JP4374785B2 - Ultrasonic fatigue testing machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic fatigue testing machine that strains a test piece with ultrasonic waves and measures the fatigue strength of the test piece.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an apparatus for measuring the fatigue strength of a test piece, an ultrasonic fatigue tester that introduces ultrasonic waves to cause fatigue breakage in the test piece and measures the fatigue strength is known. For example, in the method disclosed in Japanese Patent Application Laid-Open No. 60-17339, the amplitude of the test piece displacement is received by the light receiving element, and the fatigue test is performed with a constant amplitude. Such an ultrasonic fatigue tester can increase the repetition rate of stress change compared to a conventional mechanical fatigue tester and the like, and can perform a large amount of fatigue strength tests in a short time. In addition, a fatigue strength test in a long life range in which the number of times that it was conventionally too long to collect data has reached 10 ⁸ to 10 ⁹ times can be performed in a short period of time.
[0003]
[Problems to be solved by the invention]
As described above, the ultrasonic fatigue tester is suitable for performing a large amount of fatigue strength tests in a short period of time, but if a stress exceeding the elastic limit is applied to the test piece, it is collected by the ultrasonic fatigue tester. For example, the fatigue strength test data has a problem that the stress value for the same fatigue limit repetition number is 10 to 30% higher than that of test data collected by a conventional fatigue tester such as a mechanical type.
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic fatigue tester capable of obtaining fatigue strength test data substantially equal to a conventional mechanical fatigue tester or the like.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, an ultrasonic fatigue testing machine according to the present invention includes an oscillator that supplies electric power necessary for generating ultrasonic waves, and an ultrasonic wave that receives the output of the oscillator and applies vibration to the test piece by ultrasonic waves. In an ultrasonic fatigue testing machine that tests the fatigue strength of a test piece with a transducer and a displacement meter that detects the displacement of the end face of the test piece, using strain stress characteristic data or a calculation formula separately measured with the same test piece in advance The output of the oscillator is converted and output so as to have an end face amplitude value corresponding to the set stress, and the end face displacement data detected by the displacement meter is converted into a stress value. It is what.
The ultrasonic fatigue tester of the present invention can obtain test data that is almost similar to a conventional mechanical fatigue tester or the like by using the above-described configuration.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an ultrasonic fatigue testing machine according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram showing the configuration of the present ultrasonic fatigue tester. This ultrasonic fatigue tester is composed of a control unit 1 (a portion surrounded by a dotted line) for applying a predetermined strain due to ultrasonic vibration to the test piece S and a stress output unit 2 for obtaining a corresponding stress from the strain detection signal. Has been.
[0006]
The control unit 1 includes a stress input unit 11 that converts an end surface strain amplitude value of the test piece S corresponding to an input stress value, and an end surface amplitude setting unit 17 that generates a voltage setting signal 17a corresponding to the amplitude value. An ultrasonic transducer 13 that generates ultrasonic vibrations, a horn 14 that is coupled to the ultrasonic transducers 13 to amplify ultrasonic vibrations, and a drive unit 12 that drives the ultrasonic transducers 13; A displacement meter 15 for measuring the end face displacement X of the test piece S and a displacement meter amplifier 16 for amplifying the output of the displacement meter 15 to an output level necessary for the stress output unit 2 are configured.
[0007]
The stress input unit 11 includes a stress strain conversion / correction unit 11a for correcting and converting a strain value of the test piece S corresponding to the set test stress value, and an end face of the test piece S from the corrected strain value. It is comprised from the distortion end surface amplitude conversion part 11b for calculating an amplitude value.
[0008]
The stress strain conversion / correction unit 11a stores stress strain characteristics of the test piece S as shown in FIG. 2 measured in advance by a hydraulic material testing machine or the like. The stress value σ ₁ as shown in FIG. 2 is a stress value that falls within the elastic limit, and has a linear relationship with the corresponding strain value ε ₁ . On the other hand, the stress value σ ₂ is a stress value that falls outside the elastic limit, and has a non-linear relationship with the corresponding strain value ε ₂ .
[0009]
The drive unit 12 includes an oscillator 12a that generates an oscillation waveform (usually a sine wave waveform is used) corresponding to the necessary ultrasonic vibration, and a voltage setting signal 17a of the end face amplitude setting unit 17 using the signal waveform. The drive circuit 12b supplies the ultrasonic vibrator 13 with electric power necessary to generate an ultrasonic vibration having a strength proportional to.
[0010]
In this apparatus, when a stress value to be tested is set in the stress strain conversion / correction unit 11a, the strain value is calculated using the stress strain characteristic data of FIG. 2 or an approximate expression obtained therefrom. For example, if the set stress value is σ ₂ , the non-linearity is ignored and the distortion value is regarded as ε ₂₀ on the dotted line in the present invention, if there is no correction from FIG. Since the correction is performed by nonlinearity, the distortion value is regarded as ε ₂ . The distortion value ε ₂ is generally larger than the distortion value ε ₂₀ as can be seen from FIG. 2, but the distortion value ε ₂ is converted into a necessary end face amplitude value in the strain end face amplitude converter 11b. The voltage amplitude setting unit 17 outputs the voltage setting signal 17a to the drive circuit 12b.
[0011]
From the drive circuit 12b, a drive signal having a distortion with a predetermined amplitude width and a waveform of the oscillator 12a is supplied to the ultrasonic transducer 13, and ultrasonic vibration is generated. This ultrasonic vibration propagates in the ultrasonic vibrator 13, is amplified by the horn 14, is applied to the test piece S, and the test piece S expands and contracts to change the displacement X between the end surface and the displacement meter 15.
[0012]
The displacement X is detected by a displacement meter 15 and amplified to a signal level necessary for the stress output unit 2 by a displacement meter amplifier 16. In this way, strain corresponding to the predetermined stress values σ ₁ and σ ₂ is applied to the test piece S by ultrasonic vibration.
[0013]
On the other hand, in order to measure the stress actually generated on the test piece S, the stress output unit 2 is used. The stress output unit 2 includes an end face amplitude distortion converting unit 21 that converts an output signal 16a obtained by amplifying the end surface displacement X of the test piece S by the displacement meter amplifier 16 into a strain value, and a strain stress that corrects and converts the strain value into stress. The conversion / correction unit 22 is configured.
[0014]
Similar to FIG. 2, the stress conversion / correction unit 22 stores stress strain characteristics of the test piece S as shown in FIG. 3 measured in advance by a hydraulic material testing machine or the like. The strain value ε ₃ as shown in FIG. 3 is a strain value that falls within the elastic limit, and has a linear relationship with the corresponding stress value σ ₃ . On the other hand, the strain value ε ₄ is a strain value that falls outside the elastic limit, and has a non-linear relationship with the corresponding stress value σ ₄ .
[0015]
The displacement X of the test piece S is signal-converted by the displacement meter 15 and the displacement meter amplifier 16 and then converted into a strain value ε ₄ by the end face amplitude distortion converter 21. As the strain value ε _4, the strain stress conversion / correction unit 22 calculates the stress value σ ₄ using the stress strain characteristic data of FIG. 3 or an approximate expression obtained therefrom. This stress value σ ₄ is smaller than the stress value when correction is not performed, that is, the stress value σ ₄₀ on the dotted line.
[0016]
When the fatigue test of the specimen S is performed using the control unit 1 and the stress output unit 2 as described above, when the fatigue test is performed by applying a stress exceeding the elastic limit, the correction acts in the direction of increasing the strain. The fatigue life data acts in the direction of shortening the life. Therefore, compared to the case where the fatigue strength is not corrected, test data close to the fatigue strength measured with a conventional fatigue tester can be obtained.
Fatigue tests are performed by sequentially changing the stresses measured in this way, and the fatigue failure life (number of fatigue test repetitions) is obtained. By plotting this with Δ marks, the circles are marked as shown in FIG. Fatigue strength is reduced compared to the case where no correction is made.
[0017]
FIG. 5 is a schematic block diagram showing the configuration of the second embodiment of the present invention. The ultrasonic fatigue testing machine uses the displacement instead of the end face amplitude setting unit 17 in the first embodiment (see FIG. 1) in order to more accurately generate distortion of a predetermined amplitude in the test piece S. An end face amplitude comparison unit 18 for detecting a feedback signal 16b from the meter amplifier 16 and a deviation signal from the distortion end face amplitude conversion unit 11b and outputting a correction signal to the drive circuit 12b is used.
[0018]
In this apparatus, when a stress value to be tested is set in the stress input unit 11, the end face amplitude value is corrected and converted as in the first embodiment, and this end face amplitude value is converted by the end face amplitude comparison unit 18 into the displacement meter amplifier 16. The deviation signal is compared with the feedback signal 16b proportional to the displacement X from the input signal, and the deviation signal is input to the drive circuit 12b as the voltage signal 18a. The feedback circuit from the end face amplitude comparison unit 18 to the displacement meter amplifier 16 removes the influence of environmental changes such as ambient temperature and aging, so that the end face amplitude of the test piece S is accurately determined by the distortion end face amplitude conversion unit 11b. Controlled by output value.
[0019]
The end face strain amplitude from the displacement meter amplifier 16 is corrected and converted by the stress output unit 2 in the same manner as in the first embodiment, and is output as a stress value from the strain stress conversion / correction unit 22.
The feature of the present invention is that the stress applied to the test piece S as described above and the stress obtained from the strain of the test piece S are corrected by using pre-measured strain stress data or an approximate expression, whereby a fatigue test using a conventional fatigue tester is performed. The point is that data close to the data can be obtained. In addition, the calculation function of the component of the said stress input part 11 and the stress output part 2 can also be implemented with a microcomputer.
[0020]
【The invention's effect】
The ultrasonic fatigue testing machine of the present invention can approximate the fatigue strength data collected by the ultrasonic fatigue testing machine to the data collected by the conventional testing machine by correcting the nonlinearity of the strain stress.
[Brief description of the drawings]
FIG. 1 is a block diagram of an ultrasonic fatigue testing machine according to a first embodiment of the present invention.
FIG. 2 is a strain stress characteristic diagram showing the relationship of strain to stress applied by ultrasonic waves.
FIG. 3 is a strain stress characteristic diagram showing a relationship of stress to strain generated by ultrasonic waves.
FIG. 4 is a fatigue life characteristic diagram for explaining the effect of the presence or absence of correction of stress strain nonlinearity in an ultrasonic fatigue test.
FIG. 5 is a block diagram of an ultrasonic fatigue testing machine according to a second embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Control part 2 ... Stress output part 11 ... Stress input part 12 ... Drive part 13 ... Ultrasonic transducer 14 ... Horn 15 ... Displacement meter 16 ... Displacement meter amplifier 16a ... Output signal 16b ... Feedback signal 17 ... End face amplitude setting part 17a ... Voltage setting signal 18 ... End face amplitude comparison section 18a ... Voltage signal 21 ... End face amplitude distortion conversion section 22 ... Strain stress conversion / correction section S ... Test piece X ... Displacement

Claims (1)

Test includes an oscillator for supplying electric power necessary for generation of the ultrasonic wave, an ultrasonic transducer which gives ultrasonic vibration to the specimen in response to an output of the oscillator, a displacement meter for detecting a displacement of the test one end face In the ultrasonic fatigue testing machine for testing the fatigue strength of a piece, the oscillator amplitude value corresponding to the set stress is obtained by using strain stress characteristic data or a calculation formula separately measured with the same test piece in advance. The ultrasonic fatigue tester is characterized in that the end face displacement data detected by the displacement meter is converted into a stress value .

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