Evaluation of acoustic attenuation of composite wood panel through nondestructive test.

Stanciu, Mariana Domnica ; Curtu, Ioan ; Terciu, Ovidiu Mihai 等

Abstract: The paper presents the experimental results determined by means of nondestructive test concerning the acoustic attenuation of composite panels. The sample panel made of biodegradable materials like solid wood, wood flakes and woven inserts was studied in order to establish its practicable application. Based on ultrasonic wave propagation, the acoustic attenuation of the tested composite panel was determined. The results revealed that the investigated panel recorded a high value of the acoustic attenuation, assumed as a good acoustic insulation.

Key words: attenuation, ultrasound technique, composite panel sound barriers, textile waste,

1. INTRODUCTION

One of the nondestructive techniques used to determine the acoustic attenuation is based on the ultrasonic wave propagation. This method presents several advantages compared with the conventional ones, such as speed, versatility and lower cost. According to the purpose of research, the ultrasound technique has been used to investigate mechanical properties of wood (Bucur, 2006), defects of materials (Grimberg, 2009) resonance frequency, damping of materials(Mobley, 2009; Wrobel, 2007). The present paper focuses on the determination by a non-destructive method of the acoustic attenuation of the proposed composite panel used in ambiental design. The novelty of this study is both the combination between materials and the method.

2. MATERIALS

The sample studied in this paper is a composite panel made of wood chips and textile wastes. The panel is formed in a wooden box with the interior sizes of 650 x 180 mm and thickness of 36 mm filled inside with an agglomerated structure made of wood chips and unwoven textile inserts, compacted at a normal temperature (20-22[degrees]C) and conditioned at a temperature of 40-50[degrees]C. (Cosereanu, 2010).

[FIGURE 1 OMITTED]

The materials used in these structures are green ones and biodegradable, namely inserts of wood (chips or fibers) and textiles (wool or jute) and mineral binders as clay. The core of the sandwich structure is intended to be a light structure, easy to manipulate, easy to be cut at the required sizes, compact enough to not be damaged during the transport or when assembling it, easy to be mount on the exterior building walls and of course with similar thermal insulating properties as polystyrene has (Cosereanu, 2010).

3. EXPERIMENTAL SET-UP

In order to determine the acoustic attenuation, the transceiver method using the non-contact transducers made by NCG 100D25 ULTRANGROUP U.S. has been used, having the following features: 25 mm diameter, a central frequency of 100 kHz and the band width in the range of 1kHz--35MHz. The transducers were coupled at a Pulser--Receiver 5077 PR Panametrics NDT USA connected with a digital oscilloscope Wave Runner 64Xi--LeCroy USA, which allows the measurement of time with an accuracy of 0.1ns (Grimberg, 2011).

The distance between the emission transducer and the reception remained at a constant value of 200 [+ or -] 0.1mm during the test and the measured temperature, air pressure and relative humidity in the room were as follows: temperature 28 [+ or -] 0.50C, pressure 755 [+ or -] 1 torr (mm Hg col) and relative humidity of air 58 [+ or -] 1%. The principle scheme and the equipment are presented in Figure 2.

[FIGURE 2 OMITTED]

4. RESULTS AND DISCUSSION

First, the amplitude, the gain and preamplification of received signal without panel and than with panel between transducers (Table 1), was measured and recorded. Than, the data were insert in formulas to obtaine the value off attenation.

[FIGURE 3 OMITTED]

The signal provided by the receiving transducer in the absence of the panel will be (Grimberg, 2009, 2011):

[A.sub.without panel = 20 log [U.sub.output]/[U.sub.input] (1)

Replacing the values in relation 1, the output amplitude is:

[U.sub.output] = 10 12/20 + log 422 (2)

In the same way, it is calculated the received signal in the presence of panel, resulting that the output amplitude U is:

[U.sub.output] = 10 79/20 + log352 (3)

The acoustic attenuation [alpha] will be:

[alpha] = [U.sup.1.sub.output]/[U.sup.2.sub.output] = -65.4 dB (4)

According to calculation, the composite panel has a good acoustic insulation ([alpha] = 13.6).

The experimental results were compared with the simulated ones. For simulation, the LIMA soft has been used. Starting with the real measured noise levels from the urban traffic, virtual panels from different materials were used to simulate the sound barrier. The noise level after interposing the panel was measured. In table 2 the comparison between different materials attenuation is presented.

5. CONCLUSION

The attenuation of studied panel is around 11.5% (from simulation) and 17% (from experimental test), compared with glass (2,6%), solid wood (3,8%) and acrylic (4,05%). Thus, the composite materials made of wood and textile wastes are recommended to be used both in civil and industrial structures, as well as in urban structures used to reduce the noise. Other advantages of these materials are: relatively low density, low cost and rich resource of raw materials. In a previous research, the thermal insultation of these materials was studied.

The future research plane is based on these experimental results because implies the integration of composite panels in complex structure as noise barriers in order to be tested in open area. This stage of research assumes more and expensive experiments due to the dimensions and complexity of structure, but will provide more realistic results about sound insulation properties of tested structures.

6. ACKNOWLEDGEMENTS

This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), financed from the European Social Fund and by the Romanian Government under the contract number POSDRU POSTDOCDD, ID59323--Transilvania University of Brasov, Romania. We are also grateful to INCDFT Iasi Romania, manager Prof. Grimberg R who facilitates the measurements.

7. REFERENCES

Bucur, V. (2006). Acoustic of wood. Springer-Verlag Berlin Heidelberg New York, ISBN-13 978-3-540-26123-0, p.173-216

Cosereanu C., Lazarescu C., Curtu I., Lica D., Sova D., Brenci L., Stanciu M. D. (2010). Research on New Structures to replace Polystyrene used for Thermal Insulation of Buildings, in Rev. Materiale Plastice, MPLAAM 47 (3) 2010, Vol. 47, nr. 3--septembrie 2010, Bucuresti Romania, ISSN 0025/5289, pp.341-345

Grimberg, R., Curtu, I., Savin, A., Stanciu, M. D., Andreescu A., Leitoiu S., Bruma A., Barsanescu P. (2009). Elastic Waves Propagation in Multilayered Anisotropic Composite--Application to Multilayered Lignocellulose Composite, in Proc. of The 7th Edition of International Conference ICWSE 2009, 4-6 June 2009, Brasov, ISSN 1843-2689, pp. 688-695

Grimberg, R., Savin, A., Curtu I., Stanciu M.D., Lica, D., Cosereanu, C., (2011). Assessment of Wood Using Air Coupled US Transducer, in Proceedings of the 17th International Symposium on Nondestructive Testing of Wood, 14-17 September 2011, Sopron, Hungary.

Mobley, J., Mack, R., Gladden, J., Mantena, R. (2009). Determination of power-low attenuation coefficient and dispersion spectra in multi-wall carbon nanotube composites using Kramers-Kroning relations, in J. Acoust. Soc. Am. 126 (1), July 2009, pp. 92-97

Wrobel, G., Wierzbicki, L., Pawlak, A. (2007). A method for ultrasonic quality evaluation of glass/polyester composites. Archives of Materials Science and Engineering. Vol. 28. Issue 12, December 2007, pp 729-734

Tab. 1. Values of received signals before and during the
experiment

Cases Amplitude Gain Preamplification Amplification
 U [mV] G[dB] PA [dB] A=G-PA [dB]

Without 422 [+ or -] 12 -28 40 12
panel

With 352 [+ or -] 16 39 40 79
panel

Tab. 2. Comparison of different materials attenuation

Panel Initial Determined Attenuation
 Noise Noise Level [alpha]
 Level after
 dB dB

Without panel 73,90 73,90 0
Glass 73,90 72,00 1,90
Brick 73,90 71,60 2,30
Perforated brick 73,90 71,30 2,60
Solid Wood 73,90 71,10 2,80
Acrylic 4 mm 73,90 70,90 3,00
Acrylic 8 mm 73,90 70,90 3,00
Studied panel 73,90 65,40 8,50