Molecular dynamics (MD) simulations of 100 /{100} Cu nanowires at 10 K with varying cross-sectional areas ranging from 0.3615 × 0.3615 nm 2 to 2.169 × 2.169 nm 2 have been performed using the embedded atom method (EAM) to investigate their structural behaviors and properties at high strain rate. Our studies reported in this paper show the reorientation of 100 /{100} square cross-sectional Cu nanowires into a series of stable ultra-thin pentagon Cu nanobridge structures with diameter of ∼1 nm under a high strain rate tensile loading. The strain rates used for the present studies range from 1 × 10 9 to 0.5 × 10 7 s −1 . The pentagonal multi-shell nanobridge structure is observed for cross-sectional dimensions <1.5 nm. From these results we anticipate the application of pentagonal Cu nanowires even with diameters of ∼1 nm in nano-electronic devices. A much larger plastic deformation is observed in the pentagonal multi-shell nanobridge structure as compared to structures that do not form such a nanobridge. It indicates that the pentagonal nanobridge is stable. The effect of strain rate on the mechanical properties of Cu nanowires is also analyzed and shows a decreasing yield stress and yield strain with decreasing strain rate for a given cross-section. Also, a decreasing yield stress and decreasing yield strain are observed for a given strain rate with increasing cross-sectional area. The elastic modulus is found to be ∼100 GPa and is independent of strain rate effect and independent of size effect for a given temperature.

A body-centered pentagonal nanobridge structure with lattice constants c = 2.35 and a = 2.53 A has been observed under high strain rate tensile loading on an initially constrained [Formula: see text] Cu nanowire at various temperatures. Extensive molecular dynamics (MD) simulations have been performed using the embedded atom method (EAM) for cross-sectional dimensions ranging from 0.723 x 0.723 to 2.169 x 2.169 nm(2), temperature ranging from 10 to 600 K, and strain rates of 10(9)-10(7) s(-1). Formations of such pentagonal nanowire are observed for a temperature range 200-600 K for particular cross-sectional dimensions and strain rates. A large inelastic deformation of approximately 50% is obtained under both isothermal loading and adiabatic loading. With very high degree of repeatability of such pentagonal nanowire formation, the present findings indicate that the interesting stability property and high strength of elongated nanowires have various potential applications in nanomechanical and nanoelectronic devices. Further, we demonstrate a novel thermomechanical unloading mechanism by which it is possible to impart recovery from a pentagonal nanowire following a hysteresis loop: [Formula: see text].

Temperature and strain-rate dependent fracture strength of grapheneThe crack initiation and growth mechanisms in an 2D graphene lattice structure are studied based on molecular dynamics simulations. Crack growth in an initial edge crack model in the arm-chair and the zig-zag lattice configurations of graphene are considered. Influence of the time steps on the post yielding behaviour of graphene is studied. Based on the results, a time step of 0.1 fs is recommended for consistent and accurate simulation of crack propagation. Effect of temperature on the crack propagation in graphene is also studied, considering adiabatic and isothermal conditions. Total energy and stress fields are analyzed. A systematic study of the bond stretching and bond reorientation phenomena is performed, which shows that the crack propagates after significant bond elongation and rotation in graphene. Variation of the crack speed with the change in crack length is estimated. V C 2015 AIP Publishing LLC. [http://dx.

Extensive molecular dynamics (MD) simulations have been performed in a B2-NiAl nanowire using an embedded atom method (EAM) potential. We show a stress induced [Formula: see text]-centered-tetragonal (BCT) phase transformation and a novel temperature and cross-section dependent pseudo-elastic/pseudo-plastic recovery from such an unstable BCT phase with a recoverable strain of approximately 30% as compared to 5-8% in polycrystalline materials. Such a temperature and cross-section dependent pseudo-elastic/pseudo-plastic strain recovery can be useful in various interesting applications of shape memory and strain sensing in nanoscale devices. Effects of size, temperature, and strain rate on the structural and mechanical properties have also been analyzed in detail. For a given size of the nanowire the yield stress of both the B2 and the BCT phases is found to decrease with increasing temperature, whereas for a given temperature and strain rate the yield stress of both the B2 and the BCT phase is found to increase with increase in the cross-sectional dimensions of the nanowire. A constant elastic modulus of approximately 80 GPa of the B2 phase is observed in the temperature range of 200-500 K for nanowires of cross-sectional dimensions in the range of 17.22-28.712 A, whereas the elastic modulus of the BCT phase shows a decreasing trend with an increase in the temperature.