Buckling and Partial Phase Transition Analysis in Shockwave Compression of Vertically-aligned Carbon Nanotube Arrays, a Molecular Dynamics Study

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: 1075-UFGNSM2021-FULL
1School of Mechanical Engineering, College of Engineering, University of Tehran,Tehran,Iran
2School of Mechanical Engineering, Engineering Campus, University of Tehran, Tehran, Iran
This study aimed to analyze the buckling behavior and partial phase transition in vertically-aligned carbon nanotube (VACNT) arrays which are excited by different shockwave pressures. The material behavior of VACNT array is investigated based on Hugoniostat method by deriving Hugoniot curves. The VACNT array exhibit an elastic compression behavior ended with an instability limit in shockwave pressure of 6.5 GPa under which the VACNT columns undergo a sudden drop of pressure and buckling of CNT columns has happened. To get a precise insight into structural changes in shocked material two approaches have been conducted; Radial Distribution Function, and Coordination analysis. Implementing coordination analysis, it is found that the structure is just compressed at lower shock pressures and the initial coordination number of the whole atoms doesn’t change, stating that the diamond nucleation hasn’t developed yet. By elevation of shockwave pressure, the initial nuclei of the amorphous diamond phase are formed at the pressure of almost 4GPa after the buckling phenomena and the partial and the structural phase transition occurred at 55GPa.The final shocked material under high pressure and temperature conditions at different shockwave pressures is recovered to the ambient temperature and pressure conditions. To investigate the role of the recovery process on the final molecular structure of the shocked material, Radial Distribution Function, and Coordination analysis are implemented again as a means. It should be noted that after the recovery stage the portion of sp3 hybridization decreases where a majority of atoms retrieve their initial sp2 hybridization. Although the recovery process decreases the portion of sp3 hybridization, the shock-induced synthesized structure after the PT point preserved its amorphous diamond phase considerably. These results provide wider support for the hypothesis that the shockwave induced a partial phase transition into the initial pristine VACNT resulted in meaningful structural changes and different material characteristics.
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