| Carbon fiber reinforced plastics(CFRP),the representative of advanced composites,have the advantages of high specific strength and modulus,which have been widely used in industry and equipment instead of traditional materials.Therefore,vibration and noise that perplex the traditional materials are also prominent in the application of composite materials.Vibration and noise can affect people's working and living environment,reduce the performance and production efficiency of the system and destroy the stability and reliability of equipment.The long-term vibration may also cause damage to the structure,resulting in the decline of the effective life of the structure.The thin-walled components occupy a considerable proportion in composite.In the application fields of high-speed,the negative effects of vibration and noise will be more obvious.Therefore,the research of vibration and noise reduction of composite materials is of great significance.The vibration and noise reduction performance of composites depends on damping and modulus.The improvement of modulus can ameliorate the performance of vibration and noise reduction at low frequencies,while damping can improve the performance of vibration and noise reduction of composite materials in the whole frequency domain.Therefore,both high damping and high stiffness are essential for the reduction vibration and noise for composite materials,and high stiffness is also an inevitable requirement for composite materials as structural materials.The research on the integration design of structural damping properties of composite structures is mainly focused on the "interlayer" structure,which originated from the traditional additional damping structure and the damping layer was directly inserted into the interlayer.The co-curing damping composites materials with rubber as damping layer showed the weakness of stiffness degradation,low interfacial bonding,poor heat resistance;while other non-rubber damping composites would increase the total thickness,quality and process cost.Composite materials have the advantages of multi-component,multi-interface and designability.The structural damping composites independent of intercalation structure can be designed by making full use of these characteristics.Therefore,this paper tried to get rid of the thinking of intercalation modification and the integrated design of damping structural composites was studied from the perspective of the basic structure on the premise of making fully sense of the source and mechanism of damping of fiber reinforced composites.In this paper,the matrix-based integration design of structurl damping properties was achieved by nanoparticles modification.Three representative nanoparticles were selected to study the effects on mechanical properties,damping and thermal properties of epoxy matrix.(1)MWCNT(Multi-Walled Carbon Nanotubes).MWCNT with different dimensions were dispersed into epoxy matrix by solvent-based high-speed shear method.The dispersion process of MWCNT was qualitatively analyzed by theoretical calculation,which played a guiding role in the improving of dispersion method.The results of Halpin-Tsai model and tensile test were compared to determine whether MWCNT was well dispersed in the matrix.The results indicated that the addition of MWCNT can synchronously enhance the mechanical properties and damping properties of epoxy matrix.The tensile modulus,tensile strength and loss factor of epoxy matrix was increased by 20%,8%,and 56%(25? 1 Hz),respectively.MWCNT with large aspect ratio and specific surface area showed the most obvious enhancement effect on mechanical properties and damping properties.Agglomerations exhibited a negative impact on the mechanical properties and damping of the matrix.The influence of dimensions and agglomerations on Tg were just contrary to that on the mechanical properties and damping properties.(2)g-C3N4.g-C3N4 was prepared by thermal polycondensation method by using urea as precursor,and a series of characterization tests were carried out.Then it was dispersed into epoxy matrix by high-speed shear as a novel filler.The tensile modulus and flexural modulus of the modified epoxy matrix were increased by 17.29%and 12.38%,respectively.Tg was also increased by 4-5?.The remarkable improvement in mechanical properties and Tg was attributed to the strong interaction interfaces and the mechanical interlocking effect caused by the curly structure and the large specific surface area.The loss factor of the modified matrix increased from 0.035 to 0.049(25? 1 Hz).The enhancement of damping may caused by the combination of interlayer sliding friction,periodic breakage and reconstruction of hydrogen bond,and the micro-mechanical constrained layer damping mechanism.The initial thermal decomposition temperature(Tinitial)and 50%thermal decomposition temperature(Thaif)were both increased by 15?.3)CSR(Core-shell structure nano-rubber).CSR is a new epoxy toughening agent.In view of the close relationship between toughening and damping of matrix,nanocomposites were prepared by mixing CSR with epoxy matrix.The test results showed that the impact strength of the matrix increased from 22.33 ±4.77 KJ/m2 to 36.89±4.43 KJ/m2 by adding 10 wt%of CSR.The tensile and flexural properties decreased slightly and the Tg almost unchanged,while the addition of CSR also had little effect on the damping enhancement.Finally,fiber reinforced composites were prepared by nanoparticle modified matrix with the best comprehensive properties.The test results indicated that MWCNT and g-C3N4 modified matrix can enhance the mechanical and damping properties of fiber reinforced composites.The interface-based integration design of structural damping composites was realized by implementing multi-scale nanoparticles into the surface of fiber.Based on the study of g-C3N4,carbon fibers loaded with g-C3N4 were synthesized in situ to improve the mechanical and damping properties of fiber reinforced composites.The roughness,functional groups and wettability on the carbon fiber surface were greatly improved by introducing g-C3N4 and the interfacial properties of composite laminates were also markedly enhanced.Interlaminar shear strength and interfacial shear strength of composite laminates were increased from 51.84 MPa to 72.09 MPa and 44.62 MPa to 73.41 MPa,respectively.Tensile strength and bending strength were increased by 19.54%and 10.51%,respectively.The total absorbed energy of impact experiment was also enhanced from 1.14 to 1.78 J.The Tg was increased from 116.71 to 121.34?.The loss factor of the modified fiber reinforced composites was 2.2 times as much as that of the unmodified ones,and the merit of the modified fiber reinforced composites was increased by 114.1%.The fiber-based integration design of structural damping composites was achieved by introducing high-damping fibers into carbon fiber composites.The test results showed that the hybrid composites exhibited compromised mechanical and damping properties.The tensile modulus of hybrid composites was only determined by the hybrid ratio,while the tensile strength and failure behavior were affected by both the hybrid ratio and stacking sequence.The structure of continuous multi-layer carbon fibers in the center of hybrid structure can produce a positive hybrid effect on tensile strength.The flexural and damping properties of hybrid composites were mainly determined by the fibers of the outer layer.The special failure mode of aramid fibers in the secondary layer at the compression side accelerated the failure of carbon fibers in the outermost layer.The loss factors of hybrid composites were also affected by both hybrid ratio and stacking sequence.The abrupt of stress and mismatch of Poisson's ratio at the hybrid interface can enhance the damping performance.Based on the study of the relationship between the structure and properties of hybrid composites,a method for predicting the damping of hybrid composites under actual loads was established in this chapter.In view of the difficulty in obtaining mechanical parameters of self-made materials,this paper started with the mechanical properties of fiber and matrix which were easily obtained,then the geometric parameters of the fabric in the composites were achieved by means of metallographic microscope and scanning electron micro-scope,and then the representative volume elements were established.The engineering mechanical parameters of CFRP and AFRP were calculated by the finite element method(FEM).Subsequently,the modal strain energy and modal superposition were combined to establish a method for calculating the loss factor under actual loads.The loss factors of kinds of carbon/aramid hybrid composites in 1 Hz were predicted.The comparing of simulations and experimental results indicated that the method possesses a good accuracy. |
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