Characterization of pore structure is one of the key problems for fabrication and application research on porous materials.But,complexity of pore structure makes it difficult to characterize pore structure by Euclidea...Characterization of pore structure is one of the key problems for fabrication and application research on porous materials.But,complexity of pore structure makes it difficult to characterize pore structure by Euclidean geometry and traditional experimental methods.Fractal theory has been proved effective to characterize the complex pore structure.The box dimension method based on fractal theory was applied to characterizing the pore structure of fiber porous materials by analyzing the electronic scanning microscope(SEM)images of the porous materials in this paper.The influences of image resolution,threshold value,and image magnification on fractal analysis were investigated.The results indicate that such factors greatly affect fractal analysis process and results.The appropriate magnification threshold and fractal analysis are necessary for fractal analysis.展开更多
The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model,in which the porous material is modeled as randomly distributed parallel f...The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model,in which the porous material is modeled as randomly distributed parallel fibers specified by two basic physical parameters:fiber diameter and porosity.A self-consistent Brinkman approach is applied to the calculation of the dynamic resistivity of flow perpendicular to the cylindrical fibers.Based on the solved flow resistivity,the sound absorption of single layer fibrous material can be obtained by adopting the available empirical equations.Moreover,the recursion formulas of surface impedance are applied to the calculation of the sound absorption coefficient of multi-layer fibrous materials.Experimental measurements are conducted to validate the proposed model,with good agreement achieved between model predictions and tested data.Numerical calculations with the proposed model are subsequently performed to quantify the influences of fiber diameter,porosity and backed air gap on sound absorption of uniform(single-layer)fibrous materials.Results show that the sound absorption increases with porosity at higher frequencies but decreases with porosity at lower frequencies.The sound absorption also decreases with fiber diameter at higher frequencies but increases at lower frequencies.The sound absorption resonance is shifted to lower frequencies with air gap.For multi-layer fibrous materials,gradient distributions of both fiber diameter and porosity are introduced and their effects on sound absorption are assessed.It is found that increasing the porosity and fiber diameter variation improves sound absorption in the low frequency range.The model provides the possibility to tailor the sound absorption capability of the sintered fibrous materials by optimizing the gradient distributions of key physical parameters.展开更多
基金supported by the National Basic Research Program of China(Grant No.2006CB601201B)
文摘Characterization of pore structure is one of the key problems for fabrication and application research on porous materials.But,complexity of pore structure makes it difficult to characterize pore structure by Euclidean geometry and traditional experimental methods.Fractal theory has been proved effective to characterize the complex pore structure.The box dimension method based on fractal theory was applied to characterizing the pore structure of fiber porous materials by analyzing the electronic scanning microscope(SEM)images of the porous materials in this paper.The influences of image resolution,threshold value,and image magnification on fractal analysis were investigated.The results indicate that such factors greatly affect fractal analysis process and results.The appropriate magnification threshold and fractal analysis are necessary for fractal analysis.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2011CB610300)the National Natural Science Foundation of China(Grant Nos.11102148,11321062 and 51134003)the Fundamental Research Funds for Central Universities of China(Grant No.xjj2011005)
文摘The sound absorbing performance of the sintered fibrous metallic materials is investigated by employing a dynamic flow resistivity based model,in which the porous material is modeled as randomly distributed parallel fibers specified by two basic physical parameters:fiber diameter and porosity.A self-consistent Brinkman approach is applied to the calculation of the dynamic resistivity of flow perpendicular to the cylindrical fibers.Based on the solved flow resistivity,the sound absorption of single layer fibrous material can be obtained by adopting the available empirical equations.Moreover,the recursion formulas of surface impedance are applied to the calculation of the sound absorption coefficient of multi-layer fibrous materials.Experimental measurements are conducted to validate the proposed model,with good agreement achieved between model predictions and tested data.Numerical calculations with the proposed model are subsequently performed to quantify the influences of fiber diameter,porosity and backed air gap on sound absorption of uniform(single-layer)fibrous materials.Results show that the sound absorption increases with porosity at higher frequencies but decreases with porosity at lower frequencies.The sound absorption also decreases with fiber diameter at higher frequencies but increases at lower frequencies.The sound absorption resonance is shifted to lower frequencies with air gap.For multi-layer fibrous materials,gradient distributions of both fiber diameter and porosity are introduced and their effects on sound absorption are assessed.It is found that increasing the porosity and fiber diameter variation improves sound absorption in the low frequency range.The model provides the possibility to tailor the sound absorption capability of the sintered fibrous materials by optimizing the gradient distributions of key physical parameters.
