Design,Fabrication And Noise Reduction Properties Of Lightweight And High-strength Sound Absorption Materials

With the rapid development of modern society,the problem of noise pollution has been paid more and more attention by governments and scientific researchers.Noise can have a serious impact on human health,animal behaviors and durability of buildings,et.al.Therefore,people are actively seeking ideal sound absorption materials so as to provide us an "island of tranquility".During the past half century,from traditional porous materials to perforated panels to emerging acoustic metamaterials,humans have moved forward in exploring the ideal sound absorption materials.However,as the acoustic damping and mechanical strength of materials is normally a couple of conflicting physical quantities,existing sound absorption materials generally lack high overall acoustics/mechanics properties,i.e.,high-efficiency broadband sound absorption,lightweight and high-strength(high specific modulus).But a lightweight,high-strength and high-efficiency sound absorption material can show significant value in practical applications.For instance,it can be used as an ideal structural material to achieve high-efficiency noise reduction,meanwhile meeting the relevant national requirements on energy conservation and emission reduction.Under this background,the work of this thesis mainly involves the design and fabrication of lightweight,highstrength and high-efficiency sound absorption materials,as well as the investigation of their sound absorption and compression properties.In advance,based on the bimodal structure,we fabricated the lightweight,high-strength and high-efficiency metal foam/aerogel sound absorption composites with aids of the superior mechanical properties of metal foam and high acoustic damping characteristic of aerogel.Second,with aids of the special porous structure of natural wood,we fabricated the lightweight and high-strength cellulose wood sound absorption materials by removing the lignin from structure of natural wood through a specific lignin removed process.The main contents,innovations and conclusions of this thesis are summarized as follow:(1)The copper foam/SiO2 aerogel composite(CFSA)with typical bimodal structure was fabricated through a two-step,acid-base catalyzed sol-gel transition and CO2 supercritical drying process.In advance,SEM characterization and N2 adsorptiondesorption measurements proved that with the increase of mixing content of epoxy resin in sol-gel transition,the micro morphology as well as the pore structure parameters(specific surface area,total pore volume and average pore size)of SiO2 aerogel(SA)are almost not changed.Then it is proved by experiments that with the increase of mixing content of epoxy resin,the porosity of CFSA decreases slightly,while the compound morphology integrity and airflow resistivity of CFSA increases significantly.Meanwhile,compared with the pure copper foam matrix,the CFSA with bimodal structure exhibits superior compression properties(Young’s modulus is about 11.01 MPa,compression strength is about 0.3 MPa and specific modulus is about 0.39×105 m2/s2)and more efficient broadband sound absorption characteristic.With the increase of mixing content of epoxy resin,the sound absorption properties of CFSA increases(maximum sound absorption coefficient increases from 0.78 to 0.99 and average sound absorption coefficient increases from 0.4 to 0.48),while the improvement of compression properties of CFSA is slight and does not show obvious regularity.In addition,the Helmholtz resonance absorption of sound was induced by introducing an airgap with appropriate thickness behind CFSA,so as to improve its low-frequency sound absorption properties.The results show that the low-frequency sound absorption properties of CFSA increases with the increase of airgap thickness.Finally,the temperature resistance and hydrophobicity of CFSA were tested through experiments,which further confirmed its practical application value to be an ideal structural sound absorption material.(2)The iron foam/SiO2 aerogel composite(IFSA)with typical bimodal structure was fabricated through a two-step,acid-base catalyzed sol-gel transition and freeze drying process.In advance,SEM characterization and N2 adsorption-desorption measurements proved that the SA fabricated through freeze drying also presents highly connected complex mesoporous network and superior pore structure parameters.Second,it is proved by experiments that compared with the pure iron foam matrix,the IFSA with bimodal structure exhibits superior compression properties(Young’s modulus is 46.6 MPa,compression strength is 0.46 MPa and specific modulus is 1.6×105 m2/s2)and more efficient broadband sound absorption characteristic(maximum sound absorption coefficient is 0.99 and average sound absorption coefficient is 0.56).In addition,based on the self-designed bimodal model,Comsol Multiphysics was used to develop numerical simulation of the fluid structure interaction combining finite element method with Johnson-Champoux-Allard(JCA)acoustic model,to further investigate the enhancement mechanism of bimodal structure on sound absorption properties of IFSA.The results demonstrate that the designed bimodal model has good predictability for sound absorption behaviors of IFSA,which provides the theoretical reference for further design and fabrication of high-efficiency sound absorption materials at specific frequency ranges.Compared with CFSA,IFSA exhibits superior compression properties as well as broadband sound absorption characteristic.Meanwhile,the fabrication process of IFSA is simpler and cheaper,hence it possesses the higher practical value and economic benefits in practical applications.(3)With aids of the special porous structure of natural basswood,the lightweight and high-strength cellulose wood sound absorption materials was fabricated through lignin removed and CO2 supercritical drying process.In advance,SEM characterization and mercury intrusion porosimetry proved that the structure of cellulose wood is more permeable than that of natural basswood.For instance,the structure of cellulose wood possesses higher specific surface area,total pore volume,porosity and average pore size,meanwhile presents lower density but significant higher air permeability(33.78 Darcys).Then effects of the high permeable structure of cellulose wood on its sound absorption,compression and diffuse reflection properties were investigated experimentally.The results show that after removed the lignin,in a certain extent,the cellulose wood still exhibits superior compression properties,e.g.,Young’s modulus of 55.55 MPa,compression strength of 1.19 MPa and specific modulus of 2.14×1 05 m2/s2.Meanwhile,compared with the natural basswood,cellulose wood exhibits superior sound absorption properties and shows more efficient broadband diffuse reflection characteristic in visible band(average diffuse reflectance is up to 97.02%).The research work of this thesis not only provides new insights for developing lightweight,high-strength and high-efficiency sound absorption materials,but also has great potential applications for various fields.