CN113310610B - Ultrasonic detection method for peripheral epoxy stress of three-post insulator insert - Google Patents
Ultrasonic detection method for peripheral epoxy stress of three-post insulator insert Download PDFInfo
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Abstract
The invention discloses an ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert. The method comprises the following steps: building an ultrasonic detection system; measuring the acoustic elastic coefficient of the parallel stress of the epoxy composite material standard sample for the three-post insulator to obtain an acoustic elastic equation of the parallel stress of the epoxy composite material; carrying out ultrasonic detection on the peripheral epoxy of the insert under the axial load of the three-post insulator, and recording the sound velocity in an ultrasonic sound path at a detection position; and substituting the obtained ultrasonic sound velocity into an acoustic elastic equation of the parallel stress of the epoxy composite material to obtain the peripheral epoxy stress of the insert under the axial load of the three-post insulator. The invention can efficiently, intuitively and nondestructively detect the peripheral epoxy stress of the insert under the axial load.
Description
Technical Field
The invention relates to the field of power transmission and transformation insulating equipment, in particular to an ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert.
Background
The three-post insulator is a key electrical component in a gas insulated metal enclosed transmission line (GIL) and plays a role in electrical insulation and mechanical support, and mechanical stress of the GIL three-post insulator can be one of causes of insulator failure, and the sources of the mechanical stress include residual stress in the manufacturing process and stress caused by external loads in the processes of transportation, installation and operation. The GIL three-post insulator is formed by mixing liquid epoxy resin, a curing agent and an inorganic powder filler, integrally pouring the mixture with an insert and curing the mixture at a high temperature, and has residual stress in the manufacturing process. Insulators may have bumping vibration and mechanical friction in GIL transportation, and a three-dimensional vibration impact acceleration detector is installed at present to detect impact force applied in the GIL transportation process. The reason for the stress of the insulator in GIL installation may be inclination of the conductive rod installation or uneven fastening force of the fixing plate, etc., and the insulator bears the weight of itself and a part of the conductor in operation and the electromotive force of the housing and the conductor in the current alternating electromagnetic field, etc. Therefore, the three-post insulator is confirmed to be in a stress state as soon as possible, and the method has important significance for guaranteeing safe operation of a power system.
At present, a mechanical load test can only assess whether a three-post insulator passes a certain limit value or measure a mechanical failure load (see '550 kV GIL three-post insulator design' such as Wang Jiancheng, xie Wengang and Gong Ruilei) and cannot measure and assess mechanical performance or stress under any load, and a stress evolution process from generation and expansion of micro defects such as cracks to mechanical failure or electrical breakdown of the insulator is not known.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an ultrasonic detection method for the peripheral epoxy stress of a three-post insulator insert.
The purpose of the invention is realized by at least one of the following technical solutions.
An ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert comprises the following steps:
s1, building an ultrasonic detection system;
s2, measuring the acoustic elasticity coefficient of the parallel stress of the epoxy composite material standard sample for the three-post insulator to obtain an acoustic elasticity equation of the parallel stress of the epoxy composite material;
s3, performing ultrasonic detection on the peripheral epoxy of the insert under the axial load of the three-post insulator, and recording the sound velocity in an ultrasonic sound path at a detection position;
and S4, substituting the obtained ultrasonic sound velocity into the acoustoelastic equation of the parallel stress of the epoxy composite material in the S2 to obtain the peripheral epoxy stress of the insert under the axial load of the three-post insulator.
Further, in step S1, the ultrasonic detection system includes an ultrasonic pulse generator, an oscilloscope, an ultrasonic longitudinal wave straight probe, a probe adapting line, and a high impedance transmission line;
the ultrasonic longitudinal wave straight probe is connected with a signal output end T or a signal input end R of the ultrasonic pulse generator through a probe adaptive line, and a signal synchronization end of the ultrasonic pulse generator is connected with the oscilloscope through a high-impedance transmission line.
Furthermore, the ultrasonic pulse generator is a pulse generator with short pulse excitation, adjustable output pulse width, high gain and low noise, and the short pulse excitation can optimize broadband response and improve the near-surface detection resolution, thereby being more beneficial to the detection and measurement application of materials with strong sound beam attenuation;
the oscilloscope is a three-channel high-performance digital storage oscilloscope with the maximum sampling frequency of 2GHz and the sampling broadband of 500MHz, and the input channel of the oscilloscope and the signal output end of the ultrasonic pulse generator are connected with the electric potential through a high-impedance transmission line, so that the transmitted and received ultrasonic signals can be displayed on the oscilloscope in real time;
the ultrasonic longitudinal wave straight probe belongs to a cylindrical longitudinal wave straight probe, a circular composite material piezoelectric wafer is adopted, the bottom surface of the probe is circular, in order to increase the contact effect of the probe and a detected position of an insulator and improve the detection precision, the smaller the radius of the bottom surface of the probe is, the better the smaller the radius is, but the smaller the bottom surface of the probe requires the circular composite material piezoelectric wafer to be very small, the ultrasonic energy emitted by the probe is also very small, the detection characteristic, the detection efficiency and the manufacturing cost are comprehensively considered, the design range of the diameter (D) of the bottom surface of the probe is 5-10mm, and the design range of the height (H) of the probe is 15-20mm;
the ultrasonic longitudinal wave straight probe is a pulse ultrasonic straight probe with good response characteristics, the higher the nominal frequency of the ultrasonic longitudinal wave straight probe is, the larger the attenuation coefficient in the detected material is, the worse the sound beam propagation characteristic effect is, and the frequency design of the ultrasonic longitudinal wave straight probe is not more than 2.5MHz by combining with the actual measurement experience;
the probe adaptive line is a signal line matching the ultrasonic pulse generator and the ultrasonic longitudinal wave straight probe, has the characteristics of high impedance, strong anti-interference capability and the like, ensures that the output electric signal of the ultrasonic pulse generator can be received by the ultrasonic longitudinal wave straight probe with high quality, and simultaneously ensures that the ultrasonic signal received by the ultrasonic longitudinal wave straight probe is converted into the electric signal which is returned to the receiving end of the ultrasonic pulse generator with high quality;
the high-impedance transmission line is a transmission line with small stray inductance and resistance, phase delay of high-frequency signals in the transmission process is shortened, real-time identical potential and same phase of electric signals received by the oscilloscope and electric signals at the signal output end of the ultrasonic pulse generator are guaranteed, detection errors are greatly reduced, and detection precision is guaranteed.
Further, step S2 is specifically as follows:
adjusting an ultrasonic pulse generator, symmetrically and coaxially placing two ultrasonic longitudinal wave straight probes coated with an oil-based ultrasonic coupling agent on the surfaces of an upper plate and a bottom plate of a universal testing machine, fixedly placing an epoxy composite material standard sample between the upper plate and the bottom plate of the universal testing machine, recording the propagation time of ultrasonic longitudinal waves in the standard sample, further obtaining the acoustic-elastic coefficient of parallel stress, and finally obtaining the acoustic-elastic equation of the parallel stress of the epoxy composite material.
Furthermore, the two ultrasonic longitudinal wave straight probes are respectively connected with a signal output end T and a signal input end R of the ultrasonic pulse generator through the probe adaptive wires;
the oil-based ultrasonic coupling agent is used for increasing the contact effect of the ultrasonic longitudinal wave straight probe and the surface to be measured and ensuring the stability of ultrasonic waveforms;
the standard sample of the epoxy composite material is made of the same material and process as the three-post insulator, and has the size of length d 1 X is high d 2 X width d 3 A rectangular parallelepiped standard sample of (1);
the symmetrical coaxial arrangement means that the two ultrasonic longitudinal wave straight probes are respectively arranged on the surfaces of an upper plate and a bottom plate of the universal testing machine, and the central lines of the two ultrasonic longitudinal wave straight probes are coaxial;
the upper plate of the universal testing machine is a reverse T-shaped steel plate with a flat bottom surface, and the bottom plate is an I-shaped steel plate with a flat bottom surface; the upper plate and the bottom plate are both d in thickness 0 。
Furthermore, the propagation time of the ultrasonic longitudinal wave in the standard sample is that an ultrasonic longitudinal wave straight probe emits an ultrasonic initial wave F at one side of the epoxy composite material standard sample, the ultrasonic initial wave F is vertically incident into the epoxy part of the epoxy composite material standard sample, a penetrating wave I is received by another ultrasonic longitudinal wave straight probe at a corresponding position at the other side of the epoxy part of the epoxy composite material standard sample, and the oscillation starting time difference between the ultrasonic initial wave F and the penetrating wave I is the propagation time of the ultrasonic longitudinal wave at the position to be detected;
the sound path of the ultrasound transmitted in the standard sample of the epoxy composite material is set as 2d in sequence 0 +d 1 、2d 0 +d 2 Respectively recording ultrasonic propagation time t under the same stress 2 And t 3 (unit. Mu.s), speed of sound V 1 (unit m/s) is
Obtaining a parallel stress acoustic elastic coefficient K, which is as follows:
wherein, V 0 Is zero stress sigma 0 Measuring the zero stress sigma of the standard sample of the epoxy composite material with the unit of m/s 0 Lower ultrasonic longitudinal sound velocity V 0 Is 2 997.02m/s; sigma 0 、σ 1 The unit is MPa, and the K unit is/MPa; the external application load F is uniformly distributed on the stress area, and the sound paths are respectively 2d 0 +d 1 、 2d 0 +d 2 Stress of time σ 1 The relationship with F is respectively F = sigma 1 d 2 d 3 、F＝σ 1 d 1 d 3 F is in the unit of N; the test range of the parallel stress is 0-50 MPa, and the step length is 5MPa; the direction of the parallel stress index standard sample internal stress is parallel to the ultrasonic propagation direction.
And (3) returning the obtained parallel stress acoustic-elastic coefficient K to substitute the formula (2) to obtain the acoustic-elastic equation of the parallel stress of the epoxy composite material, wherein the formula is as follows:
that is, the stress σ can be obtained by measuring the sound velocity V.
Further, in step S3, adjusting the ultrasonic pulse generator, placing an ultrasonic longitudinal wave straight probe coated with the oil-based ultrasonic coupling agent on the surface of the solid epoxy member on the periphery of the three-post insulator mounted on the pusher, and recording the propagation time of the ultrasonic longitudinal wave in the epoxy on the periphery of the insert by using an ultrasonic reflection method, thereby recording the sound velocity in the ultrasonic sound path at the detection position.
Further, the three-post insulator comprises a solid epoxy, a center conductor and a grounding insert; the solid epoxy piece is made of epoxy composite materials and comprises three column legs, and the bottom of each column leg is combined with one grounding insert; in engineering, the joint of the grounding insert and the bottom of the column leg is most prone to stress concentration, so that the detected position is insert peripheral epoxy, and the insert peripheral epoxy is a solid epoxy piece on the periphery of the grounding insert; the central conductor is of an aluminum annular structure;
the installation on the thrust machine means that one of the three-pillar insulators and the pillar leg combined with the grounding insert are fixed on the thrust machine, the thrust machine applies a load F to the central conductor, and the vertical distance between the load F and the fixing surface of the grounding insert is 330mm; at the moment, the ultrasonic propagation direction is approximately parallel to the stress direction, and the propagation acoustic path is twice the thickness of the solid epoxy piece;
recording the propagation time t of the ultrasonic longitudinal wave in the peripheral epoxy of the insert, specifically as follows:
an ultrasonic longitudinal wave straight probe sends out an ultrasonic initial wave F on the surface of a solid epoxy piece on the periphery of the three-post insulator, the ultrasonic initial wave F vertically enters the solid epoxy piece and is reflected when reaching the interface of the solid epoxy piece and the grounding insert, a reflected wave B is received by the ultrasonic longitudinal wave straight probe, and the oscillation starting time difference between the ultrasonic initial wave F and the reflected wave B is the propagation time t in the peripheral epoxy of the insert at the position to be detected;
setting the sound path of the ultrasound on the periphery of the three-post insulator insert as D, recording the propagation time t (unit μ s) of the ultrasound under the load F, and then setting the sound velocity V (unit m/s) as:
further, in step S4, substituting the ultrasonic sound velocity V obtained in step S3 into formula (3) to obtain the peripheral epoxy stress σ of the insert under the axial load of the three-post insulator.
The invention has the beneficial effects that:
the invention provides an ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert, which is characterized in that an ultrasonic detection system is set up; firstly, measuring the acoustic elasticity coefficient of the parallel stress of a standard sample of the epoxy composite material for the three-post insulator to obtain an acoustic elasticity equation of the parallel stress of the epoxy composite material; then, carrying out ultrasonic detection on the lower column leg of the axial load of the three-column insulator, and recording the sound velocity in an ultrasonic sound path at the detection position; and finally, substituting the obtained ultrasonic sound velocity into an acoustic elasticity equation, and calculating to obtain the peripheral epoxy stress of the insert under the axial load of the three-post insulator. The method has the advantages of low detection cost, high detection precision, convenience in carrying, no radiation to a human body and the like, and can efficiently, visually and nondestructively detect the peripheral epoxy stress of the insert under the axial load of the three-post insulator.
Drawings
Fig. 1 is a schematic flow chart of an ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an ultrasonic inspection system suitable for use with the present invention in an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an ultrasonic longitudinal wave straight probe in the embodiment of the invention: wherein, fig. 3a is a front view of the ultrasonic longitudinal wave straight probe, and fig. 3b is a schematic bottom view of the ultrasonic longitudinal wave straight probe;
FIG. 4 is a schematic diagram of a system for testing the parallel stress acoustic-elastic coefficient of an epoxy composite standard sample for a three-post insulator according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of an epoxy composite standard sample for implementing a three-post insulator in the invention: wherein, fig. 5a is a schematic diagram of a standard sample, fig. 5b is a front view of the standard sample, and fig. 5c is a side view of the standard sample;
fig. 6 is a waveform diagram of ultrasonic longitudinal wave penetration method detection of an epoxy composite material standard sample for a three-post insulator in an embodiment of the present invention, wherein fig. 6a and 6b are waveform diagrams of ultrasonic longitudinal wave penetration method detection of different sound paths propagated by ultrasound on the epoxy composite material standard sample, respectively;
FIG. 7 is a schematic diagram of an ultrasonic testing system for the peripheral epoxy stress of an insert under an axial load of a three post insulator in an embodiment of the invention;
fig. 8 is a schematic structural view of a three-post insulator according to an embodiment of the present invention: fig. 8a is a front view of a three-post insulator, and fig. 8b is a schematic diagram of a peripheral epoxy detection position of a three-post insulator insert.
Detailed Description
Specific embodiments of the present invention will be described in further detail below with reference to examples and drawings, but the present invention is not limited thereto.
Example (b):
an ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert is shown in figure 1 and comprises the following steps:
s1, building an ultrasonic detection system;
as shown in fig. 2, the ultrasonic longitudinal wave reflection method detection system includes an ultrasonic pulse generator 1, an oscilloscope 2, an ultrasonic longitudinal wave straight probe 3, a probe adapting line 4 and a high impedance transmission line 5;
the two ultrasonic longitudinal wave straight probes 3 are respectively connected with the output end T and the signal input end R of the ultrasonic pulse generator 1 through the probe adapting wires 4, and the signal synchronization end of the ultrasonic pulse generator 1 is connected with the oscilloscope 2 through the high-impedance transmission line 5.
The ultrasonic pulse generator 1 is a pulse generator with short pulse excitation, adjustable output pulse width, high gain and low noise, and the short pulse excitation can optimize broadband response and improve the near-surface detection resolution, thereby being more beneficial to the detection and measurement application of materials with strong sound beam attenuation;
the oscilloscope 2 is a three-channel high-performance digital storage oscilloscope with the maximum sampling frequency of 2GHz and the sampling bandwidth of 500MHz, and the input channel of the oscilloscope 2 and the signal synchronization end of the ultrasonic pulse generator 1 are connected with the electric potential through a high-impedance transmission line 5, so that the transmitted and received ultrasonic signals can be displayed on the oscilloscope 2 in real time;
the probe adapting wire 4 is a signal wire matching the ultrasonic pulse generator 1 and the ultrasonic longitudinal straight probe 3, has the characteristics of high impedance, strong anti-interference capability and the like, ensures that an output electric signal of the ultrasonic pulse generator 1 can be received by the ultrasonic longitudinal straight probe 3 in high quality, and simultaneously ensures that the ultrasonic signal received by the ultrasonic longitudinal straight probe 3 is converted into an electric signal which returns to a receiving end of the ultrasonic pulse generator 1 in high quality;
the high-impedance transmission line 5 is a transmission line with small stray inductance and resistance, phase delay of high-frequency signals in the transmission process is shortened, real-time identical potential and phase of electric signals received by the oscilloscope 2 and the electric signals at the signal synchronization end of the ultrasonic pulse generator 1 are ensured, detection errors are greatly reduced, and detection precision is ensured.
As shown in fig. 3a and 3b, the ultrasonic longitudinal wave straight probe 3 belongs to a cylindrical longitudinal wave straight probe, and adopts a circular composite material piezoelectric wafer 31, the bottom surface 32 of the probe is circular, in order to increase the contact effect between the probe and the measured position of the insulator and improve the detection precision, the smaller radius of the bottom surface of the probe is better, but the smaller bottom surface of the probe requires the circular composite material piezoelectric wafer to be very small, the energy of the ultrasonic wave emitted by the probe is very small, and the detection characteristic, the detection efficiency and the manufacturing cost are comprehensively considered, in the present embodiment, the design range of the diameter D of the bottom surface of the probe is 8mm, the design range of the height H of the probe is 18mm, and the frequency of the ultrasonic longitudinal wave straight probe 3 is set to be 2.5MHz.
S2, measuring the acoustic elasticity coefficient of the parallel stress of the epoxy composite material standard sample for the three-post insulator to obtain an acoustic elasticity equation of the parallel stress of the epoxy composite material, which comprises the following steps:
in this embodiment, as shown in fig. 4, a schematic diagram of a system for testing a parallel stress acoustic elastic coefficient of a standard sample of an epoxy composite material for a 550kV three-post insulator is shown; as shown in fig. 5, it is a schematic structural diagram of a standard sample of an epoxy composite material for a 550kV three-post insulator;
adjusting an ultrasonic pulse generator 1, symmetrically and coaxially placing two ultrasonic longitudinal wave straight probes 3 coated with an oil-based ultrasonic coupling agent on the surfaces of an upper plate 61 and a bottom plate 62 of a universal testing machine 6, fixedly placing an epoxy composite material standard sample 7 between the upper plate 61 and the bottom plate 62 of the universal testing machine 6, recording the propagation time of ultrasonic longitudinal waves in the standard sample, further obtaining the acoustic-elastic coefficient of parallel stress, and finally obtaining the acoustic-elastic equation of the parallel stress of the epoxy composite material.
The two ultrasonic longitudinal wave straight probes 3 are respectively connected with a signal output end T and a signal input end R of the ultrasonic pulse generator 1 through probe adapting lines 4;
the oil-based ultrasonic coupling agent is used for increasing the contact effect of the ultrasonic longitudinal wave straight probe 3 and the surface to be measured and ensuring the stability of ultrasonic waveforms;
as shown in fig. 5a, 5b and 5c, the standard epoxy composite material sample 7 is made of the same material and process as the three-post insulator, and has a dimension of length d 1 X is high d 2 X width d 3 A rectangular parallelepiped standard sample of (1); in this embodiment, the length, height and width are 70mm, 60mm and 50mm, respectively.
The symmetrical and coaxial arrangement means that the two ultrasonic longitudinal wave straight probes 3 are respectively arranged on the surfaces of the upper plate 61 and the bottom plate 62 of the universal testing machine 6, and the central lines of the two ultrasonic longitudinal wave straight probes 3 are coaxial;
in this embodiment, the universal testing machine 6 is a microcomputer-controlled automatic mechanical load loading device, in this embodiment, the model WAW-500C of the universal testing machine 6 loads a mechanical load of 500kN at maximum, and the control precision is 1%;
the upper plate 61 of the universal testing machine 6 is a reverse T-shaped steel plate with a flat bottom surface, and the bottom plate 62 is an I-shaped steel plate with a flat bottom surface; the thickness of the upper plate 61 and the bottom plate 62 is d 0 In this embodiment, d 0 25mm, and the upper plate 61 and the bottom plate 62 are both made of 50 # steel.
Fig. 6 is a waveform diagram of ultrasonic longitudinal wave penetration detection of an epoxy composite standard sample for a three-post insulator in the embodiment, where the propagation time of an ultrasonic longitudinal wave in the standard sample is that an ultrasonic longitudinal wave straight probe 3 emits an ultrasonic initial wave F at one side of the epoxy composite standard sample 7, the ultrasonic initial wave F is vertically incident into an epoxy part of the epoxy composite standard sample 7, a penetrating wave I is received by another ultrasonic longitudinal wave straight probe 3 at a corresponding position on the other side of the epoxy part of the epoxy composite standard sample 7, and the difference between the start time of the ultrasonic initial wave F and the start time of the penetrating wave I is the propagation time of the ultrasonic longitudinal wave at the position to be detected;
the sound path of the ultrasonic wave propagating on the epoxy composite material standard sample 7 is set to be 2d in sequence as shown in fig. 6a and 6b 0 +d 1 、2d 0 +d 2 Respectively recording ultrasonic propagation time t under the same stress 2 And t 3 (unit. Mu.s), speed of sound V 1 (unit m/s) is
Obtaining a parallel stress acoustic elastic coefficient K, which is as follows:
wherein, V 0 Is zero stress sigma 0 Measuring the sound velocity of the standard sample of the epoxy composite material at zero stress sigma in the unit of m/s 0 Lower ultrasonic longitudinal sound velocity V 0 Is 2 997.02m/s; sigma 0 、σ 1 The unit is MPa, and the K unit is/MPa; the external applied load F is uniformly distributed on the stressed area, and the sound paths are respectively 2d 0 +d 1 、 2d 0 +d 2 Stress of time σ 1 The relationship with F is respectively F = sigma 1 d 2 d 3 、F＝σ 1 d 1 d 3 F is in the unit of N; the test range of the parallel stress is 0-50 MPa, and the step length is 5MPa;
and (3) returning the obtained parallel stress acoustic-elastic coefficient K to substitute the formula (2) to obtain the acoustic-elastic equation of the parallel stress of the epoxy composite material, wherein the formula is as follows:
that is, the stress σ can be obtained by measuring the sound velocity V.
S3, carrying out ultrasonic detection on peripheral epoxy of the insert under the axial load of the three-post insulator, and recording the sound velocity in an ultrasonic sound path at a detection position, wherein the method specifically comprises the following steps:
in this embodiment, as shown in fig. 7, a schematic diagram of an ultrasonic detection system for peripheral epoxy stress of an insert under an axial load of a 550kV three-post insulator in this embodiment is shown;
adjusting an ultrasonic pulse generator 1, placing an ultrasonic longitudinal wave straight probe 3 coated with an oil-based ultrasonic coupling agent on the surface of a solid epoxy member 91 on the periphery of a three-post insulator 9 installed on a thrust machine 8, recording the propagation time of ultrasonic longitudinal waves in an insert peripheral epoxy 931 by an ultrasonic reflection method, and further recording the sound velocity in an ultrasonic sound path at a detection position.
Fig. 8 is a schematic structural diagram of a 550kV three-post insulator in this embodiment, and as shown in fig. 8a and 8b, the three-post insulator 9 includes a solid epoxy 91, a center conductor 92 and a grounding insert 93; the solid epoxy 91 is made of epoxy composite material and comprises three legs 911, and the bottom of each leg 911 is combined with a grounding insert 93; in engineering, the stress concentration phenomenon is most likely to occur at the joint of the grounding insert 93 and the bottom of the column leg 911, so that the detection position is insert peripheral epoxy 931, and the insert peripheral epoxy refers to a solid epoxy 91 on the periphery of the grounding insert 93; the central conductor 92 is an annular structure made of aluminum;
the installation on the thrust machine means that one of the three-column insulator 9 and the column leg 911 combined with the grounding insert 93 are fixed on the thrust machine, the thrust machine applies a load F to the central conductor 92, and the vertical distance between the load F and the fixing surface of the grounding insert 93 is 330mm; at this time, the ultrasonic propagation direction is approximately parallel to the stress direction, and the propagation acoustic path is twice the thickness of the solid epoxy 91;
recording the propagation time t of the ultrasonic longitudinal wave in the insert peripheral epoxy 931 as follows:
an ultrasonic longitudinal wave straight probe emits an ultrasonic initial wave F on the surface of a solid epoxy member 91 at the periphery of the three-post insulator 9, the ultrasonic initial wave F vertically enters the solid epoxy member 91 and is reflected when reaching the interface of the solid epoxy member 91 and a grounding insert 93, a reflected wave B is received by the ultrasonic longitudinal wave straight probe, and the oscillation starting time difference between the ultrasonic initial wave F and the reflected wave B is the propagation time t in the insert peripheral epoxy 931 at the position to be detected;
the sound path of the ultrasound at the periphery of the insert 931 of the three-post insulator 9 is set as D, the propagation time t (unit μ s) of the ultrasound under the load F is recorded, and then the sound velocity V (unit m/s) is:
and S4, substituting the obtained ultrasonic sound velocity V into the formula (3) to obtain the stress sigma at the moment, namely obtaining the stress of the peripheral epoxy 931 of the insert under the axial load of the three-post insulator 9.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (1)
1. An ultrasonic detection method for peripheral epoxy stress of a three-post insulator insert is characterized by comprising the following steps:
s1, building an ultrasonic detection system;
the ultrasonic detection system comprises an ultrasonic pulse generator, an oscilloscope, an ultrasonic longitudinal wave straight probe, a probe adapting wire and a high-impedance transmission line;
the ultrasonic longitudinal wave straight probe is connected with a signal output end T or a signal input end R of the ultrasonic pulse generator through a probe adaptive line, and a signal synchronization end of the ultrasonic pulse generator is connected with an oscilloscope through a high-impedance transmission line;
s2, measuring the acoustic elastic coefficient of the parallel stress of the epoxy composite material standard sample for the three-post insulator to obtain an acoustic elastic equation of the parallel stress of the epoxy composite material, which is as follows:
adjusting an ultrasonic pulse generator, symmetrically and coaxially placing two ultrasonic longitudinal wave straight probes coated with an oil-based ultrasonic coupling agent on the surfaces of an upper plate and a bottom plate of a universal testing machine, fixedly placing an epoxy composite material standard sample between the upper plate and the bottom plate of the universal testing machine, recording the propagation time of ultrasonic longitudinal waves in the standard sample, further obtaining the acoustic-elastic coefficient of parallel stress, and finally obtaining the acoustic-elastic equation of the parallel stress of the epoxy composite material;
an ultrasonic longitudinal wave straight probe sends out an ultrasonic initial wave F at one side of an epoxy composite material standard sample, the ultrasonic initial wave F vertically enters the epoxy part of the epoxy composite material standard sample, a penetrating wave I is received by another ultrasonic longitudinal wave straight probe at a corresponding position at the other side of the epoxy part of the epoxy composite material standard sample, and the starting oscillation time difference of the ultrasonic initial wave F and the penetrating wave I is the propagation time of the ultrasonic longitudinal wave at the position to be detected in the standard sample;
the sound path of the ultrasound transmitted in the standard sample of the epoxy composite material is set as 2d in sequence 0 +d 1 、2d 0 +d 2 Respectively recording ultrasonic propagation time t under the same stress 2 And t 3 Velocity of sound V 1 Is composed of
Obtaining a parallel stress acoustic elastic coefficient K, which is as follows:
wherein, V 0 Is zero stress sigma 0 Measuring the sound velocity of the standard sample of the epoxy composite material under zero stress sigma 0 Lower ultrasonic longitudinal sound velocity V 0 Is 2 997.02m/s; the external applied load F is uniformly distributed on the stressed area, and the sound paths are respectively 2d 0 +d 1 、2d 0 +d 2 Stress of time σ 1 The relationship with F is respectively F = sigma 1 d 2 d 3 、F＝σ 1 d 1 d 3 (ii) a The test range of the parallel stress is 0-50 MPa, and the step length is 5MPa;
and (3) returning the obtained parallel stress acoustic-elastic coefficient K to substitute the formula (2) to obtain the acoustic-elastic equation of the parallel stress of the epoxy composite material, wherein the formula is as follows:
namely, the stress sigma can be obtained by measuring the sound velocity V;
s3, performing ultrasonic detection on the peripheral epoxy of the insert under the axial load of the three-post insulator, and recording the sound velocity in an ultrasonic sound path at a detection position;
s4, substituting the obtained ultrasonic sound velocity into the acoustoelastic equation of the parallel stress of the epoxy composite material in the S2 to obtain the peripheral epoxy stress of the insert under the axial load of the three-post insulator;
the ultrasonic longitudinal wave straight probe belongs to a cylindrical longitudinal wave straight probe, and adopts a circular composite material piezoelectric wafer, the bottom surface of the probe is circular, the design range of the diameter D of the bottom surface of the probe is 5-10mm, and the design range of the height H of the probe is 15-20mm; the frequency design of the ultrasonic longitudinal wave straight probe is not more than 2.5MHz;
the two ultrasonic longitudinal wave straight probes are respectively connected with a signal output end T and a signal input end R of the ultrasonic pulse generator through probe adaptive wires;
the oil-based ultrasonic coupling agent is used for increasing the contact effect of the ultrasonic longitudinal wave straight probe and the surface to be detected and ensuring the stability of ultrasonic waveforms;
the standard sample of the epoxy composite material is made of the same material and process as the three-post insulator, and has the size of length d 1 X is high d 2 X width d 3 A rectangular parallelepiped standard sample of (1);
the symmetrical coaxial arrangement means that the two ultrasonic longitudinal wave straight probes are respectively arranged on the surfaces of an upper plate and a bottom plate of the universal testing machine, and the central lines of the two ultrasonic longitudinal wave straight probes are coaxial;
the upper plate of the universal testing machine is a reverse T-shaped steel plate with a flat bottom surface, and the bottom plate is an I-shaped steel plate with a flat bottom surface; the upper plate and the bottom plate are both d in thickness 0 ；
Step S3, adjusting an ultrasonic pulse generator, placing an ultrasonic longitudinal wave straight probe coated with an oil-based ultrasonic coupling agent on the surface of a solid epoxy piece on the periphery of a three-post insulator installed on a thrust machine, and recording the propagation time of the ultrasonic longitudinal wave in the epoxy on the periphery of the insert by using an ultrasonic reflection method so as to record the sound velocity in an ultrasonic sound path at a detection position;
the three-post insulator comprises a solid epoxy piece, a central conductor and a grounding insert; the solid epoxy piece is made of epoxy composite materials and comprises three column legs, and the bottom of each column leg is combined with one grounding insert; the detection position is epoxy at the periphery of the insert, and the solid epoxy piece at the periphery of the insert is grounded; the central conductor is of an aluminum annular structure;
the installation on the thrust machine means that one of the three-pillar insulators and the pillar leg combined with the grounding insert are fixed on the thrust machine, the thrust machine applies a load F to the central conductor, and the vertical distance between the load F and the fixing surface of the grounding insert is 330mm; at the moment, the ultrasonic propagation direction is approximately parallel to the stress direction, and the propagation sound path is twice the thickness of the solid epoxy piece;
recording the propagation time t of the ultrasonic longitudinal wave in the peripheral epoxy of the insert, specifically as follows:
an ultrasonic longitudinal wave straight probe sends out an ultrasonic initial wave F on the surface of a solid epoxy piece on the periphery of the three-post insulator, the ultrasonic initial wave F vertically enters the solid epoxy piece and is reflected when reaching the interface of the solid epoxy piece and the grounding insert, a reflected wave B is received by the ultrasonic longitudinal wave straight probe, and the oscillation starting time difference between the ultrasonic initial wave F and the reflected wave B is the propagation time t in the peripheral epoxy of the insert at the position to be detected;
the sound path of the ultrasound on the periphery of the three-post insulator insert is set as D, the propagation time t of the ultrasound under the load F is recorded, and then the sound velocity V is as follows:
in the step S4, substituting the ultrasonic sound velocity V obtained in the step S3 into the formula (3) to obtain the peripheral epoxy stress sigma of the insert under the axial load of the three-post insulator.
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