| In welding, stamping, casting and other many machining process, internal residual stress of metal components may be formed. In many cases, the presence of residual stress will have an extremely adverse impact on mechanical properties of component. Vibration aging process is a new efficient environmental protection technology for eliminating residual stress in recent forty or fifty years at home and abroad for the rise of. However, up to now, this technology has not been widely applied. The reason is, in the elimination of residual stress by vibration aging, the micro mechanical properties and behavior inside the metal(or crystal) of is not very clear, which its rules is unable to understand only relying on the macro model of metal connector. Therefore, only by establishing the mechanical model of reflecting real internal crystal microstructure and micro mechanical properties of metallic crystals, the problem of eliminating residual stress can be solved.In this paper, the aluminum material as the research object, according to the space lattice structure of the aluminum crystal, we established the mechanical model of single crystal that is composed of a plurality of unit cell. Using the molecular dynamics method, we simulated the mechanical behavior of aluminum material in tension, compression, cyclic vibration condition. It provides a new idea for the research of vibration elimination mechanism from the micro level of aging. In this paper, the main research contents and conclusions are as follows:(1)According to the theory of crystallography and the space lattice structure of the aluminum crystal, we established the mechanical model of defect free crystal and the mechanical model containing crystal point defect cavity. Using the molecular dynamics method we studied the mechanical properties of micro crystal structure. In between the macro level and micro level of aluminum materials research we built a bridge which laid the foundation for the research on microscopic mechanism of vibration aging.(2)According to the theory of molecular dynamics and metal physics, by using the crystal defect model and molecular dynamics simulation software LAMMPS, we studied the mechanical properties of aluminum material in tension and compression. Our study shows that, the dislocation slip is the main reason of aluminum material deformation; deformation can be divided into two stages: the elastic deformation stage and the plastic deformation stage; in tension and compression load, single crystal aluminum materials exhibit non symmetry of yield strength; yield strength under tensile load was significantly higher than the corresponding values of the compression load.(3)Using molecular dynamics simulation software LAMMPS, we studied the effects of strain rate and temperature on the mechanical properties of tensile and compression plate. Our study showed that, the tensile yield strength of aluminum material increased with the increase of strain rate; with the increase of temperature, the yield strength and the elastic modulus of tension and compression were reduced.(4)Based on the theory of molecular dynamics and material mechanics, by using the mechanical model of defect free crystal and molecular dynamics simulation software LAMMPS, we studied the influence of dynamic stress of aluminum stress. Our results showed that the crystal produced a ratchet effect; the larger vibration force and vibration frequency is the more obvious aluminum material ratchet effect is; and when the yield strength decreased, the plastic deformation occurs more easily in the aluminum material.(5)Using a hollow point defects in the crystal model and molecular dynamics software LAMMPS, we analyzed the hole radius size, spacing and number of aluminum material tensile and yield strength and elastic modulus of compression effect. Our results showed that, the elastic modulus and yield strength decreased with the increase of the radius of the hole, hole spacing increased with the increase in the total volume of the cavity; under the same condition, the elastic modulus, yield strength decreased with the increase in the number of holes.(6)Simulation with hollow point defects in the crystal model and molecular dynamics software LAMMPS on the tensile analysis, we knew that, aluminum material in the cavity is easy to produce stress concentration, and the dynamic stress in the process of loading, the stress decreased gradually empty. We then validated by experiments, results showed that the simulation model is established by means of molecular dynamics simulation software LAMMPS is correct. |
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