Molecular Dynamics Simulation On The Effect Of Microscopic Damage On The Mechanical Properties Of Single Crystal Aluminum

The study of micro-damage of metal materials plays an important role in understanding the properties of materials,material synthesis,and engineering applications.With the rapid development of computer technology,molecular dynamics methods have gradually become an effective method for studying the microscopic mechanical behavior of metal materials,such as microscopic plastic deformation,phase transition,and micro-damage.In this paper,LAMMPS,a molecular dynamics program,was used to simulate the evolution of microscopic damage in face-centered cubic(FCC)single-crystal aluminum with designed hole shape under high-strain-rate tensile loading,and the results was analyzed in detail using different methods.Three main aspects were analyzed in this research when single crystal aluminum specimen was stressed in tension,including:(1)stress distribution on the surface of the hole and the dimensional change of the void in different directions;(2)generation and development of dislocations on the void surface;(3)the effect of different volume fraction of the void and vacancies on the mechanical properties.The stress distribution of the hole-containing single crystal aluminum under the high-strain-rate tensile loading shows stress concentrated areas existing on the void surface,and they affect the dimensional change of the void during deformation.In general,during the elastic deformation stage,the size of the void gradually increases as the loading progresses,but it is not uniform and peak-like protrusions are generated at the place where the stress on the void surface is concentrated.After entering the plastic deformation stage,dislocations are generated at these stress concentration areas.The stress-strain response of single-crystal Al under tension shows significant differences in the elastic modulus and yield strength with crystals under different loading orientations.Microscopically,the positions of generation and development of dislocations on the surface of the hole are very different during tension with different sample orientation.By introducing an octahedron,which consisting the slip planes and the slip directions of FCC crystal,the number of slip systems activated by different loading crystal orientations and their Schmid factors can be compared.As the loading progresses,the material first undergoes elastic deformation,and the stress on the void surface is concentrated to specific regions;then,the slip system is activated,and the shear dislocation loop launches and slips;and finally,the material enters the plastic deformation stage.The stress on the material suddenly drops after reaching the yield stress leading to the material failure.In this paper,the effects of different volume fractions of void and vacancies and their joint effects on the mechanical properties of the material are studied.In the elastic deformation stage,the stress-strain relationship,stress distribution,and the evolution of void shape are analyzed.In the plastic deformation stage,dislocation analysis was performed to investigate the generation and development of dislocations on the void surface,dislocation interaction,and the growth of the void until the material fracture.The numerical simulation results show that the change of the void/vacancies fraction has a significant anisotropy effect on the growth process of the void.As the void/vacancy fraction increases,the Young's modulus of the material becomes smaller,so as the yield strength and yield strain.However,under the condition of equal volume fraction,the decrease in yield strength caused by void is more obvious.The information provided by the molecular dynamics calculations on the defect structures and their interactions can serve as input data for a multi-scale study of the irradiation damage process in a larger spatial scale-mesoscale research.The results presented in this paper are of great significance for comprehensive understanding of radiation damage problems,improvement of material properties,and development of radiation-resistant materials.