| With the rapid progress of the industry,construction and transportation businesses,the noise in the daily life is getting bigger and bigger.Also,with the increasing requirement of high standard quality of people's life,sound absorption and noise reduction has turned out to be an urgent task.Ethylene propylene diene monomer(EPDM)has superior good elasticity,low temperature performance,stable heat resistance,weathering resistance,ozone aging resistance,excellent electrical insulation,chemical resistance,etc.,since EPDM has a lower density that is only 0.86~0.87g/m~3,and this is lighter than other rubber products,but with greater filling property.Thus,it can be valuable to reduce cost.Zeolite powder has molecular level and uniform pores,which has a large ratio of surface area.Kapok fiber is a natural high hollow fiber with a vacancy of 80%-90%,and has respectable sound absorption features.In our work,based on the characteristics of the material,the EPDM-based textile composite panel structure material with decent sound absorption characteristics was prepared.In addition,from the structural characteristics of the sound absorbing material,the relationship between the structural parameters and the acoustic characteristics of the material was systematically investigated to reveal the acoustic absorption mechanism of the composite sound absorbing material.This can be a theoretical basis and application for the design and production of EPDM-based textile composite panel structural materials.First,EPDM was applied as the matrix.The industrially used vermiculite powder,carbon black and zeolite powder with porous structure were adopted as fillers to prepare zeolite powder/ethylene propylene diene monomer porous sound absorbing material.Meanwhile,acoustic materials of pure EPDM rubber,graphite/ethylene propylene diene monomer porous,vermiculite powder/ethylene propylene diene monomer porous sound were prepared for the comparative samples.The standing wave tube propagation function method was utilized to examine the sound absorption performance of EPDM rubber with and without filler.Then,the parameters of the zeolite powder/ethylene propylene diene monomer porous sound absorbing material(filler content,thickness of filler rubber sound absorbing material,depth of cavity after filler rubber)and other porous adsorption of zeolite powder/ethylene propylene diene monomer were studied and analyzed.The sound absorption performance of the acoustic material was compared with the sound absorption performance of the porous sound absorbing material obtained by adding a filler such as vermiculite powder or carbon black to the EPDM rubber.Last,the sound absorption features of the zeolite powder/ethylene propylene diene monomer sound absorbing material were theoretically analyzed with the porous material sound absorption models,including Delany-Bazley empirical model and the Johnson-Allard microstructure model.Experimental and theoretical analysis indicate that the zeolite powder/EPDM porous sound absorbing material has better sound absorption properties;The larger the content of zeolite powder,the larger the sound absorption coefficient of the zeolite powder/EPDM sound absorbing material,and the frequency of the maximum sound absorption coefficient gradually shifted to the high frequency;With the increase of the zeolite powder content,the strength of the zeolite powder/EPDM rubber porous sound absorbing material was improved,when the content of zeolite powder is 35%,the maximum sound absorption coefficient reaches 0.86,and the elasticity was decreased;The thickness of the zeolite powder/EPDM rubber porous sound absorbing material was increased,and the sound absorbing performance was improved;As the thickness of the cavity increases,the peak of the sound absorption gradually shifted to the low frequency,and the sound absorption performance of the medium and high frequency decreased.The Johnson-Allard model can more precisely predict the sound absorption performance of the sound body of the zeolite powder after adding the EPDM rubber compared to the Delany-Bazley model,for johnson-allard model considers the influence of viscous effect and heat conduction on sound absorption materials.Although zeolite powder/EPDM rubber has respectable sound absorption effects,the sound absorption performance cannot satisfy the practical usage requirements.To further improve the sound absorption characteristics of the composite material,based on the zeolite powder/EPDM composite material,a series of micro-perforated plate samples were designed and the sound absorption coefficient of the samples was established by the standing wave tube propagation function method.The impact of sample parameters(aperture,perforation rate,plate thickness and thickness cavity)on the sound absorption performance of microperforated plates was analyzed.From the analysis of the absorption curve,it can be investigated that the influences of parameter variation on the maximum sound absorption coefficient,the sound absorption band and 0.5 sound absorption octave.Eventually,the sound absorption performance model was predicted by the acoustic-electric ratio model and the transfer matrix model,and compared with the examined results.The experimental findings demonstrated that with the increase of the aperture,the maximum value of the micro-perforated sound absorption coefficient first raised and then decreased,the sound absorption bandwidth decreased with the increase of the aperture,and the resonance frequency gradually moved to the low frequency direction;Based on the analysis of the maximum sound absorption coefficient and the half sound absorption octave and the 0.5 sound absorption octave,which did not introduce invalid sound absorption,and was more suitable for the analysis of the sound absorption bandwidth of the micro perforated plate.When the size of hole was between the upper limit and the lower limit,as the hole size increased,the upper and lower limits of the effective aperture range of the 0.5 sound absorption octave gradually increased,and the sound absorption bandwidth gradually decreased;With the perforation rate increased,the suction increased.The maximum value of the acoustic coefficient first increased and then decreased.With the perforation rate increased,the sound absorption bandwidth widened with the increase of the perforation rate,and the resonance frequency and bandwidth both moved to the high frequency;From the analysis of the maximum sound absorption coefficient and the half sound absorption octave and the 0.5 sound absorption octave,the effective hole size range of the 0.5 sound absorption octave was increased with the increase of the aperture if which was between the upper limit and the lower limit.The upper and lower limits of the effective aperture were gradually reduced,and the sound absorption bandwidth was gradually decreased;As the increase of the plate thickness,the maximum value of the sound absorption coefficient increased first and then decreased.With the plate thickness increased,the bandwidth of the sound absorption coefficient narrowed with the increase of the thickness and moved toward the low frequency direction.As the increase of the plate thickness,the upper and lower limits of the effective aperture range of the 0.5 sound absorption octave gradually increased;With the increase of the cavity depth after the plate,the sound absorption coefficient of the sound absorber did not alter significantly.With the increase of the depth,the frequency of the maximum sound absorption coefficient gradually shifted to the low frequency,and the sound absorption bandwidth did not change considerably;For single-layer micro-perforated plate absorbers,the predicted values from theacoustic-electrical model of Prof.Ma Dazhao has a higher coincidence degree with the experimental test values.To further enhance the sound absorption performance of the micro-perforated plate,a double-layer serial micro-perforated plate,a single-layer micro-perforated plate with different apertures and a three-layer micro-perforated plate sound absorber were designed to compare,and the acoustic-electric ratio and the transfer matrix model were also compared.The findings are as follows:The double-layer series micro-perforated plate structure was a satisfied sound absorbing body,especially the low-frequency absorption was relatively prominent and the double-layer series micro-perforated plate sound absorbing body absorption band extended to the low frequency;only the cavity distance of the second layer micro-perforated plate was altered.As the ratio of the distance between the second layer and the first layer of the cavity(D2/D1)increased,the sound absorption bandwidth of the double-layer series microperforated plate gradually increased,and the sound absorption bandwidth of the first sound absorption peak was greater than the bandwidth of the second sound absorption peak gradually shifted to the low frequency as the D2/D1 ratio increased;Two kinds of apertures of different sizes were arranged on the single-layer microperforated plate,and the two kinds of micropores were locally distributed on the plate.The sound absorption performance of the microperforated plate of this structure was better than that of the double-layer serial microperforated plate;For double-layer and three-layer micro-perforated plate sound absorbers,the transfer matrix model was more suitable for predicting the sound absorption characteristics of sound absorbers.To advance the low-frequency sound absorption performance of the micro-perforated plate,the kapok fiber and the mixed fiber nonwoven material were placed at different positions of the micro-perforation,and a composite sound absorber with light weight,simple structure and low cost was prepared.Based on the transfer matrix method,the sound absorption model of the EPDM-based textile structural composite was proposed.The consequences are as follows:The EPDM-based textile composite board structural material has reliable sound absorption performance,and the sound absorption coefficient was higher in the low frequency stage,and the sound absorption performance in the middle and high frequency was also developed;When the porous nonwoven material was put in front of the micro-perforated plate,the sound absorbing performance of the composite sound absorbing body was the best.When the porous nonwoven material was placed on the bottom layer and the upper layer of the micro-perforated plate,the sound absorbing performance of the composite sound absorbing body was not notably different.When the porous nonwoven material was placed in the middle layer of the cavity,the sound absorption performance of the composite sound absorption was better,but from the viewpoint of practical installation and use,it was difficult to install the porous nonwoven material in the middle of the cavity;With the cavity depth in the composite sound absorber increased and the thickness and bulk density of the nonwoven material in the sound absorber increased,the sound absorption performance of the composite sound absorber increased,especially in the low frequency phase,the sound absorption coefficient increases more,but the mid-high frequency sound absorption performance changes less;The sound absorption coefficient of the composite sound absorber predicted by the transfer matrix model was neatly consistent with the experimental test value.The model can be applied to predict and analyze the sound absorption characteristics of the EPDM-based textile composite panel structural materials.This can provide a theoretical foundation and application for the structural design of the composite sound absorber of the perforated plate and the porous non-woven material. |
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