Molecular Dynamics Simulation Of The Mechanical Properties Of Nano-metal

The mechanical properties of two kinds of nano-metal under different external load were studied by molecular dynamics(MD) simulation, it's based on the analytical embedded atom potential, the effect of strain Tate,temperture,cross section size of mechanical properties were studied in detail. It explain the unique mechanical properties of nano-metal in microscopic scale by studing the strain-stress curve, atomic location map, atomic energy cure,it's also develops the insights into properties of nanometer materials.The simulation results of face centered nano crystal aluminum wire show that:during the tensile load, dislocation slip is the main cause of the deformation and expansion of atomic vacancies are created nanowire fracture. At absolute zero temperature, the strain rate only effect the plastic deformation, the yield strength increased with the increase of strain rate. When the strain rate is greater than 1×108s-1, there will be a delocalized multiple necking during the breaking process. The yield strength and elastic modulus will decrease with the temperature increased. Due to the intrinsic stress, the smaller cross section size, the lower elastic modulus. In the compression load, the strain rate also did not affect the elastic stage, the elastic modulus and yield strength will remain the same when strain rate increased. The magnitude of the elastic modulus and yield strength is much larger in tension versus compression, it showed a significant asymmetry.The research result of the body centered of the a-Fe nano crystals indicate that:shear band was observed and the ductile fracture was taken place along<010> direction during the stretching agenda. The yield strength and fracture strength will increases with increasing strain rate, while the elastic modulus remained unchanged; with the increasing of temperature, the elastic modulus, yield strength and fracture strength decreases; As the cross section size increased, the yield strength will decrease, the Young's modulus and fracture strength will increase correspondingly, In the compression load, with the strain rate increases, the yield strength, elastic modulus and fracture strength also increased, but much larger than the corresponding tensile load value. This asymmetry of mechanical properties is primarily due to different slip system occurred during the tension and compression yielding.Nano-films shown a cleavage fracture during the stretching process which occurred along the {110}<111> direction. The tensile properties of nano-films is very sensitive to the presence of holes, the elastic modulus, yield strength and fracture strength decreased with the increase of the void volume fraction, especially for the fracture strength, which reduced 70%. The deformation and destruction process were occurred from the hole of the nano-iron films with a hole. As the strain increases, the holes ruptured, which resulted in the material fracture.Due to the initial stress and surface effects, three kinds of iron nanometer materials showed different deformation mechanism during the tensile process. Nanowires deformation started from the surface of the neck, and gradually extended to the interior; nano-films is also occurred void in the surface and interior space, each extension; nano-block is generated from within the space, and then extended to the surface. In the nano-films and nano-block of the drawing process, there was even a stress plateau, which may be imposed by the boundary and free surface.