Sound Absorption Characteristics of Porous Steel Manufactured by Lost Carbonate Sintering
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1188-LL07-04
Sound Absorption Characteristics of Porous Steel Manufactured by Lost Carbonate Sintering Miao Lu1, Carl Hopkins2, Yuyuan Zhao1, Gary Seiffert2 1 Department of Engineering, University of Liverpool, Liverpool, L69 3GH, UK 2 School of Architecture, University of Liverpool, Liverpool, L69 3BX, UK ABSTRACT This paper investigates the sound absorption characteristics of porous steel samples manufactured by Lost Carbonate Sintering. Measurements of the normal incidence sound absorption coefficient were made using an impedance tube for single-layer porous steel discs and assemblies comprising four layers of porous steel discs. The sound absorption coefficient was found not to vary significantly with pore size in the range of 250-1500 µm. In general, the absorption coefficient increases with increasing frequency and increasing thickness, and peaks at specific frequencies depending on the porosity. An increase in porosity tends to increase the frequency at which the sound absorption coefficient reaches this peak. An advantage was found in using an assembly of samples with gradient porosities of 75%-70%-65%-60% as it gave higher and more uniform sound absorption coefficients than an assembly with porosities of 75%. INTRODUCTION Porous metals have multifunctional properties. They retain some properties of metals such as good electrical and thermal conductivity, and also possess the special characteristics of porous structures such as good energy absorption and sound absorption. Recently, there is considerable interest in the study of the properties of porous metallic materials, especially their sound absorption. Porous metals are particularly suitable for use under extreme conditions where high temperatures, high noise levels, high air velocity, and high humidity may exist. The capability of a material to absorb sound is measured by sound absorption coefficient which is defined as the ratio of the absorbed sound intensity to the incident sound intensity. Porous metals that are effective absorbers can have sound absorption coefficients exceeding 0.9 [1]. Sound absorption coefficient of porous materials is dependent on material properties, such as pore morphology, pore tortuosity, porosity, airflow resistivity and sample thickness, and sound frequency [2]. Lu et al. investigated the sound absorption of metal foams with open and closed cells and studied the effect of different processing methods on sound absorption coefficients [3, 4]. They found that the sound absorption properties of foams with closed cells after minor compression were poor because the largely closed cell structure prevents air particles penetrating inside the material. As a result, sound energy can not be dissipated within these porous materials. Han et al.
studied the sound absorption behavior of open-cell aluminum alloy foam manufactured by the infiltration method [5, 6]. They discovered that the sound absorption of the foam at frequencies over 1000Hz is better than the commercial metal foams available. They proposed that the complex internal
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