PSI - Issue 26

A.V. Vakhrushev et al. / Procedia Structural Integrity 26 (2020) 256–262 Vakhrushev / Structural Integrity Procedia 00 (2019) 000 – 000

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As the chart shows the initial time to t = (5 ÷ 7) ps, there is a rapid movement of the nanoparticles into the microcracks. Then the speed is reduced, and at time t = 100 ps, nanoparticle movement practically is terminated. Atoms of the nanoparticles have temperature fluctuations around the equilibrium position, and the whole system of nanoparticles does not move, that corresponds to the final formation of the "bridge" structure. It is important to estimate the strength of the formed nanosystems. For this purpose, calculations are made of the crack opening under the action tensile forces without “bridge” ( Fig. 10 -1) and with “bridge” (Fig. 10 -2) from nanoparticles inside of the crack. At each step of loading, the force F stepwise increased by a certain value. Then executes the calculation of deformation of nanosystems, and for each value of the force F determines the value of the crack opening ΔS. The loading of nanosystems was carried until i ts destruction. The calculation executed for the crack with and without of nanoparticles. Fig. 10 shows the result of calculation as a function of disclosure of crack (ΔS) on the applied forces (F).

Fig. 10. ΔS crack opening size depending on th e value of the applied force F: 1 – crack without nanoparticles; 2 - crack with nanoparticles

The graph shows that the failure load for crack with the nanoparticles is 30% more load at which a crack is destroyed without nanoparticles. Note that the critical value of crack opening ΔS for cracks with nanoparticles and without them is practically the same (about 3 Å). Taking into account that the fracture toughness is linearly dependent on the load applied (Hellan (1984)) can be considered as a first approximation, that the introduction of the nanoparticles into the crack to increase the fracture toughness at 30%. In general, the presence of nanoparticles in micro crack stabilizes and strengthens it. 4. Conclusions  The interaction of a single nanoparticle with a crack does not lead to overgrowth of the crack.  During the interaction of several nanoparticles with a microcrack, a “bridge” of nanoparticles is formed connecting the walls of the crack.  The formation of a “bridge” of nanoparticles leads to both complete overgrowth of the microcrack and its transformation into micropores, due to the restructuring of the structure of the nanosystem.  Copper nanoparticles react more actively with a crack in aluminum than aluminum nanoparticles. In this case, a composite material of Al and Cu is formed at the crack site.  In general, the presence of nanoparticles in a microcrack stabilizes and strengthens it.