Study On Sound Absorption Properties And Mechanisms Of Magnetic Polyurethane Foam

With the rapid development of modern industrial manufacture and transportation,noise pollution has become increasingly serious in the environment of daily life.It has become a tricky problem to be solved among the national defense,economic and social development urgently.Sound-absorbing porous material has been found to be one of the most effective materials for sound absorption and noise reduction,but it's not satisfactory for low-frequency sound-absorbing effect and insufficient absorption performance for complex noise environment.Therefore,improving traditional sound-absorbing porous material properties and overcoming their functional defects have important significance on researching and engineering for noise pollution controlling.In this manuscript,magnetic polyurethane foam(MPUF)is took as study object.The main purposes are investigated to improve the traditional materials low-frequency sound absorption performance.To explore the relationship for its micro-structure parameters and characteristics parameters with its sound absorption properties,a series of experiment and theoretical analysis are studied.The main work of this thesis is as follows:1.This thesis expounds the hazards of noise pollution and major noise control methods currently,and points out the functional defects of traditional materials used in the field of sound absorption and noise reduction.And the current study of intelligent magnetic sound-absorbing and noise-reducing materials are summarized for clarifying the application prospects and urgent requirements by study of smart magnetic absorption.And the main work of this thesis is put forward.2.Isotropic and anisotropic magnetic polyurethane foam are prepared by a magnetic field generating device with one-step full water foaming method for solving the bad performance of porous sound-absorbing at low frequency.And then measured their acoustic properties at 64 Hz to 1600 Hz.We found that the sound absorption performance can be improved by increasing isocyanate proportion,and can be improved significantly by the addition of carbonyl iron powder at 64 Hz to 500 Hz.When the ratio of polyether polyol to isocyanate is 100: 70 with 5wt% carbonyl iron,its low-frequency sound absorption performance is the optimal and its average sound absorption coefficient could reach 0.201.The average sound absorption coefficient of isotropic MPUF increases first and then decreases with the increase of carbonyl iron mass fraction,but it's all better than polyurethane foam.sound The absorption performance of anisotropic MPUF are decreased as the increasing of the magnetic field strength,and even worse than polyurethane foam at low frequency.Therefore,the isotropic MPUF has the best sound absorption properties and the worst anisotropy.3.The representative geometry unit geometry model is established for analyzing of its micro-structure parameters statistically by observing its micro-structure with Image Pro Plus for investigating its relationship between sound absorption properties and micro-structure parameters.We found that the MPUF has better sound absorption performance when its cavity diameter is 700-900 um and hole diameter is 200-255 um.The low-frequency sound absorption performance of 64-500 Hz will be improved with the increase of the skeleton thickness and the mesh rate.At the same time,the average sound absorption coefficient of whole frequency band will be worsen by the skeleton length and the width of the gap increasingly.4.The mechanism of sound absorption in MPUF are characterized by an absorption model based on its characteristic parameters for studying its influence of the characteristic for its sound absorption performance.And its characteristic parameters of isotropic and anisotropic MPUF are identified by least squares method.The results show that its sound absorption performance can be improved by increasing the flow resistivity or decreasing the viscous characteristic length at low frequency.We found that its porosity and viscous characteristic length are increased by isocyanate ratio increasingly.But its flow resistivity will decrease by the mass fraction of carbonyl iron increasing.And its flow resistivity and porosity will be reduced by strength of the prepared magnetic field increasing while thermal characteristic length increasing.Therefore,its low sound absorption performance can be improved by increasing the isocyanate ratio or adding carbonyl iron powder.5.Its flow resistivity and porosity are measured by establishing the device for verifying the validity of the characteristic parameters identification.The measurement results were compared with the identification results,which its trend has a good consistency.And the relative error between them is within ±20%.Therefore,the characteristic parameters identification method proposed in this paper is feasible.