Plastic Deformation Constitutive Modeling And Damage Behavior Simulation Of CNTs/Al-Li Composittes

As a kind of alloy with low density,high elastic modulus,high specific strength and high specific stiffness,Al-Li alloy has a very broad application prospect in the field of aerospace where the weight reduction is urgently needed.Carbon nanotubes(CNTs)have become a high-profile reinforcement in metal matrix composites(MMCs)due to their unique structure and excellent mechanical properties.The addition of CNTs can improve the strength of MMCs,but the effect on plasticity remains to be explored.How to describe and predict these changes is very important for the design,preparation and application of CNTs/MMCs.In this work,taking CNTs/Al-Li composites as the research object,the structure-mechanical properties relationship of CNTs/Al-Li composites was explored.A constitutive model based on physical mechanism was developed,and a finite element model was established based on the interface damage theory and the matrix constitutive relationship.The elastic-plastic deformation behavior of CNTs/Al-Li composites during uniaxial tensile process was simulated,and the effects of volume fraction,aspect ratio and agglomeration degree of CNTs on mechanical properties were investigated.The main contents and conclusions are as follows.(1)The constitutive model of CNTs/Al-Li composites based on microstructure was established.After obtaining the parameters required by the model,the model was modified and the accuracy of the model was verified.The results show that the constitutive model can predict the mechanical properties of CNTs/Al-Li composites with CNTs volume fraction less than 1%.(2)The finite element model of deformation damage was established,and the CNTs/Al-Li composites with 0.3375%CNTs volume fraction were taken as an example.The establishment of the geometric model needs to ensure the randomness and uniformity of the distribution of CNTs,and set the material parameters,meshing,analysis steps,boundary conditions and load application(3)The effect of CNTs volume fraction on the mechanical properties of CNTs/Al-Li composites was discussed.The results showed that the mechanical properties of the matrix materials were improved with the increase of CNTs volume fraction.When the volume fraction of CNTs increased from 0.675%to 1.375%,the strength improvement effect of the composites gradually weakened.Among the selected composites with different CNTs volume fraction,the best comprehensive performance is 0.675%CNTs volume fraction.(4)The effect of the aspect ratio of CNTs on the mechanical properties of CNTs/Al-Li composites was discussed.The results show that the increase of the aspect ratio of CNTs has a significant effect on the stress distribution on CNTs.The aspect ratio of CNTs increases from 9.5 to 48,and the average stress difference between the end and the middle of CNTs increases from 6021 MPa to 20473 MPa,indicating that the overall stress distribution on CNTs with low aspect ratio is more uniform.However,with the increase of the aspect ratio of CNTs,the main loadbearing part of CNTs will shift from the end to the middle of CNTs,and CNTs have better loadbearing effect.(5)The effect of CNTs agglomeration degree on the mechanical properties of CNTs/Al-Li composites was discussed.The results show that the higher the CNTs agglomeration degree is,the higher the unevenness of stress distribution on CNTs is,and the damage degree of interface also increases.The agglomeration of CNTs will make the strength of the matrix not in contact with CNTs not be well improved,and the stress concentration phenomenon will occur in the matrix part in contact with CNTs,which will lead to the debonding of CNTs from the matrix and the failure of the material.Therefore,the higher the dispersion of CNTs,The lower the degree of agglomeration.