Cooperation in Science and Technology), Elsevier Publishing House. Member of the doctoral dissertation council (1996-2006), scientific supervisor.  Winner of the state scholarship of the Government of the RS(Ya) and the Academy of Sciences of the RS(Ya) for young scientists (1993-1994) and researchers (1998, 2003), Scholarship of the Swiss Academy of Technical Sciences (SATN) for young scientists from CIS countries, interned at EPFL (Polytechnic State University of Lausanne) (1998-1999). Laureate of the Foundation for Assistance to the Development of Science and Education of the RS(Ya) (V.P. Larionov Medal, 2010), Honored Veteran of the Siberian Branch of the Russian Academy of Sciences (2009), Honored Scientist of the RS(Ya) (2024), and others.