CN115494160B - Phased array air coupling transducer and plane stress ultrasonic measurement method and device thereof - Google Patents
Phased array air coupling transducer and plane stress ultrasonic measurement method and device thereof Download PDFInfo
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Abstract
A phased array air coupling transducer and a plane stress ultrasonic measurement method and device thereof belong to the technical field of ultrasonic detection. The method solves the problem that the measuring direction of the single-crystal-unit contact ultrasonic transducer only obtains the acoustic time difference information by one propagation path to obtain the stress component, and the accuracy of plane stress measurement is affected. The method comprises the following steps: the transducer signals receiving the excitation signals transmit the excitation signals to the piezoelectric ceramics, the excitation signals are converted into acoustic signals and transmitted to the to-be-detected piece, and the acoustic signals generate LCR waves in the to-be-detected piece; the to-be-tested piece sends an echo signal to a transducer for receiving the response signal, and converts the echo signal into a response signal to be transmitted to a signal connecting end for receiving the response signal; acquiring acoustic time difference through data processing according to the LCR wave and the response signal; adjusting the angle of the transducer, repeating the operation, and obtaining the acoustic time difference of the other two corresponding measuring directions; and finishing plane stress measurement of the to-be-measured area of the to-be-measured piece according to the Morse circle stress theory and the stresses in three directions. The method is suitable for the field of stress detection.
Description
Technical Field
The application belongs to the technical field of ultrasonic detection, and mainly relates to a phased array air coupling transducer and a plane stress ultrasonic measurement method thereof.
Background
In the process of manufacturing materials, the workpiece may be unevenly deformed mechanically, by temperature change or phase change due to the influence of the processing environment, and the deformation of the materials is uneven, so that residual stress is generated. The existence of residual stress can influence the strength and other mechanical properties of the workpiece, and can cause the defects of deformation, cracking and the like of the workpiece in the use process; defects ultimately affect the condition of the workpiece, such as accuracy and service life. Therefore, providing a theoretical basis for strength analysis and processing deformation prediction, and evaluating the residual stress and state of a workpiece has become an important point of current manufacturing research.
The measurement of residual stress belongs to the field of research of inverse problems, and the magnitude and direction of the residual stress are reversed by outputting strain or equivalent displacement. Currently, measurement techniques can be divided into two categories according to the test principle. One class includes destructive testing methods, such as mechanical and chemical methods; one class includes non-destructive testing methods. The principle of the destructive testing method involves releasing and measuring the workpiece stress in some way. By measuring the strain or displacement of this region, the residual stress state can be obtained according to the principles of elastomechanics. Destructive testing methods are relatively simple and generally have high test accuracy, but in some cases surface damage is unacceptable. Therefore, in order to prevent the sample from being damaged, a nondestructive testing method for measuring physical properties of the material itself using a specific type of equipment has been rapidly developed. These methods do not affect continued use of the measured workpiece, and are suitable for residual stress measurement in most cases; therefore, the nondestructive testing method is gradually becoming the development direction of the residual stress test.
The conventional plane stress measurement method mostly adopts a single-crystal-element contact type ultrasonic transducer, and because the contact type ultrasonic transducer inevitably needs to customize wedge blocks matched with the contact type ultrasonic transducer for generating different incident angles, and needs to use a couplant to ensure sufficient and effective acoustic coupling. The use of wedge blocks and couplant results in inconvenient planar stress measurement operation of the contact ultrasonic transducer, and can not be applied to automation and industrialization occasions. Meanwhile, when the single-crystal-element contact ultrasonic transducer is used for measuring, acoustic time difference information is obtained by only one propagation path in each measuring direction to obtain stress components, however, the change of the acoustic time difference caused by the stress is also ns-level due to small change of the material speed, so that the single-crystal-element contact ultrasonic transducer is very easily influenced by external noise, temperature and other external environment factors, and meanwhile, the acoustic time difference error caused by the uneven thickness of the couplant is intolerable, so that the accuracy of plane stress measurement is influenced.
Disclosure of Invention
The application solves the problems that when the single-crystal-element contact type ultrasonic transducer is used for measuring, the acoustic time difference information is obtained by only one propagation path in each measuring direction to obtain the stress component, the accuracy of plane stress measurement is affected, and the coupling agent is used for the contact type ultrasonic transducer to influence the accuracy of plane stress measurement.
The present application provides such a phased array air coupled transducer, the transducer comprising:
n piezoelectric ceramics, a matching layer and a backing layer;
the N piezoelectric ceramics are uniformly distributed and fixed on the upper surface of the matching layer, and the backing layer is fixed on the piezoelectric ceramics.
Further, there is also provided a preferred embodiment, the transducer further comprising: a housing;
the N piezoelectric ceramics, the matching layer and the backing layer are all fixed inside the shell.
Further, there is also provided a preferred embodiment, the transducer further comprising: a signal connection terminal;
the signal connection end is fixed outside the shell and is used for receiving the excitation signal and the propagation signal.
The application also provides a planar stress ultrasonic measurement method based on a phased array air-coupled transducer, the method is realized by the transducer according to any one of the above, the method comprises two transducers, one transducer is used for receiving an excitation signal, and the other transducer is used for receiving a response signal, and the method comprises the following steps:
the connection end of the transducer signal for receiving the excitation signal transmits the excitation signal to N piezoelectric ceramics, the piezoelectric ceramics convert the excitation signal into an acoustic signal and transmit the acoustic signal to the to-be-detected piece, and the acoustic signal generates LCR waves in the to-be-detected piece;
the method comprises the steps that an object to be tested sends echo signals of LCR waves to N piezoelectric ceramics of a transducer for receiving response signals, the N piezoelectric ceramics convert the received echo signals into the response signals, and the response signals are transmitted to a signal connecting end for receiving the response signals;
acquiring acoustic time difference T1 through data processing according to the LCR wave and the response signal;
adjusting the angle of the transducer, repeating the operation, and obtaining acoustic time differences T2 and T3 corresponding to the measuring directions;
stress in three directions is obtained according to the acoustic elastic effect;
and finishing plane stress measurement of the to-be-measured area of the to-be-measured piece according to the Morse circle stress theory and the stresses in three directions.
Further, there is provided a preferred embodiment, wherein the acoustic time difference T1 is obtained by data processing according to the LCR wave and the response signal, specifically:
wherein,is the acoustic time difference of the a-th propagation path signal in the 1 st measurement direction.
Further, a preferred embodiment is provided, wherein the planar stress measurement of the area to be measured of the piece to be measured is completed according to the Morse circle stress theory and the stresses in three directions, specifically:
wherein sigma 1 、σ 2 、σ 3 Stress in three directions, sigma 1 Is the first principal stress, sigma 2 And θ is the included angle between the first principal stress and the fiber direction of the orthotropic composite material.
Further, a preferred embodiment is also provided, the method further comprising matching the thickness l of the layer 1 And (3) determining:
l 1 ＝(2n-1)λ 1 /4，
wherein n is 1, 2 or 3, lambda 1 Is an ultrasonic wavelength.
The application also provides a plane stress ultrasonic measurement device based on the phased array air coupling transducer, which comprises:
the LCR wave transmitting unit is used for transmitting excitation signals to N piezoelectric ceramics through the connecting end of the transducer signals for receiving the excitation signals, the piezoelectric ceramics convert the excitation signals into acoustic signals and transmit the acoustic signals to the to-be-detected piece, and the acoustic signals generate LCR waves in the to-be-detected piece;
the response signal receiving unit is used for transmitting echo signals of LCR waves to N piezoelectric ceramics of a transducer for receiving response signals by the to-be-tested piece, the N piezoelectric ceramics convert the received echo signals into the response signals and transmit the response signals to a signal connecting end for receiving the response signals;
the acoustic time difference acquisition unit is used for acquiring acoustic time difference T1 through data processing according to the LCR wave and the response signal; adjusting the angle of the transducer, repeating the operation, and obtaining acoustic time differences T2 and T3 corresponding to the measuring directions;
the stress acquisition unit is used for acquiring the stress of the to-be-detected piece in three directions according to the acoustic elastic effect;
and the plane stress acquisition unit is used for completing plane stress measurement of the area to be measured of the piece to be measured according to the Morse round stress theory and the stress in three directions.
The application also provides computer equipment, which comprises a memory and a processor, wherein the memory stores a computer program, and when the processor runs the computer program stored in the memory, the processor executes the planar stress ultrasonic measurement method based on the phased array air coupled transducer.
The application also provides a computer readable storage medium, wherein a computer program is stored on the computer readable storage medium, and the computer program is executed by a processor to execute the planar stress ultrasonic measurement method based on the phased array air coupled transducer.
The application has the advantages that:
the application solves the problems that the traditional plane stress measuring method adopts a pair of contact ultrasonic transducers to calculate and obtain plane stress by converting at least 3 different measuring directions and obtaining the information of acoustic time differences and the like of the 3 measuring directions, the operation is complicated, and the accuracy of plane stress measurement can be influenced by using a coupling agent for the contact ultrasonic transducers.
1. According to the planar stress ultrasonic measurement method based on the phased array air coupling transducer, when stress detection is carried out, N array elements are sequentially excited by the transducer receiving the excitation signal, and the N array elements of the transducer receiving the response signal also receive LCR wave signals of the N excitation array elements. Therefore, the acoustic time differences of the propagation signals of the N multiplied by N propagation paths can be obtained in each measurement direction, and data processing (such as mean processing) is carried out on the acoustic time difference characterization information of the N multiplied by N, so that errors caused by external noise, temperature change and other external environment factors can be restrained, the stress characterization of a single measurement direction is more accurate, and the accuracy of plane stress measurement results is higher.
2. The planar stress ultrasonic measurement method based on the phased array air coupling transducer can be completed by only one pair of transducers when planar stress measurement is carried out, overcomes the defect that the stress detection is carried out by adopting a contact type ultrasonic transducer in the prior art, and ensures sufficient and effective acoustic coupling by using a coupling agent. The application adopts a non-contact transducer, and does not need a custom-matched wedge block and a coupling agent. Therefore, the measuring direction of the transducer pair is changed more conveniently, the measuring process is faster, and the automatic realization of plane stress measurement is facilitated.
3. The application adopts the phased array air coupling transducer to detect stress, overcomes the prejudice of the prior art, is applied to the defect detection field by receiving the amplitude information of the echo, and is applied to the stress measurement field by receiving the acoustic time difference information of the echo, and the stress is obtained by receiving the acoustic time difference information of the echo, so that the principle of the acoustic time difference information and the acoustic time difference information are different, and the characterization information is different, thereby leading the person skilled in the art to be free from considering the application of the acoustic time difference information to the plane stress ultrasonic detection field.
The application is suitable for the field of stress detection.
Drawings
Fig. 1 is a schematic cross-sectional structure of a phased array air-coupled transducer according to one embodiment to another embodiment, in which 1 is a signal connection end, 2 is a backing layer, 3 is a wire, 4 is a piezoelectric ceramic, 5 is a matching layer, and 6 is a housing;
fig. 2 is a schematic diagram of a planar stress ultrasonic measurement method based on a phased array air-coupled transducer according to a fourth embodiment.
Detailed Description
In order to make the technical solution and advantages of the present application more apparent, several embodiments of the present application will be described in further detail with reference to the accompanying drawings, but the following embodiments are only preferred embodiments of the present application and are not intended to limit the application.
Embodiment one, this embodiment will be described with reference to fig. 1. The phased array air coupled transducer according to the present embodiment, the transducer includes:
n piezoelectric ceramics 4, a matching layer 5 and a backing layer 2;
the N piezoelectric ceramics 4 are uniformly distributed and fixed on the upper surface of the matching layer 5, and the backing layer 2 is fixed on the piezoelectric ceramics 4.
The backing layer in the embodiment realizes unidirectional transmission of the sound wave through attenuation of the sound wave, and avoids interference of the sound wave in other directions to the propagation of the front sound wave when the transducer works.
In practical application, the array element width of the piezoelectric ceramic 4 is a×a, and then the area of the piezoelectric ceramic 4 contacting with the matching layer 5 and the backing layer 2 is a×a square, and the array elements are uniformly distributed along the one-dimensional direction to form a one-dimensional array, the array element distance between adjacent piezoelectric ceramics is b, and b > a.
Embodiment two, this embodiment will be described with reference to fig. 1. This embodiment is a further limitation of the phased array air-coupled transducer of the first embodiment, further comprising: a housing 6;
the N piezoelectric ceramics 4, the matching layer 5 and the backing layer 2 are all fixed inside the housing 6.
In this embodiment, the positions of the piezoelectric ceramic 4, the matching layer 5 and the backing layer 2 are fixed, so that the stability of the transducer structure is ensured.
Embodiment III will be described with reference to FIG. 1. This embodiment is a further limitation of the phased array air-coupled transducer of the first embodiment, further comprising: a signal connection terminal 1;
the signal connection 1 is fastened to the outside of the housing 6 for receiving the excitation signal and the propagation signal.
Specifically, each piezoelectric ceramic is connected with the signal connection end through a wire respectively and used for guaranteeing the stability of transmission of excitation signals and echo signals.
Embodiment four, this embodiment will be described with reference to fig. 2. The method for planar stress ultrasonic measurement based on a phased array air-coupled transducer according to the present embodiment is implemented by the transducer according to any one of the third embodiment, and includes two transducers, one for receiving an excitation signal and the other for receiving a response signal, and includes:
the connection end of the transducer signal for receiving the excitation signal transmits the excitation signal to N piezoelectric ceramics, the piezoelectric ceramics convert the excitation signal into an acoustic signal and transmit the acoustic signal to the to-be-detected piece, and the acoustic signal generates LCR waves in the to-be-detected piece;
the method comprises the steps that an object to be tested sends echo signals of LCR waves to N piezoelectric ceramics of a transducer for receiving response signals, the N piezoelectric ceramics convert the received echo signals into the response signals, and the response signals are transmitted to a signal connecting end for receiving the response signals;
acquiring acoustic time difference T1 through data processing according to the LCR wave and the response signal;
adjusting the angle of the transducer, repeating the operation, and obtaining acoustic time differences T2 and T3 corresponding to the measuring directions;
stress in three directions is obtained according to the acoustic elastic effect;
and finishing plane stress measurement of the to-be-measured area of the to-be-measured piece according to the Morse circle stress theory and the stresses in three directions.
Specifically, the response signal is an electrical signal.
In the planar stress ultrasonic measurement method based on the phased array air-coupled transducer, when stress detection is performed, the N piezoelectric ceramics are sequentially excited by the transducer receiving the excitation signal by the excitation signal, and the N piezoelectric ceramics of the transducer receiving the response signal also receive LCR wave signals of the N excitation piezoelectric ceramics. Therefore, the acoustic time differences of the propagation signals of the N multiplied by N propagation paths can be obtained in each measurement direction, and data processing (such as mean processing) is carried out on the acoustic time difference characterization information of the N multiplied by N, so that errors caused by external noise, temperature change and other external environment factors can be restrained, the stress characterization of a single measurement direction is more accurate, and the accuracy of plane stress measurement results is higher.
In a fifth embodiment, the present embodiment is further defined by a planar stress ultrasonic measurement method based on a phased array air coupled transducer according to the fourth embodiment, wherein the acoustic time difference T1 is obtained by data processing according to the LCR wave and the response signal, specifically:
wherein T is 1 a Is the acoustic time difference of the a-th propagation path signal in the 1 st measurement direction.
Specifically, in order to ensure that the acoustic beam has enough energy, an excitation signal is determined to be a sine pulse signal modulated by a hanning window with the center frequency f and the period N, the sine pulse signal passes through a low-pass filter and then is sequentially applied to an excitation phased array air coupling transducer through a signal connection end, 1 to N piezoelectric ceramics are sequentially excited, and the N piezoelectric ceramics of the transducer receiving response signals receive LCR wave signals during each excitation. And the response signal is amplified by the pre-amplifier and then is collected by the high-speed data collection board card. Excited by the ith piezoelectric ceramic, the jth piezoelectric ceramic is connectedThe received propagation path is named L i×j The acoustic time difference T1 after suppressing errors introduced by external environments such as the outside and temperature changes in the measurement direction is obtained by a data processing method such as mean value processing.
In a sixth embodiment, the present embodiment is further defined by the phased array air coupled transducer based plane stress ultrasonic measurement method according to the fourth embodiment, wherein the plane stress measurement of the area to be measured of the piece to be measured is completed according to the morse circle stress theory and stresses in three directions, specifically includes:
wherein sigma 1 、σ 2 、σ 3 Stress in three directions, sigma 1 Is the first principal stress, sigma 2 And θ is the included angle between the first principal stress and the fiber direction of the orthotropic composite material.
Specifically, the required propagation times of the N×N propagation paths are the same, so that the stress measurement lengths L of the N×N propagation paths 0 ＝L N×N Stress sigma in the measuring direction 1 Can be derived from the acoustic time difference T1 based on the sonoelastic effect,
σ 1 ＝K·T1
wherein λ and μ are Lame constants, and l, m and n are Murraghan constants.
The first measuring direction is overlapped with the main coordinate axis and defined as 0 DEG, and the central point of the central connecting line of the transducer for receiving the exciting signal and the transducer for receiving the response signal is taken as the rotation center to rotate by two angles theta in turn 2 And theta 3 Repeating the above operations in 2 different measurement directions to obtain acoustic time differences T2 and T3 corresponding to the measurement directions, and calculating to obtain stress sigma corresponding to the measurement directions by using the above formula 2 Sum sigma 3 。
By the theory of Morse round stress,
σ 1 ＝σ 1 cos 2 θ+σ 2 sin 2 θ
σ 2 ＝σ 1 cos 2 (θ 2 +θ)+σ 2 sin 2 (θ 2 +θ)
σ 3 ＝σ 1 cos 2 (θ 3 +θ)+σ 2 sin 2 (θ 3 +θ)
wherein sigma 1 Is the first principal stress, sigma 2 And θ is the included angle between the first principal stress and the fiber direction of the orthotropic composite material.
And 3 parameters of plane stress of a measuring point (a projection point of the rotation center corresponding to the to-be-measured piece) can be obtained through calculation, wherein the first main stress sigma 1, the second main stress sigma 2 and the included angle theta between the first main stress and the fiber direction of the orthotropic composite material. And performing step scanning on the phased array air coupling transducer, so that plane stress measurement of the to-be-measured area of the to-be-measured piece is realized.
Embodiment seven and this embodiment are further limitations of the planar stress ultrasonic measurement method based on a phased array air coupled transducer according to embodiment four, where the method further includes a thickness l of the matching layer 1 And (3) determining:
l 1 ＝(2n-1)λ 1 /4，
wherein n is 1, 2 or 3, lambda 1 Is of ultrasonic wavelength;
specifically, the value of n needs to ensure that a positive integer is taken in the balance between the structural requirement of the material and the parasitic effect.
An eighth embodiment is a planar stress ultrasonic measurement device based on a phased array air coupled transducer according to the present embodiment, including:
the LCR wave transmitting unit is used for transmitting excitation signals to N piezoelectric ceramics through the connecting end of the transducer signals for receiving the excitation signals, the piezoelectric ceramics convert the excitation signals into acoustic signals and transmit the acoustic signals to the to-be-detected piece, and the acoustic signals generate LCR waves in the to-be-detected piece;
the response signal receiving unit is used for transmitting echo signals of LCR waves to N piezoelectric ceramics of a transducer for receiving response signals by the to-be-tested piece, the N piezoelectric ceramics convert the received echo signals into the response signals and transmit the response signals to a signal connecting end for receiving the response signals;
the acoustic time difference acquisition unit is used for acquiring acoustic time difference T1 through data processing according to the LCR wave and the response signal; adjusting the angle of the transducer, repeating the operation, and obtaining acoustic time differences T2 and T3 corresponding to the measuring directions;
the stress acquisition unit is used for acquiring the stress of the to-be-detected piece in three directions according to the acoustic elastic effect;
and the plane stress acquisition unit is used for completing plane stress measurement of the area to be measured of the piece to be measured according to the Morse round stress theory and the stress in three directions.
The ninth embodiment and the present embodiment provide a specific embodiment for the planar stress ultrasonic measurement method based on the phased array air coupled transducer according to the fourth embodiment, which is also used for explaining the fourth embodiment to the seventh embodiment, specifically:
the phased array air coupling transducer of this embodiment is mainly composed of N piezoelectric ceramics, a matching layer, a backing layer, a signal connection end, a wire and a housing. In order to detect the plane stress of the specific thickness of the to-be-detected piece, the center frequency of the phased array air coupling transducer needs to be determined, so that parameters such as the diameter, the thickness and the like of the piezoelectric ceramic are determined. The material and thickness of the matching layer are determined according to the best matching principle of the matching layer.
Z 1 ＝(Z 0 Z 2 ) 1/2
Wherein Z is 0 Acoustic impedance, Z, of piezoelectric ceramics 1 To match the acoustic impedance of the layer, Z 2 Is the acoustic impedance of air.
A positive integer n is determined, where n may be 1, 2 or 3 in balancing the structural requirements of the material with parasitics. Thickness of matching layer l 1 Is that
l 1 ＝(2n-1)λ 1 /4
λ 1 Is an ultrasonic wavelength.
Ultrasonic stress measurement methods are based on the effect of sonoelasticity, where the stress of a material affects the time of flight of ultrasonic waves in the material. Critical refraction longitudinal waves (LCR waves) have a higher sensitivity to stress than other types of ultrasound waves. To excite critical refraction longitudinal wave (LCR wave), snell's law and air sound velocity c are used air Determining inclination angle theta of phased array air coupling transducer during plane stress measurement by sound velocity c of material to be measured T And theta R ：
In order to ensure that the sound beam has enough energy, an excitation signal is determined to be a sine pulse signal modulated by a hanning window with the center frequency of f and the period of N, the sine pulse signal passes through a low-pass filter and then is sequentially applied to an excitation phased array air coupling transducer through a signal connecting end, 1 to N piezoelectric ceramics are sequentially excited, and the N piezoelectric ceramics of the phased array air coupling transducer which receive response signals during each excitation receive LCR wave signals. And the response signal is amplified by the pre-amplifier and then is collected by the high-speed data collection board card. After the excitation is completed, acoustic time differences of the n×n propagating signals, i.e., acoustic time differences of the LCR wave and the response signal, will be obtained. The acoustic time difference T1 after the errors introduced by the external environment such as the outside and the temperature change are restrained in the measuring direction is obtained through data processing methods such as mean value processing and the like:
wherein,is the acoustic time difference of the a-th propagation path signal in the 1 st measurement direction.
As can be seen from fig. 2:
derivation of cocoa the product can be obtained by the method,
t 1 ＝t 2
from this, it can be seen that the required propagation time t of the N×N propagation paths 1 And t 2 Is identical, so that the stress measurement length L of N×N propagation paths 0 ＝L N×N . The stress sigma in the measuring direction 1 Can be derived from the acoustic time difference T1 based on the sonoelastic effect,
σ 1 ＝K·T1
wherein lambda and mu are Lame constants, m is Murraghan constant, and K is stress coefficient.
The first measuring direction is overlapped with the main coordinate axis and defined as 0 DEG, and the central point of the central connecting line of the transducer for receiving the exciting signal and the transducer for receiving the response signal is taken as the rotation center to rotate by two angles theta in turn 2 And theta 3 Repeating the above operations in 2 different measurement directions to obtain acoustic time differences T2 and T3 corresponding to the measurement directions, and obtaining stress sigma of 3 measurement directions by combining with the acoustic elastic effect 1 、σ 2 Sum sigma 3 . And obtaining 3 parameters of plane stress of a measuring point (a projection point of the rotation center corresponding to the to-be-measured piece) according to Morse stress theory, wherein sigma 1, sigma 2 and theta are obtained. By step-by-step scanning the phased array air coupling transducer, the plane stress measurement of the area to be measured of the piece to be measured is realized:
calculated by Morse round stress theory:
σ 1 ＝σ 1 cos 2 θ+σ 2 sin 2 θ
σ 2 ＝σ 1 cos 2 (θ 2 +θ)+σ 2 sin 2 (θ 2 +θ)
σ 3 ＝σ 1 cos 2 (θ 3 +θ)+σ 2 sin 2 (θ 3 +θ)
wherein sigma 1 Is the first principal stress, sigma 2 And θ is the included angle between the first principal stress and the fiber direction of the orthotropic composite material.
And 3 parameters of plane stress of a measuring point (a projection point of the rotation center corresponding to the to-be-measured piece) can be obtained through calculation, wherein the first main stress sigma 1, the second main stress sigma 2 and the included angle theta between the first main stress and the fiber direction of the orthotropic composite material. And performing step scanning on the phased array air coupling transducer, so that plane stress measurement of the to-be-measured area of the to-be-measured piece is realized.
While the application has been described in detail in connection with the specific embodiments thereof, the foregoing description is considered to be a preferred embodiment of the application and is not intended to limit the application to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the principles of the application.
Claims (2)
1. A method of planar stress ultrasonic measurement based on phased array air coupled transducers, the method comprising two transducers, one for receiving an excitation signal and the other for receiving a response signal, the method comprising:
the signal connection end of the transducer for receiving the excitation signals transmits the excitation signals to N piezoelectric ceramics, and the piezoelectric ceramics convert the excitation signals into LCR waves and transmit the LCR waves to the to-be-detected piece;
the method comprises the steps that a piece to be tested sends echo signals to N piezoelectric ceramics of a transducer for receiving response signals, the N piezoelectric ceramics convert the received echo signals into the response signals and transmit the response signals to a signal connecting end for receiving the response signals;
acquiring acoustic time difference T1 through data processing according to the LCR wave and the response signal;
adjusting the angle of the transducer, repeating the operation, and obtaining acoustic time differences T2 and T3 corresponding to the measuring directions;
stress in three directions is obtained according to the acoustic elastic effect;
finishing plane stress measurement of the to-be-measured area of the to-be-measured piece according to the Morse circle stress theory and the stress in three directions;
the transducer includes:
n piezoelectric ceramics, a matching layer and a backing layer;
the N piezoelectric ceramics are uniformly distributed and fixed on the upper surface of the matching layer, and the backing layer is fixed on the piezoelectric ceramics; the array element width of the piezoelectric ceramics (4) is a multiplied by a, the area of the piezoelectric ceramics (4) contacted with the matching layer (5) and the backing layer (2) is a multiplied by a square, the piezoelectric ceramics are uniformly distributed along a one-dimensional direction to form a one-dimensional array, the array element distance between adjacent piezoelectric ceramics is b, and b is more than a;
the transducer further comprises: a housing;
the N piezoelectric ceramics, the matching layer and the backing layer are all fixed in the shell;
the transducer further comprises: a signal connection terminal;
the signal connection end is fixed outside the shell and is used for receiving the excitation signal and the propagation signal;
the acoustic time difference T1 is obtained through data processing according to the LCR wave and the response signal, specifically:
，
wherein,for the 1 st measuring directionaAcoustic time differences of the individual propagation path signals.
2. The method for planar stress ultrasonic measurement based on a phased array air coupled transducer according to claim 1, further comprising matching the thickness of the layerAnd (3) determining:
，
wherein n is 1, 2 or 3,is an ultrasonic wavelength.
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