| The study on sound absorption and noise reduction performances of metal rubber (MR) material and its related experiment are important research directions for this material. As a specified material with wide working temperature range, erosion resistance, high intensity, effective porosity, stability and structure design flexibility, MR can be well used as a kind of excellent sound absorption material in the structure of modern mufflers, as well as in the fields of aviation, national defense, specific adverse civilian situations, etc. In order to clarify its sound absorption and noise reduction performance and present calculation methods to determinate acoustic parameters and sound absorption parameters, systematic study on MR material is presented theoretically and experimentally in this paper. Influencing parameters of material and specified structure on sound absorption and noise reduction performances of MR are obtained herein; effective calculation method to get acoustic parameters and sound absorption parameters is set up. These approaches are to be the theoretical and experimental basis for the design and application of MR as the material for sound absorption and noise reduction.Fabrication methods of MR metarial for its usage in sound absorption and noise reduction are presented. Influences of different fabrication approach and material type on sound absorption performance are analyzed. The structural characteristics, general physical performance, and sound absorption property of porous MR material are studied in this paper. Effects of structure parameters on sound absorption chacacteristics are investigated experimentally, which indicates that MR material has great adjustable ability in sound absorption and noise reduction. It can satisfy the requirements of sound absorption and noise reduction for modern muffers.The acoustic characteristic parameters and sound absorption performance parameters of MR, as well as their relationship in between, are analyzed. The effects of flow resistivity on sound absorption performance is studied experimentally, which shows that materials with the same flow resistivity have similar sound absorption performance. Based on the relationship that characteristic impedance and propagation constant are the exponential functional of the ratio of frequency and flow resistivity, the empirical formula of acoustic characteristics parameters is proposed experimentally. The acoustic characteristics parameters were calculated and compared with experimental results. The comparison indicate that the obtained empirical fomula is with simple experssion which can be used to evaluate the acoustic performance of MR material.Mathematical model of acoustic parameters is derived based on the hypothesis that MR material is a with the property of homogeneous isotropic and evenly distributed porosity. Structural constant and compressive modulus are analyzed experimentally, and formula of acoustic characteristic parameters as well as sound absorption performance parameter are obtained based on the relationship between structure constant, compressive modulus and material charactristic parameters. The good agreement between the calculated and experimental results of sound absorption coefficient testifies the effectiveness of theoretical method and experimental operation. The mathematical model of sound absorption parameters of MR at resonance were proposed for the application of MR. The calculated results shows good agreement with the experimental ones which indicates that theis method to investigate the acoustic parameters at resonance is effective and accurate.Sound absorption performances of single layer and bilayer structures are presented and the caculation formulas of parameters of these structures are deduced based on formula of acoustic characteristic parameters. Effects of material thickness, flow resistivity, and air layer thickness on sound absorption performances of single layer and bilayer structures are investigated by comparing the acoustic absorption performances of single layer and bilayer structures. The results show that diverse sound absorption requirements can be satisfied by adjusting structural parameters.Nonlinear sound absorption performance is studied via theoretical and experimental approaches, respectively. According to linear acoustic theory of MR material and Forchheimer nonlinear modification method, the equaitons for nonlinear effective density, acoustic mass particle velocity and nonlinear acoustic characteristic parameters are set up, respectively. The mathematic model for sound absorption parameters is established based on the conditions that MR is attached to a rigid wall with and without an air layer, respectively. The effects of stuctural parameters and incidence acoustic pressure level on nonlinear sound absorption performances are analyzed which demonstrates the effectiveness of nonlinear sound absorption theory and provides a theoritical basis for the design and application for MR in the field of sound absorption and noise reduction. |
