阅读说明：本技术 一种软质隔音毡动态弹性模量测量装置 (Soft deadening felt dynamic elastic modulus measuring device ) 是由 杨志宏 于 2020-06-05 设计创作，主要内容包括：本发明涉及一种软质隔音毡动态弹性特性测量装置,包括上振动质量块、下振动底板、激振台、上加速度传感器、下加速度传感器和测量模块,下振动底板刚性连接于激振台的震动头上,上振动质量块和下振动底板之间装夹有待测样块,上加速度传感器刚性安装于上振动质量块上,下加速度传感器刚性安装于下振动底板上,测量模块的输入端连接至上加速度传感器和下加速度传感器,输出端连接至激振台；测量模块控制激振台产生不同频率的竖向振动,并接收由上加速度传感器和下加速度传感器采集的数据,基于上加速度传感器和下加速度传感器采集的数据得到动态弹性模量和阻尼系数。与现有技术相比,本发明可以实现软质隔音毡的动态弹性模量和阻尼系数的测量。(The invention relates to a device for measuring the dynamic elastic property of a soft sound-proof felt, which comprises an upper vibration mass block, a lower vibration bottom plate, an excitation table, an upper acceleration sensor, a lower acceleration sensor and a measuring module, wherein the lower vibration bottom plate is rigidly connected to a vibration head of the excitation table; the measuring module controls the exciting table to generate vertical vibration with different frequencies, receives data collected by the upper acceleration sensor and the lower acceleration sensor, and obtains dynamic elastic modulus and damping coefficient based on the data collected by the upper acceleration sensor and the lower acceleration sensor. Compared with the prior art, the method can realize the measurement of the dynamic elastic modulus and the damping coefficient of the soft sound-proof felt.)

1. The utility model provides a soft deadening felt dynamic elastic characteristic measuring device, its characterized in that, includes vibrating mass block (1), vibration bottom plate (4), excitation platform (6), goes up acceleration sensor (2), acceleration sensor (5) and measuring module down, vibration bottom plate (4) rigid connection is on the vibrations head of excitation platform (6) down, it clamps sample piece (3) that await measuring to go up vibrating mass block (1) and vibration bottom plate (4) down, go up acceleration sensor (2) rigid mounting on last vibrating mass block (1), acceleration sensor (5) rigid mounting is down on vibration bottom plate (4), measuring module's connection is to acceleration sensor (2) and acceleration sensor (5) down, and the output is connected to excitation platform (6);

the measuring module controls the exciting table (6) to generate vertical vibration with different frequencies, receives data collected by the upper acceleration sensor (2) and the lower acceleration sensor (5), obtains the frequency and the amplitude value of a maximum amplitude point and the frequency of a half-power point based on the data collected by the upper acceleration sensor (2) and the lower acceleration sensor (5), obtains a dynamic elastic modulus according to the amplitude value of the maximum amplitude point, and obtains a damping coefficient according to the frequency of the half-power point and the frequency of the maximum amplitude point.

2. The soft deadening felt dynamic elastic characteristic measuring device according to claim 1, wherein the measuring module comprises a signal generating collector (7), a power amplifier (8) and an upper computer (9), the signal generating collector (7) is respectively connected with the upper acceleration sensor (2), the lower acceleration sensor (5), the power amplifier (8) and the upper computer (9), and the power amplifier (8) is connected with the excitation table (6).

3. The soft deadening felt dynamic elastic characteristic measuring device according to claim 2, wherein the measuring module further comprises a cable holder (15) for fixing a cable.

4. The soft deadening felt dynamic elastic property measuring device according to claim 2, wherein the upper computer (9) is a computer.

5. The soft deadening felt dynamic elastic characteristic measuring device according to claim 1, wherein the sample block (3) to be measured has a square cross section.

6. The soft deadening felt dynamic elastic characteristic measuring device according to claim 1, wherein the upper acceleration sensor (2) is fixed to a center of the upper vibrating mass (1).

7. The soft deadening felt dynamic elastic characteristic measuring device according to claim 1, wherein the upper acceleration sensor (2) is rigidly connected to the upper vibrating mass (1) by a screw.

8. The soft deadening felt dynamic elastic characteristic measuring device according to claim 1, wherein the lower acceleration sensor (5) is fixed to a lower surface of the lower vibration floor (4).

9. The soft deadening felt dynamic elastic characteristic measuring device according to claim 1, wherein the lower acceleration sensor (5) is rigidly connected to the lower vibration floor (4) by a screw.

10. The soft deadening felt dynamic elastic characteristic measuring device according to claim 3, wherein the cable holder (15) comprises a base and a holder, and cables between the upper acceleration sensor (2) and the signal generating collector (7) and between the lower acceleration sensor (5) and the signal generating collector are fixed through the cable holder (15).

Technical Field

The invention relates to the field of sound-proof felt testing, in particular to a device for measuring dynamic elastic characteristics of a soft sound-proof felt.

Background

In the field of passive sound insulation and noise reduction of automobiles, loose and porous soft layers and then dense heavy-layer composite structures are mostly adopted, and the material structure diagram is shown in figure 1.

The traditional research and development mode is material testing → part making → vehicle verification, so the real object parts are made according to the characteristics of the existing materials and judged through the real object parts, if the mode is used for analyzing and optimizing the combination of materials with different properties, a large amount of sample pieces are needed to be made, the period is long and the cost is high. At present, the sound insulation performance of the material is predicted by CAE analysis, so that the acoustic performance of the soft-hard composite sound-proof felt is analyzed by a vibration model, and the attenuation characteristic of the soft-hard composite sound-proof felt to the sound energy is quantitatively analyzed through the angle of a vibration theory, so that the NVH performance of the soft-hard composite sound-proof felt is predicted.

As shown in fig. 2, the deadening felt is mounted on the automobile, and as can be seen from fig. 3, in the analysis process, the composite deadening felt material and the automobile body sheet metal are used as a system to be analyzed, and the structural dynamic vibration of the system is expressed as a single-degree-of-freedom spring-damping-mass system vibration model under the displacement excitation. In this structural dynamic vibration model, the vibration of the vehicle body is the displacement excitation which causes the excitation, the uppermost dense heavy layer is represented as mass in the dynamic system, and the polyurethane foam PUR in the middle is the spring with the damping. Thus, for polyurethane foam PUR, the dynamic modulus of elasticity and the damping coefficient are referred to as two relatively important performance characteristics.

As for the dynamic elastic modulus of the material, a sample material rod is conventionally adopted to generate bending vibration to achieve resonance, and the Young modulus value of the material is calculated by measuring the resonance measurement frequency. This requires that the object to be measured be a material having a large elastic modulus, such as steel or aluminum, and this method is not sufficient for a material having a small elastic modulus and not capable of being used as a sample rod, such as polyurethane foam PUR.

The emerging ultrasonic resonance frequency spectrum analysis method is used for measuring dynamic elastic modulus, the elastic constant of a solid material sample is obtained through ultrasonic resonance frequency, and similarly, for a loose and porous polyurethane foam PUR material, the porous performance of the material determines that the transmission speed of ultrasonic waves in the material is unstable, so that the material is also not suitable.

For the damping factor of the material, a plurality of existing test standards exist, such as a standard method for measuring the vibration damping performance of the material in GB/T18258(ASTME756), a rectangular strip-shaped test sample is adopted, the test sample is vertically arranged, the upper end of the test sample is rigidly clamped, and the lower end of the test sample is free, so that a cantilever beam test system is formed. The modulus of elasticity of polyurethane foam PUR materials is much less than 0.1 times that of the standard requirements with respect to metal strips, and the modulus of elasticity of the adhesive also has an uncertain effect on softer polyurethane foam PUR materials, so that the cantilever beam test system adopted in GB/T18258(astm e756) cannot be realized.

The GB/T16406(ISO6721) standard of the damping factor is also tested, the resonance curve is measured by a bending vibration method, the tested material is also required to be made into a rectangular strip-shaped test sample, and the method is not suitable for softer polyurethane foam PUR material.

In summary, it is a difficult problem to measure the dynamic elastic modulus and damping factor of the polyurethane foam PUR material with soft and slow rebound in the automobile sound-proof felt.

Disclosure of Invention

The invention aims to provide a device for measuring the dynamic elastic property of a soft sound-proof felt, which can realize the measurement of the dynamic elastic modulus and the damping coefficient of the soft sound-proof felt through an upper acceleration sensor, a lower acceleration sensor and vertical vibration applied from the outside.

The purpose of the invention can be realized by the following technical scheme:

a device for measuring dynamic elastic characteristics of a soft sound-proof felt comprises an upper vibration mass block, a lower vibration bottom plate, an excitation table, an upper acceleration sensor, a lower acceleration sensor and a measuring module, wherein the lower vibration bottom plate is rigidly connected to a vibration head of the excitation table, a sample block to be measured is clamped between the upper vibration mass block and the lower vibration bottom plate, the upper acceleration sensor is rigidly mounted on the upper vibration mass block, the lower acceleration sensor is rigidly mounted on the lower vibration bottom plate, the input end of the measuring module is connected to the upper acceleration sensor and the lower acceleration sensor, and the output end of the measuring module is connected to the excitation table;

the measuring module controls the excitation table to generate vertical vibration with different frequencies, receives data collected by the upper acceleration sensor and the lower acceleration sensor, obtains the frequency and the amplitude value of a maximum amplitude point and the frequency of a half-power point based on the data collected by the upper acceleration sensor and the lower acceleration sensor, obtains a dynamic elastic modulus according to the amplitude value of the maximum amplitude point, and obtains a damping coefficient according to the frequency of the half-power point and the frequency of the maximum amplitude point.

Furthermore, the measuring module comprises a signal generating collector, a power amplifier and an upper computer, wherein the signal generating collector is respectively connected with the upper acceleration sensor, the lower acceleration sensor, the power amplifier and the upper computer, and the power amplifier is connected to the excitation table.

Furthermore, the measuring module comprises a cable support for fixing the cable.

Furthermore, the upper computer is a computer.

Furthermore, the cross section of the sample block to be detected is square.

Further, the upper acceleration sensor is fixed to the center of the upper vibrating mass.

Further, the upper acceleration sensor is rigidly connected with the upper vibrating mass through threads.

Further, the lower acceleration sensor is fixed on the lower surface of the lower vibration base plate.

Further, the lower acceleration sensor is rigidly connected with the lower vibration bottom plate through threads.

Further, the cable support comprises a base and a support, and cables between the upper acceleration sensor and the signal generation collector, the lower acceleration sensor and the signal generation collector are fixed through the cable support.

Compared with the prior art, the invention has the following beneficial effects:

1) through the upper acceleration sensor, the lower acceleration sensor and the vertical vibration applied from the outside, the measurement of the dynamic elastic modulus and the damping coefficient of the soft sound-proof felt can be realized.

2) The cross section of the sample block to be measured is square, so that the preparation is easy, and the error of half-power point measurement can be reduced.

3) The cable bearer can reduce the measurement error caused by the cable blocking vibration.

Drawings

FIG. 1 is a schematic structural view of a composite deadening felt;

FIG. 2 is a schematic view of the installation of a composite acoustic felt material on an automobile;

FIG. 3 is a structural dynamics model of a composite acoustical blanket material system;

FIG. 4 is a schematic structural view of the present invention;

FIG. 5 is a diagram showing the relationship between the amplitude and the vibration frequency of the vibration table;

FIG. 6 is a schematic diagram of an assembly of a proof mass;

FIG. 7 is a schematic diagram of a half power process;

FIG. 8 is a sectional view of a measurement portion;

FIG. 9 is a schematic view of a lower vibrating baseplate;

FIG. 10 is a schematic longitudinal cross-sectional view of the lower vibrating baseplate;

FIG. 11 is a schematic view of an upper seismic mass;

fig. 12 is a longitudinal sectional view schematically showing an upper vibrating mass.

Wherein: 1. go up vibrating mass block, 2, go up acceleration sensor, 3, the sample piece that awaits measuring, 4, vibration bottom plate down, 5, acceleration sensor down, 6, the vibration exciter, 7, the signal generation collector, 8, power amplifier, 9, the host computer, 10, signal generation collector to power amplifier cable, 11, power amplifier to excitation platform cable, 12, go up acceleration sensor to signal generation collector cable, 13, acceleration sensor to signal generation collector cable down, 14, signal generation collector to host computer cable, 15, the cable support, 16, the cable ribbon.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.

A kind of soft sound-proof felt dynamic elastic characteristic measuring device, as shown in figure 4, including vibrating mass block 1, lower vibrating bottom plate 4, exciting table 6, upper acceleration transducer 2, lower acceleration transducer 5 and measuring module, lower vibrating bottom plate 4 rigid link to shaking the head of the exciting table 6, as shown in figure 6, the sample block 3 to be measured is clamped between vibrating mass block 1 and lower vibrating bottom plate 4, the upper acceleration transducer 2 is rigidly mounted on vibrating mass block 1, the lower acceleration transducer 5 is rigidly mounted on lower vibrating bottom plate 4, the input end of the measuring module is connected to upper acceleration transducer 2 and lower acceleration transducer 5, the carry-out terminal is connected to exciting table 6; the measuring module comprises a signal generating collector 7, a power amplifier 8 and an upper computer 9, wherein the signal generating collector 7 is respectively connected with the upper acceleration sensor 2, the lower acceleration sensor 5, the power amplifier 8 and the upper computer 9, and the power amplifier 8 is connected to the excitation table 6. The cross section of the sample block 3 to be measured is square, so that the preparation is easy, and the error of half-power point measurement can be reduced.

When the vibration exciter works, firstly, the signal generation collector 7 sends out a vibration signal, the vibration signal is input into the power amplifier, the vibration signal is amplified by the power amplifier 8 and directly drives the vibration exciter 6, and the vibration head of the vibration exciter 6 vertically vibrates. The lower vibration bottom plate 4 is rigidly connected to a vibration head of the vibration exciter 6, the sample block 3 to be tested (soft polyurethane PUR) is placed on the lower vibration bottom plate 4, and the upper vibration mass block 1 is stacked on the sample block 3 to be tested. The lower vibration bottom plate 4 and the upper vibration mass block 1 are respectively and rigidly connected with a single-degree-of-freedom high-precision acceleration sensor, the upper acceleration sensor and the lower acceleration sensor transmit acceleration signals back to the signal generation collector 7 through cables, and amplitude-frequency curves of vibration shown in the figure 5 are obtained through corresponding software by using a transfer function method.

In the single-degree-of-freedom damped spring mass system, equal-amplitude forced vibration is carried out under the excitation of the lower vibration bottom plate, the excitation vibration frequency given by the excitation table is changed from small to large, in the process, acceleration sensors rigidly connected to the upper vibration mass block 1 and the lower vibration bottom plate 4 output acceleration signals, and the amplitude-frequency curve graph can be drawn by the upper acceleration signals and the lower acceleration signals through software through the front end. The resonance frequency corresponding to the resonance point can be found on the amplitude-frequency curve.

The natural frequency of an object depends on the stiffness (not strength) of the object itself and has directivity, and the stiffness is determined by the structural form of the object. When the object is forced to vibrate, the vibration frequency depends on the frequency of the external vibration. When the external vibration is applied to an object, the phenomenon of obvious vibration aggravation can be generated when the external vibration frequency is close to the natural frequency of the object. The simplified formula is as follows:

wherein: m is the mass (kg) of the upper vibrating mass 1, k is the stiffness coefficient (N/m) of the object, and T is the period(s).

Relationship of period T and frequency: f. of_RSubstituting equation (1) for 1/T yields:

wherein: m is the mass (kg) of the upper vibrating mass 1, k is the stiffness coefficient (N/m) of the object, f_RIs the frequency (Hz).

Derived from equation (2)

k＝f_R ²*4π²*m(3)

Wherein: m is the mass (kg) of the upper vibrating mass 1, k is the stiffness coefficient (N/m) of the object, f_RFrequency (Hz)

From equation (3), it can be seen that the natural frequency of an object is related to its mass, and is proportional to the mass and the square of the resonant frequency.

According to the mechanics basic principle, the elastic modulus E for a uniform cross-section object is defined:

wherein: l is the length of the system in the vibration direction (e.g. L is the height of the soft polyurethane PUR sample block), A is the sectional area of the uniform section object (e.g. A ═ a shown in FIG. 6)

According to the principle of mechanical elastic deformation:

F＝k*ΔL (5)

wherein: f, external force (N) acting on the object, k is the stiffness coefficient (N/m) of the object, and Delta L is the deformation (m) of the object in the stress direction

Obtained from (5):

wherein: f, external force (N) acting on the object, k is the stiffness coefficient (N/m) of the object, Δ L is the deformation (m) of the object in the force-bearing direction, and k in (3) is substituted into (4) to obtain:

wherein: f. of_RIs the formant frequency (Hz), in particular the first resonance frequency, m is the mass (kg) of the upper vibrating mass 1, L is the sample thickness (m), a is the square sample cross-sectional width (m)

According to the derivation formula (7), the resonance frequency of the soft polyurethane PUR sample block is obtained through forced vibration, the height and the mass of the soft polyurethane PUR sample block are measured, and the dynamic elastic modulus E of the soft polyurethane PUR sample block can be obtained through calculation.

Through forced vibration, an amplitude-frequency curve chart of the system can be drawn, and then the damping factor of the soft polyurethane PUR can be obtained through half-power bandwidth as shown in FIG. 7

For the forced vibration of the displacement-excited single-degree-of-freedom spring-mass system with damping, the amplitude amplification factor is as follows:

when resonance occurs, λ ≈ 1, the amplitude-frequency curve reaches the highest point, d β/d λ ═ 0, at this time, the amplification factor is maximum, and is:

the resonance point amplitudes are:

wherein the frequency ratio is:

then, at half-power point, its amplitude isMultiple B_maxIts corresponding frequency satisfies the equation:

taking reciprocal and square on two sides of the equation:

(1-λ²)²+4ζ²λ²＝8ζ²(1-ζ²)

finishing to obtain:

(λ²)²-2(1-2ζ²)λ²+1-8ζ²(1-ζ²)＝0

the formula is about (f/f)_R)²I.e. lambda²A quadratic equation of one unit, so that (f/f)_R)²＝λ²Substituting S into S, the above equation is:

S²-2(1-2ζ²)S+1-8ζ²(1-ζ²)＝0

so S is two roots:

the positive sign of the above formula is taken as the root f with smaller corresponding numerical value_aThe above formula takes the negative sign as the root f with larger corresponding numerical value_bThe general engineering damping is relatively small, and the square of zeta can be ignored, so the simplification is as follows:

therefore, the calculated damping ratio is obtained by solving the frequencies fa and fb corresponding to the two half-power points:

therefore, the measuring module controls the excitation table 6 to generate vertical vibration with different frequencies, receives data collected by the upper acceleration sensor 2 and the lower acceleration sensor 5, acquires the frequency and the amplitude value of a maximum amplitude point and the frequency of a half-power point based on the data collected by the upper acceleration sensor 2 and the lower acceleration sensor 5, obtains a dynamic elastic modulus according to the amplitude value of the maximum amplitude point, and obtains a damping coefficient according to the frequency of the half-power point and the frequency of the maximum amplitude point. The measurement of the dynamic elastic modulus and the damping coefficient of the soft sound-proof felt can be realized through the upper acceleration sensor 2, the lower acceleration sensor 5 and the vertical vibration applied from the outside.

In this embodiment, the sample block of the flexible polyurethane PUR to be measured is cut into a sample block of 50mm × 50mm, and is placed between the lower vibrating plate and the upper vibrating mass. Meanwhile, blind hole internal threads of M3 are respectively arranged on the lower vibrating bottom plate 4 and the upper vibrating mass block 1, and the upper acceleration sensor and the lower acceleration sensor are firmly screwed in to ensure rigidity. The connecting tool is schematically shown in figure 8.

Wherein, the lower vibration bottom plate 4 is manufactured by integral metal turning in order to transmit the vibration of the vibration exciter 6 and ensure the mode of vibration excitation. The lower part of the vibration platform is a cylindrical sinking platform, and the middle part of the vibration platform is provided with a threaded column bulge M5 which can be firmly and rigidly connected with an M5 threaded hole at the center of a vibration excitation head on the vibration excitation platform 6. The upper part is provided with a platform of 50mm multiplied by 50mm, the upper surface is smooth, and a soft polyurethane PUR sample block with a section of 50mm multiplied by 50mm can be placed. A threaded blind hole with the diameter of M3 multiplied by 3mm is formed below the platform, so that the rigid connection with the M3 thread of the lower acceleration sensor can be ensured. The structure is shown in detail in fig. 9 and 10.

The upper vibrating mass block 1 is a metal block 50mm × 50mm, has smooth upper and lower surfaces, and is placed on the upper portion of the soft polyurethane PUR sample block during testing. According to the characteristics of the flexible polyurethane PUR, the vibration mass is required to be ensured to be 50g, and the aluminum alloy is selected as the material of the upper vibration mass block, and the thickness is determined to be 7.4 mm. The center of the upper surface of the upper vibrating mass block is provided with a threaded blind hole of M3 multiplied by 3mm, which can ensure rigid connection with the M3 thread of the upper acceleration sensor. The structure is shown in detail in fig. 11 and 12.

The measuring module further comprises a cable support 15 used for fixing the cable, the cable support 15 comprises a base and a support, the cables between the upper acceleration sensor 2 and the lower acceleration sensor 5 and the signal generation collector 7 are fixed through the cable support 15, and the cable support 15 can reduce measuring errors caused by the fact that the cables block vibration.