ANALYSIS OF MECHANICAL PROPERTIES OF COMPOSITE SANDWICH PANELS WITH FILLERS A. N. Anoshkin *, V. Yu. Zuiko, A.V.Glezmn Perm Ntionl Reserch Polytechnic University, 29, Komsomolski Ave., Perm, 614990, Russi JSC Prognoz, 54, Stkhnovsky St., Perm, Russi * noshkin@pstu.ru Keywords: sndwich pnels, composite mterils, numericl simultions, strength test. Astrct This work is dedicted to experimentl-theoreticl nlysis of mechnicl properties of sndwich pnels mde of firous polymer composite mterils with different types of core: tuulr, honeycom nd cellulr. 1. Introduction Tody sound-soring coustic sndwich pnels (coustic liners) mde of composite mterils re vitl elements of mny modern ircrft turojet engines. Different types of core re used for sndwich pnels tuulr, honeycom or cellulr types (figure1). Erlier singlelyer liners with perfortion were used, ut now doule-lyer liners re used to enhnce coustic dmping. Also comintion of different types of fillers (cores) cn e used t the sme time. In ddition to noise requirements coustic liners must stisfy mny other design constrints. So the providing of strength of composite sndwich pnels in the ncelle of engine under different loding conditions is very importnt. c Figure 1. Types of fillers: tuulr (), honeycom (), cellulr (c). The ehvior of honeycom structures ws investigted, for exmple, in [1-3] using the finite element method (FEM). Tody the most reserches re devoted to mechnicl ehvior of hexgonl cell filler (honeycom-core) mde of metllic mterils nd sed on the theory of strength of mterils with some ssumptions [4-6]. The present work is dedicted to experimentl-theoreticl prediction of effective mechnicl properties of sound-soring sndwich pnels nd different types of fillers (cores) mde of firous polymer composite mterils. 1
2. Effective elstic properties of fillers The finite element method is powerful nlysis tool for solving vrious engineering prolems. However, detiled representtion of honeycom or cellulr cores is not suitle for lrge-scle models due to computtionl difficulties. To chieve the efficiency of the numericl simultion the honeycom or cellulr fillers re usully replced y equivlent homogeneous volumes with effective orthotropic properties [7]. Orthotropic mteril is defined y nine independent elstic constnts: E, E, E,,,, G, G, G. It is x y z xy yz xz xy yz xz necessry to mke six numericl experiments to otin effective properties of filler: three tensile tests to determine the Young's modulus nd Poisson's rtio, nd three sher tests to determine the sher modulus. The numericl solution of the prolem of finding effective elstic properties of fillers ws performed with the use of the ANSYS softwre. Three-dimensionl models of fillers with different structures were creted. Shell281 finite elements were used for meshing of honeycom nd cellulr cores nd Solid186 elements for tuulr core (figure 2). To perform the numericl experiment we need to select representtive re for which mechnicl chrcteristics will e determined. c Figure 2. Finite element models of fillers: - tuulr, - honeycom, c - cellulr. Effective elstic properties of fillers - Young's modulus,,, sher modulus,, nd Poisson's rtio,, - were clculted y the following equtions: (1) where strin ws initilly defined (kinemtic loding), nd verged stresses, were clculted y the equtions: ( ) ( ) (2) 2
where n mount of finite elements;, stresses t the k-th finite element; volume of the k-th finite element; volume of mteril, volume of voids. Tle 1 presents the clculted effective elstic properties of fillers mde of fierglss. Type of filler (core) MP MP MP MP MP MP Tuulr 307,1 2066,0 188,3 0,03 0,21 1,3 160,4 316,2 6,7 Honeycom 1,2 1,05 880,8 1,06 2,12e-4 1,92e-4 0,28 53,8 108,8 Cellulr 1141,8 270,2 613,5 1,61e-3 0,06 0,17 50,8 73,6 10,1 Tle 1. Effective elstic properties of fillers mde of fierglss. 3. Effective elstic properties of sndwich pnels with fillers To estimte the effective elstic properties of sound-soring coustic sndwich pnels (coustic liners), specimens with perfortion for unixil tension nd shering tests were conducted. Also three-dimensionl computer models of pnel smples for tension nd shering test simultions were creted (figure 3). As result of the numericl simultion y ANSYS softwre, stress nd strin fields were otined. Figure 4 shows the clculted xil nd sher stresses in the smples of pnel with cellulr core under lod of 1N. The stress-strin nlysis llowed us to determine the verged stresses in the smples nd effective elstic modulus of coustic liners. Figure 3. Sndwich pnel smples nd 3-D models for unixil tension () nd shering () tests. 3
Figure 4. Axil () nd sher () stresses in the smples of pnel with cellulr core under lod of 1N, MP. The results of the numericl simultions were compred with the test dt. Tests for tensile nd sher properties of sndwich pnels with cellulr core were conducted on the universl electromechnicl mchine Instron 5882 using specilly developed fixture in the Center of Experimentl Mechnics t Perm Ntionl Reserch Polytechnic University (figure 5) [8]. Tensile nd sher stress-strin curves for tested specimens re given in figure 6. Figure 5. Tensile () nd shering () tests of sndwich pnel smples with specil fixture. 4
Figure 6. Tensile () nd sher () stress-strin curves for sndwich pnels with cellulr core. Effective Young's modulus nd sher modulus of the sndwich pnels were clculted from the otined stress-strin curves. According to the rule-of-mixtures effective elstic properties of cellulr core cn e computed from the test dt. The results of simultions nd tests re given in tle 2. Good correltion etween experimentl dt nd clculted results ws found. Test method Effective elstic modulus of sndwich pnel /cellulr core, GP Experimentl dt Numericl simultions Tensile 1,62 / 1,09 1,7 / 1,14 Sher 0,242 / 0,048 0,257 / 0,051 Tle 2. Effective elstic modulus of sndwich pnel nd cellulr core mde of fierglss 4. Conclusion It is importnt to know mechnicl properties of sound-soring coustic sndwich pnels (coustic liners) nd different types of fillers (cores). This work shows tht effective mechnicl properties cn e very well determined y numericl techniques. Computer models of sound-soring pnels with different types of core were creted. Clcultions of the stress-strin stte in the pnels under vrious loding conditions nd estimtes of ggregtes strength cn e otined y ANSYS softwre using these models. Effective elstic properties of fillers nd sndwich pnels clculted with the help of verging strin nd stress fields. The results of numericl simultions of mechnicl ehviour of sndwich pnels were compred with the test dt, good correltion ws found. The creted numericl models nd results of this work will e used for new fundmentl investigtion dedicted to the development of experimentl nd theoreticl principles of the mechnicl nlysis of self-dignosle (smrt-) mterils sed on opticl fiers nd piezoelectric elements. These elements emedded in sndwich pnels will llow to control the mechnicl ehvior of constructions in rel-time mode. References [1] Gredic M. A finite element study of the trnsverse sher in honeycom cores. Interntionl Journl of Solids nd Structures, 1993, Vol. 30, No.13, P. 1777 1788. [2] Merghni F, Desrumux F, Benzegggh ML. Mechnicl ehviour of cellulr core for structurl sndwich pnels. Composites Prt A 1999, No.30, P. 767 779. 5
[3] Chen DH, Ozki S. Anlysis of in-plne elstic modulus for hexgonl honeycom core: effect of core height nd proposed nlyticl method. Compos Struct, 2009, No.88, P. 17 25. [4] Gison J.L., Ashy M.F. Cellulr, Solids Structure nd Properties. Pergmon Press, Oxford, 1988. [5] Msters I.G., Evns K.E. Models for the elstic deformtion of honeycoms. Composite Structures, 1996, Vol. 35, No. 4, P. 403 422. [6] Levent Akty, Alstir F. Johnson. Numericl modelling of honeycom core crush ehviour. Engineering Frcture Mechnics, 2008, Vol. 75, No. 9, P. 2616 2630. [7] Vildemn V.E., Sokolkin Y.V., Tshkinov А.А. Mekhnik neuprugogo deformirovniy i rzrusheniy kompozitsionnykh mterilov [Mechnics of inelstic deformtion nd frcture of composite mterils] (in Russin). Moscow: Nuk, 1997, 288 p. [8] Zuiko V.Yu., Lonov D.S., Anoshkin A. N. Technique of experimentl determintion of ultimte strength of composite sndwich pnels in tension, compression nd sher sttic tests. (in Russin). PNRPU Mechnics Bulletin, 2012, No.2, P. 99 111. Work is performed with support of the Russin Foundtion for Bsic Reserch. Project No. 14-01-96020: Experimentl nd theoreticl studies of the mechnicl ehvior of composite mterils with opticl fiers nd piezo mterils 6