JPH02248824A - Apparatus for measuring residual stress - Google Patents

Abstract

PURPOSE:To accurately measure residual stress without receiving the effect of temp. by measuring the propagation time of the electromagnetic ultrasonic wave generated on the side of a magnet over the predetermined distance in the magnet and correcting the propagation time measured value of an ultrasonic wave through a material to be inspected on the basis of the measured result. CONSTITUTION:Electromagnetic ultrasonic waves polarized in two directions mutually crossing at a right angle with respect to an iron core 11 having predetermined reference temp. in the measurement of residual stress are generated on one end surface of the iron core 11 by probe coils 13a, 13b and reflected from the other end surface thereof and one reciprocating time of said ultrasonic waves between both surfaces is measured to calculate the reference propagation speed in the iron core 11. Then, the deviation with the reference value of a propagation speed is calculated from the propagation time of a material 2 to be inspected. Since the ratio of this deviation to the reference value is equal to the ratio of the deviation of the propagation speed measured in the material 2 to be inspected with the reference value to the reference value, the propagation time over the predetermined distance in the material to be inspected is corrected on the basis of said ratio. By this method, residual stress can be accurately measured without receiving the effect of temp.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a residual stress measuring device that measures residual stress in a test material using so-called electromagnetic ultrasonic waves.

[Prior art]

In recent years, a method that utilizes the acoustoelasticity of materials has become popular as a method for non-destructively inspecting metal materials and the like. This is a polarized transverse wave (
This method takes advantage of the property of stretchability, in which the propagation speed of shear waves changes depending on the stress applied to the material.

Specifically, a polarized transverse wave is emitted from the probe toward the inside of the material to be tested, and the reflected wave from the opposite surface of the material to be tested is received as an electrical signal by the probe coil, and the time between transmission and reception is To measure time. Next, if you change the direction of the probe coil so that it emits a transverse wave polarized in a direction 90' different from the above case and perform a similar measurement, it is possible to measure the internal residual stress in the test material from the time difference between the two. It is.

The principle of measuring residual stress using the acoustic elasticity will be explained below. If the propagation velocities of two transverse waves deflected in the principal stress direction are V, V2, respectively, in the elastic body under biaxial stress, which is the test material, then the orthotropic axis of the elastic body (generally, the When the direction (the rolling direction of rolling and the direction perpendicular thereto) coincides with the principal stress direction, the principal stress σ1 of each axis of the biaxial stress. Principal stress difference (σ1
σ2) and the propagation velocity difference (V, V2) have a relationship as shown in equation 11 below.

However, VOI+ ■02'V in the stress-free state, , V2α
: Constant C that takes into consideration the tissue acoustic anisotropy of the material to be tested. ) Formula % Formula % In actual measurement of residual stress, the propagation time T of the transverse wave,
, T, are measured, and residual stress is calculated using equation (2). A residual stress measuring device using such a measurement principle, for example, generates transverse waves polarized in two orthogonal directions and measures the difference in propagation time between them to calculate the principal stress difference (σ1σ2) in two stress fields. A device for this purpose has been proposed (Japanese Utility Model Application Publication No. 175830/1983, Japanese Utility Model Application No. 63-14
Publication No. 8843).

[Problem to be solved by the invention]

When measuring the propagation time of transverse waves to determine residual stress using acoustic elasticity as described above, the rate of change in propagation time due to residual stress is, for example, approximately 5 for a wheel with a thickness of 125 mm.
ns/kg/ml112. On the other hand, the rate of change in propagation time with respect to changes in the temperature of the test material is approximately 10 ns/
"C, and the accuracy of the instrument fluctuates in the range of several + nanoseconds due to changes over time. These factors cause errors in measuring the propagation time of transverse waves, but when determining residual stress using acoustic elasticity, there are two types. Since the residual stress is determined from the difference in the propagation speed of the transverse waves, most of the error factors described above are canceled out. However, since the measurement of the propagation time of the transverse waves is performed on the order of nanoseconds, the remaining error that is not canceled out is The current situation is that the impact on results is significant.

The present invention has been made in view of the above circumstances, and it measures the propagation time required for electromagnetic ultrasonic waves generated in a magnet to propagate a predetermined distance in the magnet, and uses this measurement result to determine the electromagnetic ultrasonic wave in the specimen material. It is an object of the present invention to provide a residual stress measuring device that has good measurement accuracy without being affected by the temperature of a material to be tested and the precision of the instrument by correcting the measured value of the propagation time of a sound wave.

[Means to solve the problem]

The first residual stress measuring device according to the present invention arranges a magnet and a probe coil facing each other with respect to a test material, and receives electromagnetic ultrasonic waves polarized in two orthogonal directions by energizing the magnet and probe coil. In a residual stress measuring device that measures the residual stress of a material to be inspected by generating electromagnetic ultrasonic waves in the material to be inspected and measuring the difference in propagation time required for these electromagnetic ultrasonic waves to propagate a predetermined distance in the material to be inspected, A means for measuring the propagation time required for each ultrasonic wave to propagate a predetermined distance in the magnet, and a means for correcting the measured value of the propagation time in the test material based on the measurement result of the means. It is characterized by

Further, the second residual stress measuring device according to the present invention is characterized in that the validity of the measured value of the propagation time is determined based on the measurement result.

[Effect]

The propagation velocity of electromagnetic ultrasonic waves propagating inside a magnet is a constant value when there are no changes in temperature or instrument accuracy, so this propagation velocity is used as the reference value, and the propagation velocity is calculated from the actually measured propagation time inside the magnet. Find the deviation from the reference value. Since the ratio of the deviation to the reference value is equal to the ratio of the deviation between the propagation velocity measured in the test material and its reference value to the reference value, this ratio determines the propagation time for a predetermined distance in the test material. Make corrections. Furthermore, if the accuracy of the instrument deteriorates due to aging, abnormal values will appear in the measured values. This should be detected (base 1! value of the propagation velocity of electromagnetic ultrasound in two orthogonal directions is determined in advance, the reference value and the actual measurement value are compared, and the deviation between the reference value and the actual measurement value is a predetermined value. If it is larger than that, the actual measured value is regarded as an abnormal value and is determined to be invalid.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof. FIG. 1 is a block diagram showing the overall configuration of a residual stress measuring device according to the present invention.

In the figure, 1 is an electromagnet, and the U-shaped iron core 11 of the electromagnet 1 is
A magnetizing coil 12 is wound around each leg of the
When a current is passed through the magnetizing coil 12 from the DC power source 35, one end of the iron core 11 becomes an S pole and the other end becomes an N pole, thereby acting as an electromagnet.

The iron core 11 is disposed so that the magnetic pole surface, which is the tip thereof, faces the material to be tested, and a magnetic field is generated inside the material to be tested 2 due to the magnetic force of this electromagnet. An elliptical first probe coil 13a is provided on the magnetic pole surface, which is the tip on the N pole side, with its long axis aligned with the direction connecting both magnetic poles of the iron core 11, and an elliptical second probe coil 13a is provided. 13b is provided with its long axis in a direction perpendicular to the direction of the long axis of the probe coil 13a.

The probe coil 13a is connected to a pulse oscillation circuit 33, and the probe coil 13b is connected to a pulse oscillation circuit 34.The pulse oscillation circuit 33 or 34 receives a trigger input from the trigger circuit 31 via the switching circuit 32. A pulse signal is given to the probe coil 13a or the probe coil 13b depending on the input timing of the signal. Note that the switching circuit 32 is designed to work in conjunction with a switching circuit 43, which will be described later.

The probe coil 13a and the probe coil 13b generate eddy currents on the surface of the test material 2 by electromagnetic induction caused by the input pulse signals. This eddy current and electromagnet 1
Due to the interaction with the magnetic field generated by the Lorentz force, electromagnetic ultrasonic waves are propagated from the surface of the test material 2 toward the inside of the test material 2 . Also, similarly to this, iron core 1
Electromagnetic ultrasonic waves are propagated from the magnetic pole surface of 1 to the inside thereof. The electromagnetic ultrasonic waves emitted from the blow coil 13a and the probe coil 13b are propagated within the test material 2 and the legs of the iron core 11, are reflected at the other end faces, and are reflected again on the surface of the test material 2 and the magnetic pole face of the iron core 11. At this point, induced currents are induced in the probe coils 13a and 13b by interaction with the magnetic field.

These induced currents are applied to the preamplifier 41 from the probe coil 13a, and are applied to the preamplifier 42 from the probe coil 13b.

The preamplifier 41 and the preamplifier 42 amplify the input signal by a predetermined amount and operate the switching circuit 4 in conjunction with the switching circuit 32.
3 to the main amplifier 44. The main amplifier 44 amplifies the input signal by a predetermined amount and inputs it to the clock device 45 .

In the signal system described above, pulse signals are alternately applied from the pulse oscillation circuits 33.34 to the probe coils 13.13b by switching the connection of the switching circuit 32. As a result, each of the probe coils 13a and 13b is alternately energized, and electromagnetic ultrasonic waves in two orthogonal directions are alternately propagated within the specimen 2. The received signal of this reflected wave is input to the preamplifier 42 from the probe coil 13a, and is also input to the preamplifier 41 from the probe coil 13b.

Since the switching circuit 43 is interlocked with the switching circuit 32, the preamplifier 41 (or 42) connected to the probe coil 13a (or 13b) performing the measurement
The output is always input to the clock device 45 via the main amplifier 44.

FIG. 2 is a waveform diagram showing the received waveform of the electromagnetic ultrasound output from the main amplifier 44. (a) is a waveform received by the probe coil 13a, and (bl is a waveform received by the probe coil 13b).

In the figure, S is a transmitted wave, T is a reflected wave that has gone back and forth within the iron core 11, and B is a reflected wave that has gone back and forth within the test material 2.

In the timing device 45, the time T from the time when the pulse oscillation circuit 33 receives the pulse signal to the time when the reflected wave T reflected at the other end in the iron core 11 is received based on the result received by the probe coil 13b. , and the time B until the reflected wave B reflected at the other end of the test material 2 is received.
+ and time respectively, and also measure the time T2 from the time when the pulse oscillation circuit 34 emits the pulse signal to the time when the reflected wave T is received, and the time B2 from the time when the reflected wave B is received. Time each person. These timing results T
,,B,.

T2 and Bz are given to the arithmetic circuit 46, and the arithmetic circuit 4
In step 6, the timing result BB2 is corrected using the timing results T, T2, and the residual stress of the test material 2 is calculated based on the corrected values of Bl and B2. Determine the validity of results B,,B2.

Next, a method of correcting the time measurement results B1 and B2 performed by the arithmetic circuit 46 in the first residual stress measuring device of the present invention will be described. In the iron core 11 at a predetermined temperature, which is the reference temperature in residual stress measurement, the probe coil 1
3a and 13b, electromagnetic ultrasonic waves polarized in two orthogonal directions that are generated at one end face facing these and propagate toward the other end face are reflected at the other end face, and ■ Time it takes for it to travel back and forth. Measure the reference propagation velocity in the iron core II. Each of I+■0 is determined in advance. Assuming that the thickness of the material 2 to be inspected is 3 and the thickness of the iron core 11 in the opposite direction is DT, the time 'I'+, Tt required for one round trip is as follows (
3) It is obtained as shown in equation (4).

T+ = Dr / (V., + to -C) ... (3
) Tz -Dr / (-C to Voz+) ...(
4) However, K: The rate of change in propagation velocity due to the amount of change in core temperature from the reference temperature difference C: The amount of change in iron core temperature from the reference temperature difference (31, (41
In the formula, KC is the standard propagation velocity V 61. V6
This is the amount of change in propagation velocity due to core temperature with respect to z. The amount of change KC in the propagation velocity is determined by the following equation (5) by taking the average of equations (3) and (41).

Propagation speed■. It can be seen that the propagation velocity within the iron core 11 changes at the ratio of K C/Vow and K C/Voz. This KC/V. It K
+61. below using C/Voz. (7) (correcting the timing results B, B2 by compensating for changes in the propagation velocity of electromagnetic ultrasound caused by the temperature state in the test material 2,
Time measurement result correction values Bl and Bz' are obtained.

B+' =B+ (1+KC/Vow) ・(6)B
z' = Bz (1+KC/V.2) (7) Also, a method for determining the validity of the time measurement results B+ and Bz in the second residual stress measuring device according to the present invention will be explained. At the reference temperature, the propagation time difference of electromagnetic ultrasonic waves in two orthogonal directions within the iron core 11 is determined in advance TIT! −Δ
Measure T0, and judge whether this ΔTo and the propagation time difference ΔT of the actual timing result satisfy the condition of ΔTo - ΔT<L (L is a constant). If this condition is not satisfied, make a correction. Recognizing that the result Bl + 82' is an abnormal value due to poor accuracy of the meter and not valid, we decided to test material 2.
From the propagation time difference B, '-B, = ΔB, the deviation of the propagation time difference ΔT from its reference value ΔT (ΔT0-8T)
, and the propagation time difference ΔB in the test material 2 is ΔB−(ΔT0
−ΔT) and calculate the residual stress. In this way, abnormal values caused by deterioration of instrument accuracy due to aging are eliminated from the time measurement results.

Using the time measurement results Bl and B2 obtained in this way,
The stress value of the residual stress is calculated using the following equation (8).

The arithmetic circuit 46 outputs the calculation result of the stress value, and also outputs abnormal data if the time measurement result is abnormal.

〔effect〕

As detailed above, in the residual stress measuring device according to the present invention, the propagation time required for the electromagnetic ultrasonic waves generated on the magnet side to propagate a predetermined distance in the magnet is measured, and the measurement results are used to measure the propagation time of the electromagnetic ultrasonic waves generated on the magnet side. In addition to correcting the propagation time measurement value of electromagnetic ultrasonic waves, the validity of the propagation time measurement value is determined, so residual stress can be measured with high accuracy without being affected by the temperature of the test material and the accuracy of the instrument. The present invention exhibits excellent effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of the residual stress measuring device according to the present invention, and FIG. 2 is a waveform diagram showing the received waveform of electromagnetic ultrasonic waves. 1... Electromagnet 2... Test material 13a, 13b・
... Probe coil 45 ... Timing device 46 ...
Arithmetic circuit...(8)

Claims (1)

[Claims] 1. A magnet and a probe coil are arranged opposite to the material to be inspected, and electromagnetic ultrasonic waves polarized in two orthogonal directions are generated in the material to be inspected by energizing the magnet and the probe coil. ,
In a residual stress measurement device that measures the residual stress of a test material by measuring the difference in propagation time required for these electromagnetic ultrasound waves to propagate a predetermined distance in the test material, It is characterized by comprising means for measuring the propagation time required for propagation over a predetermined distance in the magnet, and means for correcting the measured value of the propagation time in the test material based on the measurement result of the means. Residual stress measuring device. 2. The residual stress measuring device according to claim 1, wherein the validity of the measured value of the propagation time is determined based on the measurement result.