Research On Preparation And Absorbing Properties Of Structural Absorbing Composite Materials

Structural absorbing material is radar stealthy material which has waveabsorbing properties and mechanical properties. It has strong design, absorbing bandwidth, bearing and absorbing organic combination, small weight, avoiding surfacepeeling coating, etc, which is one of the most notable material.This paper systematically studies design of the structural absorbing compositelaminated plate, preparation technology of laminated plates, preparation technologyand characterization of absorbents, surface modification of glass fiber, magneticmodified of epoxy resin, electromagnetic characteristics of absorbing agent/epoxyresin composite resin, absorbing performance and mechanical properties of S glassfiber/epoxy resin composites, optimization techniques of absorbing performance, etc,which has made a lot of research achievements of application value.（1） In the aspect of wave absorption performance design of the composite: waveabsorption performance and mechanical performance of the two typical types ofstructural absorbing wave composite materials have been designed. For the designproblem of single layer absorbing performance, the method of equivalent grid designidea was put forward, overall layer was abstractively thought as composite material ofa flake “epoxy resin powder” uniform distribution, equivalent electromagneticparameters of the layer were calculated.（2） In terms of development of absorbing agent:400meshes FeCuNbSiBamorphous powders were prepared adopting "annealing embrittlement andhigh-energy ball mill" process. Based on the amorphous powder, FeCuNbSiBnanocrystalline powders of excellent soft magnetic performance were gotton bymeans of crystallization annealing treatment which are around15nm, flake, SiO2coated. The spherical ultrafine Ni powders were prepared by liquid phase reductionmethod, which particle size of a single powder is60¹00nm, particle size ofaggregate is about250³00nm. Zinc oxide whisker was prepared by carbonreduction method. The hexagonal system Ba（Zn0.75Co0.25）2Fe16O27ferrite powdersand Ba（Zn0.25Co0.75）2Fe16O27ferrite powders were prepared by “chemical coprecipitation and high temperature to melt” process, particle size of the ferritepowder is less than38μm after400meshes selected. Electromagnetic parameters ofFeCuNbSiB nanocrystalline powder, ultrafine Ni powder, FeSiAl powder, hexagonalsystem Ba（Zn0.75Co0.25）2Fe16O27ferrite powder and Ba（Zn0.25Co0.75）2Fe16O27ferritepowder were analyzed. Every absorbing agent has characteristics. Good absorbingproperties of the absorbing agents are FeCuNbSiB nanocrystalline powders, FeSiAlpowder, ultrafine Ni powder.（3） In terms of surface modification of magnetic glass fibers, a preparationmethod of glass fiber cloth of good electromagnetic wave absorption properties hasbeen studied. Nanometer iron nickel alloy powders were prepared by liquid phasereduction process. Nano powders are well dispersed in glass fiber cloth using thephysical adsorption properties. Powders are filled in the cracks and the surface of theglass fiber cloth. Finally glass fiber cloths of good electromagnetic performance weregotton. Absorbing glass fiber is metal color, excellent adhesion, of a certainmagnetism.（4） The RTM molding technology of structural composites of the gradientdistribution of absorbent have been developed. The prepreg process was applied tothe SMC forming method, and the thixotropic agent of epoxy resin and the specialcuring agent of epoxy resin presoak were found. The interface combination of resinmatrix and fiber is strong in the composite material laminated plates, which are madein this study, with dimensional stability and smooth and clean surface and inflamingretarding. S glass fiber/epoxy composite laminates have excellent mechanicalproperties which tensile strength is greater than500MPa and bending strength isgreater than400MPa.（5） Absorbing performance of rubber matrix with four kind of absorbing agent,named FeCuNbSiB nanocrystalline powders, ultrafine Ni powders, ferrite（0.25） andferrite（0.75）, have been studied. Researches show that FeCuNbSiB nanocrystallinepowders and ultrafine Ni powders have good absorbing performance, especiallyabsorbing performance of FeCuNbSiB nanocrystalline powders with400meshes isbest.The material with the best absorbing performance and the most practical value is 80wt%FeCuNbSiB nanocrystalline powders （400meshes）/rubber compositematerial, which value of tan eand tan mis between0.6and1.4in2¹2GHzand which μ/ε is0.23. And the impedance of material and glass fiber/epoxy resinmaterial is matching. And this material can be used as interlining of glass fiber/epoxyresin composite material laminated plates, with its good absorbing function.（6） The Absorbing properties of four kinds of absorbing agents in epoxy resinmatrix have been studied in this paper. The absorbing agents are FeCuNbSiBnanocrystalline powder, ultrafine Ni powder, ferrite（0.25） and ferrite（0.75）. Studiesshow that FeCuNbSiB nanocrystalline powder and ultrafine Ni powder have goodabsorbing properties, especially the performance of400meshes FeCuNbSiBnanocrystalline powder is best.The integral absorbing characteristics of FeCuNbSiB nanocrystallinepowder/epoxy materials: when frequency is in the range of2².5GHz, it decreasessignificantly with increase of frequency. The value is4⁶when the frequency is2GHz, and it reduces to1.5when the frequency is2.5GHz. And the value isabout1when the frequency is higher than4GHz. The value is greater when theabsorbing agent content is higher. The material matches with impedance of fiberglass/epoxy plies when the frequency is higher than2.5GHz. It matches with theimpedance of the air in2².5GHz frequency range. The tan mvalue becomeslager with increasing levels of absorbing agent, which has been very stable within2.5¹2GHz band, shows excellent broadband characteristics.FeCuNbSiB nanocrystalline powder/epoxy material is the best absorbingmaterial. Formability and absorbing properties of50wt%FeCuNbSiB powder/epoxysystem can be very good by RTM molding or compression molding method. Forplywood sandwiched layers by SMC molding method, we can select80wt%FeCuNbSiB powder/epoxy system.Powder volume content of50wt%FeCuNbSiB powder/epoxy system is verylow （11%）. The whole system has good mobility, the tan mof50wt%FeCuNbSiBpowder/epoxy system has been fluctuating around0.3within2¹2GHz band, whichshows a good broadband absorbing properties. In the aspect of impedance matching:when the frequency is above2.5GHz, it matchs with the impedance of glass/epoxy laminate （≈0.25）. When frequency is2².5GHz, it matches with impedance ofair （≈1）.Compared50wt%FeCuNbSiB powder/epoxy resin system, absorbingperformance of80wt%FeCuNbSiB powder/epoxy resin system is better, butliquidity of resin is poorer, therefore it is suitable for SMC molding layers ofplywood.（7） The composite laminated plates with80wt%FeCuNbSiB powder/epoxyresin as matrix resin, and S glass fiber as reinforced material have goodcomprehensive absorbing properties.The attenuation of the surface reflectioncoefficient of the panels is about （-4）^-5 dB, the value of the tan mis0.4⁰.5, thevalue of the tan e+tan mis0.5⁰.6, and the matching thickness with the air is1.2²mm. After increasing S glass fiber/epoxy resin layer （that is through wavelayers） in front of the laminated plates as the impedance matching layer, theabsorbing properties of the laminated plates improve significantly. The doublecomposite materials which composed of through wave layer （1.62mm absorbingglass fiber/epoxy resin） and absorbing layer （1.73mm FeCuNbSiB powder/epoxyresin） have excellent electromagnetic absorbing properties: the qualified bandwidth ofR≤-4dB reaches14.24GHz （3.76-18GHz）, the qualified bandwidth of R≤-6dBreaches11.92GHz （4.4-8.8GHz,9.68-10.4GHz,11.2-18GHz）.（8） The absorbing properties of the composite laminated plates were improvedsuccessfully by the gradient layer design. When using the FeCuNbSiBnanocrystalline powders as the absorbing agent, and the thickness of the compositelaminated plates is4mm, R<-4dB within2⁸GHz, R<-8.5dB within8¹8GHz,have a good broadband absorbing properties. When using the FeSiAl powders as theabsorbing agent, laminated platescomposed of2.12mm glass fiber/epoxy resinthrough wave layers and2mm FeSiAl powder/epoxy resin absorbing layer （0.5mmFeSiAl powder/epoxy resin and0.5mm glass fiber/epoxy resin and1mm FeSiAlpowder/epoxy resin）, and the thickness of the laminated plates is4.1mm, theabsorbing properties of the laminated plates is: R<-4dB within the frequency4.08-4.56GHz and15.6-16.48GHz, R<-6dB within the frequency4.56-15.6GHz.（9） The hybrid fiber layer technology using carbon fiber and S type glass fiber according to the proportion of1:1mix together to achieve the effect of designingabsorbing properties at a fixed frequency, can effectively adjust the absorbing bandposition of the laminated plates.（10） Using the modular design can effectively broaden absorbing band of thelaminated plates.The thickness of4mm FeSiAl powder/epoxy resin composite laminated boardwas designed by modular method. Laminated plate is composed by （2.7mm glassfiber/epoxy resin+1.3mm FeSiAl/epoxy resin） and （2mm glass fiber/epoxy resin+2mm FeSiAl/epoxy resin） of two parts. Laminated plates have excellentelectromagnetic absorption properties:6dB<R<-4dB in2.24³.76GHz,8.56¹1.76GHz, and16.24¹7.2GHz ranges, R<-6dB in3.76⁸.56GHz and11.76¹6.24GHzfrequency ranges.Composite material plate formed by one part （2.46mm through wave layer+1.56mm FeSiAl absorbing layer） and the other part （2.11mm FeSiAl absorbing layer+1.5mm FeCuNbSiB absorbing layer absorbing layer+0.4mm through wave layer）shows the excellent electromagnetic absorption characteristics: R values are less than-4dB in2¹8GHz range, qualified bandwidth of R value less than-6dB reachs12.96GHz （2⁶.48GHz and9.52¹8GHz）, R values are close to-6dB within thescope of6.48to9.52GHz.（11） Structural absorbing composite laminated plate is of excellent waveabsorption performance and mechanical performance: no greater than4mm inthickness. The absorbing performances: R≤×××in2¹8GHz range. The mechanicalproperties: tensile strength≥500MPa, flexural strength≥400MPa, density ofcomposite material≤2.5g/cm3. Composite material is of good formability.