JP4480640B2 - Ultrasonic fatigue test apparatus and ultrasonic fatigue test method - Google Patents

Description

  The present invention relates to an ultrasonic fatigue test apparatus and an ultrasonic fatigue test method. More specifically, the present invention relates to an ultrasonic fatigue test apparatus and an ultrasonic fatigue test method for a material fatigue test using ultrasonic waves.

Conventionally, as a material fatigue test, a rotational bending fatigue test of a metal material and a plane bending fatigue test of a metal flat plate are known. For example, in a rotating bending fatigue test of a metal material, a repetition rate (50 Hz) is usually about 50 times per second, and therefore, a fatigue test with an ultrahigh cycle of 10 ⁸ or more requires 20 days or more. Further, it has been desired to provide a method that enables a fatigue test in a short time. However, in such a conventional fatigue test method, there is a limit to improving the repetition rate.

  Therefore, a fatigue test method using ultrasonic waves is known. The ultrasonic fatigue test is a method of performing a fatigue test by causing a test piece to resonate with ultrasonic waves, and enables a fatigue test in a short time by utilizing its fast repetition rate. As an example of the ultrasonic fatigue test, the fatigue test can be performed at a repetition rate (15 to 25 kHz) of about 15,000 to 25,000 times per second.

  However, in such an ultrasonic fatigue test, there is a problem that the temperature of the test piece rises due to heat generation due to high frequency load repetition. In order to solve this problem, cooling of the test piece is indispensable, and forced cooling is used in which the test piece is immersed in a liquid or cooled air or liquid nitrogen is blown. However, when immersed in a liquid in this way, cavitation occurs, and when cooled air is insufficiently cooled, or when liquid nitrogen is used, nitrogen gas forms a boundary layer on the surface of the test piece. Since it forms, it may not be said to be a very effective cooling method. Even if the surface of the test piece is successfully cooled by such a cooling method, the temperature rise due to the internal heat generation is not eliminated, and the change in the material properties due to the temperature increase cannot be ignored.

Therefore, a method of cooling using a periodic intermittent load has been developed. For example, after repeating 500 to 1,000 times (when the test frequency is 20 kHz, a time of 25 ms to 50 ms), a method of periodically repeating the ultrasonic load between 50 ms and 1,000 ms is used. is there. This is a method of repeatedly stopping, cooling, and restarting the ultrasonic load at a time interval that does not increase the temperature of the material due to the load (for example, Non-Patent Document 1).
Hitoshi Ishii, “Rapid Determination of Gigacycle Fatigue Strength Using an Ultrasonic Intermittent Load Fatigue Testing Machine”, FY 2001-2002 Grant-in-Aid for Scientific Research (Basic Research (C) (2)) Research Results Report, Heisei June 2015

  However, in such an ultrasonic intermittent load type fatigue test, when the envelope has a rectangular repeated intermittent constant amplitude sinusoidal load as shown in FIG. 1, the amplitude of the test piece is immediately applied to the load when the load starts. It takes time to get up because it cannot follow. Furthermore, even when the load is removed, the vibration does not stop immediately but a damped vibration remains. Therefore, the envelope of the vibration waveform of the test piece is as shown in FIG.

  In this way, not only the vibration amplitude of the test piece during loading changes, but also when damped vibration remains even when there is no load, the test piece has a constant amplitude based on loading a certain amount of load a certain number of times. It is impossible to evaluate how many times the vibration is performed, and it becomes difficult to perform a reliable ultrasonic fatigue test.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ultrasonic fatigue test apparatus or method that is more accurate than the prior art and can be performed at a high repetition rate.

  Therefore, the present inventors have intensively studied in order to solve the above problems, and as a result, the present invention has been completed. More specifically, the present invention provides the following ultrasonic fatigue test apparatus.

  (1) An ultrasonic fatigue testing apparatus including an ultrasonic transmission unit and a transducer unit, wherein the ultrasonic transmission unit generates an ultrasonic signal voltage, and a voltage proportional to a difference between two input voltages. And a current detector for obtaining a voltage proportional to the output current of the differential input type ultrasonic power amplifier, and the output of the ultrasonic oscillator is the differential input. Input to one input terminal of the ultrasonic power amplifier, and an output voltage of the differential input ultrasonic power amplifier is applied to a series circuit of a Langevin piezoelectric actuator and the current detector serving as a load, and the current detector Is input to the other input terminal of the differential input type ultrasonic power amplifier, so that the differential input type ultrasonic power amplifier detects a voltage proportional to the output current of the differential input type ultrasonic power amplifier. Ultrasonic fatigue testing device for outputting a voltage that the amplifier is proportional to the difference of the two input terminal voltage.

  (2) The ultrasonic fatigue testing apparatus according to (1), wherein the transducer unit includes a Langevin piezoelectric actuator including a Langevin transducer and a horn that increases the amplitude of the Langevin transducer.

  (3) An ultrasonic fatigue test method using an ultrasonic transmitter and a vibrator, wherein the ultrasonic transmitter comprises an ultrasonic oscillator, a differential input type ultrasonic power amplifier, and a current detector, An output voltage of the dynamic input type ultrasonic power amplifier is input to one of a pair of input terminals of the differential input type ultrasonic power amplifier, and an output current of the differential input type ultrasonic power amplifier detected by the current detector Is input to the other of the pair of input terminals of the differential input type ultrasonic power amplifier, so that the differential input type ultrasonic power amplifier is connected to the output voltage of the ultrasonic oscillator and the differential input type. A voltage proportional to the difference in voltage proportional to the output current of the ultrasonic power amplifier is supplied to the series circuit of the Langevin piezoelectric actuator of the transducer section, which is the load of the differential input type ultrasonic power amplifier, and the current detector; in front Ultrasonic fatigue testing methods differential input type ultrasonic power amplifier to output a voltage proportional to the difference of the two input terminals the voltage to the series circuit of the current detector and the Langevin piezoelectric actuator of the transducer unit.

  (4) In the ultrasonic fatigue test method according to (3), the differential input type ultrasonic power amplifier output voltage is applied to a series circuit of the Langevin piezoelectric actuator and the current detector of the vibration unit, The Langevin piezoelectric actuator is driven by the differential input type ultrasonic power amplifier to generate ultrasonic vibration, and the ultrasonic vibration is input to a horn so that the horn expands the amplitude of the ultrasonic vibration. Test method.

  As a result, the definition of the load and the count of the number of fatigue tests are clarified by the present invention, and the ultrasonic fatigue test of the intermittent load is carried out with higher accuracy and higher repetition rate (for example, 10 kHz or more). Can do.

  Hereinafter, an example of an embodiment suitable for the present invention will be described with reference to the drawings.

  As an embodiment of the present invention, the ultrasonic fatigue test apparatus 1 includes an ultrasonic transmission unit 10 and a vibrator unit 20 (see FIG. 3). The ultrasonic transmission unit 10 generates and amplifies a signal voltage, and drives the Langevin piezoelectric actuator 21 of the vibration unit 20 connected in series with the current detector 13 with this signal voltage. The Langevin piezoelectric actuator 21 generates ultrasonic vibration by a signal voltage, and the horn 22 amplifies the vibration.

  The ultrasonic transmitter 10 includes an ultrasonic oscillator 11 that generates an ultrasonic signal voltage, a differential input ultrasonic power amplifier 12 that outputs a voltage proportional to the difference between the two input voltages, and the differential input ultrasonic wave. It comprises a current detector 13 for obtaining a voltage proportional to the output current of the power amplifier.

  The ultrasonic oscillator 11 generates a constant amplitude sine wave voltage, can adjust its frequency and amplitude, and can turn on or off its output voltage by an internal or external control voltage. Further, the ultrasonic oscillator 11 can count and integrate the number of sine wave oscillations of the output signal voltage.

  Since the output voltage of the ultrasonic oscillator 11 can be turned on and off by an external control voltage, the signal output from the displacement meter 32 is input as the external control voltage, so that the output from the displacement meter 32 is the test piece 50. When the value falls below the set value due to damage, the output can be turned off, and counting and counting of the number of sine wave oscillations of the output signal voltage can be stopped.

  The differential input type ultrasonic power amplifier 12 that outputs a voltage proportional to the difference between two input voltages inputs the output voltage of the ultrasonic oscillator 11 to one of the pair of input terminals. Further, a voltage proportional to the output current of the differential input ultrasonic power amplifier 12 detected by the current detector 13 is input to the other of the pair of input terminals of the differential input ultrasonic power amplifier 12. As a result, the differential input type ultrasonic power amplifier 12 generates a voltage that is proportional to the difference between the output voltage of the ultrasonic oscillator 11 and the voltage that is proportional to the output current of the differential input type ultrasonic power amplifier 12. This is supplied to the series circuit of the Langevin piezoelectric actuator 21 of the transducer unit 20 which is a load of the sonic power amplifier 12 and the current detector 13.

  The vibrator unit 20 includes a Langevin piezoelectric actuator 21 and a horn 22, and the Langevin piezoelectric actuator 21 generates ultrasonic vibrations by applying a signal voltage output from the ultrasonic transmission unit 10, and the horn 22 vibrates. Amplify the amplitude.

  The Langevin piezoelectric actuator 21 includes a Langevin type vibrator. A Langevin type vibrator is a device that generates micro-vibration that becomes an ultrasonic wave by utilizing an electrostriction phenomenon (a phenomenon in which polarization causes mechanical elongation). Therefore, for example, a lead zirconate titanate porcelain (PZT porcelain), which is a material having a large and stable effect of the electrostriction phenomenon, may be used for the Langevin type vibrator.

  The horn 22 is a device that increases the amplitude of minute vibrations generated by the Langevin vibrator. For example, a two-stage composite conical amplitude expanding horn may be used. The amplitude magnification by the horn is determined by the geometric shape of the horn. The minute vibration generated by the Langevin vibrator is expanded by resonating the horn, and transmitted to the test piece 50 attached to the tip of the horn.

  The test piece 50 is a test material to be subjected to an ultrasonic fatigue test. The dimension of the test piece 50 is adjusted so as not to impair the resonance of the horn 22.

  The displacement detection probe 31 is disposed at the tip of the test piece 50 via a slight gap, detects the longitudinal vibration amplitude at the tip of the test piece 50, and converts it into an electrical signal.

  The displacement meter 32 processes the electrical signal output from the displacement detection probe 31 disposed at the tip of the test piece 50 through a slight gap and displays the longitudinal vibration amplitude at the tip of the test piece 50. Further, a control signal corresponding to the vibration amplitude is output to the ultrasonic oscillator 11, and when the signal voltage becomes a set value or less, the output voltage of the ultrasonic oscillator 11 is turned off.

  FIG. 4 shows an output voltage waveform when the ultrasonic oscillator 11 repeatedly outputs an intermittent constant amplitude sine wave signal voltage waveform, and FIG. 1 shows its envelope, which is rectangular. The case where the ultrasonic oscillator 11 outputs this repeated intermittent constant amplitude sine wave signal voltage will be described below.

  When the output voltage of the ultrasonic oscillator 11 is a repetitive intermittent constant amplitude sine wave signal having a rectangular envelope, the output voltage of the ultrasonic oscillator 11 is simply amplified by an ultrasonic power amplifier without providing a current detector, and the output thereof In the conventional method of driving the Langevin piezoelectric actuator 21, when the vibration of the test piece 50 is detected by the displacement detection probe 31, the result is as shown in FIG. That is, as apparent from the envelope (FIG. 2), not only does it take time until the vibration amplitude becomes substantially constant after the signal is turned on (this time, strictly speaking, when the amplitude becomes constant) For example, the time required to reach 70% of the amplitude of the signal is a rise time), and it takes time until the signal is almost lost after the signal is turned off (this time, strictly speaking, the amplitude is, for example, 30 of the maximum amplitude). Time to decay to% is the decay time.)

  As shown in FIG. 5, when the follow-up of the vibration of the test piece 50 is delayed when the signal is turned on and off, and a considerable rise and decay time is required, the vibration amplitude of the test piece 50 is like the applied voltage of the Langevin piezoelectric actuator 21. However, it is not constant or zero. Therefore, even if the number of vibrations of the repeated intermittent constant amplitude sine wave signal voltage output from the ultrasonic oscillator 11 is counted and the vibration amplitude of the test piece 50 is measured by the displacement detection probe 31, it is damaged after being oscillated several times. The conventional evaluation that it was done is difficult.

  To cause the vibration of the test piece 50 to follow the repeated intermittent constant amplitude sine wave signal having a rectangular envelope as much as possible according to the prior art, that is, to shorten the rise and decay time of the vibration amplitude as much as possible. There are two possible ways.

  In the first method, instead of applying a repetitive intermittent constant amplitude sinusoidal signal voltage having a rectangular envelope as shown in FIG. 1 to the Langevin piezoelectric actuator 21, it is amplitude-modulated that attenuates with the passage of time as shown in FIG. This is a method of adding a repeated intermittent sine wave signal. This method can be realized relatively easily by amplitude-modulating the output voltage of the ultrasonic power amplifier 13 that supplies the input voltage to the Langevin piezoelectric actuator 21 with a signal that attenuates over time from the rise. However, this method has no effect on shortening the decay time.

  In the second method, the displacement detection probe 31 detects the vibration of the test piece 50, converts it into an electrical signal, generates a voltage proportional to the vibration amplitude of the test piece 50, and uses this voltage as a differential input type ultrasonic power amplifier. 12, the method of making the vibration amplitude of the test piece 50 proportional to the output voltage of the ultrasonic transmitter 11, that is, the repetitive intermittent constant amplitude sinusoidal signal voltage having a rectangular envelope as shown in FIG. It is. This method is called motional feedback (abbreviated as MFB) and can be easily implemented at a relatively low frequency up to several hundred hertz, and is effective in shortening the decay time unlike the first method. However, when dealing with an intermittent ultrasonic signal like the present invention, coupled with the high frequency, phase lag becomes a problem during signal on-off and off-to-on transients. However, it is difficult to provide stable feedback. In addition, if the test piece 50 is damaged and the output voltage of the displacement detection probe 31 tends to decrease, the input voltage to the Langevin piezoelectric actuator 21 increases rapidly due to the negative feedback effect, which may be in a dangerous state.

  The method presented here is different from any of the above two methods, and because the input impedance of the Langevin piezoelectric actuator 21 changes depending on its vibration state, the vibration waveform is closer to the inflowing current waveform than the applied voltage waveform. Based on this. That is, the output current of the differential input type ultrasonic power amplifier 12, that is, the current flowing through the Langevin piezoelectric actuator 21 is detected by the current detector 13 and converted into a voltage. The current waveform flowing through the Langevin piezoelectric actuator 21 is made closer to the other input voltage waveform of the differential input type ultrasonic power amplifier 12, that is, the output voltage waveform of the ultrasonic transmitter 11 by feeding back to the input side. This feedback loop does not include physical vibrations such as piezoelectric actuators, horns, and test specimens as in the MFB described above, so there is little phase lag, and it is relatively easy even if the frequency is high if appropriate phase compensation is performed. A considerable amount of negative feedback can be applied.

  An ideal form of the output voltage signal of the displacement meter 32 that detects vibration of the test piece 50 and converts it into a voltage signal is a rectangular wave as shown in FIG. That is, the ideal rise time and decay time are zero.

  However, when the conventional method, that is, when the envelope is applied to the Langevin piezoelectric actuator 21 with a rectangular intermittent intermittent amplitude sine wave as shown in FIG. 1, the output voltage signal of the displacement meter 32 is as shown in FIG. The current flowing through the Langevin piezoelectric actuator 21 at that time is substantially the same as the output voltage signal of the displacement meter 32 as shown in FIG. Since both require considerable rise and decay times, the envelope is far from a rectangle.

  On the other hand, in the present method in which the above-described current feedback is performed, when the envelope has a rectangular repetitive intermittent constant amplitude sine wave as shown in FIG. The current flowing through the Langevin piezoelectric actuator 21 is as shown in FIG. 9, and the output voltage signal of the displacement meter 32 is as shown in FIG. The shapes of these waveforms are similar to each other, and all of them rise, the decay time is remarkably shortened, and the envelope becomes close to a rectangle.

  When the current feedback is performed in this way, the output voltage waveform of the differential input type ultrasonic power amplifier 12, that is, the voltage applied to the Langevin piezoelectric actuator 21 has a maximum amplitude when turned on as shown in FIG. Thus, the signal is in-phase with the output of the ultrasonic transmitter 11 that attenuates with the passage of time, and is a reverse-phase signal that attenuates with the rise time from the off time.

  As a test example clearly showing the effect of the present invention, the waveforms of the output voltage (displacement sensor output voltage) from the displacement meter 32 when the operation time was set to 100 ms were compared. The result of the conventional type is shown in FIG. 12, and the result of the present invention is shown in FIG. Obviously, the rise time up to the maximum amplitude is shortened, and the decay time up to the amplitude 0 is also shortened.

  FIG. 14 schematically shows the envelope of the voltage waveform in FIG. Both the time to reach 70% of the constant amplitude width and the time to attenuate 70% from the constant amplitude width are about 5 ms, and the rise time and attenuation time are about 10 ms. The rise time and decay time were about 30 ms). Thus, the ability to shorten the time to reach 70% of the constant amplitude width and the time to attenuate 70% from the constant amplitude width makes it possible to make the amplitude constant at an early stage, thereby improving the accuracy of the fatigue test. Can do.

  FIG. 15 is a graph showing the SN curve based on the stress amplitude value (maximum stress amplitude value) and the number of repetitions. The result of the ultrasonic fatigue test of the material SUJ2 heat-treated product (hardness HRC 60 to 62) is shown. As this graph shows, compared with the conventional result, in the fatigue test of this invention, the repetition number has shifted to the low cycle side. Thus, by making the amplitude of the signal of the present invention constant, there is an effect of reducing the number of repetitions while maintaining a high stress amplitude value.

  The present invention relates to a fatigue test apparatus and an ultrasonic fatigue test method using ultrasonic waves. By using an appropriate vibrator, the present invention is applied to a sound wave having a wavelength longer than that of ultrasonic waves, and a fatigue test is performed. You can also

FIG. 1 shows the envelope shape of a repeated intermittent constant amplitude sine wave voltage. FIG. 2 shows the shape of the envelope of the test piece vibration waveform when a repeated intermittent constant amplitude sine wave voltage is applied. FIG. 3 shows a block diagram of the ultrasonic fatigue test apparatus. FIG. 4 shows an output voltage waveform of the ultrasonic transmitter. FIG. 5 shows the vibration waveform during the test when the Langevin piezoelectric actuator was driven with a repeated intermittent constant amplitude sine wave signal voltage. FIG. 6 shows the envelope shape of a repeated intermittent sine wave signal that decays with time. FIG. 7 shows the output voltage of the displacement meter when a repeated intermittent constant amplitude sine wave voltage is input. FIG. 8 is a diagram showing a Langevin piezoelectric actuator current when a repeated intermittent constant amplitude sine wave voltage is input. FIG. 9 shows the Langevin piezoelectric actuator current in the ultrasonic fatigue test method of the present invention. FIG. 10 shows the output voltage of the displacement meter in the ultrasonic fatigue test method of the present invention. FIG. 11 shows the applied voltage of the Langevin piezoelectric actuator in the ultrasonic fatigue test method of the present invention. FIG. 12 shows a displacement meter output voltage waveform in the conventional method. FIG. 13 shows a displacement meter output voltage waveform in the ultrasonic fatigue test method of the present invention. FIG. 14 shows the envelope shape of the displacement meter output voltage waveform in the ultrasonic fatigue test method of the present invention. FIG. 15 shows changes in fatigue characteristics according to the present invention and changes in fatigue characteristics according to a conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic fatigue test apparatus 10 Ultrasonic transmission part 20 Transducer part 21 Langevin piezoelectric actuator 22 Horn 11 Ultrasonic transmitter 12 Differential input type ultrasonic power amplifier 13 Current detector 32 Displacement meter 50 Test piece 31 Displacement detection probe

Claims (4)

An ultrasonic fatigue testing apparatus comprising an ultrasonic transmission part and a vibrator part , resonating and damaging a test piece attached to the vibrator part,
The ultrasonic transmitter generates a signal voltage of repeated intermittent constant amplitude ultrasonic waves having a rectangular envelope, and differential input type ultrasonic power that outputs a voltage proportional to the difference between two input voltages. An amplifier, and a current detector for obtaining a voltage proportional to the output current of the differential input type ultrasonic power amplifier,
The vibrator unit includes a Langevin piezoelectric actuator provided with a Langevin type vibrator, and a horn that increases the amplitude of the Langevin type vibrator and transmits it to a test piece.
The output of the ultrasonic oscillator is input to one input terminal of the differential input type ultrasonic power amplifier ,
The output voltage of the differential input type ultrasonic power amplifier is applied to the series circuit of the current detector and the Langevin piezoelectric actuator,
When the voltage proportional to the current flowing through the Langevin piezoelectric actuator detected by the current detector is input to the other input terminal of the differential input type ultrasonic power amplifier, the differential input type ultrasonic power amplifier is An ultrasonic fatigue testing apparatus that outputs a voltage proportional to a difference between the two input terminal voltages. 2. The ultrasonic fatigue test apparatus according to claim 1 , further comprising a displacement detection probe and a displacement meter. 3. The ultrasonic fatigue testing apparatus according to claim 2 , further comprising a test piece having a dimension adjusted at a tip of a horn for increasing the amplitude of the Langevin type vibrator. An ultrasonic fatigue test method for resonating and damaging a test piece attached to the transducer part using an ultrasonic transmission part and a vibrator part,
An ultrasonic oscillator that generates a signal voltage of repeated intermittent constant amplitude ultrasonic waves in which the ultrasonic wave transmitter has a rectangular envelope, and a differential input ultrasonic power amplifier that outputs a voltage proportional to the difference between two input voltages And a current detector for obtaining a voltage proportional to the output current of the differential input type ultrasonic power amplifier ,
The vibrator unit includes a Langevin piezoelectric actuator provided with a Langevin type vibrator, and a horn that increases the amplitude of the Langevin type vibrator and transmits it to a test piece.
The output of the ultrasonic transmitter is input to one of a pair of input terminals of the differential input type ultrasonic power amplifier, and a voltage proportional to the current flowing through the Langevin piezoelectric actuator detected by the current detector is detected as the differential. By inputting to the other of the pair of input terminals of the input type ultrasonic power amplifier, the difference between the differential input type ultrasonic power amplifier and the voltage proportional to the output voltage of the ultrasonic oscillator and the current flowing through the Langevin piezoelectric actuator. a voltage proportional to the Langevin piezoelectric actuator and then supplied to a series circuit of said current detector, said differential input type wherein the ultrasonic power amplifier a voltage proportional to the difference of the two input terminal voltage and the Langevin piezoelectric actuator Ultrasonic fatigue test method to output to a series circuit of current detector.

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