PSI - Issue 23

Sergiy Kotrechko et al. / Procedia Structural Integrity 23 (2019) 310–315 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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… 1500 К ) 0  varies in a rather narrow time range from 0.032 till 0.037 ps.

2. Kinetics of the contact bond break in carbyne-graphene nanoelements Strain curves characterize atomic interaction in a nanoelement. They can be obtained by DFT calculations. Figure 3 [Kotrechko et al. (2017)] shows the results of such calculations obtained for the CGN under consideration. A feature of the strain curves is the existence of a zone where equilibrium states of atoms are impossible - instability zone (IZ). The width of this zone is pre-determined by the position of its lower boundary R F . Its value depends on the acting force f F . In the first approximation, the expression for R F is the following [Kotrechko et al. (2017)]: where  is the coefficient characterizing the sensitivity of the IZ width to the level of the force field. The existence of IZ is due to the redistribution of potential energy accumulated in the deformed nanoelement. This occurs as a result of instability of the weakest atomic bond. The work on breaking this bond is performed due to the potential energy accumulated in the stretched nanoelement. This effect is key one in fluctuation-induced break of interatomic bonds, since thermal fluctuations can play the role of a “trigger” to release accumulated energy and to break the bond. This greatly facilitates the atomic bond break, and can be the reason for a synergistic effect of the temperature and the force field on the stability of nanoelements. As was shown by Kotrechko et al. (2019) the possibility of realising such a failure scenario is pre-determined by the position of the level of the acting force f F relative to the lower limit of IZ, R F . If f R F F  , then short-term instability caused by fluctuation C un     (Fig. 1) will not be enough to break the bond. If the force f F is in the IZ ( f R F F  ), then a short-term bond instability is sufficient to break it, i.e. the magnitude of the critical fluctuation C  is reduced to the lower limit,   un un C    . 2 2 un R F F F   f (5)

Fig. 4. Dependence of the waiting time for the contact bond break,  , on the applied load over the temperature range 600К - 1580К: 0  = 0.037 ps is the average time of atomic vibration; f F is the value of applied load; un F is the ultimate tensile strength of a contact bond ; “A” and “B” are the regions for “ high-energy ” and “ low-energy ” mechanisms, respectively (technique of calculations is described by Kotrechko et al. (2017)).

Fig. 5. Dependence of the lifetime,  , on the number of atoms in a chain at Т = 750 К at different mechanical loads (designation is the same as in Fig. 4)

As the calculations show, this results in a significant decrease in the lifetime of nanoelements. Moreover, it changes