Mechanical Parameters And Acoustic Parameters Measurement Of Materials Using Controllable Pulse

Viscoelastic materials are widely used in vibration and noise reduction field because of their excellent damping properties.One should measure the mechanical parameters of the viscoelastic material precisely in order to use it reasonably.At the same time,most of the underwater acoustic materials are also viscoelastic materials,and the sound absorption and tansmission loss coefficients are important indexs for evaluating the acoustical property of the underwater acoustic materials.As an important index to evaluate the mechanical propertie of materials,the complex Young’s modulus is often obtained by means of longitudinal vibration test.The sound absorption and insulation tests in acoustic impedance tube are also important methods to obtain the acoustic parameters of materials.In this article,the methods for measuring the complex Young’s modulus of viscoelastic materials based on longitudinal vibration and the methods for measuring the sound absorption and the sound transmission loss in acoustic impedance tube were analyzed.Firstly,in the case of considering the transverse dimension of the sample bar,the longitudinal wave propagation in a viscoelastic bar was analyzed in detail on the basis of the constitutive relation of viscoelastic solid.At the same time,a simulation program suitable for calculating the longitudinal wave propagation in viscoelastic bar was written by combining the software MSC.Nastran and MATLAB,and the finite element analysis of wave propagation in viscoelastic bar was completed.On this basis,several validated test methods were theoretically derived in detail.To overcome their shortcomings,the wave-speed method based on incident wave extraction was proposed,and different test methods were compared through simulation to verify the feasibility of the proposed method.A complex Young’s modulus testing platform based on longitudinal vibration test was built,and a short broadband pulse signal with controllable waveform was generated at the end of the shaker by using controllable pulse generation technique.The resonance method,wave-speed method and wave-speed method based on incident wave extraction were tested by using the generated short pulse.The experimental results show that the resonance method can only obtain the parameters at the discrete resonance frequency points;the traditional wave-speed method can obtain the parameters within the scope of the broadband,but it cannot test at low frequency range;the proposed wave-speed method based on incident wave extraction,however,can expand the testing frequency range of the traditional wave-speed method especially at low frequency range and can determine the complex Young’s modulus at frequencies ranging from 200 to 6000 Hz.Based on the analysis of the sound field in the sound tube,a theoretical derivation of the traditional sound absorption and sound insulation test methods was made,and improved test methods for sound absorption and sound insulation tests were also proposed.The traditional transfer function method as well as the traditional transfer matrix method have problems such as sensor mismatch correction and half-wavelength limitation.The time-domain pulse separation method effectively avoids the influence of these two factors.However,there is not a corresponding detailed theoretical derivation for the traditional time-domain pulse separation method,and the selection of the measurement position has not been discussed in depth.In this article,a detailed theoretical derivation of the traditional time-domain pulse separation method was given.Based on this,the sound pressure at different measurement points was analyzed,and a more optimized pulse method was proposed.For the sound absorption test method,the pulse separation method proposed in this article is suitable for narrow sensor spacing and small-sized sound tubes,and the incident pulse and the first reflected pulse can be extracted when the incident pulse,the first reflected pulse and the second reflected pulse are superimposed using this method,then the length of the pulse-tube can be reduced while the advantages of the pulse tube still remain.The proposed fixed-position single-microphone sound absorption test method,however,can reduce the number of sensors and the number of measurement points,which makes the testing work more convenient.For the sound transmission loss test method,based on the wave decomposition of the traditional transfer function method,the sound field in the upstream tube was further decomposed,and an normal sound incident transmission loss test method based on the upstream-tube wave decomposition using only two microphones was also proposed.There should be at least four microphones and two different ends for the traditional transfer matrix method as well as the traditional wave decomposition method,that is,a total of eight groups of test signals.Using the proposed method,however,the required testing conditions are reduced to at least two microphones and three different lengths of back cavity,that is,at least six groups of test signals.At the same time,an optimaization of the measurement point position during the traditional time-domain pulse separation method was also conducted,and a so-called fixed-positon single sensor pulse separation method for measuring the sound transmission loss was proposed on this basis.The first transmission pulse can be directly obtained using only one sensor and one measurement point with this proposed method.In order to facilitate experimental verification and subsequent test work,an air impedance tube suitable for various sound absorption and sound insulation test methods was designed.Experimental verifications of the proposed new methods were carried out in the designed air impedance tube.The results of the proposed methods are in good agreement with that of the traditional methods,while they are simpler and easier to implement than traditional methods and have practical application value.In addition,the proposed fixed-position single-sensor sound transmission loss test method is very suitable for testing in underwater acoustic tubes because it avoids the movement of the sensor,and uncertainty analysis of this proposed method was also performed.The experimental results show that the results obtained by the fixed-position single-sensor sound transmission loss test method are in good agreement with that of the current pulse method in sound tubes,the physical meaning of the method is clearer and the operation is simpler.