Study On Micro-mechanism Failure Of Graphene/Aluminum Matrix Composites

Aluminum matrix composites are widely used in mechanical industry and aerospace industry due to their light weight and high strength,while graphene is considered as an ideal reinforcement owing to its excellent mechanical properties and ultra-high specific surface area.Related studies show that graphene reinforcement plays an important role in the load transfer and plastic deformation of metal matrix composites,but systematic analysis on the microstructure of graphene-reinforced aluminum matrix composites is still lacking.In this paper,the mechanical response behavior of graphene/aluminum matrix composites under tensile,compressive and nanoindent loading are studied by molecular dynamics method,and the influence of aluminum matrix layer thickness,size and distribution of graphene on its failure deformation mechanism are also investigated.The main research contents are as follows:(1)The mechanical response of graphene/aluminum matrix composites under uniaxial tension and compression was studied by adjusting the matrix layer thickness.By analyzing the distribution of dislocation and load,the elastic-plastic deformation of graphene/aluminum matrix composites is explored,and the failure mechanism of graphene/aluminum matrix composites under uniaxial tensile and compressive load is clarified.The results show that under tensile load,the addition of graphene can significantly enhance the yield strength of aluminum matrix composites without affecting the toughness of the material,and the smaller the thickness of aluminum matrix layer is,the more obvious the strengthening effect is.This is because graphene has the characteristics of high specific strength and bears most of the load in the tensile process.The plastic deformation of graphene in the composites shows an excellent blocking effect on the dislocation,and the dislocation of a single aluminum layer is hardly affected by the deformation of adjacent aluminum layers.At the same time,the tensile yield strength and yield strain of graphene/aluminum matrix composites are temperature dependent.The increase of temperature will lead to the decrease of yield strength and yield strain.Under compressive load,the yield strength of graphene/aluminum matrix composites increases with the decrease of matrix thickness,but the addition of graphene will greatly reduce the toughness of the materials.It can be attributed to the two-dimensional structure of graphene will wrinkle after compression.(2)The effects of the size and distribution of graphene on the crack growth of graphene/aluminum composites were studied.The results show that there is a critical value for the transformation of the promoting or inhibiting effect of graphene size on crack propagation.When the graphene size less than 3.35 nm,the existence of graphene will promote crack propagation,and the promoting effect of graphene on crack propagation decreases with the increase of the relative distance between graphene and crack;When the size of graphene larger than 3.35 nm,it can hinder the crack propagation and slow down the dislocation slip at the sub crack,so that the crack propagation is restrained.In addition,it is also found that the distribution angle of graphene can effectively regulate the crack propagation path.(3)Molecular dynamics method was used to simulate the nano indentation of periodic and aperiodic graphene/aluminum matrix composites,and the micro plastic changes of the whole system were analyzed from the perspective of dislocation interaction.Comparing the results under two different boundary conditions,it is found that graphene/aluminum matrix composites with periodic boundary have better resistance to material deformation,while graphene/aluminum matrix composites with non periodic boundary conditions are prone to "steps" after local compression,which is more in line with the experimental phenomenon.In this study,the failure forms of graphene/aluminum matrix composites are studied from the micro point of view,which is helpful to understand the failure mechanism of the material and provide a certain reference basis for the design of graphene/aluminum matrix composites with excellent mechanical properties.