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    Damping behavior of continuos fiber-metal composite materials by the free vibration method.pdf

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    Damping behavior of continuos fiber-metal composite materials by the free vibration method.pdf

    fiber/metale Barroso, CTA,dos Campos,eMaterial2004;16 Septemberover the high-strength aluminum alloys used in the FML fatigue resistance and they are promising candidates for theComposites Part B 37E-mail address ebotelhodirectnet.com.br E.C. Botelho.AbstractFiber metal laminates FML offer significant improvements over current available materials for aircraft structures due to their excellentmechanical characteristics and relatively low density. Non-destructive testing techniques are being used in the characterization of compositematerials. Among these, vibration testing is one of the most used tools because it allows the determination of the mechanical properties. Inthis work, the viscoelastic properties such as elastic E0 and viscous E00 responses were obtained for aluminum 2024 alloy; carbonfiber/epoxy; glass fiber/epoxy and their hybrids aluminum 2024 alloy/carbon fiber/epoxy and aluminum 2024 alloy/glass fiber/epoxycomposites. The experimental results were compared to calculated E modulus values by using the composite micromechanics approach. Forall specimens studied, the experimental values showed good agreement with the theoretical values. The damping behavior, i.e. the storagemodulus and the loss factor, from the aluminum 2024 alloy and fiber epoxy composites can be used to estimate the viscoelastic response ofthe hybrid FML.q 2005 Elsevier Ltd. All rights reserved.Keywords A. Hybrid; B. Mechanical properties; B. Vibration1. IntroductionFiber–metal laminate FML composites are composed ofalternating layers of fiber-reinforced polymer prepregs andaluminum 2024-T3 alloy sheets. These hybrid materials offersuperior mechanical properties over the conventional polymercomposite laminates and the high-strength monolithic alumi-num alloys. In the case of FML, the aluminum skin sheets arethe outer layers and they protect the core composed ofpolymeric composites. As a consequence, the resistance toenvironmental attack and foreign object impact can beenhanced. The specific stiffness and strength in the fiberdirection of reinforced-polymeric composites are improvedcomposites, and contribute significantly to weight savings in thedesign of tension-dominated stresses in structural components.Also, the fiber-bridging mechanism that occurs in the compositelaminae reduces crack growth and propagation in thealuminum–alloy layers under tensile fatigue conditions [1–9].Fiber/metal laminates, in the form of glass/epoxy layerinterleaved by thin aluminum sheets, were originallydeveloped at Delft University of Technology at thebeginning of 1980 [10–12]. These hybrid materials aredivided into three groups according to the type of fiber-adhesive layer used, as follows reinforced with aramidfibers ARALL; glass fibers GLARE and carbon fibersCARALL [10–12]. Their main attribute is the improvedDamping behavior of continuousby the free vibrationE.C. Botelhoa,c,*, A.N. Camposb, E. daDivisa˜o de Materiais, Instituto de Aeronautica e EspacCEP 12.228.904 Sa˜o JosebDivisa˜o de Integraca˜o e Ensaios, Instituto de AeronauticacFatigue and Aeronautic Material Research Group, Department ofReceived 14 NovemberAvailable onlinecomposite materialsmethodb, L.C. Pardinia, M.C. RezendeaPraca Mal, Eduardo Gomes, 50 Vila da Acacias,Sa˜o Paulo, BrazilEspaco, CTA, Sa˜o Jose dos Campos, Sa˜o Paulo, Braziland Technology, UNESP, Guaratingueta, 01419-901 SP, Brazilaccepted 25 April 200520052006 255–263www.elsevier.com/locate/compositesbsemi-static or dynamic mechanical tests. Static mechanicaltests are destructive while majority of dynamic mechanicaltest offers the advantage of being non-destructive. Nowa-days, various experimental methods potentially applicableto determine dynamic moduli and damping of composites1359-8368/ - see front matter q 2005 Elsevier Ltd. All rights reserved.doi10.1016/j.compositesb.2005.04.003Aeronautica e Espaco, CTA, Praca Mal, Eduardo Gomes, 50 Vila daAcacias, CEP 12.228.904 Sa˜o Jose dos Campos, Sa˜o Paulo, Brazil.Elastic properties of composites can be determined by* Corresponding author. Address Divisa˜o de Materiais, Instituto destructural materials of advanced aircraft.free vibration, rotating-beam deflection, forced vibrationresponse, continuous wave or pulse propagation techniquehave been used and reviewed [13–18,19].One of the most used tests is the vibration damping. Themeasurement principle consists of recording the vibration decayof a rectangular plate excited by a controlled mechanism toidentify the elastic and damping properties of the material undertest. The frequency amplitudes are measured by accelerometersand calculated by using a digital method [19–25].In the present study, the dynamical mechanical proper-ties were obtained by free vibration damping test of thefollowing materials aluminum 2024-T3 alloy; carbonfiber/epoxy composites; carbon fiber/aluminum 2024-specimen having 250 mm of length, 25 mm of width andyield the best overall bond durability. Details of thisE.C. Botelho et al. / Composites2562 mm of thickness, according to equation 5 [23–25]E Z4p2f23IM C33140mC20C21L31 CD24p2C20C212CDPdxxyXyLhbI,mMKLηT3/epoxy hybrid composites and glass fiber/aluminum2024-T3/epoxy hybrid composites. The results of the elasticand viscous response of these new materials were comparedwith the conventional polymer composites.2. Theoretical analysisA theoretical analysis of internal damping and dynamicstiffness for aligned continuous fiber composite wasdeveloped based on micromechanics models for thecomplex moduli. The viscoelastic response ofmaterials under stress can be modeled as depicted inFig. 1, where L is the length; h is the thickness, b is thewidth, dx is the deformation in x and y is the deflection of thebeam [23–25].The free vibration method results generally present alogarithmic damping D given by Eq. 1 [23–25]D Z lnd1dnC18C19Z1nlnd1dnC18C191where n is the number of peaks; d1is the amplitude of thefirst peak and dnis the amplitude of the final peak analyzed.The storage modulus E0 was obtained for a rectangularFig. 1. Voigt–Kelvin model for free vibration method [22–25].methodology are already described the in the literature [26].3.2. Hybrid composites processingThe hybrid composites were prepared by stackingalternating laminae of the prepregs and the aluminumsheet. The lay-up scheme of the hybrid composites was 3/2,as followsHybrid 1 Al/CF–E/Al/CF–E/AlHybrid 2 Al/GF–E/Al/GF–E/AlThe hand lay-up of the hybrid composite materials wasmade as depicted schematically in Fig. 2. After the lay-upprocess, the laminates were fit inside a vacuum bag andplaced in an autoclave system. The curing cycle was done ata heating rate to 2.5 8C/min up to 120 8C and held at thisfinal temperature for 1 h. The pressure and the vacuum usedwhere E0is the elastic modulus; f is the natural frequency; Iis the inertial moment; M is the accelerometer weight; m isthe specimen weight and L is the specimen length.The loss factor, tan d, can be calculated from thedecaying-oscillatory damping curve as followstan d Zlnd1dnnp3Loss modulus E00 can be calculated by equation 4tan d ZE00E04The term [lnd1/d2]/n, also known as the logarithmicdecrement D, can be obtained by fitting the experimentaldata. Tan d values can also be obtained theoretically byusing the rule of mixtures. So, the parameters found in thiswork were the E0, E00loss modulus and tan d values.3. Experimental3.1. MaterialsCarbon fiber/epoxy CF–E and glass fiber/epoxyGF–E prepregs with F155 specification were used forthe composite manufacture. The prepregs were supplied byHexcel Co. The fiber reinforcement was plain weavefabrics. The aluminum alloy 2024-T3 sheets with 0.50of Fe; 0.15 of Ti; 1.2–1.8 of Mg; 0.3–0.9 of Mn;0.50 of Si; 0.25 of Zn; 3.8–4.9 of Cu and 0.10 0f Crwere supplied by Empresa Brasileira de AeronauticaEMBRAER. The aluminum surfaces were prepared forthe adhesive bonding either by etching or anodizing processin Chromic Acid Anodizing CAA at Embraer facilities.These acid etching and anodizing processes generatemicrorough morphologies, which have been shown toPart B 37 2006 255–263were kept at 0.69 and 0.083 MPa, respectively.E.C. Botelho et al. / Composites Part B 37 2006 255–263 2573.3. Evaluation of fiber/aluminum 2024-T3/epoxy hybridcomposites processMicrographs of the cross section of the hybridcomposites were observed by optical microscopy OM inorder to evaluate how homogeneous was the lamination andthe curing process. The morphological evaluation was donein a Digital Scanning Microscopy from Zeiss Company,model 950.3.4. Measurement of dynamic moduliThe dynamic elastic modulus was determined byvibration damping measurements. The measurement prin-ciple consists of recording the free vibrations of a prismaticcantilever beam excited by tapping it with an appropriatehammer, as shown in Fig. 3. The amplitude decay as afunction of time and the vibration modes were detected byan acquisition data system from Spectral DynamicsCompany and recorded using a software LMS CADA-PC.The test parameters were analyses range of 1000 Hz;acquisition time of 200 ms; rectangular observation windowand frequency resolution of 5 Hz. The amplitude decay wasmeasured using a 0.6 g accelerometer. Beam dimensions areshown in Table 1. Following the testing procedure, twotypes of curves were obtained damping free vibration andFig. 2. Configuration of continuous fiber/metalfrequency response function profiles.The length, width and thickness were measured along thebeam specimens. Average values for the thickness, widthFig. 3. The experimenand standard derivation were calculated from 10 measure-ments. The upper and lower limits of the standard derivationof the sample dimensions were considered for thecalculations.The vibration test gives the free vibration damping decayand the frequency response function FRF, simultaneouslyas a result. Considering a linear system of a single degree offreedom, the FRF response is the decomposition of thenatural frequencies of a structure or specimen, whichcorresponds to a typical fingerprint identity of the vibrationmodes. The number of vibration peak frequencies vibrationmodes and the shape of the FRF response are a direct resultof the rigidity of the material.Most of the materials studied have considerably morecompliant than aluminum hence would present less problemof parasitic loss [27–30]. Due to the eventual problemsrelated to parasitic damping, this work will not approachdamping factor values. In the present work, only E0, E00andtan d values are presented. All the tan d values calculated forthe tested materials were compared to aluminum 2024-T3,because it is easy to find the tan d values for this material inthe literature.3.5. Theoretical calculationsIn order to compare the experimental results of CF–E and/epoxy hybrid composite 3/2 lay-up.GF–E composites in relation to theoretical values, theFabric Geometry Model FGM Code were used [31]. Theprogram allows predicting the stiffness of compositetal set-up.foil. The thickness of the polymeric composites between thealuminum 2024-T3 layers, were 0.24 and 0.36 mm, forThe theoretical calculations show that the CF–E compositehas an elastic modulus E similar to the aluminumw72.0 GPa one and, consequently, it is expected that forthe hybrid composite, the elastic modulus would beequivalent. On the other hand, the low elastic modulus30.6 GPa of the GF–E composite tends to lower the elasticmodulus of hybrid composites made with these twocomponents GF–E laminae and aluminum. A similarbehavior can be observed for shear modulus results.Aluminum has a shear modulus of 28.0 GPa and the hybridcomposites exhibit a shear modulus of 18.0 GPa [26].Thickness, h m Weight g Inertia m423.110K419.010K31.3310K1118.010K49.0610K30.7310K1110.410K412.410K30.1910K1119.510K418.310K31.2610K1117.210K416.810K31.0210K11 Part B 37 2006 255–263carbon fiber and glass fiber laminae, respectively. Con-sidering that both fabrics have the same style, differences inthe thickness of the polymer composite laminae are due tothe monofilament mean diameters carbon fiber is w8 mmand glass fiber is w15 mm [10]. SEM evaluation shows thatin both cases, using carbon fiber or glass fiber, it waspossible to produce a hybrid laminate with adequateconsolidation between the continuous fiber, metal andepoxy resin layers.4.2. Vibrational testsmaterials having spatially oriented reinforcements, fromconstituent material properties using composite microme-chanics approach. The FGM Code allows the calculation ofthe elastic constants for the fiber/epoxy fabric composites,taking into account the fiber orientation. The elasticconstants calculated for the polymer composites and theelastic constants of the aluminum 2024-T3 were used toestimate the E modulus for the hybrid composites by usingthe rule of mixtures. The E modulus of the hybrid compositewas calculated considering a volumetric content of thealuminum 2024 w57 and the fiber/epoxy compositesw43.4. Results and discussion4.1. Processing of hybrid compositesFig. 4 presents a cross section of the Hybrid 1 Fig. 4aand Hybrid 2 composites Fig. 4b. Fig. 4 shows the distinctlayers of the polymer composite laminae and the aluminumTable 1Dimensions and weight of specimens used in damping testsSpecimen Length, L m Width, b mGF–E 0.210 0.020CF–E 0.210 0.015Aluminum 2024-T3 0.211 0.020Hybrid 1 0.202 0.021Hybrid 2 0.211 0.021E.C. Botelho et al. / Composites258Fig. 5a–e and Table 2 present the resonant frequencyresults of all specimens studied in this work. The first modeof vibration was used in order to calculate the E0and E00moduli.The beam specimens have the frequency scanned up to500 Hz.4.3. Determination of elastic module E0The theoretical elastic constants calculated by usingcomposite micromechanics approach are shown in Table 3.Fig. 4. Optical Micrographs of continuous fiber/metal/epoxy compositematerials a carbon fiber reinforcement Hybrid 1; b glass carbonreinforcement Hybrid 2.3 mode200300400500600700800aE.C. Botelho et al. / CompositesFour primary mechanisms have been suggested tocontribute to damping in composites viscoelastic responseof the constituents, friction and slipping at the fiber–matrixinterface, thermoelastic damping due to cyclic heat flow anddamage initiation and growth. Excluding the contributionfrom any cracks and other defects, the internal damping of acomposite is determined by the following variablesproperties and relative proportions of the matrix and0 100 200 300 400 500–400–300–200–10001002003004005006007008002 mode2 mode2 mode3 mode1 mode1 mode1 modeFRF g/N–400–300–200–1000100FRF g/Nfrequency Hz0 100 200 300 400 500frequency Hz0 100 200frequency Hz–400–2000200400600800FRF g/NcdebFig. 5. Resonant frequency results from composite laminate specimens studied aPart B 37 2006 255–263 259the reinforcement; dimensions of the

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