Molecular-dynamic modeling of mechanical properties of free defect metal nanocrystals

Nowadays, nanotechnologies are rapidly progressing, and the necessity has arisen in obtaining predictable properties of nanostructures by processes using various thermomechanical actions exerted on starting systems. In the present article, results of a molecular-dynamic study of the mechanical failure of a three-dimensional copper nanocrystal under uniaxial tension are reported. Two types of uniaxial tension were considered:
• extension of the crystal with one boundary rigidly fixed and the other boundary starting moving at the initial time with a constant velocity v0;
• extension of the crystal with a Heaviside-function force F0.Based on the mesoanalysis performed, relations of continuum mechanics were checked for nanosize objects, and mechanical characteristics of copper nanoclusters, such as the stress versus strain relation and the Young’s modulus, were obtained in the whole range of external actions examined (v0 = 10–1000 m/s, F0 = 1–20 GPa). Local criteria of dynamic fracture of defect-free copper nanocrystals are established. The limiting static stress–strain diagram is shown to coincide with the results obtained for the dynamic case. The results are checked on the nanocrystals, the size of which is greater than initial one. The critical nanocrystal size is revealed, beginning with that the crystal size has not effect on calculated mechanical characteristics.