PSI - Issue 68

Kotrechko Sergiy et al. / Procedia Structural Integrity 68 (2025) 47–52 K. Sergiy et al. / Structural Integrity Procedia 00 (2025) 000–000

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1. Introduction Recently, there has been significant attention given to low-dimensional nanostructures, which are a combination of one- and two-dimensional nanostructures. Among them, carbyne-graphene nanoelements (CGN) are the most promising from a practical point of view. First of all, they are interesting as elements of straintronics since they can change the width of the band gap when deformed (La Torre et al., 2015; Ravagnan et al., 2007). In particular, this makes them essential for creating nanolasers with a tuneable wavelength, which can be utilised in optoelectronic devices with adjustable wavelengths (Lin and Ning, 2011). The practical application of CGN's effectiveness primarily depends on its strength and sensitivity to temperature. Generally accepted reason for the temperature effect on strength is thermally activated breaking of atomic bonds. General approach to this problem is formulated in the Arrhenius theory of reactions (Arrhenius, 1889a) and its modifications (Kramers, 1940; Smith, 2008). At the same time, the regularities of temperature dependence of strength are determined by the atomic structure of specific nanostructures. To date, there is a number of works related to the temperature effect on strength of graphene/graphene nanotubes and carbyne chains. According to the data, obtained by Wei et al. (2003), Tang et al. (2009), Zhao and Aluru (2010), Vijayaraghavan and Wong (2013), the strength of nanotubes decreases with growing temperature, which indicates a thermally activated mechanism of failure. The influence of temperature on the СGN lifetime was investigated by Lin et al. (2011), Kotrechko et al. (2017, 2022). As shown by Kotrechko et al. (2022), the CGN lifetime is governed by the waiting time for breaking the contact bond between carbyne chain and graphene sheet. This is evidenced, in particular, by the MD-simulation findings. In addition, according to the results of DFT calculations, the contact bond is the longest and the least strong bond in the chain (Kotrechko et al., 2017). According to the data obtained by Kotrechko et al. (2017, 2022), the stochastic nature of lifetime is a characteristic feature of CGN. The waiting time for the CGN failure is described by an exponential distribution (Kotrechko et al., 2023). The temperature dependence of the average value of CGN strength over a wide temperature range is ascertained. The phenomenon of transition from the CGN failure by breaking the contact bond to the thermally activated pulling out of the carbyne chain from the graphene sheet (unraveling) was found, which is observed at temperature higher than 1000K. 2. MD-simulations Geometry of the CGN cell is shown in Fig. 1. DFT calculations for such a CGN were performed by Kotrechko et al. (2017). To describe the interaction between atoms, the Atomic Cluster Expansion potential for carbon was used by Qamar et al. (2023). This is a representative of a new class of interatomic interaction potentials, which not only describes the fundamental properties of carbon allotropes with DFT accuracy, but is also able to maintain this accuracy in large-scale simulations. Simulations were performed by using the LAMMPS software (Thompson et al., 2023). The simulation parameters were as follows: time step was 1 fs; temperature was maintained by rescaling the atomic velocities every 10 iterations. The duration of MD-simulations was 10-20 ns depending on the temperature (at high temperatures, the specimen failure occurred earlier). Cell stretching rate was 0.01 m/s. Since the graphene sheet stiffness is much greater than that of the carbyne chain, the chain stretched at the same rate. Simulation was carried out in the cell of 32x47x20 Angstrom with periodic conditions. First, the system energy was minimized to reach a stable state, after which a dynamic simulation was conducted. To obtain the most detailed statistics, at least 50 simulations were carried out for each temperature, which differed in the initial distribution of atomic velocities. 3. Results and discussion Fig. 2 shows the results of MD-simulation of the temperature effect on CGN strength, F un . According to these data, at temperatures T≤1000 K, the average strength value decreases monotonically as temperature grows, and this dependence is close to linear. Instability and failure of CGN within this temperature range occurs as a result of the contact bond break when it is stretched along the chain axis, i.e., in the direction of the applied force (Fig. 3). At temperatures higher than 1000 K, the mechanism of the CGN instability changes. In this case, stress relaxation occurs