Study On Dynamic And Static Mechanical Properties Of Graphene Reinforced Composite Nanobeam And Nanoplate Structures

As the key research object of new materials in the 21 st century,carbon nanomaterials have been widely concerned by the scientific community since they came out in the last century.Due to the nano size and excellent optical,electrical,magnetic,thermal and other material properties,carbon nanomaterials are broadly used in nano electromechanical systems(NEMS)as a new sens-ing material.With the gradual deepening of the research on the mechanical properties of carbon nanomaterials,researchers gradually found that the classical theory of macro materials can not be fully applicable to the mechanical analysis of nano scale materials.Therefore,many scholars use molecular dynamics to simulate the mechanical properties of nanomaterials.The solutions obtained by molecular dynamics simulation have certain reference significance,but the results obtained by different scholars have some degree of discreteness.In order to obtain a more ac-curate and reasonable mechanical model of nanocomposites,it is of great academic value and significance to explore the constitutive model of nanomaterials,the form of external load and the properties of nanocomposites.In this study,the mechanical properties of graphene reinforced composite nanobeams and nanoplates are investigated.Based on the nonlocal strain gradient theory,external forces and environmental loads are introduced to establish a reasonable mechanical model of nanobeams and nanoplates.The differences between micro scale and macro scale are considered from many angles and aspects.Combined with the mixing law of nanocomposites,the effects of geometric size,mass fraction and distribution of graphene reinforcement on the mechanical properties of graphene nanocomposites are considered.Finally,combined with practical application,considering the influences of complex external field environment and viscoelastic medium on the system,the static and dynamic mechanical properties of nanobeam and nanoplate structures are comprehensively analyzed.According to the above research focus,the main contents of this study are as follows:1.Based on the nonlocal strain gradient theory,several nanostructures such as beam,curved beam,single plate and double plate are studied.With reference to Bernoulli beam model,Tim-oshenko beam model and Kirchhoff plate model,the bending,buckling and vibration of these nanostructures are analyzed.At the same time,two cases of in-phase vibration and out of phase vibration are considered in the double plate system.2.In view of the micro scale of nanobeam and nanoplate structures,combined with nonlocal theory and strain gradient theory,combining the parameters of two different theoretical models,the mechanical properties of nanobeam and nanoplate structures under external influence and different working conditions are theoretically and numerically analyzed.It is proved that the nonlocal strain gradient theory plays a very important role in exploring the properties of nanocomposites.3.Considering the bending moment caused by surface force,high-order surface effect has the following two functions: first,it improves the overall stiffness of the system? Second,the equivalent lateral force generated by the surface layer is added.Based on Gurtin and Murdoch's surface force theory,the influences of surface tension on the mechanical properties of the structures in nano scale are considered.The change of mechanical properties for graphene composites under high-order surface force is studied.It is proved that considering high-order surface force is helpful to establish a more accurate constitutive model of nanocomposites.4.Considering that the influence of graphene reinforcement on the properties of graphene nanocomposites is very significant,Halpin Tsai mixing criterion is used to analyze the properties of nanocomposites under three distribution forms of graphene reinforcement(uniform,symmetric and asymmetric).At the same time,the effects of geometric size,mass fraction,volume fraction and temperature change of graphene on the mechanical properties of graphene nanocomposites are also taken into account.5.Considering that the nano electromechanical system is often in a complex external working environment and simulating the actual situation,the electric field,magnetic field and temperature field are introduced,and the influences of the elasticity and damping characteristics of the external medium on the nanobeam and nanoplate structures are considered.6.Based on the simply supported boundary conditions,Hamilton's principle and Newton's second law are used to solve the equilibrium equation and motion equation.For the simply sup-ported boundary,the form of Navier Stokes solution is adopted.The Newmark-? method is used to solve the governing equation,so as to analyze the working conditions of nanobeam and nanoplate structures under the influence of external load.