Effect of the Number and Stacking Sequence of Membranes in Glass Fiber Felt Composite Structure on Acoustic Properties

Transcription

1 Fibers and Polymers 2017, Vol.18, No.1, DOI /s ISSN (print version) ISSN (electronic version) Effect of the Number and Stacking Sequence of Membranes in Glass Fiber Felt Composite Structure on Acoustic Properties Yong Yang 1,2,3, Zhaofeng Chen 2 *, Cao Wu 2, Zhou Chen 2,4, Shengnan Guan 2, Yanming Li 2,5, and Shuting Bao 2,5 1 College of Materials and Environmental Engineering, Hangzhou Dianzi University, Hangzhou , P.R. China 2 International Laboratory for Insulation and Energy Efficiency Materials, College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, Nanjing , P.R. China 3 Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh 27695, USA 4 School of Mechanical and Power Engineering, Nanjing Tech University, Nanjing , P.R. China 5 Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites, Nanjing , P.R. China (Received March 14, 2016; Revised August 29, 2016; Accepted December 2, 2016) Abstract: In this paper, we investigate the effect of the number and stacking sequence of membranes in different glass fiber felts and their corresponding composite structures (bilayer structure and sandwich structure) on acoustic properties. Sound absorption coefficient (SAC) and sound transmission loss (STL) are measured by a B&K impedance tube. The results show that, with the increase the number of membranes in glass fiber felt composite structures, which can effectively improve the STL. For the sandwich structure, the greater the number of membranes is, the better the STLs are. However, STL of sandwich structure improves a little with the increase the number of membranes. Stacking sequence of membranes has an effect on the total STL. STL of different glass fiber felts front with a single-layered membrane is better than that back with a single-layered membrane. However, SAC of glass fiber felts front with a single-layered membrane is worse than that back with a singlelayered membrane. This phenomenon is also found in bilayer structure and sandwich structure. The optimal stacking sequence of membranes for STL is the membranes in front of composite structures, i.e., close to the sound incident surface of composite structures. Keywords: Acoustic property, Glass fiber felt, Composite structure, Stacking sequence Introduction Porous and fibrous materials are most widely used as sound absorption and sound insulation materials in architectural and building. However, they have a critical shortcoming which allows sound to pass through rather easily and yield a low acoustic property. In recent years, a number of studies have been carried out to develop new materials, technologies and composite structure to improve the acoustic properties. Hashimoto et al. [1] explored that attaching small weights to a membrane could improve the sound insulation efficiency in a frequency range. Sakagami et al. [2,3] studied sound absorption characteristics of a double-leaf structure composed of a micro-perforated panel (MPP) and a permeable membrane (PM) with a rigid-back wall, it indicated that the absorption performance of the MPP was greatly improved by the PM. Kazem et al. [4] studied three-layered insulating boards with three densities of 0.3, 0.4 and 0.5 g/cm 3 and found that sound absorption coefficients were affected by the board-type. Liang et al. [5] measured the soundproofing of polypropylene/ inorganic particle composites, sound insulation of the PP/ nano-caco 3 roughly obeyed the law of mass and STL of composites increased nonlinearly with an addition of the filler volume fraction. Zhou et al. [6] investigated sound *Corresponding author: zhaofeng_chen@163.com transmission loss of foam-filled honeycomb sandwich panels, the predicted and experimental transmission loss values of the sandwich panels were in better agreement. Yu et al. [7] found that the fiberboard was drilled and made as a perforated plate coupling with polyester fabric, which could be obtained good sound absorption. Sui et al. [8] explored a lightweight yet sound-proof honeycomb acoustic metamaterial and found that low frequency noise reduction could be significantly improved. Na et al. [9] investigated the acoustic characteristics of nanofibers and sound absorption coefficients of nanofiber layers were superior that of microfiber fabrics in the frequency range 1-4 khz. Hao et al. [10] investigated kenaf/polypropylene nonwoven composites; samples with the lowest moduli had the best sound absorbers and excellent sound barriers due to their panel-felt-panel sandwich structure. Fan et al. [11] presented an acoustic metamaterial based on membrane-coated perforated plates, theoretical analysis and finite element simulations demonstrated that this metamaterial could effectively block acoustic waves over a wide low frequency band. Yilmaz et al. [12] studied the sound absorption coefficient of alkalized three layered nonwoven composites. Compared to lower-temperature and lower concentration treatments, alkalization at higher temperature and higher concentrations gave better results in normalized sound absorption performance. In this paper, glass fiber felts were comprised of pure glass fibers and phenolic resin adhesive. Composite structures 182

2 Glass Fiber Felt Composite Structure on Acoustic Properties Fibers and Polymers 2017, Vol.18, No were fabricated by glass fiber felts, and membranes were embedded in composite structures. The motivation of this study is to explore acoustic properties of glass fiber felt composite structures with a series of aluminum membranes. The effect of the number and stacking sequence of membranes on acoustic property of glass fiber felt composite structures was also investigated. Experimental Materials and Fabrication Glass fiber felts are produced by centrifugal-spinneretblow system (CSBS) and flame blowing process (FBP) as shown in Figure 1. For CSBS process, the primary glass fibers were formed through pores on centrifugal pan s surrounding wall. Then, the primary glass fibers were immediately affected by air current jetted and were further split and stretched into secondary fibers of diameter more than 2 µm [13]. For FBP, the mineral material molten in a furnace was drawn into primary filaments by means of drawing rollers through a die and diameters of filaments were µm. Then, primary filaments was blown out into a flame fiber and the diameter was less than 2 µm [14]. Glass fibers with phenolic resin adhesive were sent into a curing furnace where glass fiber felts were formed. Phenolic resin adhesive evenly covered the surface of every fiber. Between the glass fibers, they were bonded by phenolic resin adhesive. The main elements of glass fiber were Si, O and Na, with traces of Mg, Al, K, Ca and Fe. Table 1 provides a list of material parameters. Both the composite structures (bilayer structure and sandwich structure) were fabricated by these glass fiber felts as shown in Figure 2. Aluminum foil was used as the membrane, which had a thickness of 100 µm and the areal density was g/m 2. Measurement Sound absorption coefficient (SAC) and sound transmission loss (STL) were measured by a B&K impedance tube (ASTM C384-98). The diameters of the tube and testing samples were 29 mm. The acoustic measurements were carried out in the frequency range of Hz. In the Figure 2. Different glass fiber felts and membrane. Figure 1. Different processes for glass fiber felts; (a) centrifugal-spinneret-blow system (CSBS), (b) flame blowing process (FBP). Table 1. The parameters of different glass fiber felts Code Areal density (g/m 2 ) Thickness (mm) Glass fiber diameter (µm) Airflow resistivity (Pa s/m 2 ) Process L 3.1± ±200 CSBS M ±1 1.5± ±500 FBP H 1.5± ±1000 FBP

3 184 Fibers and Polymers 2017, Vol.18, No.1 Yong Yang et al. testing processing, each sample was tested three times and averaged. The measurement of air flow resistivity of different glass fiber felts had been standardized on a compressed-air apparatus according to ASTM C Standard Test Methods (Table 1). Acoustic Theory Sound absorption is defined as the incident sound that strikes a material that is not reflected back. SAC is defined as the ratio of the sound energy absorbed by a surface to the sound energy incident on that surface, taking values between 0 and 1. The STL characteristics can be divided into three distinct regions based on the frequency range, i.e., stiffness and resonance region, mass region and coincidence region. In the stiffness and resonance frequency region, the STL is controlled by the stiffness and the resonance frequency. In the mass region, mass plays an important role in acoustic insulation. With the increase of areal density, STL can be improved. In the coincidence region, sound waves incident make sample with tiny deformation and bending waves can result in the coincidence effect [15]. Results and Discussion There was a strong correlation among acoustic properties, glass fiber felt composite structure, membranes and the frequency of sound. The number and stacking sequence of membranes in glass fiber felt and corresponding composite structures could show distinctive SACs and STLs at different frequencies. This section would present and discuss these results. Acoustic Properties of Different Glass Fiber Felts with a Single-layered Membrane Different glass fiber felts with a single-layered membrane are shown in Figure 3, Table 2 provides the stacking sequence of a single-layered membrane. Acoustic properties of various glass fiber felts with a single-layered membrane for different stacking sequences are shown in Figure 4. Figure 4(a), 4(c) and 4(e) reveals that glass fiber felts has excellent sound absorption performance. It was also noted that SAC at the acoustic resonance frequency of glass fiber felt was better than that with membrane. In addition, SAC of glass fiber felt back with a single-layered membrane having higher acoustic absorption effect was better than that front with membrane. This phenomenon was due to the more sound reflection from the membrane. Yilmaz et al. [16] also found that when the layer including reinforcement fibers faced the sound source, SAC were higher than that including reinforcement fibers was farthest from the sound source. Figure 4(b), 4(d) and 4(f) show that the membrane can effectively improve the STLs of glass fiber felts. The STLs were improved by 5-12 db in the khz range. The higher the tested frequencies were, the more the improvement of STL was. It was also found that there was a larger difference between stacking sequences. Glass fiber felts front with a single-layered membrane exhibited higher STLs than that back with a single-layered membrane. The improvement of STLs was 2-4 db in the khz range. This was probably because membrane introduced a higher amount of reflections leading to less transmission and therefore better STL. Acoustic Properties of Bilayer Structure with a Series of Membranes Sample L and sample H were combined to form glass Figure 3. Different glass fiber felts with a single-layered membrane. Table 2. Stacking sequence of a single-layered membrane for glass fiber felts Code L M H Position 1 Position 2 No membrane L-0# (M-0#, H-0#) + (-,-) - (+,-) - (-,+) - - Single-layered L-1# (M-1#, H-1#) + (-,-) - (+,-) - (-,-) + - membrane L-2# (M-2#, H-2#) + (-,-) - (-,-) - (-,+) used, - not used (For the symbols +, it means that sample or membrane is used).

4 Glass Fiber Felt Composite Structure on Acoustic Properties Fibers and Polymers 2017, Vol.18, No Figure 4. Acoustic properties of different glass fiber felts with a single-layered membrane for different stacking sequences; (a) SAC of sample L, (b) STL of sample L, (c) SAC of sample M, (d) STL of sample M, (e) SAC of sample H, and (f) STL of sample H. fiber felt bilayer structure (LH). The bilayer structure and stacking sequence of membranes are shown in Figure 5 and Table 3, respectively. For the double-layered membranes, each membrane respectively put in different positions and was not together. Acoustic properties of bilayer structure with a single-layered membrane are shown in Figure 6. Figure 6(a) shows that SAC of bilayer structure front with membrane is lower than that middle or back with membrane. Chen et al. [17] and Yilmaz et al. [18] found that if the cover screen had very low porosity, the result would be decreased high frequency absorption and unaltered low frequency absorption. However, SAC of bilayer structure with no

5 186 Fibers and Polymers 2017, Vol.18, No.1 Yong Yang et al. Figure 5. Bilayer structure of glass fiber felts with membranes. membrane is similar to that middle or back with membrane. Figure 6(b) shows that STL of bilayer structure front with a single-layered membrane is the highest, followed by that back with membrane. The membrane in the middle of bilayer structure had the worst performance. However, there were only a little difference between the bilayer structure middle with a single-layered membrane and that back with a single-layered membrane. The improvement of STLs of bilayer structure with a single-layered membrane was about 12.5 db at 6.3 khz. The stacking sequence of a singlelayered membrane affected the STLs of bilayer structure, and the improvement of STLs was 2-5 db in the khz range. Acoustic properties of bilayer structure with doublelayered membranes are shown in Figure 7. It indicated that this phenomenon of SAC of bilayer structure was similar to that of bilayer structure with a single-layered membrane (see in Figure 7(a)). The results showed that, compared to bilayer structure with no membrane, the STLs of bilayer structure with double-layered membranes were improved by db in the khz range (see in Figure 7(b)). The difference of STLs among the bilayer structure with different stacking sequences was db in the khz range. It was also found that STL of double-layered membranes was better than a single-layered membrane in glass fiber felt bilayer structure. Double-layered membranes close to sound incident surface had the highest STL, i.e., sample LH-4#. This phenomenon was due to more reflections on the surface of membrane. Sound Insulation of Glass Fiber Felt Sandwich Structure with a Series of Membranes Lee et al. [19] found that different arrangements of perforated panels affected the absorption coefficient. Yang et al. [20] explored the STLs of different glass fiber felt sandwich structures and the air flow resistivities of glass Table 3. The stacking sequence of membranes for bilayer structures Position Code L M H No membrane LH-0# Single-layered membrane Double-layered membranes + used, - not used. LH-1# LH-2# LH-3# LH-4# LH-5# LH-6# Figure 6. Acoustic properties of bilayer structure with a single-layered membrane; (a) SAC of sample LH and (b) STL of sample LH.

6 Glass Fiber Felt Composite Structure on Acoustic Properties Fibers and Polymers 2017, Vol.18, No Figure 7. Acoustic properties of bilayer structure with two layers membrane; (a) SAC of sample LH and (b) STL of sample LH. Figure 8. Glass fiber felt sandwich structure with a series of membranes. Table 4. The stacking sequence of membranes for glass fiber felt sandwich structure Position Code L M H No membrane MLH-0# Single-layered membrane Double-layered membranes Triple-layered membranes Quadruple-layered membranes + used, - not used. MLH-1# MLH-2# MLH-3# MLH-4# MLH-5# MLH-6# MLH-7# MLH-8# MLH-9# MLH-10# MLH-11# MLH-12# MLH-13# MLH-14# MLH-15#

7 188 Fibers and Polymers 2017, Vol.18, No.1 Yong Yang et al. fiber felts are 6633 Pa s/m 2 (Loose), Pa s/m 2 (Mid) and Pa s/m 2 (Dense). It was found that sandwich structure (mid-loose-dense) had the best STL. In this section, sample L, M and H were combined to form glass fiber felt sandwich structure. Sample L was in the middle of the sandwich structure, i.e., MLH, as shown in Figure 8. Table 4 lists the stacking sequence of single-layered, double-layered, triple-layered and quadruple-layered membranes. For the double-layered membranes and triple-layered membranes, each membrane put into different positions to form doublelayer and triple-layer and was not put together. STLs of glass fiber felt sandwich structure (MLH) with different membranes in a series of stacking sequences are shown in Figure 9. It indicated that STL of sandwich structure was improved with the increase of the number of membranes. It was also found that sandwich structure front with membranes was better than that in other positions. The STLs difference of sandwich structure with a single-layered, double-layered and triple-layered membranes all reached the maximum at around 5 db between the best and the worst positions at 6.3 khz. The stacking sequence of membranes affected the STLs. However, with the increase the number of membranes, this phenomenon was not obvious. For sandwich structure with a single-layered membrane, the effect of stacking sequence on STLs was mainly in the khz range. However, this phenomenon for double-layered and triplelayered membranes was mainly in the khz range and khz range, respectively. It meant that the effect of stacking sequence of membranes could be ignored when the quantity of membranes was enough. Effect of the Number of Membranes on STLs of Sandwich Structure in the Optimal Stacking Sequence In this section, STLs of sandwich structure with a series of membranes were compared. The number of membranes was increased from 0 to 4 with an increment of 1. All the membranes located in the optimal position, i.e., MLH-0#, MLH-1#, MLH-5#, MLH-11# and MLH-15#. Effect of the Figure 9. STLs of glass fiber felt sandwich structure with a series of membranes in different stacking sequences; (a) a single-layered membrane, (b) double-layered membranes, and (c) tripe-layered membranes. Figure 10. STLs of sandwich structure with a series of membranes in the optimal stacking sequence.

8 Glass Fiber Felt Composite Structure on Acoustic Properties Fibers and Polymers 2017, Vol.18, No Acknowledgements The authors would like to thank the Priority Academic Program Development of Jiangsu Higher Education Institutions. This work was also supported by the NUAA Fundamental Research Funds (NO.NS ), Major Achievements of Jiangsu Province (BA ) and Development of Vacuum Insulation Panel of China Building Cooperative Research (2015DFI53000). The first author also thanks the NUAA for financial support for Ph.D. study at North Carolina State University. References Figure 11. The growth rate of STLs with the increase of membranes at the frequency of 6.3 khz. number of membranes on STL of sandwich structure in the optimal stacking sequence is shown in Figure 10. STL of sandwich structure could be improved with the increase of membranes. This phenomenon mainly occurred at high frequency, i.e., after 3.5 khz. However, the improvement of STLs was not obvious with the increase the number of membranes. STLs are compared at the frequency of 6.3 khz and the growth rate of STLs are 34.4 %, 18.6 %, 11.8 % and 5.3 %, respectively, as shown in Figure 11. In other words, the more the layers of membranes were, the better the STL was. However, it was not obvious for the increase of STL. STLs of sandwich structure were affected by the stacking sequence of membranes. This effect would be ignored with the increase the number of membranes. Therefore, in order to obtain a good sound insulation characteristics, it was necessary that the optimum acoustic, structural and stacking sequence parameters of each sample should be selected when composite structures had satisfied the needs of their having multifunction. Conclusion Acoustic properties of glass fiber felts and their corresponding composite structures (bilayer structure and sandwich structure) with a series of membranes and stacking sequence of membranes were investigated. The addition of membranes could effectively improve the sound transmission loss (STL). For sandwich structure, the best STL could be obtained by adding the number of membranes. However, STL only improved a little with the increase of membranes. At the same time, the stacking sequence of membranes also affected the STL. STLs of samples front with membranes were better than those in other positions. However, sound absorption coefficient of samples front with membranes were worse than those in other positions. 1. N. Hashimoto, M. Katsura, M. Yasuoka, and H. Fujii, Appl. Acoust., 33, 21 (1991). 2. K. Sakagami, Y. Fukutani, M. Yairi, and M. Morimoto, Appl. Acoust., 76, 28 (2014). 3. K. Sakagami, Y. Fukutani, M. Yairi, and M. Morimoto, Appl. Acoust., 79, 104 (2014). 4. D. H. Kazem, R. T. Hamid Reza, and A. Elyasi, Compos. Pt. B-Eng., 58, 10 (2014). 5. J. Z. Liang and X. H. Jiang, Compos. Pt. B-Eng., 43, 1995 (2012). 6. R. Zhou and M. J. Crocker, J. Sound Vib., 329, 673 (2010). 7. X. Yu, L. H. Lv, C. Y. Wei, Y. Z. Cui, X. Wang, and T. Liu, J. Text. Inst., 105, 1009 (2014). 8. N. Sui, X. Yan, T. Y. Huang, J. Xu, F. G. Yuan, and Y. Jing, Appl. Phy. Lett., 106, (2015). 9. Y. Na, T. Agnhage, and G. Cho, Fiber. Polym., 13, 1348 (2012). 10. A. Hao, H. F. Zhao, and J. Y. Chen, Compos. Pt. B-Eng., 54, 44 (2013). 11. L. Fan, Z. Chen, S. Zhang, J. Ding, X. J. Li, and Hui Zhang, Appl. Phy. Lett., 106, (2015). 12. N. D. Yilmaz, N. B. Powell, B. L. Pamela, and S. Michielsen, Fiber. Polym., 13, 915 (2012). 13. Y. Yang, Z. Chen, Z. F. Chen, R. L. Fu, and Y. F. Li, Fiber. Polym., 16, 1587 (2015). 14. A. G. Novitskii and M. V. Efremov, Refract. Ind. Ceram., 47, 121 (2006). 15. Y. Yang, B. B. Li, Z. F. Chen, N. Sui, Z. Chen, M. U. Saeed, Y. F. Li, R. L. Fu, C. Wu, and Y. Jing, Compos. Pt. B-Eng., 96, 281 (2016). 16. N. D. Yilmaz, P. B. Lee, N. B. Powell, and S. Michielsen, J. Appl. Polym. Sci., 121, 3056 (2011). 17. W. H. Chen, F. C. Lee, and D. M. Chiang, J. Sound Vib., 237, 337 (2000). 18. N. D. Yilmaz, Acoustic Properties of Biodegradable Nonwovens, F. C. Lee and W. H. Chen, J. Sound Vib., 248, 621 (2001). 20. Y. Yang, Z. Chen, Z. F. Chen, R. L. Fu, and Y. F. Li, Fiber. Polym., 16, 1568 (2015).