WO2018165999A1

WO2018165999A1 - Fiber reinforced composite material parameter identifying method based on laser nondestructive scanning, and device

Info

Publication number: WO2018165999A1
Application number: PCT/CN2017/078513
Authority: WO
Inventors: 李晖; 刘�东; 高宁; 王雨波; 薛鹏程; 闻邦椿
Original assignee: 东北大学
Priority date: 2017-03-16
Filing date: 2017-03-29
Publication date: 2018-09-20
Also published as: JP2020510837A; CN106950280A; CN106950280B; JP7109798B2

Abstract

The invention discloses a fiber reinforced composite material parameter identifying method based on laser nondestructive scanning. The method comprises the following steps: imputing first three order natural frequency, damping ratio and resonance amplitude curve, and setting an identification permissible error value to be 10%, so that fiber longitudinal elasticity modulus E 1, fiber transverse elasticity modulus E 2, shear modulus G 12, Poisson's ratio ν 21, fiber longitudinal loss factor η 22, fiber transverse loss factor η 22, and shear loss factor η 12 are obtained. Also provided is a device for implementing the method. The method combines vibration transmission with laser displacement sensing technology to achieve a one-time measurement of the mechanical properties of the test material in all directions, reducing the associated workload.

Description

Fiber reinforced composite material parameter identification method and device based on laser non-destructive scanning

Technical field

The invention relates to the field of machinery, in particular to a fiber reinforced composite material parameter identification method and device.

Background technique

Structural composites are widely used in aviation, aerospace, marine, sports equipment due to their high specific strength, high specific modulus, designability, thermal stability, and high bearing capacity and light weight. , electrical equipment, medicine, weapons industry and chemical industry. With the continuous improvement of the modern industrial level, many fiber reinforced composite thin-walled members, such as composite blades, composite whole leaf discs and composite cylindrical shells, often work in harsh environments such as high-speed rotation, high temperature, corrosive gas erosion, etc. The resulting vibration fatigue and vibration failure problems are becoming more and more prominent, making it impossible to perform the functions that people have previously envisaged.

When fiber-reinforced composite materials are used in industrial production, it is often required to have a clear understanding and understanding of the properties of various materials of such materials. However, due to the anisotropic characteristics of the composite, the fiber longitudinal elastic modulus, fiber transverse elastic modulus, shear modulus, Poisson's ratio and fiber longitudinal loss factor, fiber transverse loss factor and shear loss factor are measured. In the case of material parameters, most of the current industrial measurements are made by fatigue testers. This method has its limitations in many aspects: cost: it needs to destroy more material samples, causing a lot of waste in manpower and material resources; measuring means: high-strength stretching has special requirements on the stability of the instrument, and measurement The accuracy is difficult to guarantee, and the measurement results have large errors. In terms of safety: the material will break during the measurement process, and there is a big hidden danger in safety.

At present, the research on non-destructive testing of composite materials is not very deep, but some related researches have certain reference value. Patent CN201610166104.9 invented a new type of composite material parameter identification instrument. By changing the structure of the identification instrument, the identified parameters are more accurate. However, the principle is still to measure the composite material by traditional methods such as pressing, shearing and pulling. The parameters do not fundamentally solve the waste, there are certain security risks and other issues. The detection method of fiber reinforced composites needs to be improved, and the application of vibration and laser non-destructive scanning technology can solve the related problems well.

Summary of the invention

In view of the problems existing in the prior art, the present invention provides a fiber reinforced composite structural material parameter tester based on laser non-destructive scanning and a working method thereof. The specific technical solutions are as follows:

A method for identifying a fiber reinforced composite material based on laser non-destructive scanning includes the following steps:

Step 1: Open the vacuum casing, adjust the tightening screw, and install the test piece of the composite beam to be tested in the reference position of the clamping mechanism in sequence;

Step 2: Gradually adjust the pressure of the clamping mechanism by adjusting the tightening screw, according to the pressure output by the pressure sensor After the judgment, it is judged that the appropriate clamping force has been reached, and the adjustment is stopped;

Step 3: Adjust the lifting platform to a suitable position, tighten the vacuum casing; exhaust the gas inside the casing with an air extractor to create a vacuum environment;

Step 4: The position of the laser spot emitted by the laser vibrometer is moved by the laser scanning vibration measuring device to be in the free end position of the composite beam test piece to be tested; then, the excitation device is turned on, and the sine sweep is performed in a large frequency range. The frequency excitation test monitors the time domain waveform data of the frequency sweep excitation signal according to the acceleration sensor on the movable clamp body, and obtains the spectrum of the vibration response signal of the free end position of the composite beam test piece to be tested by the laser vibration meter, and passes the half power The bandwidth method identifies the frequency corresponding to each peak and the frequency of the half power point, thereby obtaining the first three natural frequencies and damping ratios of the composite beam specimen to be tested;

Step 5: Adjust the frequency of the excitation device to the first-order natural frequency, and the excitation composite beam test piece reaches the first-order resonance state, and the excitation amplitude corresponding to the first-order resonance state is determined by the acceleration sensor on the vibration platform; meanwhile, the laser is turned on. The control switch of the scanning vibration measuring device moves the position of the laser spot emitted by the laser vibrometer by the laser scanning vibration measuring device, and realizes the scanning test of the test piece of the composite beam from the cantilever end position to the free end position, and obtains the composite beam test to be tested. The amplitude of the vibration response signal at each scanning point position, and then the curve of the vibration amplitude of the composite beam specimen with the length of the first-order resonance state is plotted as a first-order resonance amplitude curve. The horizontal axis of the first-order resonance amplitude curve is the length, and the vertical axis is the vibration amplitude;

Step 6: adjusting the frequency of the excitation device to the second-order natural frequency and the third-order natural frequency, and illuminating the steps used in step 5 to obtain a second-order resonance amplitude curve and a third-order resonance amplitude curve;

Step 7: According to the parameter identification method of the fiber reinforced composite structural material, input the first three natural frequencies, the damping ratio and the resonance amplitude curve, and set the allowable value of the recognition error to 10% to obtain the longitudinal elastic modulus E ₁ of the fiber and the transverse elasticity of the fiber. The modulus E ₂ , the shear modulus G ₁₂ , the Poisson's ratio is ν ₂₁ and the fiber longitudinal loss factor η ₁₁ , the fiber transverse loss factor η ₂₂ and the shear loss factor η ₁₂ .

The invention further discloses a device for realizing the method, which is mainly composed of a double working platform, a lifting platform, a clamping mechanism, an excitation device, a laser scanning vibration measuring system and a vacuum device; the double working platform comprises a first working platform And the second working platform, the two platforms are supported by the "work" word supporting steel, and the bottom is supported by the base; the clamping mechanism is used for fixing and monitoring the composite beam test piece to be tested, including the reference platform and the upper pressing block thereof, The pressure block is driven by bolts to fix the composite beam test piece to be tested; two circular hole structures are arranged on the reference platform for placing the circular pressure sensing gasket of the pressure sensor, and quantitatively adjusting according to the value of the pressure sensor Acting on the pressure of the tested composite material, the quantitative characterization test of the constraint condition is realized; the excitation device consists of two parts: the vibration exciter and the vibration platform, the function of which is to generate the excitation force and transmit the vibration to the test piece of the tested composite beam; Connected to the signal source to generate a certain frequency of vibration, vibration through the vibration platform And the clamping mechanism is transmitted to the test piece of the beam to be tested; in order to realize the monitoring of the state of the excitation vibration, an acceleration sensor is arranged on the upper part of the clamping mechanism for measuring the magnitude of the vibration amplitude; the vibration exciter is fixed to the first work by bolt connection On the platform, the excitation force is generated and applied to the vibration platform; under the excitation platform, there are four shock-absorbing screws evenly distributed at the four corners, and the shock-absorbing spring can be inserted into the shock-absorbing screw to realize the second work. The platforms are connected, and only the displacement in the direction of the spring axis can be generated between the two;

The laser scanning vibration measuring system comprises a laser scanning vibrometer, a lead screw, a coupling and an electric motor; the platform carrying the laser scanning vibrometer is penetrated by a set of lead screws, and the lead screw is connected with the coupling to form a transmission mechanism; Under the power of the motor, the laser scanning vibrometer can realize the horizontal movement of the laser vibration measuring device through the transmission mechanism; the position of the laser spot emitted by the laser vibrometer can realize the test specimen of the composite beam from the cantilever at a certain scanning speed. The scanning test from the end position to the free end position obtains the amplitude of the vibration response signal of the composite beam test piece at each scanning measuring point position, and then draws a corresponding resonance amplitude curve; the laser scanning vibration measuring system is arranged on the lifting platform The adjustment of the position of the laser scanning vibrometer in the vertical direction can be realized, and the lifting frame of the lifting platform is fixed on the second working platform.

A vacuum device is arranged outside the tester, which is composed of a casing and a baffle; the baffle is tightly connected with the casing to prevent air from entering; and the baffle has a circular hole structure connected to the air pump to extract the gas inside the device, thereby creating Vacuum environment reduces experimental error.

An advantage of the present invention is that the present invention provides a fiber reinforced composite structural material parameter tester based on laser non-destructive scanning. Firstly, the parameter test method combining vibration transmission and laser displacement sensing technology was designed, which broke the traditional measurement mode by stretching and other physical methods, and achieved the goal of measuring the mechanical properties of the material to be tested in all directions at one time. The earth reduces the workload of related work; secondly, the instrument does not have any impact on the material during the whole process of testing, saves raw materials, reduces economic losses, and is more environmentally friendly; in addition, the external vacuum housing design makes The test process is carried out under vacuum, avoiding the influence of air damping, and the measurement result is more accurate. Finally, the work is easy to assemble and disassemble, and the quality of each component is not large, and can be loaded into the pull box for better portability. . The parameters of the composite materials can be measured at different locations according to actual conditions, which provides great convenience for production measurement.

DRAWINGS

1 is a front elevational view of a fiber reinforced composite structural material parameter tester according to an embodiment of the present invention;

2 is a top plan view of a fiber reinforced composite structural material parameter tester according to an embodiment of the present invention;

3 is a schematic structural diagram of a fiber reinforced composite structural material parameter tester according to an embodiment of the present invention;

Figure 4 is a theoretical model of the fiber reinforced composite beam specimen under the basic excitation of Figure 1;

Figure 5 is a theoretical and experimental obtained first-order resonance amplitude curve of the composite beam and its error upper and lower limits;

In the picture: 1-base, 2-second working platform, 3-"gong" word support steel, 4-first working platform, 5-vibration platform, 6-damper spring, 7-baffle, 8-clamping mechanism, 9-acceleration sensor, 10-screw, 11-laser scanning vibrometer, 12-shell, 13-slider, 14-lift platform, 15-beam specimen to be tested, 16-vibrator, 17-coupling, 18-motor, 19-retractable platform, 20-venting, 21-reference platform.

detailed description

The invention will be specifically described below with reference to the accompanying drawings.

1. Tester hardware structure design

As shown in FIG. 1 to FIG. 5, the device of the present invention mainly comprises a double working platform, a lifting platform, a clamping mechanism, an excitation device, a laser scanning vibration measuring system and a vacuum device;

The compound working platform comprises a first working platform 4 and a second working platform 2, wherein the two platforms are connected by the "work" word supporting steel 3, and the lower part is supported by the base 1; the clamping mechanism 8 is used for fixing and monitoring the composite beam test piece to be tested 15, comprising a reference platform 17 and an upper pressing block 18, the pressing block is driven by a bolt to press the composite beam test piece to be tested;

The upper surface of the reference platform 17 is provided with two circular hole structures for placing a circular pressure sensing gasket of the pressure sensor, and quantitatively adjusting the pressure acting on the composite material according to the value of the pressure sensor to realize quantitative characterization of the constraint condition. test.

The excitation device is composed of two parts, the vibration exciter 16 and the vibration platform 5, and the function is to generate an excitation force and transmit vibration to the test piece of the composite beam to be tested; the vibration exciter is connected with the signal source to generate vibration of a certain frequency, and the vibration passes through the vibration. The platform 5 and the clamping mechanism 8 are transmitted to the beam test piece 15 to be tested; in order to realize the monitoring of the excitation vibration state, an acceleration sensor 9 is mounted on the upper portion of the clamping mechanism 8 for measuring the magnitude of the vibration amplitude. The vibration exciter 16 is fixed to the first working platform 4 by bolt connection for generating an excitation force and applying it to the vibration platform 5; under the excitation platform 5, there are four shock-absorbing screws uniformly distributed at the four corners, The shock spring 6 can be inserted into the shock absorbing screw to be connected with the second working platform 2, and only the displacement in the direction of the spring axis can be generated between the two.

The laser scanning vibration measuring system includes a laser scanning vibrometer 11, a lead screw 10, a coupling, and an electric motor. The platform carrying the laser scanning vibrometer is penetrated by a set of lead screws, and the lead screw is connected with the coupling to form a transmission mechanism; under the power of the motor, the laser scanning vibrometer can realize the horizontal direction of the laser vibration measuring device through the transmission mechanism. exercise. The laser spot position of the laser vibrometer is used to scan the test specimen from the cantilever end position to the free end position at a certain scanning speed, and obtain the position of the composite beam test piece to be tested at each scanning point. The vibration responds to the amplitude of the signal, which in turn plots the corresponding resonance amplitude curve. The laser scanning vibration measuring system is disposed on the lifting platform 14 to adjust the position of the laser scanning vibrometer in the vertical direction. The lifting platform of the lifting platform 14 is fixed on the second working platform 2, and the two cross-hinged Supporting beams, one fixed on the working platform 2, the other one is connected with the sliding block 13, and the sliding block is connected with the motor through the screw; under the driving of the motor, the screw drives the sliding block 13 to slide on the working platform to drive the lifting The platform moves up and down;

A vacuum device is provided on the outside of the tester, which is composed of a casing and a baffle. The baffle can be tightly connected to the casing to prevent air from entering; the baffle has a circular hole structure that can be connected to the air pump to extract gas from the device, create a vacuum environment, and reduce experimental errors.

2. The fiber reinforced composite structural material parameter identification method is:

2.1 The inherent characteristics of the fiber reinforced composite beam specimen and the vibration response under the fundamental excitation;

The composite beam specimen is composed of n layers of fibers with orthogonal anisotropy characteristics and matrix materials; assuming that the layers are firmly bonded, there is no slip between the layers, no relative displacement, solid can be ignored The effect of the interlayer coupling effect; first, the midplane is used as the reference plane, and the xoy coordinate system is established; the angle between the fiber direction and the x-axis direction of the global coordinate system is θ, the plate length is a, the plate width is b, and the plate thickness is For h, each layer is located between the lower surface h _k-1 of the z coordinate axis and the higher surface h _k , and the thickness of each layer is the same; 1 in the figure represents the longitudinal direction of the fiber, 2 represents the transverse direction of the fiber, and 3 represents the vertical direction. 1-2 plane direction;

It is assumed that the composite beam specimen is affected by the base excitation load, and the motion expression of the base excitation is y(t)=Ye ^iωt (1)

i represents a virtual unit

t indicates time

Where Y is the excitation amplitude and ω is the excitation frequency;

Considering the influence of the fiber direction, the elastic modulus of the composite material is expressed as follows

among them,

Relating to the parallel fiber direction and the direction of the vertical fiber, respectively,

Representing the complex shear modulus in plane 1-2, the complex elastic modulus of E' ₁ , E' ₂ and G' ₁₂ respectively

And complex shear modulus

The real part of the stress; and the Poisson's ratio of the strain in the direction of 1 and 2 is ν ₁₂ , and the Poisson's ratio of the strain in the direction of 2 and 2 is ν ₂₁ ;

The Poisson's ratio of the directional strain is ν ₂₁ ;

Based on the classical laminate theory, the displacement field of the fiber reinforced composite beam specimen can be written as follows

w(x,y,z,t)=w ₀ (x,y,t)

Where z represents the displacement in the z-axis direction; u, v, w represents the displacement of any point in the plate; u ₀ , v ₀ , w ₀ represents the surface displacement of the plate; h is the thickness of the composite beam test piece; t represents time;

Since it is a symmetrical laminate, there is no coupling between in-plane vibration and lateral vibration. Therefore, it is only necessary to consider the lateral vibration of the thin plate, that is, ignore the mid-surface displacements u ₀ and v ₀ ; according to the assumption of the classical laminate theory, the positive strain ε _z and The shear strains γ _yz and γ _xz are all 0, that is, ε _z = γ _yz = γ _xz =0. From the relationship between strain and displacement, the strain at any point in the plate can be expressed as

ε _x represents the positive strain of the point in the x direction

ε _y represents the positive strain of the point in the y direction

ε _xy indicates the shear strain of the point on the xy plane

The bending curvature and the twist rate of the middle surface of the thin plate can be expressed as

k _x represents the flexural curvature of the point in the x direction

k _y represents the flexural curvature of the point in the y direction

k _xy represents the distortion rate of the point on the xy plane

which is

ε _x = zκ _x , ε _y = zκ _y , γ _xy = zκ _xy

For orthotropic materials, the stress-strain relationship in the direction of the major axis of the material is

1 indicates the longitudinal direction of the fiber, 2 indicates the transverse direction of the fiber, 6 indicates the direction of the vertical plate surface, and Q* indicates the elastic modulus.

among them,

When there is a certain angle θ between the main axis direction of the material and the global coordinate system, the stress-strain relationship of the k-th layer in the global coordinate system is calculated by the stress-strain rotation formula.

among them,

Where _k represents the k-th layer of the composite beam test piece, and θ _k represents the angle between the fiber direction of the k-th layer plate and the x-axis of the global coordinate system;

The bending moment and torque of the thin plate are

M _x represents the bending moment in the x-axis direction

M _y represents the bending moment in the y-axis direction

M _xy represents the torque on the xy plane

D* represents the bending stiffness coefficient

among them,

In order to facilitate the theoretical analysis and modeling, the basic excitation of the composite beam specimen is equivalent to the uniform inertial force external load.

Y represents the displacement amplitude of the base excitation

The kinetic energy of the vibration of the thin plate can be expressed by the following formula

Where ρ is the density of the thin plate and h is the thickness of the thin plate;

The strain energy stored in the bending of the thin plate is expressed by the following formula

The uniform inertial force of the thin plate is

W _q= ∫∫ _R q(t)w ₀ dxdy (13)

It is assumed that the vibration displacement of the lateral vibration of the thin plate can be expressed as

w ₀ (x,y,t)=e ^iωt W(ξ,η) (14)

Where ω is the circular frequency of the vibration of the thin plate, and the excitation frequency is the same, W _ij (ξ, η) is a vibration mode function, and has the following form

Where a _ij is a pending coefficient, p _i (ξ) (i=1, . . . , M) and q _j (η) (j=1, . . . , N) are a series of orthogonal polynomials;

Obtain a series of orthogonal polynomials by orthogonalizing the polynomial functions that satisfy the boundary conditions

P ₁ (ξ)=χ(ξ), P ₁ (η)=κ(η)

P ₂ (ζ)=(ζ-B ₂ )P ₁ (ζ)

P _k (ζ)=(ζ-B _k )P _k-1 (ζ)-C _k P _k-2 (ζ)

ζ=ξ,η,k>2 (16)

Where B _k and C _k are coefficient functions, and their expressions are respectively

Where W(ζ) is a weight function, usually taking W(ζ)=1; and χ(ξ) and κ(η) are polynomial functions satisfying the boundary conditions of solid support, simply supported, free, etc., and have the following form

χ(ξ)=ξ ^p (1-ξ) ^q , κ(η)=η ^r (1-η) ^s

ξ=x/a, η=y/b (18)

Since it is a cantilever boundary condition, take p=2, r=0, q=0, s=0; substituting formula (15) into equations (11), (12) and (13), the composite beam specimen can be obtained. The maximum kinetic energy T _max , the maximum strain energy U _max and the uniform inertial force work maximum value W _{qmax of the} vibration are respectively

W _qmax =ρhYω ² ∫∫ _R Wdxdy (21)

The expression defining the Lagrangian energy function L is

L=T _max +W _qmax -U _max (22)

By making the energy function L the partial derivative of the coefficient a _ij to be equal to zero, ie

M×N non-homogeneous linear algebraic equations can be obtained. For the convenience of solving, write it as a matrix form.

(K+iC-ω ² M)a=F (24)

Where K, C and M are structural stiffness matrix, material damping matrix and structural mass matrix, respectively, generalized displacement vector a = (a ₁₁ , a ₁₂ , ... a _ij ) ^T , F is the excitation force vector;

For the free vibration problem of composite beam specimens, it is only necessary to make the material damping matrix C and the excitation force vector F zero, ie

(K-ω ² M)a=0 (25)

From the formula (25), the natural frequency and mode shape of the composite beam specimen can be obtained; further, it is assumed that the fiber reinforced composite beam specimen is subjected to the basic excitation load and the vibration response λ (x, y) is solved under the fundamental excitation. , t) expression; taking into account the experimental test to obtain the absolute vibration response of the composite beam specimen, that is, including the sum of its own vibration response and the base excitation displacement; therefore, the vibration response of the composite beam specimen under the foundation excitation λ(x, y, t) is expressed as

λ(x,y,t)=y(t)+w ₀ (x,y,t) (26)

Equation (26) gives the expression of the vibration response of the fiber reinforced composite beam specimen under the basic excitation. In the case of clarifying the basic excitation expression (1) and the thin plate vibration response expression (14), the composite can be calculated. The vibration response of the beam test piece at any point;

2.2 Based on the first three natural frequencies and damping test results, preliminary calculation of composite parameters

First, the average value of the material parameters provided by the manufacturer

For the center, consider R _err = 10% ~ 20% error, give the range of material parameters as follows

Select the appropriate step size material parameter vector E ₁ , E ₂ , G ₁₂ , ν ₁₂ within the range of values of each material parameter. The specific expression is

Based on the theoretical and experimental natural frequencies, respectively, the frequency relative error function e _{fre is} constructed based on the least squares method:

Where R is the modal order, Δf _i is the theoretically calculated ith order natural frequency and the experimentally obtained ith order natural frequency difference,

The i-th order natural frequency obtained for the experimental test;

The material parameters are iterated in a manner of arrangement and combination. When the least squares relative error function e _{fre takes} a minimum value, the material parameters E ₁ , E ₂ , G ₁₂ , ν _{12 are} obtained by preliminary calculation;

Then, the relationship between the damping ratio and the loss factor can be used to obtain the modal loss factor η _r

η _r =2ζ _r (42)

Where ζ _r is the modal damping ratio obtained by the experiment;

According to the modal strain energy method, the strain energies U ₁ , U ₂ and U _{12 of the} fiber longitudinal direction, the fiber transverse direction and the shear direction are respectively

The modal loss factor and the loss factor in all directions of the fiber have the following relationship

Where U is the total strain energy of the composite beam test piece;

It can be known from equation (44) that as long as the results of the third-order modal damping ratio of the composite beam specimen are obtained experimentally, the loss factors η ₁ , η ₂ and η _{12 of the} fiber longitudinal direction, the fiber transverse direction and the shear direction can be initially determined;

In this way, seven material parameters such as E ₁ , E ₂ , G ₁₂ , ν ₁₂ η ₁ , η ₂ and η ₁₂ can be obtained by preliminary calculation of the first three natural frequencies and damping test results;

2.3 Based on laser non-destructive scanning experimental data to accurately identify composite parameters

Firstly, the first three natural frequencies and damping ratios of the composite beam specimens are obtained through experimental tests, and the composite beam specimens are excited to reach the resonance state by the above-mentioned natural frequencies, and then the first three-order resonance amplitudes of the composite beams are obtained by laser non-destructive scanning experiments. Curve; then, preliminary determination of fiber longitudinal elastic modulus E ₁ , fiber transverse elastic modulus E ₂ , shear modulus G ₁₂ , Poisson's ratio ν ₁₂ , fiber longitudinal loss factor η ₁ , fiber transverse loss factor η ₂ and Based on the shear loss factor η ₁₂ , consider a smaller error range (for example, 10%), construct the material parameter vector in a smaller step size, and iterate the parameters in a permutation and combination manner. A set of resonance amplitude curves corresponding to a set of first three natural frequencies is obtained by theoretical calculation;

Finally, compare the resonance amplitude curve corresponding to the first three natural frequencies obtained by a theoretical calculation with the test obtained before The deviation of the third-order resonance amplitude curve; taking the first-order resonance amplitude curve as an example, when the theoretically calculated curve is within the range of the upper and lower error curves, the material parameters are considered to be accurate, and the material used at this time is used. The parameter is the final material parameter obtained by the identification.

The identification process includes:

(1) Solving the inherent characteristics and vibration response of fiber reinforced composite beam specimens

Firstly, based on the classical laminated plate theory, the theoretical model of the fiber reinforced composite beam specimen is established, and its material parameters are expressed in the form of complex modulus. Then, the inherent characteristics and basic excitation of the composite beam specimen are solved based on the Ritz energy method. The vibration response of the lower composite beam specimen;

(2) Test the first three natural frequencies and damping ratios of the composite beam specimens

The position of the laser spot emitted by the laser vibrometer is moved by the laser scanning vibration measuring device to be at the free end position of the test piece of the composite beam to be tested; then, the excitation device is turned on, and the sine sweep excitation is performed in a large frequency range. Test, monitor the time domain waveform data of the sweep excitation signal according to the acceleration sensor on the vibration platform, and obtain the spectrum of the vibration response signal of the free end position of the test specimen to be tested by the laser vibration measuring instrument, and pass the half power bandwidth The method identifies the frequency corresponding to each peak and the frequency of the half power point, thereby obtaining the first three natural frequencies and damping ratios of the composite beam specimen to be tested;

(3) Preliminary calculation of composite parameters

Firstly, the material parameter vector is constructed with the mean value of the material parameters provided by the manufacturer, and the material parameters are iterated in a way of arrangement and combination. The relative error function of the i-th natural frequency obtained by theoretical calculation and the experimentally obtained i-th natural frequency is obtained. When taking the minimum value, the longitudinal elastic modulus E ₁ , the transverse elastic modulus E ₂ , the shear modulus G ₁₂ and the Poisson's ratio ν _{12 of the} fiber can be preliminarily calculated. Then, based on the modal strain energy method, the experiment is obtained. The results of the third-order modal loss factor of the composite beam specimen were calculated, and the longitudinal loss factor η ₁ , the transverse loss factor η ₂ and the shear loss factor η _{12 were} calculated.

(4) Through the laser non-destructive scanning experiment, the first three-order resonance amplitude curve of the composite beam is obtained by accurate test, and the frequency of the excitation device is adjusted to the first-order natural frequency, and the test beam of the composite beam is excited to reach the first-order resonance state, and the vibration is passed. The acceleration sensor on the platform determines the excitation amplitude corresponding to the first-order resonance state; at the same time, the control switch of the laser scanning vibration measuring device is turned on, and the position of the laser spot emitted by the laser vibrometer is moved by the laser scanning vibration measuring device at a certain scanning speed. To realize the scanning test of the test piece of the composite beam from the cantilever end position to the free end position, obtain the amplitude of the vibration response signal of the test piece of the composite beam to be tested at each scanning point, and then draw the first-order resonance amplitude curve. Repeating this step, the second-order resonance amplitude curve and the third-order resonance amplitude curve are sequentially obtained;

(5) Accurate identification of composite parameters

Centering on the material parameters initially obtained in step 3, consider a smaller error range (eg 10%) to be smaller The step size constructs the material parameter vector and iterates the parameters in a permutation and combination manner. Each iteration, a set of resonance amplitude curves corresponding to the first three natural frequencies can be obtained by theoretical calculation; then, a theoretical calculation is obtained. The deviation between the resonance amplitude curve corresponding to the first three natural frequencies and the first three-order resonance amplitude curve obtained by the test; when the theoretically calculated curve is within the range of the upper and lower limits of the error, the above material parameters are considered to be accurate. The material parameters used at the time are the final material parameters obtained by the identification.

Claims

A fiber reinforced composite material parameter identification method based on laser non-destructive scanning, characterized in that the method comprises the following steps:

Step 1: Open the vacuum casing, adjust the tightening screw, and install the test piece of the composite beam to be tested in the reference position of the clamping mechanism in sequence;

Step 2: gradually adjust the pressure of the clamping mechanism by adjusting the tightening screw, and according to the pressure indication outputted by the pressure sensor, judge that the appropriate clamping force has been reached, and then stop the adjustment;

Step 3: Adjust the lifting platform to a suitable position, tighten the vacuum casing; exhaust the gas inside the casing with an air extractor to create a vacuum environment;

Step 4: The position of the laser spot emitted by the laser vibrometer is moved by the laser scanning vibration measuring device to be in the free end position of the composite beam test piece to be tested; then, the excitation device is turned on, and the sine sweep is performed in a large frequency range. The frequency excitation test monitors the time domain waveform data of the frequency sweep excitation signal according to the acceleration sensor on the movable clamp body, and obtains the spectrum of the vibration response signal of the free end position of the composite beam test piece to be tested by the laser vibration meter, and passes the half power The bandwidth method identifies the frequency corresponding to each peak and the frequency of the half power point, thereby obtaining the first three natural frequencies and damping ratios of the composite beam specimen to be tested;

Step 5: Adjust the frequency of the excitation device to the first-order natural frequency, and the excitation composite beam test piece reaches the first-order resonance state, and the excitation amplitude corresponding to the first-order resonance state is determined by the acceleration sensor on the vibration platform; meanwhile, the laser is turned on. The control switch of the scanning vibration measuring device moves the position of the laser spot emitted by the laser vibrometer by the laser scanning vibration measuring device, and realizes the scanning test of the test piece of the composite beam from the cantilever end position to the free end position, and obtains the composite beam test to be tested. The amplitude of the vibration response signal at each scanning point position, and then the curve of the vibration amplitude of the composite beam specimen with the length of the first-order resonance state is plotted as a first-order resonance amplitude curve. The horizontal axis of the first-order resonance amplitude curve is the length, and the vertical axis is the vibration amplitude;

Step 6: adjusting the frequency of the excitation device to the second-order natural frequency and the third-order natural frequency, and illuminating the steps used in step 5 to obtain a second-order resonance amplitude curve and a third-order resonance amplitude curve;

Step 7: According to the parameter identification method of the fiber reinforced composite structural material, input the first three natural frequencies, the damping ratio and the resonance amplitude curve, and set the allowable value of the recognition error to 10% to obtain the longitudinal elastic modulus E 1 of the fiber and the transverse elasticity of the fiber. The modulus E 2 , the shear modulus G 12 , the Poisson's ratio is ν 21 and the fiber longitudinal loss factor η 11 , the fiber transverse loss factor η 22 and the shear loss factor η 12 .
An apparatus for implementing the method of claim 1 is characterized in that: mainly consists of a duplex working platform, a lifting platform, a clamping mechanism, an excitation device, a laser scanning vibration measuring system and a vacuum device; the duplex working platform includes the first Working platform and second working platform, the two platforms are supported by the word "work" and the bottom is supported by the base; the clamping mechanism It is used for fixing and monitoring the test piece of the composite beam to be tested, including the reference platform and the upper part of the pressure block, the pressure block is driven by the bolt, and the test piece of the composite beam to be tested is fixed; two circular holes are arranged on the reference platform. Structure, a circular pressure sensing gasket for placing a pressure sensor, quantitatively adjusting the pressure acting on the composite material to be tested according to the value of the pressure sensor, and realizing a quantitative characterization test of the constraint condition; the excitation device is composed of a vibration exciter and vibration The platform is composed of two parts, the function of which is to generate excitation force and transmit vibration to the test piece of the composite beam to be tested; the vibration exciter is connected with the signal source to generate vibration of a certain frequency, and the vibration is transmitted to the beam to be tested through the vibration platform and the clamping mechanism. In order to realize the monitoring of the excitation vibration state, an acceleration sensor is arranged on the upper part of the clamping mechanism for measuring the magnitude of the vibration amplitude; the vibration exciter is fixed on the first working platform by bolt connection for generating the excitation force, and Apply it to the vibration platform; there are four shock-absorbing screws evenly distributed at the four corners under the excitation platform, and the shock-absorbing spring can be inserted into the shock-absorbing screw to realize Working platform is connected between the spring can only be displaced in the axial direction;

The laser scanning vibration measuring system comprises a laser scanning vibrometer, a lead screw, a coupling and an electric motor; the platform carrying the laser scanning vibrometer is penetrated by a set of lead screws, and the lead screw is connected with the coupling to form a transmission mechanism; Under the power of the motor, the laser scanning vibrometer can realize the horizontal movement of the laser vibration measuring device through the transmission mechanism; the position of the laser spot emitted by the laser vibrometer can realize the test specimen of the composite beam from the cantilever at a certain scanning speed. The scanning test from the end position to the free end position obtains the amplitude of the vibration response signal of the composite beam test piece at each scanning measuring point position, and then draws a corresponding resonance amplitude curve; the laser scanning vibration measuring system is arranged on the lifting platform The adjustment of the position of the laser scanning vibrometer in the vertical direction can be realized, and the lifting frame of the lifting platform is fixed on the second working platform.
The device according to claim 1, wherein a vacuum device is disposed outside the tester, and is composed of a casing and a baffle; the baffle is tightly connected to the casing to prevent air from entering; and the baffle has a circular hole. The structure is connected to the air pump to extract the gas inside the device, creating a vacuum environment and reducing experimental errors.