PSI - Issue 13

Igor Golovnev et al. / Procedia Structural Integrity 13 (2018) 1632–1637 Author name / Structural Integrity Procedia 00 (2018) 000–000

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3

3. Results

Such a set of initial data when the crystal structure fractures is of highest interest for a researcher. Below there are the calculation results for the following parameters: 0 0.5 x ∆ = Å, 4 10 N ω = (period T = 1 ps, frequency ν = 1 THz, velocity amplitude 2 0 3.14 10 m s V − = ⋅ ). Fig. 1 presents the nanostructure in the XZ plane, when the crystal structure is already damaged. Different characteristics were calculated including the variation of the full, potential, and chaotic components of the kinetic energy of the system, temperature of the last-but-one atomic plane, mean coordinate r x of the last-but one atomic plane. Special attention was paid on the rightmost plane, since it was under the direct action of the movable clamp. It turned out that the above characteristics cannot give sufficient information about the beginning of the fracture on the atomic level. It means that it is impossible to find out the criterion of the crystal structure fracture on the base of these characteristics. The dispersion of the x-coordinate happened to be the most sensitive to occurring defects; this coordinate characterizes the mean-square deviation of the fixed atomic plane atoms from its mean coordinate at the time instant t : ( ) ( ) 2 1 1 a n i t i a D x t x n = = ⋅ − ∑ where a n is the atom amount in the plane, t x is the mean coordinate of the plane at the time instant t , i x is the coordinate of the i -atom at the same instant. Fig. 2 presents the dispersion of the utmost atomic plane versus time.

Fig.1 Nanostructure outlook in the plane XZ at t = 40 ps.

Fig.2 Dispersion of the x-coordinate of the last-but-one plane (from the moving clamp side)., 0 0.5 x ∆ = Å, 4 10 N ω = , period T = 1 ps, frequency ν = 1 THz, 2 0 3.14 10 m s V − = ⋅

4 10

Å,

, period T = 1 ps, frequency ν = 1 THz,

N

ω =

x ∆ =

0.5

0

2 3.14 10 m s −

V

= ⋅

0

The area of irreversible deformations was determined in this work as follows. At the certain time moments after the external action beginning, the massives of nanostructure coordinates and momenta were output, the rightmost plane, which simulates the moving clamp is neglected. Let us refer conventionally this structure «the cut-off one», and below we operate with this structure. In this cut-off structure, the dispersion of the rightmost plane t D is calculated. Then the nano-sized rod was cooled down in the assigned time moment, i.e. the external loading was off, and the coordinates and momenta of the disturbed nanostructure were used as the initial data for the cooling procedure. In this disturbed cooled system, the dispersion of the rightmost plane fr D was calculated. Then authors calculated the difference between the energy potentials of such a cooled disturbed structure and potential energy of