| Continuum theory has revealed the failings of some new paradigms on the nano scale, so we must investigate movement of atoms to understand the details of mechanics behaviors. Nanomechanics is mainly divided to molecular dynamics and multi-scale method based on numerical simulation. In the paper, molecular dynamics and multi-scale method are respectively employed to simulate elastic behaviour and fracture process of nanomaterial on the nano-micro scale.Tensile/compressive deformation processes of a single crystalline copper nano-plate without the void are firstly simulated by molecular dynamics. The extreme tensile/compressive elastic strains are shown as 0.08 and -0.03, respectively, and the stress-strain relation is nearly linear between them. The two Poisson ratios lie between 0.3 and 0.4, but they are different from each other, which exhibits anisotropy resulting from the size effect. Molecular dynamics is also employed to simulate a single crystalline plate with voids. It is shown from the obtained results that the modulus linearly depends on the void volume fraction for a round void but nonlinearly varies with the void shape ratio for a fixed volume; and that the atomic stress concentration factor is mainly related to atom distributions near voids although it also depends on void structural parameters.The quasicontinuum method is employed to simulate a nickel single crystalline nano-plate with a mixed-mode crack, and the energy release rate, critical stress intensity factors and J-integral around the crack tip are computed. The material response to loading is theoretically predicted by comparing the energy release rate for brittle fracture and that for ductile fracture. Critical stress intensity factors are converted to the equivalent value of the energy release rate, which compares well with numerically computed J-integral around the crack tip. The slip direction around the crack tip is determined by comparing shear stresses in some possible slip directions.
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