JP5920789B2 - Cryogenic ultrasonic fatigue nondestructive test evaluation system - Google Patents

Description

  The present invention relates to a test apparatus for monitoring fatigue progress behavior during a fatigue test at a liquid nitrogen temperature (77 K). More specifically, the vibration waveform of the test piece at the time of the ultrasonic fatigue test is detected in a non-contact and broadband manner, and the waveform analysis is performed to evaluate the occurrence of fatigue damage and the occurrence / progress of fatigue cracks.

In the present invention, the cryogenic means liquid nitrogen temperature (77K), the ultrasonic fatigue test, by resonating the excitation vibration after pre 20kHz the specimen is amplified by the ultrasonic horn in the longitudinal direction This is a high-speed fatigue test method that applies load.

  Since the ultrasonic fatigue test is capable of a high cycle fatigue test in a short time, it has been used for gigacycle fatigue or the evaluation of the size of inclusions starting from high cycle fatigue failure in Patent Document 1. Further, in the normal temperature test, the effect of heat generation due to high-speed vibration becomes a problem, and in the correction method (Patent Document 2), the temperature stability during the test is improved (Patent Document 3). The method of Patent Document 1 evaluates the size of the largest inclusions by observing the fracture surface after fracture under a gigacycle load, and is not used for evaluating fatigue progress behavior. Further, in Patent Document 2, since the influence of heat generation in the ultrasonic fatigue test cannot be removed, data of a mechanical fatigue test without heat generation is acquired in advance, and correction is performed based on this data. Since this differs depending on the material of the test piece, mechanical fatigue test data is required in advance for each material. Therefore, many test pieces and test time are required, and there is almost no advantage of performing an ultrasonic fatigue test separately. Furthermore, in Patent Document 3, the test piece is cooled using a periodic intermittent load as a method for controlling the heat generation of the test piece. However, in order to perform more accurate load control, a new test piece displacement detection is performed. Although a probe is provided and feedback control is performed, it is not necessary if a cooling method for the test piece can be established in a cryogenic environment.

  In a cryogenic environment (77K) such as liquid nitrogen temperature, the evaporation of liquid nitrogen in the liquid tank is intense in order to conduct a fatigue test. Therefore, Patent Document 4 describes the development of an apparatus for stably maintaining this temperature. In addition, a technique for measuring the strain of a test piece has been developed in a mechanical fatigue test of about 10 Hz. In this method, the test piece and the cryostat are in contact with each other with a seal packing. In an ultrasonic fatigue test using resonance due to free vibration of a test piece, such a seal structure cannot be used because the resonance frequency and the resonance mode change when the test piece is in mechanical contact.

On the other hand, in ultrasonic fatigue in a high temperature environment, an ultrasonic horn and bending test jig installed in an atmospheric furnace in Patent Document 5 enables a high temperature / high speed vibration load test, and acoustic emission outside the furnace. (AE) By installing the sensor, the high-temperature fatigue state of the ceramic test piece is monitored by detecting the occurrence of microcracking. Hereinafter, acoustic emission is also simply referred to as AE. As described above, in AE measurement using a piezoelectric element in an environment other than room temperature, a waveguide rod is generally used as a propagation medium. In an ultrasonic fatigue test, a mechanical test piece is used as a test piece. Since contact must be avoided, measurement with a waveguide rod is not possible.

  In recent years, burst waves in the ultrasonic band of a large amplitude sine wave are incident on a test piece, and the nonlinear distortion such as waveform distortion and harmonics generated at that time are measured to remove material structures, inclusions, and microcracks. A detection and evaluation method has been developed (Patent Document 6). In particular, the second harmonic (Patent Document 7) and the β parameter (Patent Document 8) based on the second harmonic are used for inclusions, fatigue damage, and residual stress evaluation.

  In the measurement of nonlinear ultrasonic waves used in these patent documents, a broadband transducer for detecting a harmonic wave is required while inputting a signal with a large amplitude, and a non-contact type probe such as a water immersion convergence type probe is required. And broadband array type probes are used. These elements are a polymer piezoelectric film and a composite piezoelectric body, but both have been reported to have a significant decrease in sensitivity and durability under a liquid nitrogen environment, and are difficult to apply directly.

  In the field of nonlinear ultrasonic measurement for ultrasonic fatigue, according to Non-Patent Documents 1 and 2 by the present inventors, at the time of ultrasonic fatigue test using a broadband laser vibrometer and continuous waveform recording analyzer at room temperature. Vibration waveforms are recorded, and subharmonic, harmonics and AE analysis are performed.

  As a method for obtaining the fatigue life, there is a rupture life depending on a life at the time of rupture, and the contents are divided into a crack generation life and a crack propagation life. In damage tolerance design in structural materials such as nuclear power plants and chemical plants, crack growth life based on fracture toughness tests is used. On the other hand, a crack generation life is required for space equipment that requires high reliability (Non-Patent Documents 3 and 4). The conventional method for determining the crack initiation life is only a destructive test method in which crack generation is detected by stopping during the fatigue test and performing microscopic observation while polishing the cross section of the test piece. Therefore, since a plurality of halfway test pieces and a great amount of polishing / observation time are required, it is not practical.

JP 2004-45363 A JP 2003-42918 A JP 2007-17288 A JP 9-138190 A Japanese Patent Laid-Open No. 7-35668 JP 2006-64571 A JP 2006-284428 A JP 2007-155730 A

Mitsuharu Shiba, Yoshiyuki Furuya, Hisashi Yamawaki, Kaita Ito, Manabu Tsuji: “Evaluation of Fatigue Progression of High Strength Steel by AE / Nonlinear Ultrasonic Analysis during Ultrasonic Fatigue Test”, Journal of the Japan Institute of Metals, 73, 3 (2009) , 205-210. M.M. Shiwa, Y .; Fruya, H. et al. Yamawaki, K .; Ito, and M.M. Enoki, "Fatigue Process Evaluation during Ultrasonic Fatigue Testing Analyzed by Using Laser Doppler Vibrometer and Continuous AE Waveform Analysis System", Progress in Acoustic Emission XV, JSNDI, (2010), Kumamoto. 319-324. Koichi Okita: “Non-destructive inspection of spacecraft”, Non-destructive inspection, 59, 10 (2010), 486-500. Toshio Ogata: “Domestic Space Rocket Engine Material and NIMS Material Data Sheet”, Nondestructive Inspection, 59, 10 (2010), 501-503. Mitsuharu Shiba and Teruo Kishi: “Following Micro Scratches”, Maruzen, (1989), p124.

  For non-destructive evaluation of fatigue damage growth processes such as fatigue crack initiation life in a cryogenic environment, in the liquid nitrogen environment based on the principle of nonlinear ultrasonic measurement method of ultrasonic fatigue at room temperature described above. It needs to be feasible. To that end, it is necessary to solve the problems of the stability of the specimen temperature, the non-contact measurement method in the liquid nitrogen environment including noise countermeasures, and the fatigue damage evaluation method.

  The present invention provides a cryogenic environment ultrasonic fatigue nondestructive evaluation device capable of detecting vibration during ultrasonic fatigue in a test piece cooled with liquid nitrogen in a cryostat in a non-contact manner and evaluating fatigue damage. It is to be.

Therefore, in order to solve the above-mentioned problems, the invention of this application is an ultrasonic fatigue nondestructive testing apparatus for material test pieces at a liquid nitrogen temperature (77 K), in which liquid nitrogen is injected into the inside. The cryostat is immersed in liquid nitrogen in the cryostat, the material test piece is placed at the tip, and a cryostat unit having an ultrasonic horn for applying ultrasonic vibration, and pressure control of liquid nitrogen to be press-fitted into the cryostat and liquid nitrogen pressurization control unit for performing an ultrasonic fatigue control unit for vibration control of the ultrasonic horn for the ultrasonic fatigue test, to detect the vibration of the material specimen, laser oscillation to obtain vibration data Using the velocity waveform data and displacement waveform data in the vibration data acquired by the laser vibrometer, and using these waveform data as targets, nonlinear ultrasonic waves Performs analysis and Acoustic Emission (AE) analysis, is constituted by the vibration detecting and analyzing section for evaluating the fatigue damage propagation behavior of said material specimen based on the analysis result, and said cryostat liquid nitrogen liquid surface on A liquid level control lid made of glass paper for stabilizing a change in liquid level due to boiling of liquid nitrogen due to heat transmitted through the ultrasonic horn, above the liquid level control lid inside the cryostat. A cryogenic ultrasonic fatigue nondestructive testing apparatus is provided in which a laser beam path of the laser vibrometer is formed in the space .

And second, an ultrasonic fatigue nondestructive testing apparatus for material test pieces at a liquid nitrogen temperature (77K), wherein the liquid nitrogen is pressed into the cryostat and immersed in the liquid nitrogen in the cryostat, A cryostat unit having an ultrasonic horn that applies ultrasonic vibration to a material test piece installed at the tip, a liquid nitrogen pressurization control unit that performs pressurization control of liquid nitrogen that is press-fitted into the cryostat, and an ultrasonic fatigue test Therefore, an ultrasonic fatigue control unit that performs vibration control of the ultrasonic horn and a laser vibrometer that detects vibration of the material specimen and acquires vibration data are provided, and the speed in the vibration data acquired by the laser vibrometer using the waveform data and displacement waveform data, targeting these waveform data, non-linear ultrasonic analysis and acoustical Etikku emission (AE) solution And a vibration detection / analysis unit that evaluates fatigue damage progress behavior of the material test piece based on the analysis result, and a mist shield is provided on the test piece inside the cryostat via a seal packing. The present invention provides a cryogenic ultrasonic fatigue nondestructive testing device.

  As shown in FIG. 1, the cryogenic ultrasonic fatigue nondestructive evaluation tester according to the present invention has a cryostat unit incorporating an ultrasonic horn, a liquid nitrogen pressurization control unit, an ultrasonic fatigue control unit, vibration detection / analysis. It consists of parts. Here, a commercially available product (for example, USF-2000 manufactured by Shimadzu Corporation) is used as the ultrasonic fatigue control unit.

  FIG. 2 shows the configuration of a cryostat unit incorporating an ultrasonic horn. The cryostat unit includes an ultrasonic horn (4) with heat insulation measures in the cryostat (1), an observation window (3) for laser vibration measurement, liquid nitrogen (2), a liquid level control lid (9), a seal packing (10 ) And a mist shield (11).

  In the ultrasonic fatigue test, a test piece is installed at the tip of an ultrasonic horn, and the test piece is attached to the horn using a screw. At this time, the ultrasonic horn part including the ultrasonic transducer outside the cryostat has a heat insulating structure. During the test, the ultrasonic vibrator (5) serves as an intrusion heat source, and heat is transmitted through the ultrasonic horn (4) to boil the liquid nitrogen (2) in the cryostat (1). Due to this boiling phenomenon, a large-scale convection is generated in the cryostat and the liquid level becomes unstable. Therefore, the liquid level control lid (9) made of glass paper with a thickness of several mm is provided in the opening of the liquid nitrogen discharge pipe (7), and the liquid level is increased by boiling because the wet glass paper layer is at the set liquid level. To stabilize the change.

  Since ultrasonic fatigue applies a stress load to the test piece (8) using a resonance phenomenon, the vicinity of the center of the test piece becomes a stress load area, and this area needs to be maintained at the liquid nitrogen temperature during the test. Therefore, it is desirable to immerse 2/3 or more of the test piece length in liquid nitrogen. During the ultrasonic fatigue test, mist is generated around the test piece due to the influence of heat generated by internal friction of the test material and high-frequency vibration, and the laser light is scattered to cause measurement noise in the laser vibrometer. Therefore, as a method for preventing the generated mist from entering the laser beam path (12), a mist shield (11) is provided, and a glass paper thickness seal packing (10) made of glass paper is inserted into the gap between the test piece and the mist shield. . By installing this packing so as to get wet with liquid nitrogen during the test, it is possible to shield mist and reduce the occurrence of mechanical friction noise.

  Liquid nitrogen is pressed into the cryostat (1) from the liquid nitrogen inflow pipe (6) by being pressurized with nitrogen gas, and is discharged from the liquid nitrogen discharge pipe (7). During the ultrasonic fatigue test, in order to reduce the boiling of liquid nitrogen in the cryostat, liquid nitrogen is always injected from the outside through the liquid nitrogen inflow pipe (6). The flow rate of the liquid nitrogen to be press-fitted is controlled by the liquid nitrogen pressurization control unit.

  The vibration frequency band to be detected of the test piece is several Hz to several MHz and is detected using a laser vibrometer that can detect displacement and velocity. The laser beam is incident on the upper end of the test piece through a viewing window provided in the upper part of the cryostat, and this becomes a laser beam path (12). At this time, seal packing (10) is inserted in the gap between the test piece and the mist shield so that the liquid nitrogen and its mist are applied to the upper end surface of the test piece and the laser beam is not scattered.

  The displacement and velocity signals detected by the laser vibrometer are simultaneously recorded by a continuous waveform recording device having a resolution of 12 bits or more at a sampling speed of several MHz or more.

  FIG. 3 shows an analysis flow diagram. Nonlinear ultrasonic analysis and AE analysis are performed on the velocity waveform and displacement waveform detected by the laser vibrometer. The velocity waveform simultaneously recorded by the continuous waveform recording device is fundamental wave (excitation frequency), harmonic (second to fifth) and subharmonic (1/2 of the fundamental wave frequency) by continuous FFT or wavelet analysis. The intensity of each frequency is extracted. Further, an acoustic emission (AE) signal is extracted using a high-pass filter (HPF) having a frequency five times or more the excitation frequency, and an AE event is extracted by setting a threshold value.

On the other hand, the displacement waveform recorded by the continuous waveform recording device is used for the measurement of the vibration displacement amount of the test piece and the analysis of the stress phase. The AE events extracted from the velocity waveform are classified into those accompanying the occurrence of noise and fatigue damage such as microcracking and crack propagation. FIG. 4 shows an example of the stress phase and high-pass filter waveform in the noise signal.
In the noise waveform, an AE waveform (burst signal) is generated regardless of the stress phase.

FIG. 5 shows an AE waveform (high-pass filter waveform) associated with microcracking, and FIG. 6 shows a relationship between the AE waveform and the stress phase (displacement). Crack AE is detected in the vicinity of the maximum tensile stress (= maximum displacement). Therefore, the AE waveform accompanying the crack is detected with a correlation with the stress phase. Correspondence with the stress phase at the time of AE generation requires correction of the arrival time difference of the AE wave.
Since AE accompanying microcracking occurs from the center of the test piece, a time delay occurs when detecting at the end of the test piece. The time delay ΔT is obtained by the following formula.
[Formula 1]
ΔT = L / v _LN
However, L is the length from the center of the test piece to the end, and v _LN is the speed of the AE wave at the liquid nitrogen temperature.
In the waveform associated with microcracking, the stress phase is generated near the positive maximum value after the AE arrival time correction, that is, the maximum tensile stress. This corresponds to the AE (peak load AE) of crack generation during a normal fatigue test shown in Non-Patent Document 5, and the same phenomenon was also observed in the ultrasonic fatigue test. As a result, the stress phase of the detected AE event can be matched, and in addition to crack generation, information on macroscopic fracture surfaces such as crack closure and crack opening can be obtained.

  Information on harmonics and subharmonics is described as non-linear ultrasonic waves in Patent Documents 6 to 8 and Non-Patent Documents 1 and 2, and correspondence with plastic deformation and microcracks can be seen. Fatigue damage progress evaluation combining these nonlinear ultrasonic parameters and AE information enables non-destructive evaluation of material damage and crack generation life.

  With the apparatus of the present invention, fatigue damage progress behavior during a high cycle fatigue test can be evaluated nondestructively at a liquid nitrogen temperature (77 K), and fatigue damage and crack generation life can be evaluated in addition to fracture life.

The block diagram of the cryogenic ultrasonic fatigue nondestructive evaluation testing machine which is embodiment of this invention. The block diagram of the cryostat part incorporating the ultrasonic horn. Analysis flow diagram. Example of noise waveform (speed). Example of microscopic crack waveform (speed). The AE waveform which corrected the stress phase and arrival time difference of FIG. Nonlinear ultrasound and AE analysis example.

The vibration waveform detected during the ultrasonic fatigue test and an analysis example will be described.
FIG. 4 is an example of noise due to mist detected during the test. A broken line is a velocity waveform, and a solid line is an AE waveform extracted by a 100 kHz high-pass filter. This AE waveform is noise generated by the mist scattering laser light, and has no correlation with the stress phase.
FIG. 5 is an example of an AE signal associated with the occurrence of microcracking detected in the later stage of the fatigue test. A broken line is a velocity waveform, and a solid line is an AE waveform (velocity) extracted by a 100 kHz high-pass filter. In the velocity waveform, an AE waveform is observed at the minimum amplitude of the negative phase.
FIG. 6 is obtained by performing ΔT correction on the basis of the displacement time on the same time axis as in FIG. 5 and the detection time of the AE waveform (velocity) extracted by the 100 kHz high-pass filter. This initial movement of the AE waveform is detected when displacement (= stress) is maximum, and corresponds to AE of crack generation as Peak Load AE. As described above, when the correspondence between the stress phase and the AE waveform is performed, the correspondence between the phase in the displacement and the time when the arrival time from the position of the AE source (the center of the test piece) to the detection end position is corrected is performed. There must be.
FIG. 7 collectively shows the number of cycles and the subharmonic, second harmonic, third harmonic, and AE event numbers in the vicinity of the final break. Fatigue damage progress can be evaluated from the correlation of the parameters. The subharmonic, second harmonic, third harmonic, and AE event numbers all rose sharply at 4.36 × 10 ⁵ cycles, just before the final break, and broke at 4.38 × 10 ⁵ cycles, from 4.36 × 10 ⁵ cycles 4. It is considered that the crack continuously propagated in 4.38 × 10 ⁵ cycles (crack growth period). On the other hand, a sharp increase in the AE event was observed at 4.27 × 10 ⁵ cycles, followed by changes in the second and third harmonics. (Crack nucleation). Although AE events from 3.70X10 ⁵ cycles rises slowly until the detected 4.27X10 ⁵ cycles, the third harmonic variation can not be observed, seen slightly changed to the second harmonic wave Therefore, it is considered that damage occurred because microcracks accompanied with local plastic deformation were generated in various places.
From the above, the crack initiation life at this time is considered to be 4.27 × 10 ⁵ cycles.

  In space materials for liquid rockets used at cryogenic temperatures, the fatigue damage propagation mechanism of materials can be evaluated non-destructively, and crack generation life and the like can be evaluated.

DESCRIPTION OF SYMBOLS 1 Cryostat 2 Liquid nitrogen 3 Peep window 4 Ultrasonic horn 5 Ultrasonic vibrator 6 Liquid nitrogen inflow pipe 7 Liquid nitrogen discharge pipe 8 Test piece 9 Liquid level control lid 10 Seal packing 11 Mist shield 12 Laser optical path

Claims (2)

An ultrasonic fatigue nondestructive testing device for a material specimen at a liquid nitrogen temperature (77K),
A cryostat unit in which liquid nitrogen is press-fitted and a cryostat unit immersed in liquid nitrogen in the cryostat, the material test piece is installed at the tip, and an ultrasonic horn for applying ultrasonic vibration;
A liquid nitrogen pressurization control unit for controlling the pressurization of liquid nitrogen press-fitted into the cryostat;
An ultrasonic fatigue control unit for controlling vibration of the ultrasonic horn for an ultrasonic fatigue test;
A laser vibrometer that detects vibrations of the material test piece and acquires vibration data is provided. Using the velocity waveform data and the displacement waveform data in the vibration data obtained by the laser vibrometer, these waveform data are subjected to nonlinearity. It is composed of a vibration detection / analysis unit that performs ultrasonic analysis and acoustic emission (AE) analysis, and evaluates fatigue damage progress behavior of the material specimen based on the analysis result, and
On the liquid nitrogen liquid level inside the cryostat, equipped with a liquid level control lid made of glass paper for stabilizing the change in liquid level due to the boiling of liquid nitrogen by the heat transmitted through the ultrasonic horn ,
A cryogenic ultrasonic fatigue nondestructive testing apparatus , wherein a space is formed above the liquid level control lid inside the cryostat, and a laser beam path of the laser vibrometer is formed in the space . An ultrasonic fatigue nondestructive testing device for a material specimen at a liquid nitrogen temperature (77K),
A cryostat unit in which liquid nitrogen is press-fitted and a cryostat unit immersed in liquid nitrogen in the cryostat, the material test piece is installed at the tip, and an ultrasonic horn for applying ultrasonic vibration;
A liquid nitrogen pressurization control unit that performs pressurization control of liquid nitrogen press-fitted into the cryostat, an ultrasonic fatigue control unit that performs vibration control of the ultrasonic horn for an ultrasonic fatigue test, and
A laser vibrometer that detects vibrations of the material test piece and acquires vibration data is provided. Using the velocity waveform data and the displacement waveform data in the vibration data obtained by the laser vibrometer, these waveform data are subjected to nonlinearity. It is composed of a vibration detection / analysis unit that performs ultrasonic analysis and acoustic emission (AE) analysis and evaluates fatigue damage progress behavior of the material specimen based on the analysis result, and
A cryogenic ultrasonic fatigue nondestructive testing apparatus, wherein a mist shield is provided on the test piece inside the cryostat via a seal packing.

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