CN112710417B - Plane stress measurement system and method for unknown thickness of test piece - Google Patents
Plane stress measurement system and method for unknown thickness of test piece Download PDFInfo
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Abstract
The invention discloses a plane stress measurement system and a plane stress measurement method under the condition of unknown thickness of a test piece, belongs to the technical field of nondestructive testing, and aims to solve the problem that the stress of a material with unknown thickness cannot be measured by an ultrasonic method in the prior art. The ultrasonic transverse and longitudinal wave transducer comprises an electromagnetic ultrasonic transverse and longitudinal wave transducer, a transmitting circuit array, a receiving circuit array, an acquisition circuit array, a control circuit and an upper computer; the electromagnetic ultrasonic transverse-longitudinal wave transducer comprises a permanent magnet, an orthogonal butterfly coil, a spiral coil and a shell; the transmitting circuit array drives the electromagnetic ultrasonic transverse and longitudinal wave transducer to send ultrasonic transverse waves and longitudinal waves, the receiving circuit array conditions echo signals received by the electromagnetic ultrasonic transverse and longitudinal wave transducer and then transmits the conditioned echo signals to the acquisition circuit array, the acquisition circuit array converts the ultrasonic echo signals into digital signals through analog-to-digital conversion, the digital signals are transmitted to an upper computer through a control circuit, and the upper computer calculates stress and displays data and waveforms. The invention is used for detecting the metal material.
Description
Technical Field
The invention relates to a plane stress measurement system and a plane stress measurement method for a test piece with unknown thickness, and belongs to the technical field of nondestructive testing of materials.
Background
Under the action of internal and external factors such as rolling, welding and surface motion, a metal product can generate local stress concentration. Stress concentration not only can cause harmful deformation, but also can affect the rigidity and stability of the product, so that the fatigue strength, the stress corrosion cracking resistance and the service life of the product are reduced. Therefore, the stress condition of the metal product is measured, the health state of the metal product is evaluated, and the method has important significance for reducing the occurrence rate of major safety accidents such as fracture, explosion and the like.
The stress is measured by the ultrasonic method based on the acoustic elastic effect, and the stress is measured by the influence of the stress on the ultrasonic wave speed. Two methods for measuring stress by using ultrasonic waves are proposed in the prior patent: CN105158342A, a method for evaluating residual stress without damage by ultrasonic water immersion, which needs to soak a tested piece in water, uses water as an ultrasonic coupling agent, is easy to cause material rusting, and is difficult to be applied to a test piece in service such as a pipeline; CN111307351A, a method for measuring residual stress by an electromagnetic ultrasonic apparatus, which cannot measure stress under the condition of unknown thickness, is very inconvenient in practical application.
In the method proposed in CN111307351A, the thickness of the tested piece is required to be known, otherwise, the sound velocity cannot be calculated by measuring the sound by an ultrasonic system, and the measurement formula is as follows:
in the case of unidirectional stresses, i.e. σ 1 ≠0,σ 2 =0, the sensitivity analysis of the thickness is performed on the second equation of the above formula:
according to a set of X70 pipeline steel calibration experimental data with thickness d =15.25mm, for this material: v 0 ＝3309.1m/s，C＝-3.350×10 -6 ，T 1T And T 2T The magnitude is about 10us, the influence of stress change on sensitivity analysis is negligible, and T is taken during analysis 1T ＝T 2T ＝2d/V 0 ＝9.217*10 -6 And s. It can be calculated from this that a 0.01mm change in the thickness d of the test piece, i.e., Δ d =0.01mm, will result in a stress calculation error Δ σ =182.0MPa, whereas the yield strength of X70 pipeline steel is between 400MPa and 600MPa, and therefore, cannot be used to evaluate the stress state thereof from the above error. In addition, in practical situations, the actual thickness of the pipeline or other equipment in service is often unknown due to factors such as corrosion or scouring, which greatly limits the application range of the method proposed in patent CN 111307351A.
Disclosure of Invention
The invention aims to solve the problem that the plane stress of a material with unknown thickness cannot be measured by adopting an ultrasonic method in the prior art, and provides a plane stress measuring system and a plane stress measuring method for a test piece with unknown thickness.
The invention relates to a plane stress measurement system for the case that the thickness of a test piece is unknown, which comprises an electromagnetic ultrasonic transverse-longitudinal wave transducer, a transmitting circuit array, a receiving circuit array, an acquisition circuit array, a control circuit and an upper computer;
the transmitting circuit array drives the electromagnetic ultrasonic transverse-longitudinal wave transducer to transmit ultrasonic transverse waves and ultrasonic longitudinal waves, the receiving circuit array conditions echo signals received by the electromagnetic ultrasonic transverse-longitudinal wave transducer and transmits the conditioned echo signals to the acquisition circuit array, the acquisition circuit array converts the ultrasonic echo signals into digital signals through analog-to-digital conversion and transmits the digital signals to the upper computer through the control circuit, and the upper computer calculates stress according to the digital signals of the ultrasonic echo and displays data and waveforms;
the electromagnetic ultrasonic transverse-longitudinal wave transducer comprises a permanent magnet (1), an orthogonal butterfly coil (2), a spiral coil (3) and a shell (4);
the permanent magnet (1), the orthogonal butterfly coil (2) and the spiral coil (3) are sequentially overlapped from top to bottom, and the axial center lines of the permanent magnet, the orthogonal butterfly coil and the spiral coil are overlapped;
the shell (4) is arranged outside the permanent magnet (1), the orthogonal butterfly coil (2) and the spiral coil (3);
the orthogonal butterfly coils are formed by orthogonally overlapping and combining two groups of butterfly coils, and the two groups of butterfly coils respectively excite transverse waves of which the propagation directions are thickness directions and the polarization directions are mutually vertical;
the length of the orthogonal butterfly coil (2) in the radial direction is larger than the diameter of the permanent magnet (1), and a coil area which can excite the transverse wave of which the polarization direction is vertical to the axis is arranged right below the permanent magnet (1);
the spiral coil (3) is used for exciting longitudinal waves propagating in the thickness direction.
The invention relates to a measuring method of a plane stress measuring system under the condition that the thickness of a test piece is unknown, which comprises the following steps:
s1, processing a cross-shaped calibration test block with the same material as a to-be-tested piece;
s2, measuring the cross-shaped calibration test block by adopting a plane stress measurement system to obtain experimental calibration data of the material;
the experimental calibration data includes: the material inherent anisotropy coefficient alpha, a constant f (alpha) related to the material inherent anisotropy coefficient, and an acoustic-elastic coefficient C of transverse wave acoustic-elastic characteristic quantity to stress parallel to the rolling direction A1 Coefficient of acoustoelasticity C of characteristic quantity of sound and elasticity of transverse and longitudinal waves to stress parallel to rolling direction B1 The acoustic-elastic coefficient C of the characteristic quantity of transverse wave acoustic elasticity to the stress perpendicular to the rolling direction A2 And the acoustic-elastic coefficient C of the acoustic-elastic characteristic quantity of the transverse and longitudinal waves to the stress perpendicular to the rolling direction B2 ；
S3, measuring the to-be-tested piece by adopting a plane stress measuring system, adsorbing an electromagnetic ultrasonic transverse-longitudinal wave transducer on the to-be-tested piece, enabling the axial direction of the orthogonal butterfly coil (2) to coincide with the rolling direction of the to-be-tested piece, and obtaining T 1T 、T 2T And T L ，T 1T T represents the transverse wave sound with the polarization direction along the x1 axis and the propagation direction along the x3 axis 2T T represents the transverse wave sound with the polarization direction along the x2 axis and the propagation direction along the x3 axis L When the polarization direction and the propagation direction are both longitudinal wave sound along the x3 axis;
s4, the upper computer obtains T according to the material experiment calibration data stored in the database and the material experiment calibration data obtained in the S3 1T 、T 2T And T L The stress σ parallel to the rolling direction is obtained by calculation according to the following formula 1 And stress σ in the direction perpendicular to the rolling direction 2 ：
Preferably, the step S1 of processing a cross-shaped calibration test block with the same material as the test piece to be tested further includes:
and annealing the cross-shaped calibration test block to release the residual stress.
Preferably, in S2, the specific method for obtaining the experimental calibration data of the material by measuring the cross calibration test block with the plane stress measurement system includes:
s2-1, adsorbing an electromagnetic ultrasonic transverse-longitudinal wave transducer at the intersection of two main shafts of a cross calibration test block, and enabling the axes of two groups of butterfly coils of the orthogonal butterfly coil (2) to be parallel and perpendicular to the rolling direction respectively;
s2-2, applying stress sigma parallel to rolling direction to the cross-shaped calibration test block 1 Testing the cross calibration test block at a certain stress value interval within the yield strength range of the material to obtain the ultrasonic propagation time at the moment;
the ultrasonic wave propagation time includes: t of transverse wave sound with polarization direction along x1 axis and propagation direction along x3 axis 1T Transverse wave sound time T with polarization direction along x2 axis and propagation direction along x3 axis 2T And T of longitudinal wave sound with both polarization direction and propagation direction along x3 axis L ；
S2-3, calculating by the upper computer according to the ultrasonic propagation time obtained in the S2-2 and according to the following formula to obtain a transverse wave acoustic elastic characteristic quantity phi and a longitudinal wave acoustic elastic characteristic quantity R:
s2-4, fitting phi, R and sigma through linearity 1 According to the following formula, the acoustic-elastic coefficient C of the transverse wave acoustic-elastic characteristic quantity to the stress parallel to the rolling direction is obtained A1 Coefficient of acoustic elasticity C of characteristic quantity of acoustic elasticity of transverse and longitudinal waves to stress parallel to rolling direction B1 ：
S2-5, applying stress sigma perpendicular to rolling direction to the cross-shaped calibration test block 2 Testing the cross calibration test block at certain stress value intervals within the yield strength range of the material to obtain the ultrasonic propagation time at the moment;
the ultrasonic wave propagation time includes: transverse wave sound time T with polarization direction along x1 axis and propagation direction along x3 axis 1T Transverse wave sound time T with polarization direction along x2 axis and propagation direction along x3 axis 2T And direction of polarization and propagationT when all longitudinal waves are along the x3 axis L ；
S2-6, calculating by the upper computer according to the ultrasonic propagation time obtained in the S2-5 according to the following formula to obtain a transverse wave acoustic elastic characteristic quantity phi and a transverse wave acoustic elastic characteristic quantity R:
s2-7, by linear fitting of phi, R and sigma 2 According to the following formula, the acoustic-elastic coefficient C of the transverse wave acoustic-elastic characteristic quantity to the stress perpendicular to the rolling direction is obtained A2 And the acoustic elastic coefficient C of the transverse and longitudinal wave acoustic elastic characteristic quantity to the stress vertical to the rolling direction B2 ：
S2-8, unloading stress applied to the cross-shaped calibration test block to enable the cross-shaped calibration test block to be in a zero-stress state, obtaining ultrasonic propagation time at the moment, and calculating according to the ultrasonic propagation time at the moment to obtain phi and R:
at this time, the process of the present invention,
s2-9, using an upper computer to convert alpha, f (alpha) and C of the material A1 、C B1 、C A2 And C B2 And storing the data into a database.
Preferably, said T is 1T 、T 2T And T L All the time differences of the ultrasonic waves propagating on the thickness path of the measured piece are time differences;
the tested piece comprises a piece to be tested and a cross-shaped calibration test block;
the time difference of propagation is one of a time difference of one propagation and a time difference of multiple reciprocal propagation.
The plane stress measuring system and the plane stress measuring method for the unknown thickness of the test piece are mainly used for detecting metal materials, and have the following beneficial effects:
1. the electromagnetic ultrasonic technology is adopted to directly generate ultrasonic waves on the surface of the material to be detected, so that the method has the advantages of non-contact type, no need of a coupling agent and no need of surface pretreatment, and effectively avoids the problems of low efficiency, rusting of the material and incapability of resisting high temperature caused by the coupling agent;
2. by adopting a transverse wave and longitudinal wave combination method and utilizing the relation between the speed and the propagation time, the thickness is eliminated in a formula, the measurement error caused by the thickness is effectively avoided, and the two-dimensional plane stress measurement can be directly carried out on the service pipeline under the condition that the thickness is unknown.
Drawings
FIG. 1 is a schematic structural diagram of an electromagnetic ultrasonic transverse-longitudinal-axis transducer according to the present invention;
FIG. 2 is a schematic diagram of a plane stress measurement system of the present invention for an unknown specimen thickness;
FIG. 3 is a schematic diagram of a cross-shaped calibration test block of the measuring method of the plane stress measuring system for the case of unknown thickness of the test piece according to the present invention;
FIG. 4 is a schematic diagram of a coordinate system established according to a second embodiment of the present invention;
fig. 5 is a schematic diagram of relative positions of a set of butterfly coils and permanent magnets in orthogonal butterfly coils of the electromagnetic ultrasonic transverse-longitudinal-wave transducer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the 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 inventive efforts based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.
The first embodiment is as follows: the plane stress measuring system for the unknown thickness condition of the test piece in the embodiment is described below with reference to fig. 1, fig. 2 and fig. 5, and comprises an electromagnetic ultrasonic transverse-longitudinal transducer, a transmitting circuit array, a receiving circuit array, an acquisition circuit array, a control circuit and an upper computer;
the transmitting circuit array drives the electromagnetic ultrasonic transverse-longitudinal wave transducer to transmit ultrasonic transverse waves and ultrasonic longitudinal waves, the receiving circuit array conditions echo signals received by the electromagnetic ultrasonic transverse-longitudinal wave transducer and transmits the conditioned echo signals to the acquisition circuit array, the acquisition circuit array converts the ultrasonic echo signals into digital signals through analog-to-digital conversion and transmits the digital signals to the upper computer through the control circuit, and the upper computer calculates stress according to the digital signals of the ultrasonic echo and displays data and waveforms;
the electromagnetic ultrasonic transverse-longitudinal wave transducer comprises a permanent magnet (1), an orthogonal butterfly coil (2), a spiral coil (3) and a shell (4);
the permanent magnet (1), the orthogonal butterfly coil (2) and the spiral coil (3) are sequentially overlapped from top to bottom, and the axial center lines of the permanent magnet, the orthogonal butterfly coil and the spiral coil are overlapped;
the shell (4) is arranged outside the permanent magnet (1), the orthogonal butterfly coil (2) and the spiral coil (3);
the orthogonal butterfly coils are formed by orthogonal overlapping combination of two groups of butterfly coils, and the two groups of butterfly coils respectively excite transverse waves of which the propagation directions are thickness directions and the polarization directions are mutually vertical;
the length of the orthogonal butterfly coil (2) in the radial direction is larger than the diameter of the permanent magnet (1), and a coil area capable of exciting transverse waves with the polarization direction vertical to the axis is arranged right below the permanent magnet (1);
the spiral coil (3) is used for exciting longitudinal waves propagating in the thickness direction.
In the embodiment, the length of the orthogonal butterfly coil (2) in the radial direction is larger than the diameter of the permanent magnet (1), and a coil area capable of exciting transverse waves with the polarization direction vertical to the axis is arranged right below the permanent magnet (1).
In this embodiment, the control circuit not only transfers parameters and ultrasonic data, but also coordinates the working timings of the transmitting circuit array, the receiving circuit array and the collecting circuit array, thereby avoiding mutual interference between them. The control circuit further comprises a gain control. The gain control is to control the amplification factor of the receiving circuit array to the signal, the parameter is set on the upper computer and then transmitted to the control circuit, and then the control circuit controls the signal according to the control mode specified by the integrated chip.
In this embodiment, the transmitting circuit array includes three high-frequency high-power transmitting circuit units, each of which can drive a pulse voltage of 500V or more and a pulse current of 20A or more, and supports an operating frequency of 1 to 10MHz and a repetition frequency of 1 kHz.
In this embodiment, the receiving circuit array includes three low-noise high-gain circuit units, and each receiving unit can achieve a signal-to-noise ratio of more than 5 dB. The gain of the receiving unit can be controlled by the control circuit, and the gain range comprises 0dB-90dB.
In this embodiment, the acquisition circuit array includes three high-speed acquisition circuit units, the sampling frequency of each high-speed acquisition circuit unit is above 40MHz, and the number of sampling bits is above 10 bits.
Further, the length of the orthogonal butterfly coil (2) in the radial direction is larger than the diameter of the permanent magnet (1), and the difference between the length and the diameter is larger than or equal to 1cm.
Still further, the permanent magnet (1) is of a cylindrical structure and is magnetized in the thickness direction.
Still further, the data displayed by the upper computer comprises: and (4) calculating the obtained stress value according to the digital signal of the ultrasonic echo.
The second embodiment is as follows: in the following, the present embodiment will be described with reference to fig. 2, 3 and 4, and the ultrasonic method for measuring stress is based on the acoustic elastic effect, and the stress is measured by the influence of the stress on the ultrasonic wave velocity, and the method is established on the three-dimensional coordinate systems x1, x2 and x 3. The measurement method of the plane stress measurement system for the case of unknown thickness of the test piece according to the embodiment includes:
s1, processing a cross-shaped calibration test block which is made of the same material as a to-be-tested piece;
s2, measuring the cross-shaped calibration test block by adopting a plane stress measurement system to obtain experimental calibration data of the material;
the experimental calibration data includes: the material inherent anisotropy coefficient alpha, a constant f (alpha) related to the material inherent anisotropy coefficient, and an acoustic-elastic coefficient C of transverse wave acoustic-elastic characteristic quantity to stress parallel to the rolling direction A1 Coefficient of acoustoelasticity C of characteristic quantity of sound and elasticity of transverse and longitudinal waves to stress parallel to rolling direction B1 Acoustic elastic coefficient C of transverse wave acoustic elastic characteristic quantity to stress perpendicular to rolling direction A2 And the acoustic-elastic coefficient C of the acoustic-elastic characteristic quantity of the transverse and longitudinal waves to the stress perpendicular to the rolling direction B2 ；
S3, measuring the to-be-tested piece by adopting a plane stress measuring system, adsorbing an electromagnetic ultrasonic transverse-longitudinal wave transducer on the to-be-tested piece, enabling the axial direction of the orthogonal butterfly coil (2) to coincide with the rolling direction of the to-be-tested piece, and obtaining T 1T 、T 2T And T L ，T 1T T represents the transverse wave sound with the polarization direction along the x1 axis and the propagation direction along the x3 axis 2T T represents the transverse wave sound with the polarization direction along the x2 axis and the propagation direction along the x3 axis L Representing longitudinal wave sound with both polarization and propagation directions along the x3 axis;
s4, the upper computer obtains the T according to the material experiment calibration data stored in the database and the T obtained in the S3 1T 、T 2T And T L The stress σ parallel to the rolling direction is obtained by calculation according to the following formula 1 And stress σ in the direction perpendicular to the rolling direction 2 ：
Further, the step S1 of processing the cross-shaped calibration test block with the same material as the to-be-tested test block further includes:
and annealing the cross-shaped calibration test block to release the residual stress.
Further, in S2, the specific method for obtaining the experimental calibration data of the material by measuring the cross calibration test block with the plane stress measurement system includes:
s2-1, adsorbing an electromagnetic ultrasonic transverse-longitudinal-wave transducer at the intersection of two main shafts of a cross-shaped calibration test block, and enabling the axes of two groups of butterfly coils of an orthogonal butterfly coil (2) to be parallel and vertical to the rolling direction respectively;
s2-2, applying stress sigma parallel to rolling direction to the cross-shaped calibration test block 1 Testing the cross calibration test block at certain stress value intervals within the yield strength range of the material to obtain the ultrasonic propagation time at the moment;
the ultrasonic wave propagation time includes: t of transverse wave sound with polarization direction along x1 axis and propagation direction along x3 axis 1T Transverse wave sound time T with polarization direction along x2 axis and propagation direction along x3 axis 2T And T of longitudinal wave sound with both polarization direction and propagation direction along x3 axis L ；
S2-3, calculating by the upper computer according to the ultrasonic propagation time obtained in the S2-2 and according to the following formula to obtain a transverse wave acoustic elastic characteristic quantity phi and a transverse wave acoustic elastic characteristic quantity R:
s2-4, fitting phi, R and sigma linearly 1 The acoustic-elastic coefficient C of the characteristic quantity of the transverse wave acoustic elasticity versus the stress parallel to the rolling direction is obtained according to the following formula A1 Coefficient of acoustic elasticity C of characteristic quantity of acoustic elasticity of transverse and longitudinal waves to stress parallel to rolling direction B1 ：
S2-5, applying stress sigma perpendicular to rolling direction to the cross calibration test block 2 Testing the cross calibration test block at a certain stress value interval within the yield strength range of the material to obtain the ultrasonic propagation time at the moment;
the describedThe ultrasonic wave propagation time includes: transverse wave sound time T with polarization direction along x1 axis and propagation direction along x3 axis 1T Transverse wave sound time T with polarization direction along x2 axis and propagation direction along x3 axis 2T And T of longitudinal wave sound with both polarization direction and propagation direction along x3 axis L ；
S2-6, calculating by the upper computer according to the ultrasonic propagation time obtained in the S2-5 according to the following formula to obtain a transverse wave acoustic elastic characteristic quantity phi and a transverse wave acoustic elastic characteristic quantity R:
s2-7, by linear fitting of phi, R and sigma 2 The acoustic-elastic coefficient C of the characteristic quantity of the transverse wave acoustic elasticity against the stress perpendicular to the rolling direction is obtained according to the following formula A2 And the acoustic-elastic coefficient C of the acoustic-elastic characteristic quantity of the transverse and longitudinal waves to the stress perpendicular to the rolling direction B2 ：
S2-8, unloading the stress applied to the cross calibration test block to enable the cross calibration test block to be in a zero-stress state, obtaining the ultrasonic propagation time at the moment, and calculating according to the ultrasonic propagation time at the moment to obtain phi and R:
at this time, the process of the present invention,
s2-9, using an upper computer to convert alpha, f (alpha) and C of the material A1 、C B1 、C A2 And C B2 And storing the data into a database.
In the embodiment, the axes of the two groups of the orthogonal butterfly coils (2) are respectively parallel and vertical to the rolling direction, so that orthogonal transverse waves which are transmitted along the thickness direction and have polarization directions respectively vertical and parallel to the rolling direction can be excited.
In this embodiment, in the process of obtaining the stress test value by testing the cross-shaped calibration test block, for accurately measuring the stress and strain of the delayed body material, the stress value is kept for 5 minutes before each measurement.
Still further, said T 1T 、T 2T And T L All the time differences of the ultrasonic wave propagating on the thickness path of the measured piece are time differences;
the tested piece comprises a piece to be tested and a cross-shaped calibration test block;
the time difference of propagation is one of a time difference of one propagation and a time difference of multiple reciprocal propagation.
In this embodiment, T 1T 、T 2T And T L Obtaining according to the proposal of 'nondestructive testing electromagnetic ultrasonic pulse echo type thickness measuring method'.
In the invention, the principle of measuring the stress on the surface of the metal material by adopting an electromagnetic ultrasonic transverse-longitudinal transducer is as follows:
in the transmitting process, high-power current with the frequency of megahertz is firstly conducted in the orthogonal butterfly coil (2) and the spiral coil (3). According to the electromagnetic field theory, the current can induce eddy current with the same frequency and the opposite direction in the skin depth of the surface of the metal test piece to be tested. The alternating eddy currents are subjected to a lorentz force under the electrostatic field exerted by the permanent magnet (1), the direction of which can be determined by the left-hand rule. The surface of the metal test piece generates periodic vibration and elastic deformation under the action of Lorentz force. When such vibrations propagate in the metal in the form of waves, ultrasonic waves are formed. The receiving process is the reverse of the transmitting process.
The current flow directions of all wires of the orthogonal butterfly coil (2) in the axial line area are parallel to the axial line and have the same direction, so that eddy currents induced in the test piece by the part of the current are only subjected to Lorentz force perpendicular to the axial line, and in combination with the fact that as shown in the figure 1, the orthogonal butterfly coil (2) is magnetized in the thickness direction, so that transverse waves with the propagation direction along the thickness direction and the polarization direction perpendicular to the axial line of the orthogonal butterfly coil (2) are excited. The polarization direction of the ultrasonic wave of this portion is most easily controlled, so that only this portion is located in the magnetic field range, and the remaining portion is not used for exciting the ultrasonic wave.
With reference to fig. 1, the permanent magnet (1) is magnetized in the thickness direction, the direction of the magnetic field right below the magnet can be considered to be approximately perpendicular to the surface of the test piece to be tested, but the magnetic field has a certain angle with the surface of the test piece to be tested at the oblique lower part of the permanent magnet (1), the magnetic field has a horizontal component, and the spiral coil (3) can effectively utilize the component to excite longitudinal waves with the propagation direction and the polarization direction along the thickness direction.
In the invention, the stress is measured by the ultrasonic method based on the acoustic-elastic effect through the influence of the stress on the ultrasonic wave speed.
According to the acoustic-elastic theory proposed by Tokuoka and Iwashimizu, the relationship between the horizontal and longitudinal wave sound time and the stress in the isotropic material can be deduced, so that the plane stress is calculated:
where Φ represents a transverse wave acoustoelastic characteristic quantity, R represents a transverse wave and longitudinal wave acoustoelastic characteristic quantity, and V 1T Representing the wave speed of the transverse wave with the polarization direction along the x1 axis and the propagation direction along the x3 axis; v 2T Representing the wave speed of the transverse wave with the polarization direction along the x2 axis and the propagation direction along the x3 axis; (ii) a V L The longitudinal wave sound velocity along the x3 axis represents the polarization direction and the propagation direction; c A Acoustic elastic coefficient of transverse wave, C R Represents the acoustic elastic coefficient of longitudinal waves; sigma 1 Stress in the direction along the x1 axis; sigma 2 Indicating stress in the direction along the x2 axis.
The equation can be transformed according to the acoustic path formula D = T V, and the expression about the speed of the transverse wave and the longitudinal wave is converted into the expression about the sound of the transverse wave and the longitudinal wave:
in the formula, T 1T Representing the polarization directionWhen the transverse wave sound along the x1 axis and the x3 axis is propagated; t is 2T Represents the time of transverse wave sound with the polarization direction along the x2 axis and the propagation direction along the x3 axis; t is a unit of L Indicating longitudinal wave sound along the x3 axis for both polarization and propagation.
As can be seen from the above equation, the measured value of the stress is independent of the thickness of the test piece, and is related only to the acoustic elastic coefficient of the test piece. Under normal conditions, the acoustic elastic coefficients of the same materials are the same, so that the stress received by a test piece under unknown thickness can be measured only by calibrating the acoustic elastic coefficients of the materials before measurement, and the method is very useful for products in service.
In the industrial field, there are also a large number of orthotropic materials due to the rolling factor. For orthotropic materials, the acoustic elastic coefficients parallel to the rolling direction and perpendicular to the rolling direction are different, and therefore the stress measurement equation is modified by introducing the material intrinsic anisotropy coefficient α and a constant f (α) related to the material intrinsic anisotropy coefficient, and introducing different acoustic elastic coefficients in different directions.
In the formula, α represents an anisotropy coefficient inherent to the material; f (α) represents a constant related to the intrinsic anisotropy coefficient of the material; c A1 Acoustic-elastic coefficients representing the acoustic-elastic characteristic quantity of the transverse wave against stress parallel to the rolling direction; c B1 Acoustic-elastic coefficients representing the characteristic quantity of the longitudinal and transverse wave acoustic elasticity versus stress parallel to the rolling direction; c A2 Acoustic-elastic coefficients representing the acoustic-elastic characteristic quantity of the transverse wave against stress in a direction perpendicular to the rolling direction; c B2 The acoustic-elastic coefficient of the transverse-longitudinal wave acoustic-elastic characteristic quantity to the stress perpendicular to the rolling direction is shown.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that 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 features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.
Claims (7)
1. The plane stress measuring system for the unknown thickness of the test piece comprises an electromagnetic ultrasonic transverse-longitudinal wave transducer, a transmitting circuit array, a receiving circuit array, an acquisition circuit array, a control circuit and an upper computer;
the transmitting circuit array drives the electromagnetic ultrasonic transverse-longitudinal wave transducer to transmit ultrasonic transverse waves and ultrasonic longitudinal waves, the receiving circuit array conditions echo signals received by the electromagnetic ultrasonic transverse-longitudinal wave transducer and transmits the conditioned echo signals to the acquisition circuit array, the acquisition circuit array converts the ultrasonic echo signals into digital signals through analog-to-digital conversion and transmits the digital signals to an upper computer through a control circuit, and the upper computer calculates stress according to the digital signals of the ultrasonic echo and displays data and waveforms;
the electromagnetic ultrasonic transverse-longitudinal wave transducer comprises a permanent magnet (1), an orthogonal butterfly coil (2), a spiral coil (3) and a shell (4);
the permanent magnet (1), the orthogonal butterfly coil (2) and the spiral coil (3) are sequentially overlapped from top to bottom, and the axial center lines of the permanent magnet, the orthogonal butterfly coil and the spiral coil are overlapped;
the shell (4) is arranged outside the permanent magnet (1), the orthogonal butterfly coil (2) and the spiral coil (3);
the orthogonal butterfly coils are formed by orthogonal overlapping combination of two groups of butterfly coils, and the two groups of butterfly coils respectively excite transverse waves of which the propagation directions are thickness directions and the polarization directions are mutually vertical;
the length of the orthogonal butterfly coil (2) in the radial direction is larger than the diameter of the permanent magnet (1), and a coil area capable of exciting transverse waves with the polarization direction vertical to the axis is arranged right below the permanent magnet (1);
the spiral coil (3) is used for exciting longitudinal waves propagating along the thickness direction;
the plane stress measurement system is characterized in that the measurement method based on the plane stress measurement system comprises the following steps:
s1, processing a cross-shaped calibration test block with the same material as a to-be-tested piece;
s2, measuring the cross-shaped calibration test block by adopting a plane stress measurement system to obtain experimental calibration data of the material;
the experimental calibration data includes: the material inherent anisotropy coefficient alpha, a constant f (alpha) related to the material inherent anisotropy coefficient, and an acoustic-elastic coefficient C of transverse wave acoustic-elastic characteristic quantity to stress parallel to the rolling direction A1 Coefficient of acoustoelasticity C of characteristic quantity of sound and elasticity of transverse and longitudinal waves to stress parallel to rolling direction B1 Acoustic elastic coefficient C of transverse wave acoustic elastic characteristic quantity to stress perpendicular to rolling direction A2 And the acoustic elastic coefficient C of the transverse and longitudinal wave acoustic elastic characteristic quantity to the stress vertical to the rolling direction B2 ；
S3, measuring the to-be-tested piece by adopting a plane stress measuring system, adsorbing an electromagnetic ultrasonic transverse-longitudinal wave transducer on the to-be-tested piece, enabling the axial direction of the orthogonal butterfly coil (2) to coincide with the rolling direction of the to-be-tested piece, and obtaining T 1T 、T 2T And T L ，T 1T T represents the transverse wave sound with the polarization direction along the x1 axis and the propagation direction along the x3 axis 2T T represents the transverse wave sound with the polarization direction along the x2 axis and the propagation direction along the x3 axis L Representing longitudinal wave sound with both polarization and propagation directions along the x3 axis;
s4, the upper computer obtains the T according to the material experiment calibration data stored in the database and the T obtained in the S3 1T 、T 2T And T L The stress σ parallel to the rolling direction is obtained by calculation according to the following formula 1 And stress σ in the direction perpendicular to the rolling direction 2 ：
2. The system for measuring the plane stress of the unknown thickness of the test piece according to claim 1, characterized in that the length of the orthogonal butterfly coil (2) in the radial direction is greater than the diameter of the permanent magnet (1), and the difference between the two is greater than or equal to 1cm.
3. The system for measuring the plane stress of the test piece with unknown thickness according to claim 1 or 2, characterized in that the permanent magnet (1) is of a cylindrical structure and is magnetized in the thickness direction.
4. The system for measuring the plane stress of the test piece with unknown thickness according to claim 1, wherein the data displayed by the upper computer comprises: and (4) calculating the obtained stress value according to the digital signal of the ultrasonic echo.
5. The system for measuring plane stress of unknown specimen thickness according to claim 1, wherein the step S1 of processing a cross-shaped calibration block having the same material as the specimen to be tested further comprises:
and annealing the cross-shaped calibration test block to release the residual stress.
6. The system for measuring the plane stress of the unknown thickness specimen of claim 1, wherein the step S2 of measuring the cross calibration test block by using the plane stress measuring system comprises the following steps:
s2-1, adsorbing an electromagnetic ultrasonic transverse-longitudinal-wave transducer at the intersection of two main shafts of a cross-shaped calibration test block, and enabling the axes of two groups of butterfly coils of an orthogonal butterfly coil (2) to be parallel and vertical to the rolling direction respectively;
s2-2, applying stress sigma parallel to rolling direction to the cross-shaped calibration test block 1 Testing the cross calibration test block at certain stress value intervals within the yield strength range of the material to obtain the ultrasonic propagation time at the moment;
the ultrasonic wave propagation time includes: transverse wave sound time T with polarization direction along x1 axis and propagation direction along x3 axis 1T Transverse wave sound time T with polarization direction along x2 axis and propagation direction along x3 axis 2T And direction of polarization and propagationLongitudinal wave sound time T along x3 axis L ；
S2-3, calculating by the upper computer according to the ultrasonic propagation time obtained in the S2-2 and according to the following formula to obtain a transverse wave acoustic elastic characteristic quantity phi and a longitudinal wave acoustic elastic characteristic quantity R:
s2-4, fitting phi, R and sigma linearly 1 The acoustic-elastic coefficient C of the characteristic quantity of the transverse wave acoustic elasticity versus the stress parallel to the rolling direction is obtained according to the following formula A1 Coefficient of acoustic elasticity C of characteristic quantity of acoustic elasticity of transverse and longitudinal waves to stress parallel to rolling direction B1 ：
S2-5, applying stress sigma perpendicular to rolling direction to the cross-shaped calibration test block 2 Testing the cross calibration test block at certain stress value intervals within the yield strength range of the material to obtain the ultrasonic propagation time at the moment;
the ultrasonic wave propagation time includes: transverse wave sound time T with polarization direction along x1 axis and propagation direction along x3 axis 1T Transverse wave sound time T with polarization direction along x2 axis and propagation direction along x3 axis 2T And T when the polarization direction and the propagation direction are both longitudinal wave sound along the x3 axis L ；
S2-6, calculating by the upper computer according to the ultrasonic propagation time obtained in the S2-5 according to the following formula to obtain a transverse wave acoustic elastic characteristic quantity phi and a transverse wave acoustic elastic characteristic quantity R:
s2-7, by linear fitting of phi, R and sigma 2 The acoustic-elastic coefficient C of the characteristic quantity of the transverse wave acoustic elasticity against the stress perpendicular to the rolling direction is obtained according to the following formula A2 And the acoustic-elastic coefficient C of the acoustic-elastic characteristic quantity of the transverse and longitudinal waves to the stress perpendicular to the rolling direction B2 ：
S2-8, unloading stress applied to the cross-shaped calibration test block to enable the cross-shaped calibration test block to be in a zero-stress state, obtaining ultrasonic propagation time at the moment, and calculating according to the ultrasonic propagation time at the moment to obtain phi and R:
at this time, the process of the present invention,
s2-9, using an upper computer to convert alpha, f (alpha) and C of the material A1 、C B1 、C A2 And C B2 And storing the data into a database.
7. The method of claim 1 or 6, wherein T is the thickness of the specimen and the thickness of the specimen is unknown 1T 、T 2T And T L All the time differences of the ultrasonic wave propagating on the thickness path of the measured piece are time differences;
the tested piece comprises a piece to be tested and a cross-shaped calibration test block;
the time difference of propagation is one of a time difference of one propagation and a time difference of multiple reciprocal propagation.
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