Method for calculating ultrasonic stress coupling parameters of material

Abstract

The invention belongs to the field of ultrasonic non-destructive testing, and particularly relates to an ultrasonic stress coupling parameter calculation method which comprises the steps of establishing a critical refraction longitudinal wave velocity analytical equation of a to-be-tested material, carrying out stretching and ultrasonic testing experiments, and obtaining the critical refraction longitudinal wave velocity of the material. Carrying out nonlinear fitting by utilizing an L-M nonlinear fitting algorithm to obtain equivalent engineering constants and equivalent elastic coefficients of the to-be-tested material in different tensile stress directions, and finally generating an ultrasonic stress coupling parameter data set of the to-be-tested material; the method can solve the problem that key parameters of an ultrasonic stress coupling field cannot be obtained, is suitable for ultrasonic stress coupling simulation of structures such as alloys and composite materials with anisotropic mechanical properties, and greatly improves the accuracy, applicability and consistency of simulation calculation results of wave velocity changes of ultrasonic critical refraction longitudinal waves caused by stress.

Description

Technical Field

[0001] The present invention belongs to the field of ultrasonic non-destructive testing, and particularly relates to a method for calculating ultrasonic stress coupling parameters. Background Art

[0002] With the continuous popularization and wide application of new materials, anisotropic materials with excellent performance are gradually used in industrial equipment fields such as aviation, new energy equipment, and automobiles. Stress widely exists in mechanical parts. At present, the detection and evaluation of structural stress are roughly divided into two methods: destructive testing and non-destructive testing. The non-destructive testing method does not affect the mechanical properties of materials and structures and has been widely used for the reliability verification of parts and the structural safety assessment. In the existing stress detection technologies, ultrasonic non-destructive testing has strong reliability and wide applicability. Among them, the acoustic time difference stress detection method has become mature. Based on the characteristics that the critical refraction longitudinal wave velocity is highly sensitive to stress, it is widely used in the stress detection field.

[0003] In the prior art, the ultrasonic stress coupling parameters of anisotropic materials depend on the mechanical parameters of the material itself, including material density, engineering constants, and elastic coefficients, etc. However, under stress-induced conditions, the method for obtaining ultrasonic stress coupling parameters is still unclear, especially the coupling parameters of anisotropic materials cannot be accurately obtained. Summary of the Invention

[0004] In order to solve the problem that the ultrasonic stress coupling parameters of anisotropic materials cannot be accurately obtained in the prior art, a method for calculating the ultrasonic stress coupling parameters of materials is proposed;

[0005] A method for calculating the ultrasonic stress coupling parameters of materials includes:

[0006] Step 1: Obtain the engineering constants of the material to be tested, and establish an analytical equation for the critical refraction longitudinal wave velocity of the material to be tested according to the obtained engineering constants; set the tensile stress direction and multiple ultrasonic detection directions of the material to be tested;

[0007] Step 2: Measure the ultrasonic pulse flight time in different ultrasonic detection directions under the tensile stress direction by an ultrasonic time measurement device, and calculate the critical refraction longitudinal wave velocity corresponding to each ultrasonic detection direction according to the ultrasonic pulse flight time;

[0008] Step 3: Obtain the equivalent engineering constants in the tensile stress direction of the material to be tested through the L-M nonlinear fitting algorithm according to the multiple ultrasonic detection directions and the calculated corresponding critical refraction longitudinal wave velocities; the fitting objective function of the L-M nonlinear fitting algorithm is the analytical equation for the critical refraction longitudinal wave velocity of the material to be tested; calculate the equivalent elastic coefficients according to the obtained equivalent engineering constants through the calculation relationship between the equivalent engineering constants and the elastic coefficients;

[0009] Step 4: Change the set tensile stress direction of the material to be measured, and repeat Steps 2 to 3 to obtain the equivalent engineering constants and equivalent elastic coefficients of the material to be measured under different tensile stress directions. Generate an ultrasonic stress coupling parameter dataset of the material to be measured based on the obtained equivalent engineering constants and equivalent elastic coefficients of the material to be measured under different tensile stress directions.

[0010] Advantages of the present invention: A method for calculating ultrasonic stress coupling parameters of a material according to the present invention establishes an analytical equation for the critical refraction longitudinal wave velocity of the material to be measured based on the photoelasticity and equivalent stiffness principles, conducts tensile and ultrasonic detection experiments to obtain the critical refraction longitudinal wave velocity of the material, and uses the L-M nonlinear fitting algorithm to perform nonlinear fitting to obtain the equivalent engineering constants and equivalent elastic coefficients of the material to be measured under different tensile stress directions, and finally generates an ultrasonic stress coupling parameter dataset of the material to be measured; this method can solve the problem of inability to obtain key parameters of the ultrasonic stress coupling field; this method is widely applicable to ultrasonic stress coupling simulations of structures such as alloys and composite materials with anisotropic mechanical properties, greatly improving the accuracy, applicability, and consistency of the simulation calculation results of the change in the ultrasonic critical refraction longitudinal wave velocity caused by stress, and can be widely used in non-destructive testing and reliability assessment of structural stresses in fields such as aerospace, power equipment manufacturing, and new energy equipment manufacturing. Description of the Drawings

[0011] Figure 1 It is a flowchart of a method for calculating ultrasonic stress coupling parameters of a material in a specific embodiment of the present application;

[0012] Figure 2 It is a schematic diagram of the tensile stress direction, ultrasonic detection direction, and specimen main direction in a specific embodiment of the present application;

[0013] Figure 3 It is a structural diagram of an ultrasonic time measurement device in a specific embodiment of the present application;

[0014] Figure 4 It is a structural diagram of a variable angle acoustic wedge in a specific embodiment of the present application;

[0015] Figure 5 It is a diagram of the non-linear fitting result of the wave velocity of a unidirectional ply and the measured result of the actual critical refraction longitudinal wave velocity in a specific embodiment of the present application;

[0016] Figure 6 It is a diagram of the non-linear fitting result of the wave velocity of an orthogonal ply and the measured result of the actual critical refraction longitudinal wave velocity in a specific embodiment of the present application;

[0017] Figure 7 It is a simulation modeling diagram of an ultrasonic stress simulation experiment in a specific embodiment of the present application;

[0018] Figure 8The ultrasonic stress simulation experiment ultrasonic wave position change diagram with time for the specific implementation mode of this application;

[0019] Figure 9 The time-domain offset of the critically refracted longitudinal wave waveform with the equivalent stress for the specific implementation mode of this application;

[0020] Figure 10 The ultrasonic equivalent stress simulation result with θ1 = 0° and ω1 = 0° for the specific implementation mode of this application;

[0021] Figure 11 The ultrasonic equivalent stress simulation result with θ2 = 45° and ω2 = 0° for the specific implementation mode of this application. Specific implementation mode

[0022] Specific implementation mode one: Next, in combination with the appended drawings in the embodiments of the present invention Figure 1 to appended drawing Figure 11 , this implementation mode will be described, and the technical solutions in the embodiments of the present invention will be clearly and completely described:

[0023] A method for calculating ultrasonic stress coupling parameters of a material, including:

[0024] Step one: Obtain the engineering constants of the material to be measured, and establish an analytical equation for the critically refracted longitudinal wave velocity of the material to be measured according to the obtained engineering constants; set the tensile stress direction and multiple ultrasonic detection directions of the material to be measured;

[0025] Step two: Measure the ultrasonic pulse flight time in different ultrasonic detection directions under the tensile stress direction through an ultrasonic time measurement device, and calculate the critically refracted longitudinal wave velocity corresponding to each ultrasonic detection direction according to the ultrasonic pulse flight time;

[0026] Step three: Obtain the equivalent engineering constants in the tensile stress direction of the material to be measured through the L-M nonlinear fitting algorithm according to the multiple ultrasonic detection directions and the calculated corresponding critically refracted longitudinal wave velocities; the fitting objective function of the L-M nonlinear fitting algorithm is the analytical equation for the critically refracted longitudinal wave velocity of the material to be measured; calculate the equivalent elastic coefficients according to the obtained equivalent engineering constants through the calculation relationship between the equivalent engineering constants and the elastic coefficients;

[0027] Step four: Change the set tensile stress direction of the material to be measured, and repeat steps two to three to obtain the equivalent engineering constants and equivalent elastic coefficients in different tensile stress directions of the material to be measured, and generate an ultrasonic stress coupling parameter data set for the material to be measured according to the obtained equivalent engineering constants and equivalent elastic coefficients in different tensile stress directions of the material to be measured.

[0028] Specifically, the engineering constant matrix [C] of the material is expressed as

[0029]

[0030] If a material has two planes of elastic symmetry and the two planes are orthogonal, the material is called an orthotropic material. In the engineering constant matrix of an orthotropic material, C 14 , C 15 , C 16 , C 24 , C 25 , C 26 , C 34 , C 35 , C 36 , C 41 , C 42 , C 43 , C 45 , C 46 , C 51 , C 52 , C 53 , C 54 , C 56 , C 61 , C 62 , C 63 , C 64 and C 65 are all zero, and C 12 = C 21 , C 13 = C 31 , C 23 = C 32 . Therefore, the engineering constant matrix of an orthotropic material contains a total of nine elements; based on the acoustoelasticity and equivalent stiffness principle, an analytical equation for the critical refraction longitudinal wave velocity of the material to be measured is established according to some elements in the engineering constant matrix of the orthotropic material;

[0031] Set the tensile stress direction and the ultrasonic detection direction, and conduct tensile and ultrasonic detection experiments. Use an ultrasonic time measurement device to measure the ultrasonic pulse flight time and further calculate the critical refraction longitudinal wave velocity in each ultrasonic detection direction;

[0032] Use the Levenberg - Marquardt (L - M) nonlinear fitting algorithm. Take the analytical equation of the critical refraction longitudinal wave velocity of the material as the fitting objective function. Set the step size δ, damping μ, and convergence condition s of the nonlinear fitting. Substitute the critical refraction longitudinal wave velocity measured in each ultrasonic detection direction in the ultrasonic detection experiment into the target value of the fitting function, and perform iterative calculations until the convergence condition is reached to obtain the equivalent engineering constants of the material in the tensile stress direction. According to the relationship between the engineering constants and the elastic coefficients, calculate the equivalent elastic coefficients of the material;

[0033] Change the direction of the tensile stress, repeat the tensile and ultrasonic detection tests, obtain the equivalent engineering constants of the material in different tensile stress directions, and calculate the equivalent elastic coefficients of the material in different tensile stress directions; finally, obtain the ultrasonic stress coupling parameter dataset of the material based on all the obtained equivalent engineering constants and equivalent elastic coefficients.

[0034] Furthermore, the engineering constants of the material to be measured include the first engineering constant, the second engineering constant, the third engineering constant, and the fourth engineering constant;

[0035] The method for establishing the analytical equation of the critical refraction longitudinal wave velocity of the material to be measured based on the obtained engineering constants includes: obtaining the engineering constants of the material to be measured, calculating the first algebraic parameter and the second algebraic parameter according to the engineering constants of the material to be measured, and establishing the analytical equation of the critical refraction longitudinal wave velocity of the material to be measured based on the first algebraic parameter and the second algebraic parameter.

[0036] Furthermore, the method for calculating the first algebraic parameter and the second algebraic parameter according to the engineering constants of the material to be measured is:

[0037] The first algebraic parameter:

[0038] H = C 11 cos 2 ω + C 22 sin 2 ω + C 66 ;

[0039] The second algebraic parameter:

[0040] K = (C 11 cos 2 ω + C 66 sin 2 ω) + (C 66 cos 2 ω + C 22 sin 2 ω) - (C 12 + C 66 ) 2 cos 2 ωsin 2 ω;

[0041] Where, C 11 is the first engineering constant, C 12 is the second engineering constant, C 22 is the third engineering constant, C 66 is the fourth engineering constant, and ω is the angle between the ultrasonic detection direction and the main direction of the material to be measured;

[0042] The method for establishing the analytical equation of the critical refraction longitudinal wave velocity of the material to be measured based on the first algebraic parameter and the second algebraic parameter is:

[0043]

[0044] Among them, v LCR is the critical refractive longitudinal wave velocity of the material to be tested, and ρ is the density of the material to be tested.

[0045] For an isotropic medium, the determinant can be simplified to the value of the speed of sound v T According to the linear equation, stress waves with the same polarization mode have the same sound speed in all directions.

[0046]

[0047] Where E is the Young's modulus of the isotropic material and λ is the Poisson's ratio.

[0048] Furthermore, a method for setting a tensile stress direction of a material to be tested and multiple ultrasonic testing directions of the material to be tested; measuring the ultrasonic pulse flight time in different ultrasonic testing directions under the set tensile stress direction of the material to be tested by an ultrasonic acoustic time measurement device, and calculating the critical refracted longitudinal wave velocity corresponding to each ultrasonic testing direction based on the ultrasonic pulse flight time includes:

[0049] Step 21: Set the tensile stress direction of the material to be tested; set the stress value σ = 0 and the stress step size to σ s , the maximum stress is σ z , iteration number i = 0;

[0050] Step 22: Use the ultrasonic acoustic time measurement device to measure the ultrasonic pulse flight time t corresponding to the current tensile stress direction and the current stress value in different ultrasonic detection directions, and calculate the critical refracted longitudinal wave velocity v corresponding to each ultrasonic detection direction based on the measured ultrasonic pulse flight time t LCR_ω , v LCR_ω =L / t, L is the ultrasonic pulse sound path;

[0051] Step 2 and 3: Determine whether the stress value σ is less than the maximum stress value σ z If yes, go to step 24, if no, end;

[0052] Step 24: Let the number of iterations i = i + 1 and the stress value σ = iσ s ; and go to step 22.

[0053] Specifically, if Figure 2 As shown, X0 is the main direction of the material to be tested, Y0 is perpendicular to X0, X0OY0 coordinates are the coordinate system of the main direction of the material to be tested, X is the ultrasonic testing direction, X σ is the direction of tensile stress, X σ The angle with X0 is θ; when stretched, at a certain stress value σ sTaking [[ID=]] as the step size, the step size of this method is a certain value in the middle of 1 / 10 to 1 / 20 of the elastic limit, detecting multiple ω directions, where ω is in the range of 0 to π / 2 (rad), and ω = 0 and ω = π / 2 correspond to Figure 3 experiments i and ii in

[0054] Furthermore, the method for obtaining the equivalent engineering constants of the tensile stress direction of the material to be measured through the L-M nonlinear fitting algorithm according to the multiple ultrasonic detection directions and the critical refraction longitudinal wave velocities corresponding to each ultrasonic detection direction respectively includes:

[0055] Taking the analytical equation of the critical refraction longitudinal wave velocity of the material to be measured as the fitting objective function of the L-M nonlinear fitting algorithm, inputting the angles between the multiple ultrasonic detection directions and the main direction of the material and the critical refraction longitudinal wave velocities corresponding to each ultrasonic detection direction into the L-M nonlinear fitting algorithm, and obtaining the equivalent engineering constants.

[0056] Furthermore, the equivalent engineering constants include the first equivalent engineering constant, the second equivalent engineering constant, the third equivalent engineering constant, and the fourth equivalent engineering constant;

[0057] The equivalent elastic coefficients include the first equivalent elastic coefficient, the second equivalent elastic coefficient, the third equivalent elastic coefficient, and the fourth equivalent elastic coefficient;

[0058] The calculation relationship between the equivalent engineering constants and the elastic coefficients includes:

[0059]

[0060] where Q 11 is the first equivalent engineering constant, Q 12 is the second equivalent engineering constant, Q 22 is the third equivalent engineering constant, Q 66 is the fourth equivalent engineering constant, M1 is the first equivalent elastic coefficient, M2 is the second equivalent elastic coefficient, U 12 is the third equivalent elastic coefficient, N 12 is the fourth equivalent elastic coefficient.

[0061] Specifically, using the Levenberg-Marquardt method (abbreviated as L-M) nonlinear fitting algorithm, taking the analytical equation of the critical refraction longitudinal wave velocity of the material as the fitting objective function, setting the step size δ, damping μ, and convergence condition s of the nonlinear fitting, substituting the wave velocities measured in each detection direction in the ultrasonic detection experiment into the target value of the fitting function, and iteratively calculating until the convergence condition is reached, and inversely obtaining the equivalent engineering constants of the material in the set tensile stress direction. The inversion results of ω = 0 and ω = π / 2 respectively correspond to the first equivalent engineering constant Q 11 and the third equivalent engineering constant Q 22 .

[0062] Change the set tensile stress direction of the material to be tested, repeat steps 2 to 3, obtain the equivalent engineering constants and equivalent elastic coefficients of the material to be tested under different tensile stress directions, and generate the ultrasonic stress coupling parameter data set of the material to be tested based on the obtained equivalent engineering constants and equivalent elastic coefficients of the material to be tested under different tensile stress directions, as shown in Table 1 below;

[0063] Table 1 Ultrasonic stress coupling parameter data set of the tested materials

[0064]

[0065] Furthermore, the stress step σ s The value should be within the range of 1 / 10 to 1 / 20 of the elastic limit of the material to be tested in the direction of tensile stress.

[0066] Specifically, the stress step size σ s The step size is selected according to the mechanical properties of the material to be tested, and is a value between 1 / 10 and 1 / 20 of the elastic limit. Taking carbon fiber composite materials as an example, the stress step value in the fiber direction of the unidirectional ply of a 5mm thick laminate is 10MPa.

[0067] Furthermore, the ultrasonic acoustic time measuring device includes a stretching machine 1, an ultrasonic transducer, a variable angle acoustic wedge and an ultrasonic acoustic time measuring instrument 5, wherein the ultrasonic transducer includes an ultrasonic excitation transducer 301 and an ultrasonic receiving transducer 302;

[0068] The ultrasonic acoustic time measuring instrument comprises an ultrasonic signal excitation terminal 501, an ultrasonic signal receiving terminal 502 and a processor;

[0069] The stretching machine 1 is used to stretch the material to be tested according to the set tensile stress direction and stress value;

[0070] The ultrasonic signal excitation end 501 is used to generate ultrasonic signals and transmit the ultrasonic signals to the ultrasonic excitation transducer 301 and the processor; the ultrasonic excitation transducer 301 is threadedly connected to the variable angle wedge block, and the ultrasonic excitation transducer 301 transmits the ultrasonic signals to the variable angle wedge block. The variable angle wedge block transmits the ultrasonic signals to the material to be tested that is stretched by the stretcher 1 according to the set ultrasonic detection direction. The ultrasonic signals propagate in the material to be tested that is stretched by the stretcher 1. The ultrasonic receiving transducer 302 is threadedly connected to the variable angle wedge block. The variable angle wedge block is also used to receive the ultrasonic signals transmitted by the material to be tested that is stretched by the stretcher 1 and transmit the received ultrasonic signals transmitted by the material to be tested that is stretched by the stretcher 1 to the ultrasonic receiving transducer 302. The ultrasonic receiving transducer 302 is used to transmit the received ultrasonic signals transmitted by the material to be tested that is stretched by the stretcher 1 to the ultrasonic signal receiving end 502. The ultrasonic signal receiving end 502 sends the ultrasonic signals transmitted by the material to be tested stretched by the stretcher to the processor; the processor is used to obtain the ultrasonic pulse flight time corresponding to different ultrasonic detection directions according to the ultrasonic signals generated by the ultrasonic signal excitation end 501 received and the ultrasonic signals transmitted by the material to be tested that is stretched by the stretcher 1.

[0071] Specifically, as Figure 3As shown in the figure, the ultrasonic transit time measuring device further includes a pulse signal transceiver card, a high-voltage power supply, an industrial computer, a temperature sensor 503, an ultrasonic signal excitation terminal 501, and an ultrasonic signal receiving terminal 502. Among them, the pulse signal transceiver card serves as the core component for exciting and receiving ultrasonic waves. Its main functions include performing A / D and D / A conversions, converting the digital electrical signals at the transmitting end into ultrasonic analog signals, and at the same time converting the ultrasonic analog signals obtained at the receiving end into digital signals. The key performance parameters include the sampling frequency and resolution. According to the Nyquist sampling theorem, the sampling frequency of the signal should be twice the highest frequency of the ultrasonic signal. The ZXUS-80SM type ultrasonic pulse transceiver card is selected, with a receiving bandwidth of 0.5 MHz - 30 MHz, a sampling frequency of up to 100 MS / s, and a sampling interval of 10 ns. The high-voltage power supply provides high voltage for the ultrasonic transit time measuring instrument, generating ultrasonic electrical signals with sufficient energy thresholds. The industrial computer contains ultrasonic signal control and processing software, and its functions include setting parameters such as the high and low levels, pulse period, and gain of the pulse signal transceiver card, and controlling the amplification and filtering of the received signals. The signal is subjected to cross-correlation operation and piecewise linear interpolation processing to obtain and store detection data such as the time difference of sound. According to experience, since the change in transit time caused by stress reaches dozens of nanoseconds, the 100 MS / s sampling frequency cannot directly obtain effective sound signals for the operation and extraction of the time difference of sound. In order to improve the detection accuracy of the time difference of sound, densification processing is carried out between limited data points. The ultrasonic transit time measuring instrument used in this application adopts the piecewise linear interpolation method, with 20 interpolation operations performed between each acquisition point, resulting in a time resolution of 0.5 ns and a transit time measurement accuracy of 0.1 ns, meeting the requirements for the resolution of the time difference of sound measurement. The flight time of the ultrasonic pulse signal is obtained through cross-correlation calculation. The principle is that the ultrasonic signal control and processing software performs piecewise linear interpolation on the digital signals of the ultrasonic signal excitation terminal 501 and the ultrasonic signal receiving terminal 502, and performs cross-correlation calculation on the two obtained discrete waveforms to obtain the time point corresponding to the maximum value of the cross-correlation function, which is used as the time experienced by the ultrasonic pulse from the excitation terminal to the receiving terminal, that is, the flight time of the ultrasonic pulse. The ultrasonic signal excitation terminal 501 and the ultrasonic signal receiving terminal 502 provide BNC interfaces for the ultrasonic excitation transducer 301 and the ultrasonic receiving transducer 302.

[0072] The temperature sensor 503 is connected to the ultrasonic transit time measuring instrument 5. The temperature sensor 503 mainly monitors the experimental temperature conditions to ensure that the experimental temperature conditions for ultrasonic detection remain unchanged.

[0073] Furthermore, the variable angle acoustic wedge block includes an incident slider 401 and a receiving slider 402. The incident slider 401 is threadedly connected to the ultrasonic excitation transducer 301, and the receiving slider 402 is threadedly connected to the ultrasonic receiving transducer 302. The incident slider 401 is used to receive the ultrasonic signal sent by the ultrasonic excitation transducer 301 and transmit the ultrasonic signal to the material to be measured stretched by the stretching machine. The receiving slider 402 is used to receive the ultrasonic signal transmitted by the material to be measured stretched by the stretching machine and transmit the received ultrasonic signal transmitted by the material to be measured stretched by the stretching machine to the ultrasonic receiving transducer 302.

[0074] As Figure 4 shown, the ultrasonic transducer is used to transmit and receive ultrasonic signals. According to the piezoelectric effect and the inverse piezoelectric effect, the mutual conversion between electrical energy and the mechanical energy of particle vibration is achieved. The incident slider 401 and the receiving slider 402 are marked with angle values. According to the critical refraction longitudinal wave velocity being different in different propagation directions, the ultrasonic incident angle is adjusted to meet the excitation conditions of the critical refraction longitudinal wave. The material of the variable angle acoustic wedge block used in this application is polymethyl methacrylate (PMMA).

[0075] The longitudinal wave described in this application is the critical refraction longitudinal wave. The critical refraction longitudinal wave is excited and received according to Snell's law. The principle is as follows:

[0076] When ultrasonic waves travel from one medium to another, reflection and refraction will occur on the contact surface. The critical refraction longitudinal wave is based on Snell's law (Snell Laws). When the refraction angle of the refracted longitudinal wave is 90°, the refracted longitudinal wave excited is called the critical refraction longitudinal wave. For the dependence of the critical refraction longitudinal wave velocity on the angle in anisotropic media, the wave velocities in different propagation directions have obvious differences. Therefore, the variable angle acoustic wedge block is used to achieve the excitation of the critical refraction longitudinal wave in different directions. Before conducting the experiment, the sound velocity is measured and the ultrasonic incident angle, that is, the first critical angle, is calibrated. Specific Embodiment 1:

[0078] The material prepared is the T300 carbon fiber reinforced resin matrix material. When this material is hot-pressed and formed, since the fiber direction determines the mechanical properties and ultrasonic properties of the laminate, the carbon fiber laminate has strong anisotropy. However, due to certain regularities, the laminate structure has a certain symmetry and is a typical orthotropic material. A 5-mm-thick unidirectional laminate and a 5-mm-thick cross-ply laminate are used as the tensile specimens for the ultrasonic stress coupling parameter inversion experiment;

[0079] The analytical equations for the critical refraction longitudinal wave velocity of the 5-mm-thick unidirectional laminate and the 5-mm-thick cross-ply laminate are established respectively. The ultrasonic detection experiment pulse frequency is set to 2.25 MHz. In the stress-free state, the two laminates are measured at ω = 0, and The critical refraction longitudinal wave velocity in 5 directions; set the corresponding analytical equation of the critical refraction longitudinal wave velocity as the non-linear fitting objective function. Further, set the L-M step size δ and damping μ, substitute the critical refraction longitudinal wave velocities of the unidirectional ply laminate with a thickness of 5 mm and the cross-ply laminate with a thickness of 5 mm in the ultrasonic testing experiment into the target value of the fitting function, and after iterative calculation, reach the convergence condition to obtain the inversion results of the equivalent engineering constants and equivalent elastic coefficients of the two plies, as shown in Table 2 below. The non-linear fitting results of the unidirectional ply wave velocity and the actual measured results of the critical refraction longitudinal wave (LCR) velocity are as Figure 5 shown, and the non-linear fitting results of the cross-ply wave velocity and the actual measured results of the critical refraction longitudinal wave (LCR) velocity are as Figure 6 shown. The maximum deviation of the longitudinal wave velocity of the unidirectional ply is 14 m / s, and the deviation is 0.15%; the maximum deviation of the longitudinal wave velocity of the cross-ply is 155 m / s, and the maximum deviation is 2.40%.

[0080] Table 2 Inversion results of ultrasonic stress coupling coefficients for two plies

[0081]

[0082] Specific Example 2:

[0084] Prepare materials as T300 carbon fiber reinforced resin matrix materials, and use a 5-mm-thick unidirectional ply laminate as the inversion target material for ultrasonic stress coupling parameters and equivalent elastic coefficients. According to the Figure 1 method and process shown, obtain the engineering constants of the 5-mm-thick unidirectional ply laminate, and establish an analytical equation for the critical refraction longitudinal wave velocity of the 5-mm-thick unidirectional ply laminate based on the obtained engineering constants;

[0085] Set the angle θ1 between the first tensile stress direction and the material main direction to 0, the stress value to σ1, the initial stress value σ0 to 0, and the stress step σ s1 to 20 MPa. The angle ω1 between the ultrasonic testing direction and the main direction of the 5-mm-thick unidirectional ply laminate is 0, and respectively. Conduct tensile and ultrasonic testing experiments to obtain the ultrasonic pulse flight times corresponding to different testing directions when θ1 = 0, σ1 = iσ s1 , i ∈ [1, 2, 3 ···, n], and calculate the critical refraction longitudinal wave velocity based on the ultrasonic pulse flight times;

[0086] Meanwhile, measure the ultrasonic pulse flight time at θ1 = 0, ω1 = 0, and σ = 0 as the stress-free ultrasonic pulse flight time using an ultrasonic time-of-flight measuring device. Measure the ultrasonic pulse flight times at different stress values when θ1 = 0 and ω1 = 0. Subtract the stress-free ultrasonic pulse flight time from the ultrasonic pulse flight times at different stress values to obtain multiple time differences Δt. Plot the relationship curve between the time difference Δt and the stress σ based on the obtained multiple time differences Δt and the corresponding stress values σ. Obtain the ultrasonic stress coefficient k0 = -0.780 ns / MPa for the 5-mm-thick unidirectional ply laminate at θ1 = 0 and ω1 = 0 according to the obtained relationship curves between all the time differences Δt and the stress σ;

[0087] Set the step size δ and damping μ of the L-M nonlinear fitting algorithm, and use the analytical equation of the critical refracted longitudinal wave velocity of the 5-mm-thick unidirectional ply laminate as the fitting function of the L-M nonlinear fitting algorithm. Substitute the multiple critical refracted longitudinal wave velocities obtained from the ultrasonic detection experiment into the target value of the fitting function, and after iterative calculation, reach the convergence condition to obtain the equivalent engineering constants and equivalent elastic coefficients at different stress values under the condition of θ1 = 0;

[0088] Set the angle between the second tensile stress direction and the material principal direction The stress value is σ2, the initial stress value σ0 is 0, and the stress step σ s2 is 10 MPa. The angles ω2 between the ultrasonic detection direction and the principal direction of the 5-mm-thick unidirectional ply laminate are 0, and Conduct tensile and ultrasonic detection tests to obtain the ultrasonic pulse flight times corresponding to different detection directions when σ2 = jσ s2 , where j ∈ [1, 2, 3 ···, n], and calculate the critical refracted longitudinal wave velocity based on the ultrasonic pulse flight times;

[0089] Meanwhile, measure the ultrasonic pulse flight times at different stress values when, subtract the stress-free ultrasonic pulse flight time from the ultrasonic pulse flight times at different stress values to obtain multiple time differences Δt. Plot the relationship curve between the time difference Δt and the stress σ based on the obtained multiple time differences Δt and the corresponding stress values σ. Obtain the ultrasonic stress coefficient k for the 5-mm-thick unidirectional ply laminate when 45 = -0.428 ns / MPa;

[0090] Set the step size δ and damping μ of the L-M nonlinear fitting algorithm, substitute the angle between the ultrasonic detection direction and the principal direction of the 5-mm-thick unidirectional ply laminate and the corresponding critical refracted longitudinal wave velocity obtained from the ultrasonic detection experiment into the target value of the fitting function, and after iterative calculation, reach the convergence condition to obtain The equivalent engineering constants and equivalent elastic coefficients for different stress values in the case are shown in Table 3;

[0091] Table 3 Ultrasonic stress coupling parameters in two directions of unidirectional ply

[0092]

[0093] An ultrasonic stress simulation experiment was carried out. The simulation modeling is as Figure 7 shown, and the change of the ultrasonic wave position with time is as Figure 8 shown; the material properties are set according to the equivalent engineering constants and equivalent elastic coefficients of the 5-mm-thick unidirectional ply laminate in Table 3. The input signal frequency f of the simulation model is set to 2.25 MHz, and the vibration source function F(t) = exp(-((t - 1.3T0) / (T0 / 2)) 2 )×sin(5πf0t); where, T0 is the ultrasonic incident wave period, t is the time, f0 is the ultrasonic incident wave frequency, the grid size is 1 / 10 of the wavelength, the time-domain diagram of the ultrasonic signal for each stress value is calculated and further the time-domain offset of the waveform is calculated. The time-domain offset of the waveform is as Figure 9 shown;

[0094] Furthermore, a linear relationship diagram of the acoustic time difference Δt and the stress σ of the simulation experiment is plotted. The ultrasonic equivalent stress simulation results for θ1 = 0°, ω1 = 0° are as Figure 10 shown, and the slope k0 = -0.8310 ns / MPa is obtained by linear fitting; the ultrasonic equivalent stress simulation results for θ2 = 45°, ω2 = 0° are as Figure 11 shown, and the slope k 45 = -0.4537 ns / MPa is obtained by linear fitting; by comparison, the relative values of the deviation between the ultrasonic stress simulation results and the actual measurement are 6.137% and 6.004% respectively.

[0095] The consistency between the simulation results and the actual experimental results in this embodiment proves that the parameter inversion results are credible. A method for calculating the ultrasonic stress coupling parameters of materials in this application realizes the accurate acquisition of the low-order linear coupling parameters of ultrasonic stress of materials, indicating that the method described in this invention can solve the problem that the key parameters of the ultrasonic stress coupling field cannot be obtained, and perfects the critical refraction longitudinal wave velocity stress simulation model based on the ultrasonic linear elastic principle.

[0096] Although the present invention has been described herein with reference to particular embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that numerous modifications may be made to the exemplary embodiments, and other arrangements may be devised, without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the different dependent claims and the features described herein may be combined in ways different from those described in the original claims. It should also be understood that the features described in connection with separate embodiments may be used in other described embodiments.

Claims

1. A method for calculating ultrasonic stress coupling parameters of a material, characterized in that: include: Step 1: Obtain the engineering constants of the material to be tested, and establish an analytical equation for the critical refraction longitudinal wave velocity of the material to be tested based on the obtained engineering constants; Set the tensile stress direction of the material to be tested and multiple ultrasonic testing directions; Step 2: measuring the ultrasonic pulse flight time in different ultrasonic detection directions under the tensile stress direction by an ultrasonic acoustic time measurement device, and calculating the critical refracted longitudinal wave velocity corresponding to each ultrasonic detection direction according to the ultrasonic pulse flight time; Step 3: Obtaining an equivalent engineering constant in the tensile stress direction of the material to be tested by using an LM nonlinear fitting algorithm based on the multiple ultrasonic detection directions and the corresponding calculated critical refracted longitudinal wave velocities; the fitting objective function of the LM nonlinear fitting algorithm is an analytical equation for the critical refracted longitudinal wave velocity of the material to be tested; and calculating an equivalent elastic coefficient based on the obtained equivalent engineering constant using a calculation relationship between the equivalent engineering constant and the elastic coefficient; Step 4: Change the set tensile stress direction of the material to be tested, repeat steps 2 to 3, obtain the equivalent engineering constants and equivalent elastic coefficients of the material to be tested under different tensile stress directions, and generate an ultrasonic stress coupling parameter data set for the material to be tested based on the obtained equivalent engineering constants and equivalent elastic coefficients of the material to be tested under different tensile stress directions.

2. The method for calculating ultrasonic stress coupling parameters of a material according to claim 1, characterized in that: The method for establishing an analytical equation for the critical refraction longitudinal wave velocity of a material to be tested based on the obtained engineering constants includes: calculating first algebraic parameters and second algebraic parameters based on the engineering constants of the material to be tested, and establishing an analytical equation for the critical refraction longitudinal wave velocity of the material to be tested based on the first algebraic parameters and the second algebraic parameters: The engineering constants of the material to be measured include a first engineering constant, a second engineering constant, a third engineering constant and a fourth engineering constant; The method for calculating the first algebraic parameters based on the engineering constants of the material to be tested is: H=C 11 cos 2 ω+C 22 sin 2 ω+C 66 ; The method for calculating the second algebraic parameters based on the engineering constants of the material to be tested is: K=(C 11 cos 2 ω+C 66 sin 2 ω)+(C 66 cos 2 ω+C 22 sin 2 ω)-(C 12 +C 66 ) 2 cos 2 ωsin 2 oh; Among them, H is the first algebraic parameter, K is the second algebraic parameter, C 11 is the first engineering constant, C 12 is the second engineering constant, C 22 is the third engineering constant, C 66 is the fourth engineering constant, ω is the angle between the ultrasonic testing direction and the main direction of the material to be tested; The method for establishing the analytical equation of the critical refraction longitudinal wave velocity of the material to be tested based on the first algebraic parameters and the second algebraic parameters is: Among them, v LCR is the critical refractive longitudinal wave velocity of the material to be tested, and ρ is the density of the material to be tested.

3. The method for calculating ultrasonic stress coupling parameters of a material according to claim 2, wherein: The method includes setting a tensile stress direction and multiple ultrasonic testing directions of a material to be tested; measuring the ultrasonic pulse flight time in different ultrasonic testing directions under the set tensile stress direction of the material to be tested by an ultrasonic acoustic time measurement device, and calculating the critical refracted longitudinal wave velocity corresponding to each ultrasonic testing direction based on the ultrasonic pulse flight time, including: Step 21: Set the tensile stress direction of the material to be tested; set the stress value σ = 0 and the stress step size to σ s , the maximum stress is σ z , iteration number i = 0; Step 22: Use the ultrasonic acoustic time measurement device to measure the ultrasonic pulse flight time t corresponding to the current tensile stress direction and the current stress value in different ultrasonic detection directions, and calculate the critical refracted longitudinal wave velocity v corresponding to each ultrasonic detection direction based on the measured ultrasonic pulse flight time t LCR_ω , v LCR_ω =L / t, L is the ultrasonic pulse sound path; Step 2 and 3: Determine whether the stress value σ is less than the maximum stress value σ z If yes, go to step 24, if no, end; Step 24: Let the number of iterations i = i + 1 and the stress value σ = iσ s ; and go to step 22.

4. The method for calculating ultrasonic stress coupling parameters of a material according to claim 3, wherein: The method of obtaining the equivalent engineering constant in the tensile stress direction of the material to be tested by using the LM nonlinear fitting algorithm according to the multiple ultrasonic testing directions and the critical refracted longitudinal wave velocity corresponding to each ultrasonic testing direction includes: The analytical equation of the critical refracted longitudinal wave velocity of the material to be tested is used as the fitting objective function of the LM nonlinear fitting algorithm. The angles between multiple ultrasonic testing directions and the main direction of the material and the critical refracted longitudinal wave velocity corresponding to each ultrasonic testing direction are input into the LM nonlinear fitting algorithm to obtain the equivalent engineering constants.

5. The method for calculating ultrasonic stress coupling parameters of a material according to claim 4, characterized in that: The equivalent engineering constants include a first equivalent engineering constant, a second equivalent engineering constant, a third equivalent engineering constant and a fourth equivalent engineering constant; The equivalent elastic coefficient includes a first equivalent elastic coefficient, a second equivalent elastic coefficient, a third equivalent elastic coefficient and a fourth equivalent elastic coefficient; The calculation relationship between equivalent engineering constants and elastic coefficients includes: Among them, Q 11 is the first equivalent engineering constant, Q 12 is the second equivalent engineering constant, Q 22 is the third equivalent engineering constant, Q 66 is the fourth equivalent engineering constant, M1 is the first equivalent elastic coefficient, M2 is the second equivalent elastic coefficient, U 12 is the third equivalent elastic coefficient, N 12 is the fourth equivalent elastic coefficient.

6. The method for calculating ultrasonic stress coupling parameters of a material according to claim 3, wherein: Stress step σ s The value should be within the range of 1 / 10 to 1 / 20 of the elastic limit of the material to be tested in the direction of tensile stress.

7. The method for calculating ultrasonic stress coupling parameters of a material according to claim 1, characterized in that: The material to be tested is an orthotropic material.

8. The method for calculating ultrasonic stress coupling parameters of a material according to claim 3, wherein: The ultrasonic acoustic time measuring device includes a stretching machine, an ultrasonic transducer, a variable angle acoustic wedge and an ultrasonic acoustic time measuring instrument, wherein the ultrasonic transducer includes an ultrasonic excitation transducer and an ultrasonic receiving transducer; The ultrasonic acoustic time measuring instrument comprises an ultrasonic signal exciting end, an ultrasonic signal receiving end and a processor; The stretching machine is used to stretch the material to be tested according to the set tensile stress direction and stress value; The ultrasonic signal excitation end is used to generate an ultrasonic signal and transmit the ultrasonic signal to the ultrasonic excitation transducer and the processor; the ultrasonic excitation transducer is threadedly connected to the variable-angle acoustic wedge, and the ultrasonic excitation transducer transmits the ultrasonic signal to the variable-angle acoustic wedge. The variable-angle acoustic wedge transmits the ultrasonic signal to the material to be tested stretched by the stretcher according to the set ultrasonic detection direction, and the ultrasonic signal propagates in the material to be tested stretched by the stretcher. The ultrasonic receiving transducer is threadedly connected to the variable-angle acoustic wedge. The variable-angle acoustic wedge is also used to receive the ultrasonic signal transmitted by the material to be tested stretched by the stretcher, and transmit the received ultrasonic signal transmitted by the material to be tested stretched by the stretcher to the ultrasonic receiving transducer. The ultrasonic receiving transducer is used to transmit the received ultrasonic signal transmitted by the material to be tested stretched by the stretcher to the ultrasonic signal receiving end, and the ultrasonic signal receiving end sends the ultrasonic signal transmitted by the material to be tested stretched by the stretcher to the processor; the processor is used to obtain the ultrasonic pulse flight time corresponding to different ultrasonic detection directions based on the ultrasonic signal generated by the received ultrasonic signal excitation end and the ultrasonic signal transmitted by the material to be tested stretched by the stretcher.

9. The method for calibrating ultrasonic stress coefficient of anisotropic materials according to claim 8, characterized in that: The variable-angle acoustic wedge includes an incident slider and a receiving slider. The incident slider is threadedly connected to the ultrasonic excitation transducer, and the receiving slider is threadedly connected to the ultrasonic receiving transducer. The incident slider is used to receive the ultrasonic signal sent by the ultrasonic excitation transducer and transmit the ultrasonic signal to the material to be tested stretched by the stretching machine. The receiving slider is used to receive the ultrasonic signal transmitted by the material to be tested stretched by the stretching machine, and transmit the received ultrasonic signal transmitted by the material to be tested stretched by the stretching machine to the ultrasonic receiving transducer.

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