闭孔泡沫铝吸声性能及降噪频段可控性研究

The higher sound absorption coefficient will be obtained by means of perforation in the closed-cell aluminum foam. It will have great significant in the filed of sound absorption and noise reductionIt is difficult to make sure frequency band accurately for sound absorption in a relatively tight range.The sound absorption coefficient of closed-cell aluminum foam with different structure and perforation ways will be measured by standing-wave method, and the effect of combining form and structural parameter on the sound adsorption of closed-cell aluminum foam perforated will be studied. The purpose is to establish the sound absorption constitutive relation with various structure parameter. Multi-parameter characterization of the absorption coefficient of the closed-cell aluminum foam will be conducted to analyze the acoustic wave propagation feature in the perforated foam structure and to reveal the sound absorption mechanisms by the characterization for parameters with structural parameters. On the basis of research and data analysis, it is expected to establish the sound absorption model by combining with sound absorption theory of acoustic and porous materials. Perforated closed-cell aluminum foam sound absorption mechanism will be analyzed and amended by experiments. The sound-absorbing structure for different noise reduction will be designed according to the conclusions of the experiments and model to achieve the controllability of sound absorption frequency in engineering applications, especially to provide a theoretical basis for low frequency noise reduction which is now more difficult to achieve.

闭孔泡沫铝打孔后可获得较高的吸声系数，将其用于吸声降噪领域，意义重大。目前闭孔泡沫铝的吸声系数虽吸声峰值较高，但吸声频带较窄，且难以准确控制吸声频段。使用驻波管吸声系数测试仪对不同结构及不同打孔方式的闭孔泡沫铝材料进行吸声系数测试，通过研究组合吸声结构不同组合部分的结构参数及孔的结构参数对吸声性能的影响，建立包含各结构参数的闭孔泡沫铝吸声的相关本构关系。以多参数表征闭孔泡沫铝的吸声系数，通过表征参数随结构参数变化的规律，分析声波在打孔泡沫结构中传播的特性，揭示其吸声机理。在实验研究及数据分析的基础上，结合声学及多孔材料、泡沫材料的吸声理论建立吸声模型，从理论上分析打孔闭孔泡沫铝的声吸收机制，并通过实验进行检验和修正。根据性能测试及模型分析的结论，设计针对不同降噪频段的吸声结构，为工程应用中不同频段的降噪，尤其是现在较难实现的低频降噪提供理论依据，实现吸声频段的可控性。

吸声系数的测试结果显示：孔隙率的变化主要是影响吸声系数的大小，而不影响吸声峰值出现的频段。厚度的改变主要是使吸声系数的峰值出现的频段发生了变化。孔隙率相当，孔径大的闭孔泡沫铝吸声系数要比孔径小的闭孔泡沫铝吸声系数大的多，吸声系数峰值的增加更明显。打孔之后的闭孔泡沫铝，吸声系数比未打孔时大大提高，仅吸声峰值就提高0.3左右，过高或过低的打孔率对吸声都不利，1%～3%的打孔率是比较有利于吸声的。具有相同打孔率的闭孔泡沫铝试样随打孔孔径增大，吸收峰由低频向高频迁移。太小的打孔孔径会导致吸声系数峰值的下降，太大的打孔孔径会使峰宽变窄，1.5mm～2.5mm的孔径有利于吸声；背后空腔深度的变化引起了吸声系数峰值的迁移，孔隙率88.1%的试样厚度从5mm变化到30mm，峰值中心频率从1250Hz变化到630Hz，但对吸声系数的大小未有明显改变，这主要是由于空腔厚度具有类厚度的效应；对闭孔泡沫铝进行打孔后的孔排列方式的不同对于吸声效果并无太大的影响。双层结构更有利于吸声，双层共振相当于两层共振结构串联，两层结构具有各自的吸声主频率，组合后吸声频带变宽，单层打孔闭孔泡沫铝的吸声效果比铝板要好，两层打孔闭孔泡沫铝板复合后的吸声效果也优于一层闭孔泡沫铝板与一层铝板复合的形式，但若铝板与泡沫铝之间不加空腔则吸声效果下降。对打孔闭孔泡沫铝试样表面覆盖软质吸声布后其高频吸声系数得到提高，这种形式相当于共振结构与多孔材料复合，结合二者的优点，对吸声系数有所改善。在打孔闭孔泡沫铝板后添加不同厚度的玻璃棉，吸声有所提高，吸声频带变窄，总体影响不大，但考虑玻璃棉的环境问题，不建议使用。利用Design expert软件结合闭孔泡沫铝的吸声测试结果建立最优吸声模型，并通过实验进行验证，实验结果与模型基本相符。