The interest of this article lies in the proposition of develop the relationship of the adding of Rice Husk (RH) and acoustic characteristic parameters of Polyurethane (PU) foam. In this article, different amount of RH (2%, 5%, and 8%) was employed into the formation of PU foam system. A rapid method based on professional acoustic measurement was used to determine the acoustic characteristic parameters of the PU foam and PU‐RH composites, such as porosity, flow resistance, tortuosity, and characteristic constants, and analyze the effect of RH on the acoustic characteristic parameters. The measured results indicated that the sound absorption coefficients of PU‐RH composites increased at low frequency along with a small decrease at high frequency on the addition of RH. And adding more RH will be helpful to improve the low‐frequency sound absorption performance of PU foam without increasing the thickness. With the increase of RH additive amount, the flow resistance decreased first and then increased, while the porosity declined slowly generally. Overall, the PU‐RH composite containing 5% RH showed the most satisfactory absorption performance. POLYM. COMPOS., 40:2653–2661, 2019. © 2018 Society of Plastics Engineers

A series of new smectic and cholesteric liquid crystalline elastomers was prepared by graft polymerization of mesogenic monomer with the chiral and nonmesogenic crosslinking agent using polymethylhydrosiloxane as backbone. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance spectra ( 1 H-NMR). The mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction measurements (XRD). M 1 showed smectic (S B , S C , S A ) and nematic phases during the heating and the cooling cycles. Polymer P 0 and elastomer P 1 exhibited smectic B phase, elastomers P 2 -P 5 showed smectic A phase, P 6 and P 7 showed cholesteric phase, and P 8 displayed stress-induced birefringence. The elastomers containing less than 15 mol % M 2 displayed elasticity and reversible phase transition with wide mesophase temperature ranges. Experimental results demonstrated that the glass transition temperatures decreased first and then increased; melting temperatures and the isotropization temperatures and the mesophase temperature ranges decreased with increasing content of crosslinking unit.

AbstractPorous material (PM) shows good sound absorption performance, however, the sound absorbing property of PM with different parameters are greatly different. In order to match the most suitable absorbing materials with the most satisfactory sound-absorbing performance according to the noise spectrum in different practical applications, multi-population genetic algorithm is used in this paper to optimize the parameters of porous sound absorbing structures that are commonly used according to the actual demand of noise reduction and experimental verification. The results shows that the optimization results of multi-population genetic algorithm are obviously better than the standard genetic algorithm in terms of sound absorption performance and sound absorption bandwidth. The average acoustic absorption coefficient of PM can reach above 0.6 in the range of medium frequency, and over 0.8 in the range of high frequency through optimization design. At a mid-to-high frequency environment, the PM has a better sound absorption effect and a wider frequency band than that of micro-perforated plate. However, it has a poor sound absorption effect at low frequency. So it is necessary to select suitable sound absorption material according to the actual noise spectrum.

Abstract. In this paper, the influence of the preparation temperature on the absorption coefficient and acoustic parameters of polyurethane was studied. Best sound absorption coefficient of polyurethane at high frequency is at 50℃, followed is 30℃ and 40℃,70℃ is lowest. Between 20~50℃, the flow resistance increased rapidly with the temperature increasing, the minimum flow resistance at 50℃, maximum value at 70℃.The trend of porosity with temperature is similar to that with flow resistance. With the temperature increasing, the porosity decreases first and then increases, minimum value at 50℃. Flow resistance dominating the flow resistance of the sound absorption performance.

This article aims to investigate the sound absorbing properties of a thick microperforated panel (MPP) with tapered sections with finite element analysis (FEA) models. The FEA model was validated by using the measured sound absorption coefficients of a classic MPP sample and a proposed MPP sample. The FEA simulation and the experiments indicate that the tapered section can enhance the sound absorption coefficient. Moreover, the FEA model shows that the structural parameters of the tapered section can be optimized. The resonance frequency of the sound absorption coefficient moves to the high-frequency range, and the maximum sound absorption coefficient increases in three conditions, the tapered section moving toward the backing cavity, and the increase of the thickness and the bottom radius of the tapered section. Although the optimized configurations of the tapered section may vary with the structure parameters of the MPP, the tapered section can improve the sound absorbing properties of the classic MPP and could be promising in the noise and vibration engineering projects.