RU2723146C1 - Ultrasonic method for determination of mechanical stresses in rails and device for its implementation - Google Patents

Abstract

FIELD: measurement technology.SUBSTANCE: invention can be used for determination of strained condition of rail strings. Essence of invention consists in that by radiating piezoelectric transducer into loaded rail and its unloaded analogue, pulses of ultrasonic longitudinal and transverse waves are introduced, receive by receiving transducers of transformed transverse waves from longitudinal waves incident on analyzed object and transformed longitudinal waves from incident on analyzed object transverse waves, measuring passage time of these waves in loaded and unloaded rails, determining the delay time of the transmitted signals and determining the voltage thereof from their difference, wherein the probing signal with resonance frequency of the piezoelectric transducers is pre-formed, and the passage time of waves is carried out by a high-frequency analogue-to-digital converter when the maximum value of the signal amplitude is achieved in the sampling interval of not more than Δτ=10⋅10s.EFFECT: high reliability of determining mechanical stress and shorter time for processing information.4 cl, 3 dwg

Description

The invention relates to non-destructive testing and technical diagnostics and can be used to determine internal mechanical stresses in rails.

A known method of measuring the speed of a surface ultrasonic wave, including determining the time interval between ultrasonic pulses, at which a surface ultrasonic wave is excited by a piezoelectric transducer, receives ultrasonic pulses transmitted through the product and determines the time intervals between these pulses, and when the wave propagates through the product, ultrasonic pulses are recorded, at least at three points, then the pulses are transmitted to a digital oscilloscope and ultrasound pulses are digitized into a computer to determine the dependence of the amplitudes of the ultrasonic pulses on the distance traveled by the wave, then the amplitudes of the ultrasonic pulses are normalized, starting from the second, to the amplitude of the first, and after alignments determine the time intervals between these pulses (see RF patent No. 2490606, G0H 5/00, priority dated February 20, 2013, bull. No. 23), adopted as an analogue.

The disadvantage of this method is that the surface ultrasonic wave is sensitive only to surface defects of the product, but does not allow to determine internal defects. This reduces the resolution and accuracy of measuring the speed of propagation of the ultrasonic wave. In addition, the surface wave is not sensitive to the stress-strain state of the material, which does not allow using it to control mechanical stresses.

A device for measuring the propagation velocity of a head ultrasonic wave is known, which contains a laser pulse generator, an optical-acoustic transducer, an article, ultrasonic pulse pick-up points for the first and second piezoelectric receiver, the first ADC unit, a computer, the second ADC unit, a thin immersion layer of contact liquid, sound ducts (see RF patent No. 2643232, G0H 5/00, G0N 29/34, priority dated January 31, 2018, bull. No. 4), adopted as an analogue.

The main disadvantage is that the device does not provide the ability to adjust the frequency and shape of the generator pulses, which limits the possibility of obtaining high-precision results of measuring the propagation velocity of the head ultrasonic wave in the product, and, consequently, mechanical stresses. In addition, it is not possible to isolate modes to provide the required sensitivity to rail deformations, since the head wave velocity changes less from the deformation of the test object than the speed of transverse and transformed waves.

A known ultrasonic method for determining mechanical stresses in rails, which consists in the fact that converters are installed on the rail threads, connect them to the receiving device, make initial (reference) measurements, the value of mechanical stresses is determined by measuring the time delays of the arrival of the ultrasonic signal to the receivers from the initial measurements while measuring the initial voltage is carried out connected to the receiving device, a transducer mounted on a piece of rail placed on a trolley moving along the rail, additionally measure the time delay of the arrival of an ultrasonic signal to the receiving device depending on the height of the rail connected to it by the longitudinal wave transducers installed on the rail segment, and the surface of the rail threads and mechanical stresses are determined by the formula:

- время распространения сигнала продольной волны в ненагруженном отрезке рельса и в рельсовой нити, мс;

- время распространения сигнала от излучателя к приемнику в ненагруженном отрезке рельса и в рельсовой нити, нс;

- разность времен распространения сигнала продольной волны, в ненагруженном отрезке рельса, нс;

- разность времен распространения сигнала от излучателя к приемнику в ненагруженном отрезке рельса, нс; k - акустоупругий коэффициент, МПа^-1 (см. патент РФ №2619842 МПК G01N 29/07, приоритет от 18.05.2017 г., бюлл. №14, Степанова Л.Н., Курбатов А.Н., Тенитилов Е.С. Исследование продольных напряжений в рельсах с использованием эффекта акустоупругости на действующем участке железнодорожного пути // Контроль. Диагностика. 2019. №2. С. 14-21), принятый за прототип.Where

- the propagation time of the longitudinal wave signal in the unloaded section of the rail and in the rail filament, ms;

- the propagation time of the signal from the emitter to the receiver in the unloaded section of the rail and in the rail filament, ns;

- the difference in the propagation times of the longitudinal wave signal in the unloaded section of the rail, ns;

- the difference in the propagation times of the signal from the emitter to the receiver in the unloaded section of the rail, ns; k is the acoustoelastic coefficient, MPa ^-1 (see RF patent No. 2619842 IPC G01N 29/07, priority dated 05/18/2017, bull. No. 14, Stepanova L.N., Kurbatov A.N., Tenitilov E.S. The study of longitudinal stresses in rails using the effect of acoustoelasticity on the existing section of the railway track // Control. Diagnostics. 2019. No. 2. P. 14-21), adopted as a prototype.

The disadvantage of this method is that it does not change the shape and frequency of the signals supplied to inclined piezoelectric transducers emitting ultrasonic waves into the rails, which reduces the accuracy of determining the arrival times of longitudinal L, transverse T and transformed waves LT and the accuracy of measuring stresses in the rail.

The closest in technical essence is a device for non-destructive testing of the stress state of the rail lashes of a continuous path, containing a pulsed laser, the output of which through an optical fiber is connected to the input of the laser-ultrasonic transducer, a combined multifunction power supply, a data processing system, two orthogonally located prisms made with the possibility of simultaneously measuring the head wave velocity in mutually perpendicular directions, each of the prisms along one of the faces through an optical-acoustic generator is connected to the optical system and optical fiber, and along the opposite side - to its corresponding broadband piezoelectric receiver, each of which is connected through an appropriate amplifier of electrical signals with an input of a two-channel analog-to-digital converter, which is connected to a pulsed laser and a data processing system at the input and output (see patent for PM RF No. 164233 IPC G01N 29/04, priority 20. 08.2016, bull. No. 23), adopted as a prototype.

The disadvantages of this device include the fact that to ensure the accuracy of measuring the speed of the ultrasonic wave in the transverse direction of the rail due to the small distance corresponding to the width of the rail, it is impossible to achieve high accuracy in measuring the time of arrival of the signal, and, consequently, the rail voltage in the longitudinal direction .

When developing the inventive ultrasonic method for determining mechanical stresses in a rail and a device for its implementation, the task was to increase the reliability of determining mechanical stresses and reduce information processing time, which would make it possible to determine stresses in real time during the movement of a railway trolley.

The problem is solved due to the fact that in the proposed ultrasonic method for determining the internal mechanical stresses in rails, which consists in the fact that the pulsed ultrasonic longitudinal and transverse waves are introduced into the loaded rail and its unloaded analog by the emitting piezoelectric transducer, transformed transverse waves from incident longitudinal waves and transformed longitudinal waves from the transverse waves incident on the studied object, measure the propagation times of these waves in the loaded and unloaded rails, determine the change in the delay time of the transmitted signals and determine the voltage from their difference, and a probe signal with a resonance frequency is preliminarily formed emitting piezoelectric transducers in the frequency range of at least 2.5 MHz, and the countdown of the propagation time of the waves is carried out by a high-frequency analog-to-digital converter when reaching the maximum the signal amplitude in the sampling interval is not more than Δτ = 10⋅10 ^-9 s, which is controlled in accordance with the velocities of longitudinal, transverse and transformed waves, while the number of periods of the probing signal varies within 1≤n≤5.

The problem is also solved due to the fact that the device for determining the stress state of rail lashes contains a signal source, a control system and a data processing system connected to the control system, the data processing system contains two channels, each of which consists of a piezoelectric transducer operating in series receiving mode of ultrasonic signals, high and low-pass filters, programmable normalizing amplifiers and analog-to-digital converters connected via random access memory of the received signal form and control system to a signal source in the form of a highly stable generator, the first analog output of the control system is connected to the input of random access memory the shape of the probe pulse, the digital output of which is connected to the input of the digital-to-analog converter, the shape of the probe pulse, the analog output of which is connected to the input of the bandpass smoothing filter, and its o output - with the input of a high-voltage transformer with a buffer amplifier connected to two radiating converters installed in a loaded rail and its analog unloaded, in addition, the analog inputs of analog-to-digital converters are connected to the outputs of programmable counters of the number of measurements, to the inputs of which programmable time counters are connected delays connected to the control system, the output of which is connected to the digital input of the central processor.

In FIG. 1 is a functional diagram of a system for ultrasonic monitoring of stresses in rails; FIG. 2 shows a graph of approximation of an ultrasonic signal by its recorded samples when it reaches its maximum value for a signal frequency of 2.5 MHz, in FIG. Figure 3 shows the maximum readout of an ultrasonic signal at a frequency of 2.5 MHz.

A device that implements an ultrasonic method for determining mechanical stresses in rails (Fig. 1), contains:

1 - highly stable master oscillator;

2 - system control device;

3 - random access memory of the form of the probe pulse;

4 - digital-to-analog converter of the form of the probe pulse;

5 - bandpass smoothing filter;

6 - high-voltage transformer with a buffer amplifier;

7 - a piezoelectric transducer operating in a radiation mode;

8 - unloaded analogue of the rail;

9 - rail;

10 - piezoelectric transducer operating in the reception mode;

11 - tunable low-pass filter;

12 - tunable high-pass filter;

13 - programmable rated amplifier;

14 - analog-to-digital Converter;

15 - programmable counter of the number of measurements of the analog-to-digital Converter;

16 - random access memory of the form of the received signal;

17 - programmable counter delay time;

18 is the central processor of the computer.

The practical implementation of the proposed device that implements an ultrasonic method for determining mechanical stresses in rails is performed according to known schemes using the following components:

1. The analog-to-digital converter is assembled on the AD9246BCPZ-105 chip.

2. The digital-to-analog converter is implemented on the AD9744ACPZ chip.

3. The band-pass smoothing filter and the programmable normalizing amplifier are assembled on LT1363CS8 microcircuits.

4. The high-voltage transformer with a buffer amplifier is assembled on the elements of the LTC6090IFE-5 # PBF, WB16-1SL.

5. The operational memory of the probe pulse shape, programmable counters of the number of measurements of the analog-to-digital converter, programmable counters of the delay time, random access memory of the form of the received signal and the system control device are assembled on a chip from Altera EP3C25Q240.

Information about the chips is:

1. Altera Web sites, www.altera.com, Analog Devices, www.analog.com.

An ultrasonic device for determining mechanical stresses in rails (Fig. 1) consists of a highly stable master oscillator 1, the output of which is connected to a control device of system 2, the first analog output of which is connected to the input of random access memory of the form of a probe pulse 3, the digital output of which is connected to the input of the digital-to-analog transducer of the shape of the probe pulse 4, the analog output of which is connected to the input of the bandpass smoothing filter 5, the output of which is connected to the input of the high-voltage transformer 6 with a buffer amplifier, connected to inclined ultrasonic transducers with an angle of 18 °, operating in radiation mode 7 and installed on an unloaded analogue of rail 8 and on loaded rail 9, connected to a data processing system containing two channels, each of which consists of a piezoelectric transducer 10 connected in series, operating in the mode of receiving ultrasonic signals, connected output from the tunable low-pass filter 11, the output of which is connected to the input of the tunable high-pass filter 12, the output of which is connected to the input of a programmable normalizing amplifier 13, the output of which is connected to the analog input of the analog-to-digital converter 14, the other analog input of which is connected to the analog output a programmable counter of the number of measurements of the analog-to-digital converter 15, and the digital output of the analog-to-digital converter 14 is connected to the digital input of the random access memory of the received signal form 16, the output of which through the control system 2 is connected to a highly stable generator 1, programmable delay time meters 17, the inputs of which connected to the second and third analog outputs of the control device 2, and analog outputs to the second analog inputs of the programmable counters of the number of measurements by the analog-to-digital converter 15, the third digital input of the control device of the system 2 is connected to the main input of the central processor of the system 18.

The proposed system and method work as follows.

Before starting the control, two piezoelectric transducers 7, 10 are installed on the loaded rail 9 and its unloaded analog 8. After that, the initial system parameters are loaded. The central processor of the computer 18 sends to the control device of the system 2 a command to load the shape of the probe signal with a resonance frequency of the piezoelectric transducers 7, 10 equal to 2.5 MHz. This signal is converted to the digital equivalent by analog-to-digital Converter 14 with a sampling interval of Δτ = 10⋅10 ^-9 s. In this case, the control device of system 2 via serial lines loads into the random access memory a probe pulse shape 3 an array of data representing the shape of the probe signal in the form of several periods of sinusoidal oscillations at the resonant frequency of ultrasonic transducers 7, 10. Then, the control device of system 2 loads through serial lines the values in the programmable counters of the delay time 17 corresponding to the propagation time of the measured wave mode and in the programmable counters of the number of measurements of the analog-to-digital Converter 15 recorded values of the number of samples that define the measuring range of the propagation time of the ultrasonic signal. Moreover, the delay time counters 17 can be programmed into various modes of the received ultrasonic signal.

System operation in measurement mode.

The central processor of computer 18 sends a command to the control device of system 2, by which it generates a control signal of random access memory of the form of the probe pulse 3. According to this signal, codes from the random access memory 3 are fed to the input of a digital-analog converter of the shape of the probe pulse 4 with the frequency generated highly stable master oscillator 1. At the same time, the same command starts the delay time counters 17. At the same time, a probing signal is generated at the output of the digital-to-analog converter 4, which passes through the band-pass smoothing filter 5 and the high-voltage transformer with buffer amplifier 6 to the inputs of the ultrasonic transducers 7. Band-pass smoothing filter 5 provides suppression of sampling noise, and a high-voltage transformer with a buffer amplifier 6 provides the necessary amplitude level of the probing signal. After passing through the rail 9 and its unloaded analog 8, the acoustic signals are fed to the inputs of the ultrasonic transducers 10, which convert the acoustic signals coming from the soles of the rails 8 and 9 into electrical signals coming to the inputs of the tunable filters of the lower 11 and upper 12 frequencies, providing the necessary amplitude -frequency characteristics of the receiving measuring channels, and suppression of spurious components of the received signal. Then the signals are fed to the inputs of the normalizing amplifiers 13, where they are amplified to the amplitudes necessary for measuring by analog-to-digital converters 14. After the delay time formed by the delay time counters 17 channels, the highly stable master oscillator 1 starts programmable counters of the number of measurements of the analog-to-digital converter 15, allowing the recording of measurement codes by analog-to-digital converters 14, clocked by the generator 1, into the random access memory of the received signal form 16. At the end of the measurement, programmable counters of the number of measurements of the analog-to-digital converter 14 stop recording the measurements. Then the central processor of the computer 18 through the control device of the system 2 reads the measurement results from two measuring channels. Based on the measured results, the central processor 18 calculates the propagation time of the selected signal mode, taking into account the delay time. In this case, the transit times of the ultrasonic waves in the unloaded section of the rail 8 and in the loaded rail 9 are compared and the longitudinal mechanical stresses in each rail thread are determined by the difference in time.

The ultrasonic probe signal U (t), arriving at the ultrasonic transducers 7 from the output of the high-voltage transformer with a buffer amplifier 6, puts them into the radiation mode of the ultrasonic signal that enters the rail 9, and the unloaded analog of the rail 8 is reflected from their sole and comes to the piezoelectric transducers 10 operating in the reception mode and converting ultrasonic signals into electrical signals (Fig. 1). After the passage of the electrical signal through the filters 11, 12 low and high frequencies of the first and second measuring channels, it is amplified by programmable amplifiers 13 and fed to the inputs of analog-to-digital converters 14 installed in the first and second measuring channels. In each measuring channel, the digital equivalent of the signal from the output of the analog-to-digital converter 14 is presented in the form of a set of samples U _i through the sampling interval Δ _t = 10⋅10 ^-9 s. The arrival time of the signal is determined by the time t _max corresponding to the amplitude reaching its leading edge of the maximum value (Fig. 2). Since the signal arrival time is determined when the amplitude of its leading edge reaches its maximum value in the sampling interval Δt _disk = 10⋅10 ^-9 s (see Fig. 2), the arrival time of the transformed signal is 5⋅10 ^-9 s (see Fig. . 3). Since the voltage in the rail is determined by the time the ultrasonic signal reaches its maximum value, the error in its determination is not higher than Δt = 5⋅10 ^-9 s.

The difference between this method and the prototype lies in the fact that in the proposed method, probing signals are formed at the resonance frequency of two piezoelectric transducers with different numbers of oscillation periods from 1 to n, and the measurement results of the signal propagation time are averaged over n measurements. In the prototype, since it is impossible to precisely determine the selection threshold due to noise and it varies over time, large errors arise in measuring the propagation time of ultrasonic waves. In addition, the transformed waves arrive later than the longitudinal waves and the selection threshold cannot be set due to acoustic noise and interference.

In the proposed method, the arrival time of the transformed waves to the piezoelectric transducers operating in the reception mode is determined by the time it takes to reach the maximum amplitude of the ultrasonic signal in a predetermined period of time, which is located through the maximum and minimum propagation speeds of the corresponding transformed waves. When the tensile strain of the rails there is a minimum propagation speed C _{min of the} ultrasonic signal:

where S is the distance between the sensors; t _max - the maximum propagation time of the ultrasonic signal.

If the rail experiences a compression deformation, then the maximum propagation speed C _{max of the} ultrasonic signal is achieved:

where t _min is the minimum propagation time of the ultrasonic signal.

To reduce the measurement error of the propagation time of the ultrasonic signal, a sinusoidal approximation of the received signal at the resonant frequency of the piezoelectric transducer is used. As a result, at a sampling frequency of 100 MHz, the time between samples is 10⋅10 ^-9 s and the measurement error of the arrival time of the transformed signal is 5⋅10 ^-9 s. Improving the accuracy of measuring the propagation time of an ultrasonic signal leads to an increase in the accuracy of measuring voltage in rails and is associated with a decrease in the error of measuring the arrival time of the transformed signal.

Claims (4)

1. A method for determining the stress state of rail lashes, namely, that pulsed ultrasonic longitudinal and transverse waves are introduced into a loaded rail and its unloaded analog by a radiating piezoelectric transducer, receiving transformed transverse waves from longitudinal waves incident on the object under investigation and transformed longitudinal waves from shear waves incident on the object under study, measure the propagation times of these waves in loaded and unloaded rails, determine the change in the delay time of the transmitted signals and determine the voltage value by their difference, characterized in that the probing signal with the resonance frequency of the piezoelectric transducers is preliminarily formed, and the countdown of the propagation time waves carry out a high-frequency analog-to-digital Converter when reaching the maximum value of the signal amplitude in the sampling interval of not more than Δτ = 10⋅10 ^-9 s. 2. The method for determining the stress state of rail lashes according to claim 1, characterized in that the sampling frequency is controlled in accordance with the speeds of longitudinal, transverse and transformed waves. 3. The method for determining the stress state of rail lashes according to claim 1, characterized in that the number of periods of the probe signal varies within 1≤n≤5 at a resonant frequency of the piezoelectric transducer, not less than 2.5 MHz. 4. A device for determining the stress state of rail lashes, comprising a signal source, a control system and a data processing system connected to a control system, characterized in that the data processing system contains two channels, each of which consists of a piezoelectric transducer operating in a receiving mode connected in series ultrasonic signals, high-pass and low-pass filters, programmable normalizing amplifiers and analog-to-digital converters connected via a random-access memory of the received signal form and a control system to a signal source in the form of a highly stable generator, the first analog output of the control system is connected to the input of the operative memory of the sounding form pulse, the digital output of which is connected to the input of the digital-to-analog converter of the probe pulse shape, the analog output of which is connected to the input of the bandpass smoothing filter, and its output is connected to the input of a high a voltage transformer with a buffer amplifier connected to two radiating converters installed in a loaded rail and its unloaded analog, in addition, the analog inputs of the analog-to-digital converters are connected to the outputs of the programmable counters of the number of measurements, to the inputs of which are programmable delay time counters connected to the system control, the output of which is connected to the digital input of the central processor.

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