CN114964580A - Orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb wave and readable storage medium - Google Patents
Orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb wave and readable storage medium Download PDFInfo
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Abstract
The invention discloses an orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb waves and a readable storage medium. Connecting equipment and debugging; using the detected signal as a reference based on the direction of the carbon fiber composite material and carrying out theta based on a rotating platform (4) 1 、θ 2 、θ 3 Measuring quasi-longitudinal wave velocity values in three different directions; measuring the quasi-longitudinal wave velocity values in three different directions to obtain corresponding quasi-longitudinal wave velocity values v QL1 、v QL2 、v QL3 (ii) a Measuring the quasi-longitudinal wave velocity value of the detection signal by theta 1 、θ 2 、θ 3 Sum quasi-longitudinal wave velocity value v QL1 、v QL2 、v QL3 Obtaining the principal stress sigma taking the fiber direction as the reference in the plane of the orthotropic composite material through the relationship between the Christoffel sound tensor and the quasi-longitudinal wave 11 、σ 21 And τ 12 And displaying the detection result of the plane stress of the orthotropic composite material. The method is used for solving the problem that the performance and the detection result of the carbon fiber composite material are influenced by using the coupling agent in the prior art.
Description
Technical Field
The invention belongs to the field of ultrasonic detection; in particular to a method for detecting the plane stress of an orthotropic composite material based on air coupling Lamb waves and a readable storage medium.
Background
The composite material has the advantages of light weight, high strength, high temperature resistance, high fatigue resistance and the like, and is widely applied to the fields of aerospace and the like. The carbon fiber composite material is an important novel material, and plays an important role in the civil and military fields due to the excellent performance and low cost of the carbon fiber composite material. Due to the special manufacturing process and the anisotropic structural characteristics of the composite material laminated plate, the stress concentration phenomenon is easily formed in the processing and using processes of the composite material laminated plate. Researches show that the performance of the composite material structure is rapidly reduced along with the expansion and accumulation of stress concentration, so that the research on a nondestructive testing method capable of effectively detecting the structural stress of the fiber reinforced composite material has important significance and value in detecting and monitoring the plane stress of the composite material. A large number of researches and applications show that the ultrasonic detection method is the most practical, most effective and widely applied nondestructive detection technology for the composite material. Lamb waves can completely cover the thickness direction of the whole material on a propagation path, and particularly have the advantages of small attenuation, long propagation distance, high detection sensitivity and the like, so the Lamb waves are widely used for detecting board structures such as carbon fiber composite materials. Generally, a large amount of couplant is needed for detection by exciting Lamb waves in a carbon fiber composite material plate by using a contact sensor, and the performance and detection result of the carbon fiber composite material are influenced to a certain extent. Although laser ultrasound does not require a coupling agent, the carbon fiber composite material is easily damaged when the energy is too high. Due to the advantages of no coupling agent, no contact, no secondary pollution and the like, the air-coupled ultrasound has unique advantages in the detection of the carbon fiber composite board.
Disclosure of Invention
The invention provides an orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb waves and a readable storage medium, which are used for solving the problem that the performance and the detection result of a carbon fiber composite material are influenced by using a coupling agent in the prior art.
The invention is realized by the following technical scheme:
an orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb waves comprises the following steps:
step 1: connecting equipment and debugging;
step 2: based on the signals detected in the step 1, the direction of the carbon fiber composite material is taken as a reference, and omega is carried out based on the rotating platform 4 1 、ω 2 、ω 3 Acoustic time difference measurements in three different directions;
and 3, step 3: measuring the sound time difference in three different directions in the step 2 to obtain corresponding sound time difference T 1 、T 2 、T 3 ；
And 4, step 4: the acoustic time difference T of the detection signal and the principal stress sigma borne by the material 1 、σ 2 The maximum main stress and the included angle theta of the carbon fiber composite material are deduced through the acoustoelastic effect to obtain three characterization parameters sigma of the plane stress of the orthotropic composite material 1 、σ 2 And θ;
and 5: 3 characterization parameters σ based on step 4 1 、σ 2 Theta and Mohr stress circle theory can obtain the stress state of any direction in the plane of the orthotropic composite material, namely the normal stress sigma xx 、σ yy And shear stress tau xy And displaying the detection result of the plane stress of the orthotropic composite material through an upper computer.
In the detection method, the equipment in the step 1 specifically comprises an excitation air coupling transducer 1, a receiving air coupling transducer 2, a carbon fiber composite material plate 3, a rotating platform 4, a two-dimensional motion platform 5, a signal generator, a voltage amplifier, an upper computer, an oscilloscope and a preamplifier;
the linear guide rail 5-1 of the two-dimensional motion platform 5 is respectively connected with an excitation air coupling transducer 1 and a receiving air coupling transducer 2 through a fixed connector 1-1, the excitation air coupling transducer 1 and the receiving air coupling transducer 2 are respectively arranged at two sides of a carbon fiber composite material plate 3, the carbon fiber composite material plate 3 is arranged on a rotary platform 4,
the excitation air coupling transducer 1 is sequentially connected with a voltage amplifier and a signal generator, and the receiving air coupling transducer 2 is sequentially connected with an upper computer, an oscilloscope and a preamplifier.
The detection method is characterized in that a fiber coordinate system, namely a material main direction coordinate system X is known 0 OY 0 (ii) a Knowing the actual direction of detection, i.e. measuring coordinate system X i OY i (ii) a Always taking the fiber direction as an angular reference;
provided with resonant plane waves
u i ＝A i exp[i(k m x m -ωt)] (1)
In the formula, k m Is a unit wave vector, A i ＝Aα i A is the amplitude of the plane wave, alpha i Direction cosine of the particle displacement;
when the elastic wave is transmitted in the stressed medium in the deformation state, the wave equation under the deformation state coordinate system is as follows,
in the formula, C ijkl Is the stiffness coefficient of the solid medium, t jl Is the Cauthy stress tensor, δ, relative to deformation state il Is a function of Kronecher, and rho is the density of the material;
let A ijkl ＝C ijkl +t jl δ ik The equivalent stiffness coefficient of the stress medium is changed into the formula (2),
substituting the resonant plane wave in the formula (1) to obtain a Christoffel equation when the anisotropic medium has initial predeformation:
(C ijkl k j k k -ρω 2 δ il )u l ＝0 (4)
defining the christofel sound tensor in the presence of an initial pre-deformation of the anisotropic medium,
Η il ＝A ijkl l j l k ＝C ijkl l j l k +t jl δ ik l j l k (5)
in the formula I j 、l k Is the directional cosine of the wave front normal vector, with k j ＝kl j ，k k ＝kl k ，v 2 ＝ω 2 /k 2 K is wave number, v is wave velocity, and omega is angular frequency;
equation (4) can be simplified to
(H il -ρv 2 δ il )u l ＝0 (6)
The above formula is actually about v 2 The cubic equation of (2) gives three secondary equations, three real roots and three different sound velocities, thereby generating a classical orthogonal eigenvalue problem;
writing equation (6) in matrix form as
The determinant of the coefficient is zero when the equation (7) has a sufficient condition of non-zero solution, i.e. the
The above formula (8) is expressed as ρ v 2 For the unknown plane wave equation, three plane waves vi can be obtained by solving (i ═ 1,2, 3). The expanded expression of the Christoffel sound tensor in the presence of initial pre-deformation for a forward anisotropic medium is
Taking any wave vector direction in the plane of the carbon fiber composite material plate
At this time l 1 ＝cosθ、l 2 ＝sinθ、l 3 0; wherein, theta is an included angle between the ultrasonic wave propagation direction and the fiber direction.
In the detection method, assuming that only the stress existing in the plane of the carbon fiber composite material plate is considered, the formula (9) is rewritten as,
substituting equation (10) into equation (8) yields three plane waves:
wherein the quasi-longitudinal wave v QL ＝v 1 Therefore, the relation between the Christoffel sound tensor and the quasi-longitudinal wave is obtained:
by making a pass of theta 1 、θ 2 、θ 3 Measuring the quasi-longitudinal wave velocity values in three different directions to obtain corresponding quasi-longitudinal wave velocity values v QL1 、v QL2 、v QL3 (ii) a As the elastic constant of the material is known, the Christoffel sound tensor and quasi-longitudinal wave relation formula (12) are combined to obtain the principal stress sigma taking the fiber direction as the reference in the plane of the orthotropic composite material 11 、σ 21 And τ 12 。
In the detection method, in the step 5, specifically, an air coupling transducer is placed on one side of the orthotropic composite plate sample according to the previously determined inclination angle θ, and the distance between the excitation air coupling transducer and the receiving air coupling transducer is set to be L. By the same side and pitch catching methodWith A 0 Carrying out plane stress detection on the composite material plate in a modal mode;
assuming measured time taken by theta 1 ＝0°、θ 2 ＝45°、θ 3 When the angle is equal to 90 degrees, the angle,
the principal stress sigma in the plane of the orthotropic composite material based on the fiber direction can be calculated by three equations of the simultaneous formula (13) 11 、σ 21 And τ 12 。
According to the detection method, an air coupling transducer is placed on one side of a composite material plate sample according to the determined inclination angle theta, and the distance between an excitation air coupling transducer and a receiving air coupling transducer is set to be L; using ipsilateral and pitch capture methods, and using A 0 Carrying out layering defect detection on the composite material plate in a modal mode;
the signal generator is used for generating a sine pulse series excitation signal with the center frequency of f, Hanning window modulation and the pulse number of 5, which is required by the air coupling transducer;
the voltage amplifier is used for carrying out voltage increase on the excitation signal generated by the signal generator so as to ensure that the air coupling transducer excites enough sound energy;
the two-dimensional motion platform is used for adjusting the horizontal distance between the transmitting air coupling transducer and the receiving air coupling transducer and the height distance between the transmitting air coupling transducer and the orthogonal anisotropic composite material plate;
the rotary platform is used for realizing the detection of the acoustic time difference in different directions of the composite material plates in the orthogonal directions;
the preamplifier is used for amplifying and receiving an echo signal of the air coupling transducer;
the oscilloscope is used for displaying Lamb wave signals and storing data;
the upper computer is used for displaying the detection result of the plane stress of the orthotropic composite material.
A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the method steps of the above.
The beneficial effects of the invention are:
the invention fundamentally avoids the problem of secondary pollution caused by the coupling material to the part to be detected, has the advantages of no contact, no invasion and no damage in the detection process, can also greatly prolong the service life of the air coupling ultrasonic transducer, realizes online rapid detection of air coupling ultrasonic Lamb wave detection, and is suitable for defect ultrasonic detection of composite material plates which can not be subjected to contact detection by using a coupling agent.
The invention effectively realizes the stress state of any direction in the plane of the orthotropic composite material.
Drawings
FIG. 1 is a graph showing Lamb wave dispersion characteristics according to the present invention.
FIG. 2 is a schematic diagram of ultrasonic planar stress testing according to the present invention.
Fig. 3 is a schematic diagram of the connection of the apparatus of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
An orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb waves comprises the following steps:
step 1: connecting equipment and debugging;
step 2: based on the signals detected in the step 1, the direction of the carbon fiber composite material is taken as a reference, and omega is carried out based on the rotating platform 4 1 、ω 2 、ω 3 Acoustic time difference measurements in three different directions;
and step 3: measuring the sound time difference in three different directions in the step 2 to obtainCorresponding acoustic time difference T 1 、T 2 、T 3 ；
And 4, step 4: the acoustic time difference T of the detection signal and the principal stress sigma borne by the material 1 、σ 2 The maximum main stress and the included angle theta of the carbon fiber composite material are deduced through the acoustoelastic effect to obtain three characterization parameters sigma of the plane stress of the orthotropic composite material 1 、σ 2 And θ;
and 5: 3 characterization parameters σ based on step 4 1 、σ 2 Theta and Mohr stress circle theory can obtain the stress state of any direction in the plane of the orthotropic composite material, namely the normal stress sigma xx 、σ yy And shear stress tau xy And displaying the detection result of the plane stress of the orthotropic composite material through an upper computer.
In the detection method, the equipment in the step 1 specifically comprises an excitation air coupling transducer 1, a receiving air coupling transducer 2, a carbon fiber composite material plate 3, a rotating platform 4, a two-dimensional motion platform 5, a signal generator, a voltage amplifier, an upper computer, an oscilloscope and a preamplifier;
the linear guide rail 5-1 of the two-dimensional motion platform 5 is respectively connected with an excitation air coupling transducer 1 and a receiving air coupling transducer 2 through a fixed connector 1-1, the excitation air coupling transducer 1 and the receiving air coupling transducer 2 are respectively arranged at two sides of a carbon fiber composite material plate 3, the carbon fiber composite material plate 3 is arranged on a rotary platform 4,
the excitation air coupling transducer 1 is sequentially connected with a voltage amplifier and a signal generator, and the receiving air coupling transducer 2 is sequentially connected with an upper computer, an oscilloscope and a preamplifier.
The determination of the excitation frequency and the inclination angle of the air coupled transducer is specifically described with reference to fig. 1. Lamb waves have symmetrical and antisymmetric modes and frequency dispersion characteristics, and can excite multiple-order symmetric modes (S) under the same excitation frequency 0 ，S 1 ，…，S i ) With anti-symmetric mode (A) 0 ，A 1 ，…，A i ). For air coupling of transducers in the piece to be measuredExciting a purer mode, and knowing that the excitation frequency of the transmitting air coupling transducer is less than a certain upper limit value f according to the dispersion curve of the guided wave and the thickness of the piece to be detected 0 . The excitation frequency f is then determined from the actual performance of the air-coupled transducer. According to research and analysis, the in-plane displacement of the symmetric mode is large, and the out-of-plane displacement of the anti-symmetric mode is large, so that the anti-symmetric mode is adopted for air coupling ultrasonic detection. When the frequency-thickness product (frequency x the thickness of the object) is determined, the antisymmetric mode A 0 The group velocity of (a) can also be known, and then the tilt angle θ of the air-coupled transducer is determined according to the first critical refraction angle of snell's law in combination with the propagation velocity in air.
The detection method is characterized in that a fiber coordinate system, namely a material main direction coordinate system X is known 0 OY 0 (ii) a Knowing the actual direction of detection, i.e. measuring coordinate system X i OY i (ii) a Always taking the fiber direction as an angle reference;
provided with resonant plane waves
u i ＝A i exp[i(k m x m -ωt)] (1)
In the formula, k m Is a unit wave vector, A i ＝Aα i A is the amplitude of the plane wave, alpha i Is the direction cosine of the particle displacement;
when the elastic wave is transmitted in the stressed medium in a deformation state, the wave equation under the deformation state coordinate system is as follows,
in the formula, C ijkl Is the stiffness coefficient of the solid medium, t jl Is the Cauthy stress tensor, δ, relative to deformation state il Is a function of Kronecher, and rho is the density of the material;
let A ijkl ＝C ijkl +t jl δ ik Is the equivalent stiffness coefficient of the stressed medium, the formula (2) is changed into,
substituting the resonant plane wave in the formula (1) to obtain a Christoffel equation when the anisotropic medium has initial predeformation:
(C ijkl k j k k -ρω 2 δ il )u l ＝0 (4)
defining the christofel sound tensor in the presence of an initial pre-deformation of the anisotropic medium,
Η il ＝A ijkl l j l k ＝C ijkl l j l k +t jl δ ik l j l k (5)
in the formula I j 、l k Is the directional cosine of the wave front normal vector, with k j ＝kl j ，k k ＝kl k ，v 2 ＝ω 2 /k 2 K is wave number, v is wave velocity, and omega is angular frequency;
equation (4) can be simplified to
(H il -ρv 2 δ il )u l ＝0 (6)
The above formula is actually about v 2 The cubic equation of (2) gives three secondary equations, three real roots and three different sound velocities, thereby generating a classical orthogonal eigenvalue problem;
writing equation (6) in matrix form as
The determinant of the coefficient is zero when the equation (7) has a sufficient condition of non-zero solution, i.e. the
The above formula (8) is expressed as ρ v 2 For the unknown plane wave equation, three plane waves vi can be obtained by solving (i ═ 1,2, 3). For positive anisotropyThe expanded expression of the Christoffel sound tensor in the presence of initial pre-distortion is
Taking any wave vector direction in the plane of the carbon fiber composite material plate
At this time l 1 ＝cosθ、l 2 ＝sinθ、l 3 0; wherein, theta is an included angle between the ultrasonic wave propagation direction and the fiber direction.
In the detection method, if only the stress existing in the plane of the carbon fiber composite material plate is considered, the formula (9) is rewritten as,
substituting equation (10) into equation (8) yields three plane waves:
wherein the quasi-longitudinal wave v QL ＝v 1 Therefore, the relation between the Christoffel sound tensor and the quasi-longitudinal wave is obtained:
by making a pass of theta 1 、θ 2 、θ 3 Measuring the quasi-longitudinal wave velocity values in three different directions to obtain corresponding quasi-longitudinal wave velocity values v QL1 、v QL2 、v QL3 (ii) a As the elastic constant of the material is known, the Christoffel sound tensor and quasi-longitudinal wave relation formula (12) are combined to obtain the principal stress sigma taking the fiber direction as the reference in the plane of the orthotropic composite material 11 、σ 21 And τ 12 。
In the detection method, the step 5 is to specifically describe a plane stress detection flow of the orthotropic composite material with reference to fig. 3. And placing an air coupling transducer at one side of the orthotropic composite plate sample according to the previously determined inclination angle theta, and setting the distance between an excitation air coupling transducer and a receiving air coupling transducer to be L. Using ipsilateral and elevation trapping methods, and using A 0 Carrying out plane stress detection on the composite material plate in a modal mode;
to simplify the measurement and calculation, the detection angle may be chosen in favor of experimental conditions, assuming that θ is taken during the measurement 1 ＝0°、θ 2 ＝45°、θ 3 When the angle is equal to 90 degrees, the angle,
the principal stress sigma in the plane of the orthotropic composite material based on the fiber direction can be calculated by three equations of the simultaneous formula (13) 11 、σ 21 And τ 12 。
According to the detection method, an air coupling transducer is placed on one side of a composite material plate sample according to the determined inclination angle theta, and the distance between an excitation air coupling transducer and a receiving air coupling transducer is set to be L; using ipsilateral and pitch capture methods, and using A 0 Carrying out layered defect detection on the composite plate in a modal manner;
the signal generator is used for generating a sine pulse series excitation signal with the center frequency of f, Hanning window modulation and the pulse number of 5, which is required by the air coupling transducer;
the voltage amplifier is used for carrying out voltage increase on the excitation signal generated by the signal generator so as to ensure that the air coupling transducer excites enough sound energy;
the two-dimensional motion platform is used for adjusting the horizontal distance between the transmitting air coupling transducer and the receiving air coupling transducer and the height distance between the transmitting air coupling transducer and the orthogonal anisotropic composite material plate;
the rotary platform is used for realizing the detection of the acoustic time difference in different directions of the composite material plates in the orthogonal directions;
the preamplifier is used for amplifying and receiving an echo signal of the air coupling transducer;
because Lamb wave signals are greatly attenuated in air, the preamplifier is used for amplifying and receiving echo signals of the air coupling transducer; the oscilloscope is used for displaying Lamb wave signals and storing data;
the upper computer is used for displaying the detection result of the plane stress of the orthotropic composite material.
A computer-readable storage medium, in which a computer program is stored which, when being executed by a processor, carries out the method steps of the above.
Claims (7)
1. An orthogonal anisotropy composite material plane stress detection method based on air coupling Lamb waves is characterized by comprising the following steps:
step 1: connecting equipment and debugging;
step 2: based on the signals detected in the step 1, theta is carried out based on a rotating platform (4) by taking the direction of the carbon fiber composite material as a reference 1 、θ 2 、θ 3 Measuring quasi-longitudinal wave velocity values in three different directions;
and step 3: measuring the quasi-longitudinal wave velocity values in the three different directions in the step 2 to obtain corresponding quasi-longitudinal wave velocity values v QL1 、v QL2 、v QL3 ；
And 4, step 4: measuring the quasi-longitudinal wave velocity value of the detection signal by theta 1 、θ 2 、θ 3 Sum quasi-longitudinal wave velocity value v QL1 、v QL2 、v QL3 Obtaining the principal stress sigma which takes the fiber direction as the reference in the plane of the orthotropic composite material through the relation between the Christoffel sound tensor and the quasi-longitudinal wave 11 、σ 21 And τ 12 And displaying the plane stress detection result of the orthotropic composite material through an upper computer.
2. The detection method according to claim 1, wherein the device of step 1 specifically comprises an excitation air coupling transducer (1), a reception air coupling transducer (2), a carbon fiber composite material plate (3), a rotating platform (4), a two-dimensional motion platform (5), a signal generator, a voltage amplifier, an upper computer, an oscilloscope and a preamplifier;
the linear guide rail (5-1) of the two-dimensional motion platform (5) is respectively connected with the excitation air coupling transducer (1) and the receiving air coupling transducer (2) through the fixed connectors (1-1), the excitation air coupling transducer (1) and the receiving air coupling transducer (2) are respectively arranged at two sides of the carbon fiber composite material plate (3), the carbon fiber composite material plate (3) is arranged on the rotary platform (4),
the excitation air coupling transducer (1) is sequentially connected with the voltage amplifier and the signal generator, and the receiving air coupling transducer (2) is sequentially connected with the upper computer, the oscilloscope and the preamplifier.
3. The inspection method according to claim 1, wherein the step 4 is to know a fiber coordinate system, i.e. a material principal direction coordinate system X 0 OY 0 (ii) a Knowing the actual direction of detection, i.e. measuring coordinate system X i OY i (ii) a Always taking the fiber direction as an angle reference;
provided with resonant plane waves
u i ＝A i exp[i(k m x m -ωt)] (1)
In the formula, k m Is a unit wave vector, A i ＝Aα i A is the amplitude of the plane wave, alpha i Is the direction cosine of the particle displacement;
when the elastic wave is transmitted in the stressed medium in the deformation state, the wave equation under the deformation state coordinate system is as follows,
in the formula, C ijkl Is the stiffness coefficient of the solid medium, t jl Is the Cauthy stress tensor, δ, relative to deformation state il As a function of Kronecher, pIs the material density;
let A ijkl ＝C ijkl +t jl δ ik Is the equivalent stiffness coefficient of the stressed medium, the formula (2) is changed into,
substituting the resonant plane wave in the formula (1) to obtain a Christoffel equation when the anisotropic medium has initial predeformation:
(C ijkl k j k k -ρω 2 δ il )u l ＝0 (4)
defining the christofel sound tensor in the presence of an initial pre-deformation of the anisotropic medium,
Η il ＝A ijkl l j l k ＝C ijkl l j l k +t jl δ ik l j l k (5)
in the formula I j 、l k Is the directional cosine of the wave front normal vector, with k j ＝kl j ，k k ＝kl k ，v 2 ＝ω 2 /k 2 K is wave number, v is wave velocity, and omega is angular frequency;
equation (4) can be simplified to (H) il -ρv 2 δ il )u l ＝0 (6)
The above formula is actually about v 2 The cubic equation of (2) gives three secondary equations, three real roots and three different sound velocities, thereby generating a classical orthogonal eigenvalue problem;
writing equation (6) in matrix form as
The determinant of the coefficient is zero when the equation (7) has a sufficient condition of non-zero solution, i.e. the
The above formula (8) is expressed as ρ v 2 For the unknown plane wave equation, three plane waves vi can be obtained by solving (i ═ 1,2, 3).
The expanded expression of the Christoffel sound tensor in the presence of initial pre-deformation for a forward anisotropic medium is
Taking any wave vector direction in the plane of the carbon fiber composite material plate
At this time l 1 ＝cosθ、l 2 ＝sinθ、l 3 0; wherein, theta is an included angle between the ultrasonic wave propagation direction and the fiber direction.
4. The detection method according to claim 3, wherein, assuming that only the presence of stress in the plane of the carbon fiber composite material plate is considered, the formula (9) is rewritten as,
substituting equation (10) into equation (8) yields three plane waves:
wherein the quasi-longitudinal wave v QL ＝v 1 Therefore, the relation between the Christoffel sound tensor and the quasi-longitudinal wave is obtained:
by making a pass of theta 1 、θ 2 、θ 3 Measuring the quasi-longitudinal wave velocity values in three different directions to obtain corresponding quasi-longitudinal wave velocity values v QL1 、v QL2 、v QL3 (ii) a The elastic constant of the material is known, and the principal stress sigma which takes the fiber direction as the reference in the plane of the orthotropic composite material is obtained by combining the Christoffel sound tensor and the quasi-longitudinal wave relation formula (12) 11 、σ 21 And τ 12 。
5. The method according to claim 4, wherein the step 5 is to place an air coupling transducer at a previously determined tilt angle θ on one side of the orthotropic composite plate sample, and set the distance between the exciting air coupling transducer and the receiving air coupling transducer to be L. Using ipsilateral and elevation trapping methods, and using A 0 Carrying out plane stress detection on the composite material plate in a modal mode;
assuming measurement time taken as θ 1 ＝0°、θ 2 ＝45°、θ 3 When the angle is equal to 90 degrees, the angle,
the principal stress sigma in the plane of the orthotropic composite material based on the fiber direction can be calculated by three equations of the simultaneous formula (13) 11 、σ 21 And τ 12 。
6. The detection method according to claim 5, characterized in that an air coupling transducer is arranged at one side of the composite material plate sample according to the previously determined inclination angle theta, and the distance between an excitation air coupling transducer and a receiving air coupling transducer is set to be L; using ipsilateral and pitch capture methods, and using A 0 Carrying out layering defect detection on the composite material plate in a modal mode;
the signal generator is used for generating a sine pulse series excitation signal with the center frequency of f, Hanning window modulation and the pulse number of 5, which is required by the air coupling transducer;
the voltage amplifier is used for carrying out voltage increase on the excitation signal generated by the signal generator so as to ensure that the air coupling transducer excites enough sound energy;
the two-dimensional motion platform is used for adjusting the horizontal distance between the transmitting air coupling transducer and the receiving air coupling transducer and the height distance between the transmitting air coupling transducer and the orthogonal anisotropic composite material plate;
the rotary platform is used for realizing the detection of the acoustic time difference in different directions of the composite material plates in the orthogonal directions;
the preamplifier is used for amplifying and receiving an echo signal of the air coupling transducer;
the oscilloscope is used for displaying Lamb wave signals and storing data;
the upper computer is used for displaying the detection result of the plane stress of the orthotropic composite material.
7. A computer-readable storage medium, characterized in that a computer program is stored in the computer-readable storage medium, which computer program, when being executed by a processor, carries out the method steps of any one of claims 1 to 6.
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