The Multiscale Analysis Of PMMA/CNT Composite Plate

Due to remarkable physical and mechanical properties,such as light weight,high resistivity and rigidity,excellent insulation and thermal stability,the functionally graded(FG)Poly(methyl methacrylate)(PMMA)/carbon nanotube(CNT)composite plates are extensively used in aviation and aerospace fields.For instance,the PMMA/CNT composite has been increasingly adopted in the manufacturing of nanocomposite neuron sensor to detect the damages in the large areas of an aircraft,and of electromagnetic interference shielding materials in the aircraft.During intended service life,the PMMA/CNT composite structure may be destroyed due to the external disterbance,hence,it requires a fundamental understanding of the vibrational behavior of composite structures.The experimental and macroscopic numerical methods can obtain the vibration response directly,but the internal mechanism of the response is not able to be understood.In order to understand clearly the vibration behavious of PMMA/CNT composites,it is necessary to comprehensively understand and analyze the mechanical properties of composite structure using a multiscale method.Based on the above description,the sequential multiscale method is adopted to comprehensively study the vibration response of FG-based PMMA/CNT composite plate structure.The mechanical properties of SWCNT,PMMA polymer and PMMA/CNT nanocomposites are firstly evaluted via molecular dynamics(MD)simulation,and the mechanical parameters from MD simulation are then transformed as the inputs of the continuum mechanics based on the extended rule of mixtures(EROM).Finally,the above inputs are applied to the nonlinear dynamic equation,and the dynamic response of PMMA/CNT composite plate is further studied.Specific work is as follows:(1)The multiscale method based on MD simulation is systematically presented.The fundamental framework of MD simulation in this paper is constructed by determining the intermolecular interaction potential of PMMA/CNT nanocomposite and its components,and giving the calculation scheme of intermolecular stress.The mechanical properties from the framework are transformed as the inputs of continuum mechanics via EROM.Based on the classical plate theory,the nonlinear dynamic equation is derived to analyze the effects of the functional gradient distribution,volume fraction of CNT and size of the composite plate on the vibration response.(2)The effect of temperature on the mechanical properties of PMMA/CNT nanocomposites is considered.The mechanical properties such as Young's modulus,thermal expansion coefficient,and Poisson's ratio of nanocomposites under multitemperature and multi-volume fraction conditions are systematically studied by molecular dynamics simulation,which provideds the abundant input parameters for theoretical research in the future.(3)The nonlinear dynamic responses of composite plates in temperature and pressure conditions are investigated.The mechanical properties are first obtained via molecular dynamics simulation,which are translated to the mechanical properties of composite plate based on a method of homogenization.The nonlinear dynamic response of the composite plate is studied using the nonlinear dynamic equation based on the third-order shear deformation theory and Hamilton's principle.The results show that the distributed reinforcements close to top and bottom surfaces are more efficient to increase the stiffness of the composite plate than those distributed near the mid-plane;CNT carries most of the load during the longitudinal deformation,which causes a significant increase in the longitudinal modulus.For transverse and shear deformations,it is observed that the atomistic stress of PMMA/CNT nanocomposite is kept at a low level with increasing CNT volume fraction,therefore,CNT shows the strong enhancement effect on the polymer in the longitudinal deformation compared with the transverse and shear deformations;With increasing CNT volume fraction,the fundamental frequency of composite plate increases,but the nonlinear to linear frequency ratio decreases;The results also show that the temperature has a significant effect on the mechanical properties of the nanocomposites.With the increase of temperature,the mechanical properties of the composites show a downward trend;Both temperature and pressure affect the mechanical properties of the composites,but the effect of temperature is more significant;With the decreasing temperature and pressure levels,the maximum amplitude of nonlinear vibration of composite plate decreases gradually.In addition,the second order maximum vibration amplitude is significantly lower than the first one,which indicates that the first order vibration is the main vibration form of the system.The innovation point is foucused on the thress sets of efficiency parameters of PMMA/CNT composite relevant to CNT contents,temperature,and temperature and pressure conditions,meanwhile,the function expressions are derived to extend the range of these parameters.The quantitative transfer of physical and mechanical properties between molecular and macroscale scales is established to provide a theoretical basis for the design and optimization of FG-based CNT-reinforced composites.Several sets of efficiency parameters of CNT relavant to PMMA/CNT composites are provided under different conditions,which provides more data to contribute the subsequent theoretical research.