Study On Acoustics Property And Application Of Closed-cell Aluminum Foam

Aluminum foam is a new-style material with cells (second phase) stochasticly distributed in the metal matrix, which combines the characteristics of consecutive phase aluminum and dispersive phase cell. Nowadays, the application of aluminum foam in the field of sound absorption, sound insulation and damping has been emphasized more and more, since the influence of the air pollution on people's daily life become increasingly bad. In this paper, the sound absorption coefficient of closed-cell aluminum foams with different porosity,thickness,perforation percentage and cavity behind were studied; The sound absorption effectiveness of closed-cell aluminum foam and several other kinds of sound-absorbing material under the same test condition were compared; the application of closed-cell aluminum foam is also researched.The sound absorption coefficient of the material is tested by standing wave tube methods, the acoustic performances are analyzed thoroughly from the aspects of porosity, thickness, perforation percentage and cavity behind, results show that, with the increasing of the frequency, the sound absorption coefficient of closed-cell aluminum foam increases at first and then decreases, the relationship between sound absorption coefficient and porosity of closed-cell aluminum foam is an increasing function, which is to say the sound absorption coefficient increases with increasing of the porosity of closed-cell aluminum foam. The relationship between sound absorption coefficient and thickness of closed-cell aluminum foam is that sound absorption coefficient increases with increasing of the thickness when LLo. With increasing of the thickness, sound absorption coefficient increases under low-frequency region, decreases under high-frequency region, though the highest sound absorption coefficient travels to the low-frequency region, the whole sound absorption property is not affected obviously. The sound absorption coefficient of closed-cell aluminum foam increases obviously after being perforated, with the increasing of perforation percentage, the highest sound absorption coefficient increases at first and then decreases, the highest sound absorption coefficient travels to the high-frequency region. With the increasing of cavity thickness, sound absorption coefficient increases in the low-frequency region, decreases in the high-frequency region, the highest sound absorption coefficient increasing slightly, but showing the trend of traveling to low-frequency region.The sound absorption properties of perforated aluminum plate, plastic plate, cements board, slotted plastic plate with glass wool behind, and closed-cell aluminum foam board with cavity are tested by standing wave tube methods respectively. Results show that, they all have higher absorption peak except open-cell aluminum foam, but the absorption peaks appear at different frequency regions, for the perforated closed-cell aluminum foam, it's at high frequency, while at low and medium frequencies for the others. The frequency that the peak appears for the perforated closed-cell aluminum foam can be adjusted through the change of perforation percentage, thickness or cavity thickness, peak of open-cell aluminum foam is lower, and the whole sound absorption coefficient is not high.The field measurement and analysis of the noise of expressway are carried out, the frequency of the noises mainly localized below 1000Hz; therefore, the closed-cell aluminum foam with density is 0.3g/cm3, thickness is 10mm, perforation percentage is 1% or 1.5%, is suitable for the sound barrier of expressway.According to the noise spectrogram of subway, we can find that the noise mainly is localized in about 1000Hz, then the closed-cell aluminum foam with density is 0.3g/cm3, thickness is 10mm, perforation percentage is 2.5% or 3%, is suitable for the sound barrier of subway.Based on the spectrogram of noise in the carriages of trains, combining with its sound insulation and damping properties, the design of closed-cell aluminum foam sandwich as the surrounding wall and floor inside the carriages of trains is done, and the floor has a higher bending strength, better performances of sound insulation and damping, and a longer lifespan, compared with the floors made of wood or aluminum honeycomb materials.