Molecular Dynamics Simulation And Coupled MD/PD Multi-scale Algorithm Of Graphene/Aluminum Composites

Graphene reinforced metal matrix composites have excellent mechanical,electrical,and thermal conductivity properties.Therefore,they are expected to have wide applications in aerospace industry,transportation,and electronic industry.In recent studies,graphene/aluminum(Gr/Al)composites with enhanced strength and toughness have drawn extensive attention,but the formation mechanism of microstructure and its effect on mechanical properties of Gr/Al composites have not been fully studied.Experimental observation and computer simulation are two methods to study the microstructure of materials.However,it is difficult to study the characteristics of microstructural evolution of materials from the microscopic level only by means of experiments.Therefore,it is of great significance for material design and fabrication process control to explore the evolution of microstructure and its relationship with mechanical properties in Gr/Al composites by means of computer simulation.In this thesis,the heat treatment process of Gr/Al composites was simulated by molecular dynamics(MD)method.The formation and evolution mechanism of torsional grain boundary(GB)microstructure were analyzed,and the influence of grain microstructure on tensile and compressive mechanical properties of Gr/Al composites was investigated.Furthermore,in order to extend our simulations to much larger time and length scales,we proposed a coupled molecular dynamics/peridynamics(MD/PD)multiscale simulation method.The main research includes the following three parts.(1)The initial model of the Gr/Al composite was established,and the heat treatment process of the composite was simulated by MD method.By observing the recrystallization of the Al matrix,it was found that the graphene sheet leads to torsional GB in the Al matrix.The formation mechanism and structural characteristics of the torsional GB were analyzed.Based on the processing simulation,MD models of Al/Gr composite with twist GBs were established to study the mechanical behaviors under uniaxial tensile load.The mechanical behavior of the Gr/Al composite with a torsional GB under uniaxial tensile loads was studied.The variation of yield and plastic deformation behavior of the composite with torsional angle was discussed,and the influence mechanism of torsional GB on dislocation nucleation and propagation mechanism was revealed.(2)MD models of graphene/polycrystalline aluminum(Gr/PAl)composite were established to investigate the effect of grain size on the mechanical responses of the composites under uniaxial compression.The strengthening effect of graphene was explored by comparing the results of pure aluminum and composites.Furthermore,the effects of the grain thickness and averaged size on the mechanical properties of the composite were studied,and the stress-strain relationship and dislocation slip features of the composite were analyzed.It was found that the geometry necessary dislocation is nucleated by the plastic deformation gradient between aluminum and graphene,which was accompanied by the back stress strengthening effect.(3)A multiscale algorithm based on coupled molecular dynamics and peridynamics was established.A novel connection condition for the displacement between atoms and material points in the transition region was proposed.Then,the motion equation of particles in the transition region was derived according to the Lagrangian multiplier method.The governing equation of particles was numerically discretized.Finally,one-dimensional wave propagation and three-dimensional examples were performed to validate the present multi-scale algorithm.Based on the established algorithms,the crack expansion process in Gr/Al composites was simulated.