A Study On Micromechanics Model Of Composite Materials And Related Properties Of Materials

Carbon nanotubes(CNTs)reinforced composites have shown incomparable superior properties in many fields and have broad prospects for development.Carbon nanotubes have large aspect ratio and low bending stiffness,which make CNTs easy to bend and agglomerate in the matrix.The mechanical and thermal properties of composites with dispersed inclusions have been a particular interest for decades.Therefore,the superior mechanical or thermal properties of composites,such as high strength to weight and high stiffness to weight ratios,depend largely on the shape,size,property and dispersive form of the reinforced fiber.In this study,carbon nanotubes,nanoparticles and fibers are selected as the reinforcement materials,whereas the polymer and metal as matrix materials.Based on the shape,distribution and size of reinforcing fibers,the micro-mechanical and thermal properties of nano/fiber composites are studied by using the equivalent inclusion theory,self-consistent scheme and Mori-Tanaka method.This paper assumes that curved carbon nanotubes have bow shape waviness and are equivalent to solid short fibers.The bulk modulus and shear modulus of the wavy carbon nanotube reinforced composites are predicted by using the equivalent inclusion theory and Mori-Tanaka method in the micromechanics.The effects of different bending degrees of carbon nanotubes on the effective properties of composites are analyzed with introducing wavelength and amplitude parameters.In the present investigation,a micromechanical agglomeration model is proposed according to the aggregation mechanism of carbon nanotubes.The regions with concentrated carbon nanotubes are regarded as spherical inclusions,and the randomly dispersed carbon nanotubes and partial initial matrix are regarded as fictitious matrix.Two agglomeration parameters are introduced to characterize the degree of agglomeration of carbon nanotubes.Analytical expressions are also derived for predicting the effective elastic modulus of carbon nanotube reinforced composites based on a combination of the Mori-Tanaka method with self-consistent scheme.The effect of different degree of carbon nanotube agglomeration on the elastic properties of nanocomposites is predicted.In addition,the representative volume unit is divided into the high concentration and low concentration areas according to the distribution of carbon nanotubes in the matrix.Based on the morphological image of carbon nanotubes in composites,a reasonable dispersion model of carbon nanotubes is established.The influences of high and low CNTs agglomerations on the thermal expansion coefficient and thermal conductivity of the composite are analyzed by Mori-Tanaka method and Halpin-Tsai equation,respectively.The material constants representing the effective stiffness of composites are introduced by using the correlation between the effective medium of composites.Based on the equivalent inclusion theory and Mori-Tanaka method,a micromechanical model of unidirectional fiber reinforced composites is established to study the thermal expansion coefficient and effective properties of composites with fibers of different aspect ratios.The effects of fiber arrangement and direction on the longitudinal and transverse thermal expansion coefficients and elastic properties of the composites are analyzed.Hybrid composites have great potential in energy and structural applications,among which the most common hybrid composites are those with a combination of glass fibers and carbon fibers.Carbon fiber and glass fiber hybrid composites have good mechanical properties and greatly reduce the cost.This paper investigate the effective properties of composites,in which the change of the hybrid fiber volume contents and the influence of the fiber arrangement mode are considered.This study introduces the interfacial phase between nanoparticles and polymer matrix and considers the influence of interfacial thickness,stiffness and particle size.A micromechanical model of nanoparticle agglomeration in the composite with interfacial phase is established.The particles encapsulated by an interphase can be defined as a system.The effects of nanoparticle agglomeration and interfacial properties on the mechanical properties of three-phase composites are further studied.