Application of Taguchi Method for Investigating the Acoustical Prop- erties of Synthetic Foam Composite Structure Nurşah Öner 1 İstanbul Technical University İTÜ Gümüşsuyu Kampüsü, Makina Fakültesi, 34437, Beyoğlu - İstanbul / Türkiye Sinem Öztürk 2 İstanbul Technical University İTÜ Gümüşsuyu Kampüsü, Makina Fakültesi, 34437, Beyoğlu - İstanbul / Türkiye Sevinç Aycan Yetim 3 İstanbul Technical University İTÜ Gümüşsuyu Kampüsü, Makina Fakültesi, 34437, Beyoğlu - İstanbul / Türkiye Uğur Tatlier 4 İstanbul Technical University İTÜ Gümüşsuyu Kampüsü, Makina Fakültesi, 34437, Beyoğlu - İstanbul / Türkiye

ABSTRACT In this paper, the Taguchi method was used to optimize the parameters for determining the acoustical properties of synthetic foam composite structures. Synthetic foam consists of micro glass balloons, resin and epoxy. Two types of composite structures have been studied; synthetic foam composite structures reinforced with silicon carbide nanopowders and multi-walled carbon nanotubes. As op- timization parameters, thickness of composite structure (up to 12 cm), glass micro balloon volume ratios (up to 50%), silicon carbide nanopowder volume ratios (up to1.5%) and multi-walled carbon nanotube volume ratios (up to 1.5%) were determined. The optimal parameters for synthetic foam composite structures were obtained by the Taguchi method. The samples were prepared using the optimal parameters for constructing synthetic foam composite structures. The acoustical properties of samples were examined in the frequency range up to 6400 Hz.

1. INTRODUCTION

Many studies examine the acoustic properties of polyurethane foam structures in the literature, but there are limited publications examining the properties of synthetic foam composite structures. In

1 onernursah@itu.edu.tr

2 ozturksi@itu.edu.tr

3 yetim17@itu.edu.tr

4 tatlier15@itu.edu.tr

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their study, Gao et al. [1] investigated the effects of the HGM content on the composites' sound prop- agation characteristics and dielectric properties. Jiejun et al. [2] studied the acoustical properties of composite foams produced by two methods. They determined the sound absorption and noise prop- erties of the foams. Bandarian et al. [3] demonstrated the mechanical and acoustical properties of open-cell flexible polyurethane foams incorporating multi-walled carbon nanotubes. Orfali [4] stud- ied the material polyurethane composition. A small amount of carbon-nanotube and silicon-oxide nanopowder (S-type, P-Type) were added to the host material polyurethane composition and the acoustical properties of these new materials were measured.

This study compared the acoustic properties of synthetic foam composite materials reinforced with silicon carbide and multi-walled carbon nanotubes. The number of experiments with the Taguchi method has been reduced to save time and cost. The frequency-dependent sound absorption coeffi- cients and sound transmission loss values of the composite structures produced according to the re- sults of the Taguchi method were measured with an acoustic impedance tube and the results were compared for each material.

2. EXPERIMENTS

2.1. Design of Samples with the Taguchi Method

Experimental design with the Taguchi method is a statistical method and is an approach used to determine the appropriate combination between different levels of different parameters [5]. The Taguchi method is a statistically designed method using orthogonal arrays to obtain the best results with the least number of experiments. Thus, cost and time savings are achieved by reducing the num- ber of experiments [6]. The S/N ratio given in Equation 1 is used to analyze the experimental results found due to the design of orthogonal arrays. This ratio is calculated depending on the characteristic

n type, using the "smaller is better" or vice versa "bigger is better" methods. In Equation 1, repre-

i y th i sents the number of experiments and represents the value of the obtained acoustic properties [5]. "The bigger is better" method was used in this study.

              (1)

n

1 1 10

S log N n y 

2 1

i i

This study used the Taguchi design creation module in DOE (Design of Experiments) in the Minitab program. L9 orthogonal design was chosen for the design of the samples in the Taguchi method. Three factors were considered as control factors: glass micro balloon ratio (Factor A), parti- cle additive ratio (Factor B) and thickness (Factor C). The level for each factor can be defined as the conditions whose effect is investigated. Levels of 0, 30% and 50% for Factor A, 0, 1% and 1.5% for Factor B, and 40, 80 and 120 mm levels for Factor C were considered. The design for silicon carbide and multi-walled carbon nanotube doped composite is shown in Table 1.

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Table 1: Variations of composite samples by Taguchi method a) Silicon carbide nanopowder

alloyed b) Multi-walled carbon nanotube alloyed

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2.2. Making of Composite Samples

According to the variations created according to the Taguchi method, the test samples were pro- duced with SiC and MWCNT additives. First, the nanopowder and nanotubes, the amounts of which were determined, were added to the epoxy. Then they were dispersed into the epoxy at a speed of 650 rpm for 30 minutes with the help of a mechanical mixer to obtain a homogeneous mixture. Figure 1 shows the mechanical and hand stirring.

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Figure 1: Mechanical Stirring - Hand Stirring – Sample

Since wetting of the particles is significant and is significant to prevent aggregation, the beaker was heated to 50°C with the help of a heater during the mixing process. Since a temperature above 50°C will deteriorate the epoxy properties, a higher temperature was not exceeded. After the mechan- ical mixing process was finished, the glass micro-balloon was added to the mixture in the calculated ratios and mixed manually for 15 minutes. It is made by hand because the micro balloons are very sensitive. They are broken with mixing equipment. Otherwise, the porous structure will disappear due to breaking the micro-balloons. Glass micro balloons can be seen in Figure 2.

Figure 2: Glass Micro Balloons

After this process, the hardener was added and mixing by hand was continued for another 5 minutes. It was poured into previously prepared molds and left to cure for 48 hours. At the end of this period, it was left to cure for another 2 hours in a 100 °C oven environment. After the curing process was completed, the composite samples were measured in the impedance tube.

2.3. Acoustical Measurements

Acoustic measurements were performed using the Brüel&Kjær impedance tube. Two-microphone impedance tube was used to measure the normal incident absorption coefficient and a four-micro- phone impedance tube was used to measure the sound transmission loss of the materials according to the standard procedure detailed in ISO (10534 –2). The frequency range for the measurements was 0-6400 Hz. Figure 3 and Figure 4 show the measurement system used to determine the sound absorp- tion coefficient and the sound transmission loss depending on the frequency, respectively.

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Figure 3: The measurement system used to determine the sound absorption coefficient depending

on the frequency.

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Figure 4: The measurement system used to determine the sound transmission loss depending on the

frequency .

Samples prepared according to the results of the Taguchi method were cut with a 29 mm diameter. Three samples were prepared for each material and tested.

3. CONCLUSIONS

In this study, synthetic foam composite structures were fabricated by adding silicon carbide na- nopowders and multi-walled carbon nanotubes into the synthetic foam. The design of those composite samples was chosen by the Taguchi method according to three factors considered as control factors: glass micro balloon ratio, particle additive ratio and thickness.

Acoustical measurements were carried out on samples produced according to the determined de- sign. Sound absorption coefficients and sound transmission loss of the composites were obtained from the acoustical measurements.

Although more samples are required to determine an accurate acoustical characteristic for the ma- terials, the results can be used as guidance for the future design of composite materials used acoustical usage. 4. REFERENCES

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