CN106596723A - Acoustic detection method of structural mechanical parameters of multilayer composite material - Google Patents

Abstract

The invention relates to an acoustic detection method for mechanical parameters of a multilayer composite material structure. The relationship between the elastic modulus and shear modulus of the multilayer composite material structure and the geometric size, mass, and resonance frequency are respectively established through empirical formulas, and then excited at one end, and the time-domain vibration signal is obtained at the other end to obtain f _f and f _t , The geometric dimensions and mass of the multilayer composite structure are used as the input of the empirical formula to finally obtain the dynamic Young's modulus E and the dynamic shear modulus G. The present invention overcomes the shortcoming of preparing a rectangular section sample in the standard method of detecting mechanical parameters by pulse excitation, overcomes the damage to the mechanical structure during the traditional mechanical parameter detection process, simplifies the detection steps, greatly shortens the detection time, and is suitable for The actual application conditions of the multilayer composite material structure; through the identification of the bending resonance frequency and shear resonance frequency of the multilayer composite material plate, the dynamic mechanical parameters of the multilayer composite material plate can be detected efficiently, accurately and non-destructively.

Description

An acoustic detection method for mechanical parameters of multilayer composite structures

technical field

The invention belongs to the technical field of non-destructive testing of mechanical structures, and relates to an acoustic testing method for mechanical parameters of a multilayer composite material structure.

Background technique

At present, with the rapid development of the country's manufacturing industry, the society's demand for mechanical equipment is expanding day by day. High-performance composite materials are widely used in various manufacturing fields. The industry has higher and higher requirements for material performance. Since the characteristics of the material itself may change with the application environment and working conditions, this will lead to the stability of the material and the entire mechanical equipment. And the reliability is reduced, which leads to safety accidents from time to time. Therefore, it is particularly important to carry out digital simulation of the system in advance to realize the evaluation of the stability of the mechanical structure and the prediction of the service life, which will greatly improve the overall operation safety and reliability of the mechanical equipment and avoid malignant accidents. In the process of digital modeling and simulation, elastic modulus and shear modulus are the most basic mechanical characteristic parameters. Due to the uncertainty of working conditions and application environment, the values of mechanical parameters will change. In order to make the simulation prediction results more accurate Accurate, an efficient, non-destructive, accurate mechanical parameter detection method becomes very necessary.

Impulse Excitation Technique (Impulse Excitation Technique) is a so-called non-destructive testing method, which is a method to obtain the Young's modulus, shear modulus and Poisson's ratio of the material through the natural frequency, size and quality of the sample. The pulse excitation method refers to a continuous pulse excitation signal given to a specific position of the sample by an appropriate external force. When a certain frequency in the excitation signal is consistent with the natural frequency of the sample, resonance is generated. At this time The amplitude is the largest and the delay is the longest. The vibration signal is received by the measuring sensor, and then the natural frequency of the sample is obtained through data analysis and processing. The natural frequency obtains different types of frequencies according to the vibration mode of the sample, such as bending frequency, Then the Young’s modulus E, shear modulus G, Poisson’s ratio and damping ratio are calculated by the empirical formula of the standard sample. It is currently recognized as an advanced non-contact measurement of various materials in the world. An ideal test method for elastic modulus.

In recent years, the identification technology of material mechanical parameters based on structural vibration information has attracted extensive attention from researchers in the field of nondestructive testing of engineering structures. The pulse excitation detection method is a newly developed method with broad application prospects. This method accurately identifies the mechanical parameters of the multilayer composite material plate through a non-destructive method, and has achieved good results in laboratory research. . However, previous studies were limited to traditional engineering materials, and the rapid identification of mechanical parameters of multilayer composite plate structures under actual operating conditions has not been reported due to the lack of applicable methods.

Contents of the invention

In order to overcome the above technical deficiencies, the present invention provides an acoustic detection method for mechanical parameters of a multilayer composite material structure.

The invention provides an acoustic detection method for mechanical parameters of a multilayer composite material structure, the steps of which are as follows:

1) Calculate the modal frequency of the simulated multilayer composite structure by finite element analysis method, obtain the first-order bending resonance frequency f _f and the first-order shear resonance frequency f _t , and process and fit the obtained data, The relationship between the elastic modulus E and the shear modulus G and the geometric size and mass of the multilayer composite structure is obtained respectively, and the empirical formula for obtaining the mechanical parameters is obtained;

2) Suspend the multi-layer composite material structure with elastic metal wires at a distance of 0.198L from both ends, so that it is in a state of free vibration, and use a hammer to excite the left end of the multi-layer composite material structure, while the right end uses The sound pressure sensor picks up the vibration signal of the multilayer composite material structure, and obtains the first-order bending resonance frequency f _f through fast Fourier transform;

3) Suspend the multi-layer composite material structure with elastic metal ropes at the midline of the length and width directions, so that it is in a state of free vibration, and use a hammer to excite the left end of the multi-layer composite material structure, and use a sound at the right end. The pressure sensor picks up the vibration signal of the multi-layer composite material structure, and obtains the first-order shear resonance frequency f _t through fast Fourier transform;

4) Substitute the first-order bending resonance frequency f _f and the first-order shear resonance frequency f _t into the empirical formula in 1) to obtain the elastic modulus E and Shear modulus G.

1) The relational expression for obtaining the modulus of elasticity E is as follows:

where m is the mass of the multilayer composite structure, _f is the _first -order bending resonance frequency, T is the correction coefficient under bending vibration, μ is the Poisson’s ratio of the material,

.

1) The relational expression for obtaining the shear modulus G is as follows:

where A and B are the correction coefficients for the width b and thickness t of the multilayer composite structure in the shear state,

When the Poisson's ratio is unknown, the method to obtain the value of each mechanical parameter of the multilayer composite structure is as follows:

(1) When the dimensions, mass, first-order bending resonance frequency f _f and first-order shear resonance frequency f _t of the multilayer composite material plate are measured, use

The shear modulus G of the resulting multilayer composite sheet was obtained.

(2) pass Obtain the elastic modulus E of the multilayer composite plate, using the relationship between elastic modulus E, shear modulus G and Poisson's ratio μ

Get the updated Poisson's ratio μ _n .

(3) Pass the judgment standard

To check whether the updated Poisson’s ratio μ _n meets the requirements, if the requirements are met, the mechanical parameters E, G and μ of the multilayer composite material plate are determined; if the updated Poisson’s ratio μ _n does not meet the requirements, then Taking μ _n as the Poisson’s ratio value of the next iteration process, repeat step (2) until the required Poisson’s ratio μ _n is obtained, and then determine the final mechanical parameters E, G and μ of the multilayer composite plate.

Beneficial effects of the present invention: it only needs to excite the multi-layer composite material plate to generate a vibration response signal and collect and analyze the vibration signal through a non-contact sound pressure sensor, which overcomes the damage to the mechanical structure in the traditional mechanical parameter detection process Influence, realize the non-destructiveness of the detection, and also apply to the actual application conditions of the multi-layer composite structure. Through the identification of the bending resonance frequency and shear resonance frequency of the multilayer composite material engineering structure, the dynamic mechanical parameters of the multilayer composite material can be detected efficiently, accurately and non-destructively only through empirical formulas.

Description of drawings

Figure 1 is a cross-sectional view of a multilayer composite material panel.

Figure 2 shows the support mode of the structure, in which 1 is the support mode of bending vibration, and 2 is the support mode of shear vibration.

Figure 3 is a flowchart of the iterative process when Poisson's ratio is unknown.

Fig. 4 is a flow chart of the transmission shaft damage detection method.

Fig. 5 is a vibration response diagram and a vibration spectrum diagram of bending vibration, wherein 1 is a vibration response diagram, and 2 is a spectrum diagram.

Figure 6 is the vibration response diagram and vibration spectrum diagram of shear vibration, wherein 1 is the vibration response diagram and 2 is the frequency spectrum diagram.

detailed description

Embodiments of the present invention will be further described below in conjunction with accompanying drawings:

As shown in the figure, the empirical formulas for the elastic modulus and shear modulus of the multilayer composite structure pulse excitation detection are obtained through the finite element analysis method and the data processing software Design-expert, and the elastic modulus and shear modulus of the multilayer composite structure are respectively established. The relationship between the shear modulus and the geometric size, mass, and resonance frequency, and then the hammer is used to excite one end of the multilayer composite structure, and the other end uses a sound pressure sensor to measure the bending vibration and shear vibration of the multilayer composite material plate non-contact The time-domain vibration signal in the state, through the data acquisition analyzer to perform fast Fourier transform (FFT) on the time-domain vibration signal to extract the resonance frequency of the signal and take the average, and calculate the first-order bending resonance of the multi-layer composite material plate The frequency f _f and the first-order shear resonance frequency f _t , and the geometric dimensions and mass of the multilayer composite material structure are used as the input of the empirical formula for the final calculation to obtain the dynamic elastic modulus E and dynamic shear modulus of the multilayer composite material plate Quantity G. Taking the multi-layer composite material 3240 epoxy board as the research object, the implementation of the detection method includes the following steps:

1. Empirical formulas for pulse excitation to detect elastic modulus and shear modulus of multilayer composite material structures under different temperature loads.

Figure 1 is a simplified cross-sectional model diagram of the multilayer composite structure, where b and t are the length, width and thickness of the multilayer composite structure; Figure 2 is a simplified diagram of the support position of the multilayer composite structure, where L is the length of the structure. As shown in Figure 2, the support position is 0.198L from both ends in the bending vibration state; the support position is the midline of the structure length and width (0.5L and 0.5b) in the shear vibration state. The empirical formulas of elastic modulus and shear modulus for multilayer composite plate pulse excitation detection are obtained by finite element analysis, and the relationship between elastic modulus and shear modulus of multilayer composite material structure and its geometric size, mass and resonance frequency is established. relation. Specific implementation process:

Through the finite element method, using the finite element analysis software ANSYS, using the solid element "Solid 186", the material parameters of the spindle of the four-step machine tool are Poisson's ratio μ = 0.3, the material density ρ = 7860kg/m ³ , and the restraint position is at At 0.198L, for shear vibration, the constrained position is at 0.5L and 0.5b (as shown in Figure 2), and the modal frequency is calculated to obtain the first-order bending resonance frequency f _f and the first-order shear resonance frequency f _t . After a large number of simulation experiments, enough simulation data are obtained, and then the simulation data is processed and fitted by the software Design-expert with powerful data fitting capabilities, and the elastic modulus E and shear modulus G are obtained respectively. The relationship between the geometrical dimensions and the mass of the structure gives empirical formulas for calculating the mechanical parameters.

(1) Calculation of elastic modulus when Poisson's ratio is known

After the first-order bending resonance frequency is extracted, the empirical calculation formula of the Young's modulus of the multilayer composite plate is:

where m is the mass of the multilayer composite plate, f _f is the first-order bending resonance frequency, T ₁ is the correction coefficient under bending vibration, and μ is the Poisson's ratio of the material.

(2) Calculation of shear modulus

When the first-order shear resonance frequency is reached, the shear modulus of the multilayer composite plate can be obtained by the following empirical formula:

where A and B are correction coefficients for the width b and thickness t of the multilayer composite sheet in the shear state.

(3) Calculation of elastic modulus and Poisson's ratio when Poisson's ratio is unknown

In the process of calculating Young's modulus, if the value of Poisson's ratio μ is unknown, it is necessary to perform an iterative operation through the flow chart shown in Figure 3 to finally determine the elastic modulus E and Poisson's modulus of the multilayer composite plate. than μ.

From the mechanics of materials, Poisson's ratio calculation formula:

The steps of the iterative process are described as follows:

(1) When the size, mass, first-order bending resonance frequency f _f and first-order shear resonance frequency f _t of the multi-layer composite material plate are measured, use the formula (3) to calculate the multi-layer composite material plate Shear modulus G (independent of Poisson's ratio).

(2) Calculate the elastic modulus E (related to Poisson's ratio) of the multilayer composite material plate by formula (1). The updated Poisson's ratio μ _n is calculated by using the relational formula (6) of the elastic modulus E, the shear modulus G and the Poisson's ratio μ.

(3) Pass the judgment standard To check whether the updated Poisson’s ratio μ _n meets the requirements, if the requirements are met, the mechanical parameters E, G and μ of the multilayer composite material plate are determined; if the updated Poisson’s ratio μ _n does not meet the requirements, then Taking μ _n as the Poisson’s ratio value of the next iteration process, repeat the iterative step (2) until the Poisson’s ratio μ _n that meets the requirements is obtained, and then determine the final mechanical parameters E, G and μ of the multilayer composite plate

From the above steps, it can be seen that in the first iteration, an original Poisson's ratio value μ ₀ (the range can be 0.23-0.35) should be assumed.

2. Acoustic testing method for structural mechanical parameters of multilayer composite materials Non-destructive testing method.

Fig. 4 is a flow chart of the detection method. The operation flow of the non-destructive testing method for elastic modulus and shear modulus of multi-layer composite material board:

First, as shown in Figure 2, for the state of bending vibration, the multi-layer composite material plate is suspended with elastic metal wires at a distance of 0.198L from both ends; for the state of shear vibration, at the midline of the length and width directions The multi-layer composite panels are suspended by elastic metal ropes. make it in a state of free vibration.

Then the hammer is used to excite the left end of the multi-layer composite material plate, and the sound pressure sensor is used to pick up the vibration signal of the multi-layer composite material plate at the right end (as shown in Figure 5(1) and Figure 6(1)), after signal conditioning amplifier, digital sampling, filtering and other processing, the digital signal is input to the computer, and the first-order bending resonance frequency f _f and the first-order shearing resonance frequency f _t are obtained through fast Fourier transform (as shown in Figure 5(2) and Figure 6 (2) shown);

Finally, the first-order bending resonance frequency f _f and the first-order shear resonance frequency f _t are substituted into the empirical formulas (1) and (3) to calculate the Elastic modulus E and shear modulus G.

The embodiment should not be regarded as limiting the present invention, and any improvement based on the spirit of the present invention should be within the protection scope of the present invention.

Claims (4)

1. a kind of multilayer materials structural mechanics parameter acoustic detection method, it is characterised in that：Its step is as follows：

1) model frequency calculating is carried out to simulating multilayer materials structure by limited element analysis technique, obtains first-order flexure and be total to Vibration frequency f_fResonant frequency f is sheared with the first rank_t, and to obtain data carry out process fitting, respectively obtain elastic modulus E and Relation between shear modulus G and the physical dimension and quality of multilayer materials structure, and obtain obtaining the Jing of mechanics parameter Test formula；

2) it is at 0.198L apart from both ends of the surface and has suspended multilayer materials structure in midair with elastic metal wire so as in freedom The state of vibration, and the left end excitation in multilayer materials structure is hammered into shape by power, and pick up many with sound pressure sensor in right-hand member The vibration signal of layer composite structure, and the first rank flexural resonance frequency f is obtained by fast Fourier transform_f；

3) midline in length and width direction has suspended multilayer materials structure in midair with elastic metallic rope so as in freedom The state of vibration, and the left end excitation in multilayer materials structure is hammered into shape by power, and pick up many with sound pressure sensor in right-hand member The vibration signal of layer composite structure, and the first rank shearing resonant frequency f is obtained by fast Fourier transform_t；

4) by the first rank flexural resonance frequency f_fResonant frequency f is sheared with the first rank_tWith the dimensioning of multilayer materials structure Very little, mass parameter, in the empirical equation in substituting into 1), obtains respectively elastic modulus E and shear modulus G.

2. a kind of multilayer materials structural mechanics parameter acoustic detection method according to claim 1, it is characterised in that 1) relational expression that elastic modulus E is obtained in is as follows：

$E=0.9658({\mathrm{mf}}_f^2/b)(L^3/t^3)T_1$

Wherein, m is the quality of multilayer materials structure, f_fIt is the first rank flexural resonance frequency,

T₁It is the correction coefficient under bending vibration, μ is the Poisson's ratio of material,

$T_1=1+7.158(1+0.0812\mathrm{\μ}+0.7905{\mathrm{\μ}}^2){(t/L)}^2-0.828{(t/L)}^4-\[\frac{8.450(1+0.2123\mathrm{\μ}+2.007{\mathrm{\μ}}^2){(L/t)}^4}{1.000+6.386(1+1.3125\mathrm{\μ}+1.637{\mathrm{\μ}}^2){(L/t)}^2}\].$

3. a kind of multilayer materials structural mechanics parameter acoustic detection method according to claim 1, it is characterised in that 1) relational expression that shear modulus G is obtained in is as follows：

$G=\frac{4{\mathrm{Lmf}}_t^2}{bt}\[B/(1+A)\]$

Wherein A and B be in shearing condition with regard to multilayer materials structure width b and the correction coefficient of thickness t,

$A=\[\frac{\[0.6008-0.8560(b/t)+0.2966{(b/t)}^2-0.0086{(b/t)}^3\]}{\[11.99(b/t)+9.892{(b/t)}^2\]}\]$

$B=\[\frac{b/t+t/b}{4.06(t/b)-2.86{(t/b)}^2+0.26{(t/b)}^6}\].$

4. according to a kind of multilayer materials structural mechanics parameter acoustic detection method according to claim 1, its feature It is that, when Poisson's ratio is unknown, the method for obtaining the value of each mechanics parameter of multilayer materials structure is as follows：

(1) size when multilayer plate made of composite material, quality and the first rank flexural resonance frequency f_fResonant frequency is sheared with the first rank f_tWhen being measured, utilizeObtain the shear modulus G of multilayer plate made of composite material.

(2) pass throughThe elastic modulus E of multilayer plate made of composite material is obtained, using elasticity The relation of modulus E, shear modulus G and Poisson's ratio μPoisson's ratio μ after being updated_n。

(3) by criterionTo check Poisson's ratio μ after updating_nWhether satisfaction is required, if meet will Ask, then mechanics parameter E, G and μ of multilayer plate made of composite material is just determined；If Poisson's ratio μ after updating_nIt is unsatisfactory for requiring, then By μ_nAs the Poisson ratio of next iteration process, repeat step (2), until being met Poisson's ratio μ of requirement_n, and then really Determine final mechanics parameter E, G and μ of multilayer plate made of composite material.