Molecular Dynamic Simulation Of Nanoindentation Response Of Al-graphene Composites

Graphene is widely used in various fields due to its unique structure and physical and chemical properties.In recent years,graphene often appears in metal matrix composites in the form of reinforcement phase.In previous studies,many mechanisms for graphene to strengthen metal matrix composites have been described,such as grain refinement,graphene-metal matrix interface effect,the effect of the uniform distribution of graphene sheets in the composite material on the dislocation motion,etc.,but there are still many mechanical stirring times of the same volume of graphene in the composite material,the lower the strength of the composite material.The dislocation reaction and the change of the microstructure in this process still need to be discussed carefully.In this paper,a similar model system is constructed,and the reason for this phenomenon is explored through the nanoindentation method of molecular dynamics simulation method.In this work,Al composites with eight different sizes of graphene were firstly constructed.Then observe the change of the indentation force curve under the same nanoindentation simulation parameters,and observe the change of its microstructure and the change of the dislocation motion law.When the indenter is not in contact with graphene,the overall strength and indentation force of the composite material increase significantly as the graphene size decreases,but when the graphene size decreases to a certain value,the strength of the composite material hardly continue to increase,there will be a limit.The strengthening mechanism at this stage is mainly related to the hindering effect of the graphene interface on dislocations.When the size of graphene is too large,the dislocations react with the interface to form new dislocations at the interface.This phenomenon have a certain softening effect on the composite material,which is also the indentation of the composite material with a larger graphene size.The reason for the decrease in strength of compisites in the later stage of the nanoindentation simulation,as the indenter contacts graphene,the strength and indentation force of the composite material with large-sized graphene are greatly improved.The strengthening of the composite material at this stage is related to the excellent load transfer ability of graphene.In this paper,the effect of Al crystal orientation([001];[110];[111])on the mechanical properties of composites with graphene of the same size is also investigated.In the early stage of indentation,the Al crystal orientation has little effect on the strength and indentation force of the composite material.The strength of the Al[110]-G system is lower than the other two systems.In this control group,the strengthening mechanisms within the composite were essentially the same.Due to the different crystal orientations of Al,the types of dislocations and the degree of stacking are different,resulting in the differences between the systems.In addition to the influence of Al crystal orientation,the influence of indenter load speed and indenter radius on the indentation force of the system was also tested.The results are as follows: At first,indentation load speed is concerned,there is no significant difference in the effect of the load speed on the indentation force at low speed.But when the indentation speed reaches 50m/s,the indentation force changes significantly,this phenomenon There will be large errors in the judgment of the research system.Based on the Hertzian contact theory,the indentation force is proportional to the radius of the indenter,but as the indenter contacts graphene,the indentation force far exceeds the theoretical value caused by the change of the indenter radius.In the study of graphene-metal matrix composites,an appropriate indenter radius should be selected to reduce errors.In this paper,the effect of graphene on the strengthening mechanism of Al composites,the effect of Al crystal orientation on the mechanical properties of composites,and the effects of nanoindentation-related parameters on the mechanical properties of graphene-Al composites are studied.Scientific design of materials provides theoretical guidance...