In recent years, kenaf fibre has been highlighted for its superiority as the filler for composite materials. However, study of the fibres as an acoustic absorber is still lacking. In this paper, the ...sound absorption of kenaf fibre specimens are studied both under normal and random sound incidence. The normal-incidence sound absorption coefficient measurement was conducted using the impedance tube method. The effects of thickness involving full fibre and air-fibre specimen and the effect of bulk density were discussed. For the random-incidence sound absorption coefficient, the test was conducted in a reverberation chamber. From both methods, the results in general reveal that for bulk density of 140–150kg/m3 and thickness of 25–30mm, the absorption coefficient is above 0.5 starting from 500Hz and can reach 0.85 on average above 1.5kHz. These frequency bandwidth of absorption and the level of absorption coefficient improve significantly when bulk density and thickness are increased. Additional air gap also improve the absorption toward lower frequency.
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In this paper, the effect of graphene oxide (GO) loading on sound-absorbing properties of open cell polyurethane foam (PU) was investigated. GO was impregnated into PU foam by a ...step-by-step vacuum-assisted process. It was found that sound-absorbing properties can be greatly enhanced by GO impregnation. Especially, sound-absorbing properties can be tuned to be maximized to specific frequency range by controlling GO impregnation density. To evaluate sound absorption performance, sound absorption coefficients were measured using an impedance tube. The averaged sound absorption coefficient (α¯800Hz∼6300Hz) from 800 Hz to 6300 Hz was increased more than four times by impregnating 15 wt% of GO into 5-mm-thick PU foam with a bulk density of 51 kg/m3. Foam parameters such as porosity, Young's modulus, and flow resistivity were determined as a function of GO concentration. Among those parameters, specific flow resistance had the greatest influence on sound-absorbing properties. Elastic porous material theory was used to model sound-absorbing properties of GO impregnated PU foam, which showed good agreement with measurements at every GO loading condition. The pore tortuosity, which was determined using a fitting procedure, exhibited a good linear relationship with GO loading. It was found that impregnation of GO significantly increased tortuosity. The results given here suggest theoretical and experimental guidelines for use of GO to improve and optimize the sound-absorbing properties of PU foam.
•Sound absorption coefficients of the samples made of Yucca fibers were studied.•Yucca fibers effectively dissipate energy of sound wave and enjoy high absorption.•The effects of sample thickness and ...airgap behind the samples were investigated.•A computational method for prediction of sound absorption coefficient was proposed.•Predicted absorption coefficients have a good agreement with the measured data.
The aim of this study is to provide a better comprehension and predict acoustic behavior of Yucca Gloriosa (YG) fiber using experimental and computational approaches. To this end, the FESEM images of fibrous samples with thickness of 15 and 30 mm were obtained and fiber diameter and orientation distribution were calculated using image analysis techniques. An in house Matlab-based code capable of generating fibrous structures was developed. The obtained parameters from experimental and morphological analysis of samples were implemented into the code to simulate 3D virtual structure of samples. Flow resistivity and tortuosity were calculated by numerically solving Stokes flow and Fick’s law through the 3D void space of generated structures, respectively. Different models able to predict the acoustic impedance and frequency-dependent sound absorption coefficient (SAC) of porous materials, including Delany and Bazley (D-B), Garai and Pompoli (G-P) and Johnson-Champoux-Allard (JCA) were analyzed and their suitability for prediction of acoustic behavior of YG fibers was evaluated. The results were compared with experimental data obtained using impedance tube method.
It was concluded that at frequency range of 63–6300 Hz, the JCA model has superior predictive ability compared to D-B and G-P models and is well suited to YG fibers. It was found that the peak of SAC for samples with thickness of 15 and 30 mm emerges at 4000 and 2500 Hz, respectively. It was established that, YG fibrous samples effectively dissipate the energy of sound waves. This was attributed to the longer depreciation process of thermal and viscous transfer between the air and the absorbing media.
This study aims to investigate the natural cellulosic fibers extracted from novel Ziziphus Mauritiana plants. The fibers were treated with alkali solution and epoxy composites were developed for both ...untreated and chemically modified fibers through hand lay-up process. Physico-chemical and thermomechanical characterization were carried for both untreated and alkali treated Ziziphus Mauritiana fibers through physical analysis, chemical analysis, Thermogravimetric analysis, Fourier transform infrared spectroscopy, X-Ray diffraction test and single fiber tensile test. The alkali treatment facilitates to remove amorphous constituents and improves the crystalline index by 1.31 times, thermal stability by 1.15 times and fiber strength by 1.44 times, which is supported by chemical analysis and Fourier transform infrared spectroscopy analysis. Later, developed Ziziphus Mauritiana composites were analyzed as per ASTM for its mechanical and sound absorption characteristics. The reduction in amorphous constituents after chemical treatment improved the surface roughness in alkali-treated Ziziphus Mauritiana fibers which influenced the bonding behavior. Also it improved the ultimate tensile strength by 2.12 times, flexural strength by 1.38 times and sound absorption coefficient by 1.15 times. Thus, the Ziziphus Mauritiana fibers are potentially suitable for use in lightweight structures.
The use of broom to produce fibers has ancient roots. The Greeks appreciated its resistance to water and for this reason they used it to manufacture sailing ropes. But broom fiber was also ...appreciated for its sound absorption qualities. In this study, a new methodology was developed for the numerical modeling of the acoustic behavior of broom fibers. First, the characteristics of the different varieties of broom were examined and the procedures for processing the samples to be analyzed were described. Subsequently, the results of the measurements of the following acoustic properties of the material were analyzed: air flow resistance, porosity, and sound absorption coefficient. Finally, the results of the numerical modeling of the acoustic coefficient were reported using an algorithm based on artificial neural networks. The results obtained are compared with a model based on linear regression. The model based on neural networks showed high values of the Pearson correlation coefficient (0.989), indicating a high number of correct predictions.
Porous asphalt concrete (PAC) has attracted significant attention in the road industry due to its excellent noise reduction capabilities. However, clogging in PAC decreases its sound absorption ...performance, as mesoscopic pore parameters play a crucial role in influencing PAC’s sound absorption abilities. To further investigate the influence of mesoscopic pore parameters on the sound absorption performance of PAC, CT scanning and digital image processing technology were employed. The principal component analysis method was employed to determine the weighting of the influence of mesoscopic pore parameters on the sound absorption coefficient. The correlation between different pore parameters and the sound absorption coefficient of PAC specimens was analyzed. The results showed that the minimum Feret diameter has the most significant effect on the sound absorption performance of PAC, while the concavity and the length-short axis ratio have the least impact. The correlation between mesoscopic pore parameters and sound absorption coefficients was found to be inconsistent before and after clogging. Mesoscopic pore parameters that were positively correlated with sound absorption coefficients before clogging turned negatively correlated after clogging. Connected large pores and smooth regular pore structure enhance the sound absorption performance of PAC, but clogging disrupts this structure, resulting in a decrease in sound absorption performance.
•The mesoscopic pore parameters were screened by principal component analysis.•The minimum Feret diameter has the greatest effect on the sound absorption performance of PAC.•Clogging disrupts PAC’s smooth, interconnected pores, causing decline in its sound absorption performance.
Porous asphalt concrete (PAC) generates significant less noise during the loading of vehicles compared to conventional pavements. However, it might be clogged during lifespan, which results in a ...reduced noise reduction function. To evaluate the noise reduction function of PAC during service, the change in sound absorption coefficients of PAC under different clogging conditions was investigated by the means of laboratory tests. The standing wave tube method was used in this paper, with considering the changes in void ratios, clogging materials, and cleaning methods. The attenuation parameters of PAC sound absorption coefficients under continuous clogging and cyclic clogging-cleaning conditions were investigated. Based on this, the prediction model of the sound absorption coefficient under two clogging states was proposed. The results showed that aeolian sand had the most negative impact on the noise reduction function, with a 56 % decrease in the sound absorption coefficient after clogging. The sound absorption coefficient of the PAC remained between 0.3 and 0.4 after completely clogged. The sound absorption coefficient of the PAC can be partially even fully restored after cyclic clogging cleaning. High-pressure water washing is the most effective approach, recovering up to 80 % of the original value before clogging. Therefore, regular cleaning and maintenance of the PAC during its survice life is necessary. Predictive modeling of the sound absorption coefficient was highly correlated with measured values, allowing accurate prediction of changes after clogging and cleaning.
•PAC sound absorption coefficient changes during continuous and cyclic clogging cleaning.•Clogging times has the most significant on the PAC sound absorption coefficient.•A prediction model of PAC sound absorption coefficient based on mix parameters and plugging parameters was developed.
The effect of cellular structure in the flexible polyurethane foams on the sound absorption behavior is investigated for improved sound environment within vehicles. Two types of gelling catalyst and ...water are used for producing well-defined cavity and pore structure in the foams. The catalyst, having high activity in urethane reaction, produces a larger number of small cavities and pores in the foams compared to the catalyst having low activity. A high number of small cavities can also be obtained at high water content from the restraint of neighboring cavities due to actively formed urethane matrix. The foam density decreases with increasing water and catalyst contents. Sound absorption efficiency is usually low at low foam density, but the results show improved sound absorption efficiency even at the reduced foam density because of the high number of well dispersed small cells in the foams.
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•Flexible polyurethane foams for sound absorption materials•Sound absorbing ability of well-designed cellular structured foams•High number of small cells for high sound absorbing ability•Use of a strong gelling catalyst for high number of small cells
•FHCS structure is lighter than traditional devices and has better effects.•Smaller specifications of honeycombs will consume more extra sound waves.•The density and thickness of the filling can make ...the SAC significantly increase.•The SAC of the experimental specimen will become stable at high frequencies.
A new composite structure was formed by filling Nomex honeycomb with polyester fibre to achieve the goal of improving its acoustic characteristics. By using the impedance tube method, the sound absorption coefficient (SAC) of porous materials was determined. Moreover, the effects of different specifications of honeycomb, porosities of fibre, and amount of filler on SAC were studied to achieve the experimental objective. The experimental results demonstrate that the increase of porosity of filler can improve the SAC of the test sample. Honeycombs with different specifications slightly influence the SAC of the sample and the influencing factor may be additional absorption of sound waves caused by contact between materials. Different filling amounts can change the SAC of the sample, while SAC does not improve significantly in the high-frequency range. Simulation results using Virtual Lab. show that porosity of the materials affects the sound absorption performance thereof. The data and conclusions obtained in experiments and simulation provide support for the application of honeycomb sandwich panels in acoustics and noise reduction.
•Weighted sound reduction index of 15db were obtained by green wall.•Weighted sound absorption coefficient of 0.40 were found by green wall.•Green wall have significant potential sound insulation for ...vegetal architecture.
Greenery on buildings is being consolidated as an interesting way to improve the quality of life in urban environments. Among the benefits that are associated with greenery systems for buildings, such as energy savings, biodiversity support, and storm-water control, there is also noise attenuation. Despite the fact that green walls are one of the most promising building greenery systems, few studies of their sound insulation potential have been conducted. In addition, there are different types of green walls; therefore, available data for this purpose are not only sparse but also scattered. To gather knowledge about the contribution of vertical greenery systems to noise reduction, especially a modular-based green wall, two different standardised laboratory tests were conducted. The main results were a weighted sound reduction index (Rw) of 15dB and a weighted sound absorption coefficient (α) of 0.40. It could be concluded that green walls have significant potential as a sound insulation tool for buildings but that some design adjustments should be performed, such as improving the efficiency of sealing the joints between the modular pieces.
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