CN113639911A - Ultrasonic nondestructive testing method for measuring circumferential compressive stress of surface layer of energetic grain - Google Patents

Ultrasonic nondestructive testing method for measuring circumferential compressive stress of surface layer of energetic grain Download PDF

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CN113639911A
CN113639911A CN202110853724.0A CN202110853724A CN113639911A CN 113639911 A CN113639911 A CN 113639911A CN 202110853724 A CN202110853724 A CN 202110853724A CN 113639911 A CN113639911 A CN 113639911A
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stress
ultrasonic
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grain
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CN113639911B (en
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潘勤学
李双阳
徐晓宇
张云淼
常梅乐
李飒
李伟
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Beijing Institute of Technology BIT
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
    • G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/07—Analysing solids by measuring propagation velocity or propagation time of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/46—Processing the detected response signal, e.g. electronic circuits specially adapted therefor by spectral analysis, e.g. Fourier analysis or wavelet analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/44—Processing the detected response signal, e.g. electronic circuits specially adapted therefor
    • G01N29/50—Processing the detected response signal, e.g. electronic circuits specially adapted therefor using auto-correlation techniques or cross-correlation techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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    • G01N2291/102—Number of transducers one emitter, one receiver

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Abstract

The invention provides an ultrasonic nondestructive testing method for measuring circumferential compressive stress of a surface layer of an energy-containing grain, which comprises a detection device, a verification-loading device and a detection method, wherein the detection device, the verification-loading device and the detection method are used for verifying the effectiveness and the accuracy of the detection of the circumferential stress by obtaining the sound time difference of the grain in the circumferential stress state and the stress-free state, calculating the circumferential compressive stress of the grain by using the previously measured circumferential force ultrasonic detection coefficient of the energy-containing grain and comparing the calculated circumferential compressive stress with the reading of a pressure sensor. The method of contacting the outer surface of the grain is adopted to measure the residual stress, the existing ultrasonic longitudinal transducer can be normally used, the performance is good, and the reverse thrust precision of the loading-verifying device is reasonable. The device has small volume, simple manufacturing process, convenient use and lower cost.

Description

Ultrasonic nondestructive testing method for measuring circumferential compressive stress of surface layer of energetic grain
Technical Field
The invention provides an ultrasonic nondestructive testing method for measuring circumferential compressive stress of a surface layer of an energy-containing grain, which comprises a testing device, a verification-loading device and a testing method, and is suitable for circumferential stress testing of energy-containing columnar materials.
Background
Residual stress is one of the main defects of high polymer bonded explosive products, the residual stress in the explosive can accelerate the aging of explosive pieces, the storage life of the weapon is influenced, and the influence on the stock, the integral loading or the integral storage of the weapon is complex and often brings harm. Practice has shown that residual stresses can severely reduce the structural strength and fatigue life of the explosive, etc. In the charging structure of the weapon, the explosive structure (or part) is the weakest link, the safety of the weapon determines the safety of the weapon under the stimulation of external factors, and the mechanical behavior of energetic materials determines the vulnerability and the viability of the weapon.
The residual stress is used as an important characteristic of mechanics, the residual stress state of each part is determined through research on a distribution detection principle and a distribution detection method of the residual stress in the explosive, the size and the distribution of the residual stress are accurately judged and evaluated, and the performance and the durability of the explosive are improved, so that the safety and the reliability of weapon equipment are guaranteed, and the striking effect of the weapon is guaranteed to have very important theoretical research value and engineering application requirements.
The ultrasonic nondestructive detection method is flexible in use mode, harmless to human bodies and capable of quantitatively detecting residual stress on the basis of nondestructive extraction of detected pieces. The method provided by the invention is used for detecting the circumferential stress of the grain by adopting the ultrasonic critical refraction longitudinal wave aiming at the circumferential stress generated by the grain in the life cycle, can be used for rapidly detecting the grain in batches, and has very important significance for quality detection, fatigue life evaluation, production quality inspection and the like of the grain.
Through inquiring a patent retrieval and service system and related published documents, no similar thesis, patent invention or proprietary technology which adopts an ultrasonic detection device to detect and reversely verify the circumferential stress publication of the energetic grain is found at present.
Disclosure of Invention
1. Objects of the invention
The invention provides an ultrasonic nondestructive testing method for measuring circumferential compressive stress of a surface layer of an energy-containing grain, which comprises a detection device, a verification-loading device and a detection method, wherein the detection device is used for measuring the circumferential surface stress generated by the energy-containing grain in the life cycle of the energy-containing grain and comparing the circumferential surface stress with the stress limit of a material so as to evaluate the use performance of the energy-containing grain; and detecting the circumferential residual stress of the energetic grain by adopting a one-transmitting-one-receiving mode.
2. Technical scheme
The invention provides an ultrasonic nondestructive testing method for measuring circumferential compressive stress of a surface layer of an energy-containing grain, which comprises a testing device, a verification-loading device and a testing method, and specifically comprises the following steps:
A. the detection device comprises: consists of an industrial personal computer, a polytetrafluoroethylene wedge block and a longitudinal wave ultrasonic transducer. Based on the propagation theory of ultrasonic waves in a medium, the mathematical relationship between the residual stress of the surface layer and the variation of sound time is established. And carrying out a pressure stress loading experiment on the energetic grain, carrying out ultrasonic detection, and calculating the sound time variation of ultrasonic wave transmission under different pressure stress states by utilizing a cross-correlation algorithm. Fitting the loaded compressive stress and the corresponding acoustic time variation to determine an ultrasonic detection coefficient of the energetic grain, and finally obtaining a relational expression of the circumferential compressive stress and the acoustic time variation of the energetic grain;
B. verification-loading device: the device consists of an annular energetic grain to be detected, a left pressure column of a loading-verifying device, a threaded sleeve, a force application nut, a thrust ball bearing, an annular pressure sensor and a right pressure column of the loading-verifying device. Adjusting a force application nut to push the right part of the device to compress the right end of the explosive column, carrying out stage-type load application, reading at each stress stage, and acquiring a circumferential stress value at the moment;
C. the detection method comprises the following steps: in the stress detection and verification stage, the acoustic time difference of the explosive column in the circumferential stress state and the stress-free state is detected, the circumferential stress is calculated by utilizing the previously measured circumferential force ultrasonic detection coefficient of the energetic explosive column, and the comparison is carried out with the reading of the pressure sensor, so that the detection effectiveness and accuracy of the circumferential stress are verified.
The method comprises the following steps of A, establishing a mathematical relation between the circumferential surface residual stress and the acoustic time variation based on the propagation theory of ultrasonic waves in a medium, which is described in the detection device A, and specifically:
according to the Snell theorem, when an ultrasonic wave propagates from a low-sound-velocity medium to a high-sound-velocity medium, a refraction phenomenon of the ultrasonic wave occurs, and when a refraction angle is equal to 90 degrees, a corresponding incident angle of the ultrasonic wave is called a first critical angle, and a calculation formula is as follows:
Figure BDA0003183323020000031
in the formula:
αCR-a first critical angle (°);
cL1-longitudinal wave velocity (m/s) in media with slower acoustic velocity;
cL2-longitudinal wave velocity (m/s) in a medium with faster speed of sound.
And (3) the sound wave is transmitted along the surface of the explosive column after being refracted, and for the detection of the circumferential residual stress of the explosive column, a first critical angle at the point is calculated according to the Snell theorem, the wedge block and the sound velocity of the energetic explosive column material.
According to the theory of acoustic elasticity, when ultrasonic waves propagate in an isotropic solid medium, when the vibration direction of a sound wave mass point is consistent with or opposite to the stress direction, the change of the ultrasonic wave speed and the change of the residual stress are changed linearly. Therefore, when the critical refraction longitudinal wave method is adopted to measure the stress, the sound velocity change can be reflected by the change of the propagated sound because the propagation distance of the sound wave is not changed and the change of the sound velocity can not be accurately measured. When the wave velocity of the critical refracted longitudinal wave is increased, the characteristic material has residual compressive stress, otherwise, residual tensile stress, and under the condition that the characteristic parameter (stress coefficient) of the material is determined, the relationship between the wave velocity variation of the critical refracted longitudinal wave and the residual stress variation is as follows:
Figure BDA0003183323020000041
in the formula:
d σ — amount of change in residual stress (MPa);
dV-variation (m/s) of wave velocity of sound wave;
V0-initial speed of sound (m/s) of the medium in a zero stress state;
k-coefficient of acoustic elasticity (ns/m)2)。
When the distance L over which the critically refracted longitudinal wave propagates is determined, the speed of sound in the measured medium can be characterized by the time of the propagating sound, as follows:
Figure BDA0003183323020000042
in the formula:
dt-the amount of acoustic time variation(s) of propagation of a critically refracted longitudinal wave;
T0-an initial acoustic time(s) of propagation of an ultrasonic longitudinal wave in the medium at zero stress;
let stress constant K be-2/kT0Wherein T is0The time required for the longitudinal wave to propagate a fixed distance L under the condition of zero stress is the time, and the change of the stress and the change of the ultrasonic wave propagation sound are in a linear relation.
Wherein B verifies that loading device's left compression leg 2 arranges the internal surface of the diameter direction of cyclic annular grain 1 in, arranges threaded sleeve 3, nut 4, thrust ball bearing 5, pressure sensor 6 and right compression leg 7 in proper order inside the grain concentrically, because nut and threaded sleeve have the assembly jack, assembles nut and threaded sleeve. When no stress is applied initially, the force application nut is adjusted to enable the right pressure column to be in complete contact with the inner end face of the right portion of the annular explosive column, certain pretightening force is applied, and the reading of the pressure sensor at the moment is guaranteed to be zero.
When detecting and verifying, adjust application of force nut and promote the right part of device and compress tightly the powder column right-hand member, carry out stage formula and apply the load this moment, carry out the reading at each stress stage, acquire the circumference stress value that the powder column received this moment. After the loading-verifying unit is assembled, the annular force sensor 6 generates an initial force F due to the weight of the unit itself0(the basis weight of the device and charge dispensed at this time is the pressure exerted by the forcing nut), the annular force sensor 6 will generate a real-time force F after the force is exerted1The total coupling force acting on the coupling surface is F ═ F0-F1。
The method C is characterized in that the acoustic time difference of the explosive column in the circumferential stress and stress-free state is detected, the circumferential stress is calculated by utilizing the previously measured circumferential force ultrasonic detection coefficient of the energetic explosive column, and the method comprises the following steps:
and (4) obtaining the variation dt of the propagation time of the ultrasonic wave by utilizing residual stress ultrasonic detection software and combining a cross-correlation algorithm. Supposing that the time of a sampling point of an ultrasonic signal is N, the ultrasonic echo signal acquired in a natural state is x (N), the ultrasonic echo signal in a bolt stress state is y (N), the ultrasonic echo signal is y (N + m) after being delayed by m sampling intervals, the number of the sampling points is N, and a correlation function calculation formula according to a discrete signal comprises the following steps:
Figure BDA0003183323020000051
correlation function Rxy(m) reflects the degree of similarity of y (n + m) to x (n). Suppose when m is equal to mmaxWhen R isxy(m) reaches a maximum value, indicating that y (n + m)max) Most similar to x (n), i.e. the time difference between y (n) and x (n) is mmaxΔ T (Δ T is the sampling interval).
In order to verify that the measurement accuracy of 0.5ns can be achieved by performing cross-correlation operation after interpolation on data acquired by a 100MHz data acquisition card, simulation verification is required. After two rows of sinusoidal signals are dispersed, the time interval of adjacent sampling points is 10ns (sampling time interval of a data acquisition card of 100 MHz), and interpolation processing of 20 times is carried out on original sampling data by adopting a Fast Fourier Transform (FFT) interpolation algorithm, so that the time resolution is improved to 0.5 ns. Meanwhile, in order to reduce the calculated amount, only the sampling data of the first reflection echo signal is intercepted by arranging a sampling gate to carry out interpolation calculation.
By obtaining the acoustic time difference of the explosive column in the circumferential stress and stress-free states, the circumferential compressive stress applied to the explosive column is calculated by utilizing the previously measured ultrasonic detection coefficient of the circumferential force of the energetic explosive column, and the circumferential compressive stress is compared with the reading of the pressure sensor, so that the effectiveness and accuracy of the detection of the circumferential stress are verified.
Advantages and effects
For detecting the circumferential residual stress of the energy-containing grain, the residual stress is detected by transmitting sound waves along the surface layer according to the critical refraction longitudinal waves excited by the Snell theorem on the circumferential surface layer of the energy-containing grain. The first critical angle is accurately calculated, so that the contact surface of the ultrasonic longitudinal transducer and the acoustic wedge block is assembled at the first critical angle, and the two ultrasonic transducers adopt a transmitting-receiving mode to obtain the circumferential stress.
For loading-verification of circumferential stress, a set of circumferential stress loading tool is designed, and pressure is applied to two sides of the inner diameter direction of the annular grain, namely, compressive stress is generated on the upper side surface and the lower side surface of the grain, and the magnitude of the compressive stress is twice of the applied pressure. And on the basis of the measured stress coefficient, comparing the circumferential stress with the applied stress according to the measurement of the circumferential stress, and verifying the effectiveness and the accuracy of the circumferential stress detection method.
The invention has the advantages that: the method of contacting the outer surface of the grain is adopted to measure the residual stress, the existing ultrasonic longitudinal transducer can be normally used, the performance is good, and the reverse thrust precision of the loading-verifying device is reasonable. The device has small volume, simple manufacturing process, convenient use and lower cost.
Drawings
Fig. 1 is a 3D structural schematic diagram of a charge column circumferential stress loading-verifying device.
Fig. 2 is a schematic diagram of a 3D structure for detecting circumferential residual stress of a grain.
FIG. 3 is a cross-correlation operation diagram of ultrasonic signals before and after loading a charge.
FIG. 4 shows the waveforms of the original data and the interpolated signals before and after loading the grains.
FIG. 5 is a plot of the fit between the surface compressive stress and acoustic time difference for an energetic charge.
The numbers in the figure illustrate the following:
1. detecting an annular energetic grain to be detected; 2. loading-verifying the device left compression leg; 3. a threaded sleeve;
4. a force application nut; 5. a thrust ball bearing; 6. an annular pressure sensor;
7. loading-verifying device right compression leg; 8. and a circumferential stress detection wedge block.
Detailed Description
The invention provides an ultrasonic nondestructive testing method for measuring circumferential compressive stress of a surface layer of an energy-containing grain, which comprises a testing device, a verification-loading device and a testing method. The invention is further described with reference to the following description and embodiments in conjunction with the accompanying drawings.
The implementation of the invention takes 8701 simulation material as an example, and the circular-ring-shaped grain with the outer diameter of 118mm, the inner diameter of 78mm and the thickness of 30mm is processed, and the method of the invention is explained.
In order to achieve the purpose, the technical scheme adopted by the method is 'an ultrasonic nondestructive testing method for measuring circumferential compressive stress of the surface layer of the energetic grain'.
A. The detection device comprises: consists of an industrial personal computer, a polytetrafluoroethylene radian wedge block and a longitudinal wave ultrasonic transducer. Based on the propagation theory of ultrasonic waves in a medium, the mathematical relationship between the residual stress of the surface layer and the variation of sound time is established. And carrying out a pressure stress loading experiment on the energetic grain, carrying out ultrasonic detection, and calculating the sound time variation of ultrasonic wave transmission under different pressure stress states by utilizing a cross-correlation algorithm. Fitting the loaded compressive stress and the corresponding acoustic time variation to determine an ultrasonic detection coefficient of the energetic grain, and finally obtaining a relational expression of the circumferential compressive stress and the acoustic time variation of the energetic grain;
B. verification-loading device: the device consists of an annular energetic grain to be detected, a left pressure column of a loading-verifying device, a threaded sleeve, a force application nut, a thrust ball bearing, an annular pressure sensor and a right pressure column of the loading-verifying device. Adjusting a force application nut to push the right part of the device to compress the right end of the explosive column, carrying out stage-type load application, reading at each stress stage, and acquiring a circumferential stress value at the moment;
C. the detection method comprises the following steps: in the stress detection and verification stage, the acoustic time difference of the explosive column in the circumferential stress state and the stress-free state is detected, the circumferential stress is calculated by utilizing the previously measured circumferential force ultrasonic detection coefficient of the energetic explosive column, and the comparison is carried out with the reading of the pressure sensor, so that the detection effectiveness and accuracy of the circumferential stress are verified.
The method comprises the following steps of A, establishing a mathematical relation between the circumferential surface residual stress and the acoustic time variation based on the propagation theory of ultrasonic waves in a medium, which is described in the detection device A, and specifically:
according to the Snell theorem, when an ultrasonic wave propagates from a low-sound-velocity medium to a high-sound-velocity medium, a refraction phenomenon of the ultrasonic wave occurs, and when a refraction angle is equal to 90 degrees, a corresponding incident angle of the ultrasonic wave is called a first critical angle, and a calculation formula is as follows:
Figure BDA0003183323020000081
in the formula:
αCR-a first critical angle (°);
cL1-longitudinal wave velocity (m/s) in polytetrafluoroethylene;
cL28071 simulates the velocity (m/s) of longitudinal waves in a material.
And (3) the sound wave is transmitted along the surface of the explosive column after being refracted, and for the detection of the circumferential residual stress of the explosive column, a first critical angle at the point is calculated according to the Snell theorem, the wedge block and the sound velocity of the energetic explosive column material. In order to change the incidence part jointed with the material into a radian structure consistent with the radius, so that the sound wave can be effectively propagated on the surface of the grain, the first critical angle is increased by a radian correction angle of 46.22 degrees.
According to the theory of acoustic elasticity, when ultrasonic waves propagate in an isotropic solid medium, when the vibration direction of a sound wave mass point is consistent with or opposite to the stress direction, the change of the ultrasonic wave speed and the change of the residual stress are changed linearly. Therefore, when the critical refraction longitudinal wave method is adopted to measure the stress, the sound velocity change can be reflected by the change of the propagated sound because the propagation distance of the sound wave is not changed and the change of the sound velocity can not be accurately measured. When the wave velocity of the critical refracted longitudinal wave is increased, the characteristic material has residual compressive stress at the moment, otherwise, residual tensile stress exists, and under the condition that the characteristic parameter (stress coefficient) of the material is determined, the relationship between the wave velocity variation of the critical refracted longitudinal wave and the variation of the residual stress is as follows:
Figure BDA0003183323020000091
in the formula:
d σ — amount of change in residual stress (MPa);
dV-variation (m/s) of wave velocity of sound wave;
V0-initial speed of sound (m/s) of the medium in a zero stress state;
k-coefficient of acoustic elasticity (ns/m)2)。
When the distance L over which the critically refracted longitudinal wave propagates is determined, the speed of sound in the measured medium can be characterized by the time of the propagating sound, as follows:
Figure BDA0003183323020000092
in the formula:
dt-the amount of acoustic time variation(s) of propagation of a critically refracted longitudinal wave;
T0-an initial acoustic time(s) of propagation of an ultrasonic longitudinal wave in the medium at zero stress;
let stress constant K be-2/kT0Wherein T is0The time required for the longitudinal wave to propagate a fixed distance L under the condition of zero stress is the time, and the change of the stress and the change of the ultrasonic wave propagation sound are in a linear relation.
1) Writing a stress program in a stretching system, and carrying out module program design of a loading step according to the limit of 5Mpa, the step of 0.5Mpa and the waiting time of 60 s;
2) assembling an ultrasonic transducer, a wedge block, a signal wire and a control computer detection platform and debugging to ensure that clear and effective echo waves appear under zero initial stress;
3) smearing glycerol on an upper pressure head and a lower pressure head to reduce torsion caused by friction, placing a to-be-tested explosive column on a pressure table, and adjusting the pre-pressure of a tensile testing machine to be zero (the error is plus or minus 0.05 Mpa);
4) running a set pressure program, collecting waveforms, obtaining sound time change amount dt under the pressure through an internal software cross-correlation algorithm, performing three repeated experiments, and taking a sound time change amount average value dt (checking the damage degree of the surface of the grain after the loading program is finished every time to prevent shearing damage);
5) and performing curve fitting according to the stress reading of the stretching system and the acquired average acoustic time difference to obtain a stress-acoustic time difference dispersion point and a fitting curve, and finally obtaining a stress coefficient K which is 0.0109.
Wherein B verifies that loading device's left compression leg 2 arranges the internal surface of the diameter direction of cyclic annular grain 1 in, arranges threaded sleeve 3, nut 4, thrust ball bearing 5, pressure sensor 6 and right compression leg 7 in proper order inside the grain concentrically, because nut and threaded sleeve have the assembly jack, assembles nut and threaded sleeve. When no stress is applied initially, the force application nut is adjusted to enable the right pressure column to be in complete contact with the inner end face of the right portion of the annular explosive column, certain pretightening force is applied, and the reading of the pressure sensor at the moment is guaranteed to be zero.
When detecting and verifying, the device is arranged inside the explosive column, and the zero setting of the pressure sensor is carried out at the moment. And adjusting the force application nut to push the right part of the device to compress the right end of the explosive column, carrying out stage type load application at the moment, reading at each stress stage, and acquiring the circumferential stress value of the explosive column at the moment.
After the loading-verifying unit is assembled, the annular force sensor 6 generates an initial force F due to the weight of the unit itself0(the basis weight of the device and charge dispensed at this time is the pressure exerted by the forcing nut), the annular force sensor 6 will generate a real-time force F after the force is exerted1Acting on the couplerThe total coupling force of the combined surfaces is F ═ F0-F1。
The method C is characterized in that the acoustic time difference of the explosive column in the circumferential stress and stress-free state is detected, the circumferential stress is calculated by utilizing the previously measured circumferential force ultrasonic detection coefficient of the energetic explosive column, and the method comprises the following steps:
and (4) obtaining the variation dt of the propagation time of the ultrasonic wave by utilizing residual stress ultrasonic detection software and combining a cross-correlation algorithm. Supposing that the time of a sampling point of an ultrasonic signal is N, the ultrasonic echo signal acquired in a natural state is x (N), the ultrasonic echo signal in a bolt stress state is y (N), the ultrasonic echo signal is y (N + m) after being delayed by m sampling intervals, the number of the sampling points is N, and a correlation function calculation formula according to a discrete signal comprises the following steps:
Figure BDA0003183323020000111
correlation function Rxy(m) reflects the degree of similarity of y (n + m) to x (n). Suppose when m is equal to mmaxWhen R isxy(m) reaches a maximum value, indicating that y (n + m)max) Most similar to x (n), i.e. the time difference between y (n) and x (n) is mmaxΔ T (Δ T is the sampling interval).
In order to verify that the measurement accuracy of 0.5ns can be achieved by performing cross-correlation operation after interpolation on data acquired by a 100MHz data acquisition card, simulation verification is required. After two rows of sinusoidal signals are dispersed, the time interval of adjacent sampling points is 10ns (sampling time interval of a data acquisition card of 100 MHz), and interpolation processing of 20 times is carried out on original sampling data by adopting a Fast Fourier Transform (FFT) interpolation algorithm, so that the time resolution is improved to 0.5 ns. Meanwhile, in order to reduce the calculated amount, only the sampling data of the first reflection echo signal is intercepted by arranging a sampling gate to carry out interpolation calculation.
By obtaining the acoustic time difference of the explosive column in the circumferential stress and stress-free states, the circumferential compressive stress applied to the explosive column is calculated by utilizing the previously measured ultrasonic detection coefficient of the circumferential force of the energetic explosive column, and the circumferential compressive stress is compared with the reading of the pressure sensor, so that the effectiveness and accuracy of the detection of the circumferential stress are verified.
Figure BDA0003183323020000112

Claims (7)

1. An ultrasonic nondestructive testing method for measuring circumferential compressive stress of a surface layer of an energy-containing grain comprises a testing device, a verification-loading device and a testing method, and is characterized in that:
A. the detection device comprises: the system consists of an industrial personal computer, a polytetrafluoroethylene wedge block and a longitudinal wave ultrasonic transducer; establishing a mathematical relation between the residual stress of the surface layer and the variation of sound time based on the propagation theory of ultrasonic waves in a medium; carrying out a pressure stress loading experiment on the annular energetic grain and carrying out ultrasonic detection, and calculating the time variation of ultrasonic wave transmission under different pressure stress states by utilizing a cross-correlation algorithm; fitting the loaded compressive stress and the corresponding acoustic time variation to determine an ultrasonic detection coefficient of the annular energetic grain, and finally obtaining a relational expression of the circumferential compressive stress and the acoustic time variation of the annular energetic grain;
B. verification-loading device: the device consists of an annular energetic explosive column, a left pressure column of a loading-verifying device, a threaded sleeve, a force application nut, a thrust ball bearing, an annular pressure sensor and a right pressure column of the loading-verifying device; adjusting a force application nut to push the right part of the verification-loading device to press the right end of the annular energetic grain, carrying out stage-type load application, reading at each stress stage, and acquiring a circumferential stress value at the moment;
C. the detection method comprises the following steps: in the stress detection and verification stage, the acoustic time difference of the annular energetic grain in the circumferential stress and stress-free states is detected, the circumferential stress is calculated by utilizing the previously measured circumferential force ultrasonic detection coefficient of the annular energetic grain, and the comparison is carried out with the reading of the annular pressure sensor, so that the effectiveness and accuracy of the detection of the circumferential stress are verified.
2. The ultrasonic nondestructive testing method for measuring circumferential compressive stress of the surface layer of the energetic grain of powder of claim 1, which is characterized in that: the detection device establishes a mathematical relationship between the circumferential surface residual stress and the acoustic time variation based on the propagation theory of ultrasonic waves in a medium, and the method comprises the following specific steps:
according to the Snell theorem, when an ultrasonic wave propagates from a low-sound-velocity medium to a high-sound-velocity medium, a refraction phenomenon of the ultrasonic wave occurs, and when a refraction angle is equal to 90 degrees, a corresponding incident angle of the ultrasonic wave is called a first critical angle, and a calculation formula is as follows:
Figure FDA0003183323010000021
in the formula:
αCR-a first critical angle (°);
cL1-longitudinal wave velocity (m/s) in media with slower acoustic velocity;
cL2-longitudinal wave velocity (m/s) in a medium with faster speed of sound.
The sound wave is refracted and then transmitted along the surface of the annular energetic grain, and for the detection of the circumferential residual stress of the annular energetic grain, a first critical angle at the point is calculated according to the Snell theorem, the wedge block and the sound velocity of the material of the annular energetic grain;
when the stress measurement is carried out by adopting a critical refraction longitudinal wave method, because the distance of sound wave propagation is unchanged and the variation of the sound velocity cannot be accurately measured, the variation of the sound velocity is reflected by the variation of the propagated sound time; when the wave velocity of the critical refraction longitudinal wave is increased, the characteristic material has residual compressive stress at the moment; on the contrary, the residual tensile stress exists, and under the condition that the material characteristic parameters are determined, the relationship between the wave velocity variation of the critical refracted longitudinal wave and the residual stress variation is as follows:
Figure FDA0003183323010000022
in the formula:
d σ — amount of change in residual stress (MPa);
dV-variation (m/s) of wave velocity of sound wave;
V0zero stressAn initial sound velocity (m/s) of the medium in the state;
k-coefficient of acoustic elasticity (ns/m)2)；
When the distance L over which the critically refracted longitudinal wave propagates is determined, the speed of sound in the measured medium can be characterized by the time of the propagating sound, as follows:
Figure FDA0003183323010000031
in the formula:
dt-the amount of acoustic time variation(s) of propagation of a critically refracted longitudinal wave;
T0-an initial acoustic time(s) of propagation of an ultrasonic longitudinal wave in the medium at zero stress;
let stress constant K be-2/kT0Wherein T is0The time required for the longitudinal wave to propagate a fixed distance L under the condition of zero stress is the time, and the change of the stress and the change of the ultrasonic wave propagation sound are in a linear relation.
3. The ultrasonic nondestructive testing method for measuring circumferential compressive stress of the surface layer of the energetic grain of powder of claim 1, which is characterized in that: the left pressure column of the verification-loading device is arranged on the inner surface of the annular energetic grain in the diameter direction, the threaded sleeve, the force application nut, the thrust ball bearing, the annular pressure sensor and the right pressure column of the loading-verification device are sequentially and concentrically arranged inside the annular energetic grain, the force application nut and the threaded sleeve are assembled, and when stress is not applied initially, the force application nut is adjusted to enable the right pressure column of the loading-verification device and the right inner end surface of the annular energetic grain to be in complete contact and apply certain pre-tightening force, but the reading of the annular pressure sensor at the moment is guaranteed to be zero.
4. The ultrasonic nondestructive testing method for measuring circumferential compressive stress of the surface layer of the energetic grain of powder of claim 3, which is characterized in that: when the detection and verification are carried out, the force application nut is adjusted to push the right part of the verification-loading device to compress the right end of the annular energetic grain, and at the moment, the step-type load application is carried out, and every time when the step-type load application is carried out, the step-type load application is carried outReading in a stress stage to obtain the circumferential stress value of the annular energetic grain; after the loading-verifying device is assembled, the annular pressure sensor generates an initial force F due to the gravity of the verifying-loading device0Namely, the basic gravity distributed by the verification-loading device and the annular energetic grain at the moment is subtracted to be the pressure applied by the force application nut, and the annular pressure sensor can generate real-time acting force F after the force is applied1The total coupling force acting on the coupling surface is F ═ F0-F1。
5. The ultrasonic nondestructive testing method for measuring circumferential compressive stress of the surface layer of the energetic grain of powder of claim 1, which is characterized in that: the method for detecting the sound time difference of the annular energetic grain in the circumferential stress and stress-free states and calculating the circumferential stress by using the previously measured circumferential force ultrasonic detection coefficient of the annular energetic grain described by the detection method comprises the following steps:
obtaining the variable dt of the ultrasonic wave propagation time by utilizing residual stress ultrasonic detection software and combining a cross-correlation algorithm; setting the sampling point time of an ultrasonic signal as N, the ultrasonic echo signal acquired in a natural state as x (N), the ultrasonic echo signal in a bolt stress state as y (N), the ultrasonic echo signal is delayed by m sampling intervals and then is y (N + m), the number of sampling points is N, and a correlation function calculation formula according to a discrete signal comprises the following steps:
Figure FDA0003183323010000041
correlation function Rxy(m) reflects the degree of similarity of y (n + m) to x (n); suppose when m is equal to mmaxWhen R isxy(m) reaches a maximum value, indicating that y (n + m)max) Most similar to x (n), i.e. the time difference between y (n) and x (n) is mmaxΔ T, Δ T is the sampling interval.
6. The ultrasonic nondestructive testing method for measuring circumferential compressive stress of the surface layer of the energetic grain of powder of claim 5, wherein the method comprises the following steps: in order to verify that the data acquired by the 100MHz data acquisition card is subjected to cross-correlation operation after interpolation to achieve the measurement precision of 0.5ns, simulation verification is required; after two rows of sinusoidal signals are dispersed, the time interval of adjacent sampling points is 10ns, and interpolation processing of 20 times is carried out on original sampling data by adopting a fast Fourier FFT interpolation algorithm, so that the time resolution is improved to 0.5 ns; meanwhile, in order to reduce the calculated amount, only the sampling data of the first reflection echo signal is intercepted by arranging a sampling gate to carry out interpolation calculation.
7. The ultrasonic nondestructive testing method for measuring the circumferential compressive stress of the surface layer of the energetic grain of powder according to claim 1 or 6, which is characterized in that: by obtaining the acoustic time difference of the annular energetic grain in the circumferential stress and stress-free states, the circumferential pressure stress borne by the annular energetic grain is calculated by utilizing the previously measured circumferential force ultrasonic detection coefficient of the annular energetic grain, and compared with the reading of the annular pressure sensor, the effectiveness and accuracy of the detection of the circumferential stress are verified.
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