Numerical Simulation Analysis Of Carbon Nanotubes Reinforced Rubber Materials

Rubber materials are widely used in petrochemical,aerospace and automotive industries due to their excellent oil resistance,corrosion resistance and wear resistance.However,in the application of rubber materials,they often bear the coupling effect of complex factors such as high temperature,high pressure and abrasive wear,which leads to premature fracture and wear of the matrix materials,shortens the service life of the equipment and causes a lot of economic losses.Therefore,it is of great engineering significance to explore the methods to improve the mechanical properties of rubber materials.At present,the traditional reinforcing systems such as carbon black,silica and fiber are still widely used,but most of these reinforcing materials have the limitations of difficult degradation,low specific surface area and non renewable,which lead to environmental pollution problems,and their reinforcing ability is also very limited.At present,the main methods and approaches are still based on the calculation of continuum theory and macro experiments,which can't observe and analyze the change process of its structure and conformation from the atomic dimension in real time,making the micro theoretical analysis and support relatively weak.In recent years,with the continuous progress of nanotechnology and materials science,carbon nanotubes(CNTs)as the representative of carbon nano materials,with its excellent mechanical and thermodynamic properties,light weight,high specific surface area and other excellent characteristics,leading to the limitations of the traditional reinforcement system is broken,and become the ideal nano reinforcement material of the new generation of rubber materials.At the same time,with the continuous development of materials science and the continuous improvement of computer ability,the combination of the two makes molecular dynamics methods mature and applied to various fields.Through this method,the trajectory of particles and the microscopic information in the process of movement can be obtained,and the physical and chemical properties of materials can be inferred.Reasonable use of molecular dynamics method can provide effective theoretical support for the following macro experiments,reduce the workload of the experiment,and save time and effort.In the present paper,the nitrile rubber(NBR)was used as the polymer matrix,the effects of carbon nanotubes with different characteristics on the mechanical properties of NBR composites were studied from the atomic scale using molecular dynamics simulations.Firstly,the molecular models of CNT/NBR composites with different tube chirality were established.The mechanical properties of CNT/NBR composites,such as Young's modulus,Shear modulus,Bulk modulus,Cauchy pressure and Poisson's ratio,were calculated respectively via the constant strain method.The simulation results show that: the(7,5)spiral CNT has the best reinforcement effect on the deformation resistance and plasticity of the NBR matrix,while(6,6)armchair CNT/NBR composite has a better ductility.By extracting and analyzing the interfacial binding energy between CNT and NBR matrix,the fractional free volume of CNT/NBR system and the mean square displacement of NBR molecular chain,the strengthening mechanism of CNT with different chiral indices on the mechanical properties of NBR matrix was elucidated from the atomic scale.The results show that a stronger interfacial bonding strength are formed between the(7,5)spiral CNT and NBR matrix,which reduces the free space of atoms in the composite system and limits the motion energy of NBR molecular chain,leading to a more stable and compact composite structure and thus significantly improving the mechanical properties of NBR composites.Secondly,the molecular models of(6,6),(8,8)and(10,10)armchair CNT reinforced NBR composites were constructed.The young's modulus,shear modulus,bulk modulus,Cauchy pressure and poisson's ratio of CNT/NBR composites were determined,respectively.The simulation results indicate that(6,6)CNT with smaller diameter has the best enhancement effect on the deformation resistance of NBR matrix.The corresponding enhancement mechanism is analyzed from the atomic scale.The results show that: with the increase of the diameter of CNT,some NBR molecular chains will enter into the CNT,which will deform the CNT and reduce its reinforcement effect.In contrast,the(6,6)CNT with smaller diameter can form a more compact and stable composite structure with the NBR matrix without affecting its own structural characteristics,thus endowing the molecular system a better mechanical properties.In addition,with the increase of CNT diameter,owing to the significant decrease in the mechanical stiffness and strength of CNT/NBR composites,the plasticity and ductility of CNT/NBR composites are relatively improved.Finally,the molecular models of single-walled carbon nanotube(SWCNT),double-walled carbon nanotube(DWCNT)and triple-walled carbon nanotube(TWCNT)/NBR systems were developed.The young's modulus,shear modulus,bulk modulus,Cauchy pressure and poisson's ratio of CNT/NBR composites were calculated,seperately.The results show that the TWCNT has the best reinforcing efficiency on the mechanical strength and stiffness of NBR matrix among these CNTs with different number of walls.In addition,with the increase of the number of CNT walls,the plasticity of CNT/NBR composites are gradually decreased,and the ductility of CNT/NBR composites are improved to a certain extent,among which the DWCNT has a better enhancing effect on the ductility of the NBR matrix.Further microscopic information analysis revealed the reinforcement mechanism of CNT with different number of walls on the mechanical properties of the NBR matrix.The results show that with the increase of the number of CNT walls,less NBR molecular chains is able to enter into the CNT,resulting in smaller deformation of CNT,effectively maintaining the mechanical properties of CNT itself,so as to make CNT play a better reinforcement effect.