Junji Takatsubo

Quantitative characterization of advanced porous ceramics based on a probabilistic theory of ultrasonic wave propagation

A straightforward nondestructive method based on the probabilistic theory of ultrasonic wave propagation [JSME Int. J., Ser. A, Mech. Mater. Eng. 39, 266 (1996)] was developed to quantitatively evaluate porosities, pore shapes, and pore sizes in advanced porous ceramics merely by measuring the ultrasonic delay time and pulse width. The extensive ultrasonic measurements and image microanalyses were conducted in advanced porous alumina, sialon, and zirconia with different porosities. A universal equation was established for porous ceramics, clarifying the intrinsic relationships between ultrasonic characteristics (propagation time and pulse width) and pore distribution (porosity, pore shape, and pore size). The critical volume fraction porosity were estimated separately as approximately 0.06, 0.11, and 0.10 in these ceramics using image microanalysis techniques, at which the transition from the continuous to discontinuous pore phase takes place during sintering. An excellent agreement of two useful corollar...

Quantitative Acoustic Emission Source Characterization of Microcrackings in Steel

Acoustic emission (AE) source wave analysis is a new NDE technique for the investigation of dynamic fracture process. We applied this technique to the quantitative characterization of crack sources in ductile fracture. Using two samples of ASTM A533B steel with different sulfur content, acoustic emissions during fracture toughness tests were detected, located, and analyzed. The detected AE signals were classified into two types according to the analyzed source waveforms. One was a signal due to microcracking at the MnS inclusion, and the other was a signal due to coalescence of the voids. The results of the source wave analysis showed that microcracking at the inclusions was due to Mode I type tension crack with sizes of 10–30 µm, and the coalescence of the voids was due to tension shear mixed cracks with sizes of 60–100 µm. It was confirmed that this technique is very effective for the quantitative evaluation of microcrackings and for the detection of the nucleation and growth of cracks.

Extraction of Characteristic Lines from Visualized Images of Surface Transient Displacements for the Analysis of Ultrasonic Propagation

In this paper, a feature extraction method has been presented for the non-destructive detection of defects. This method is performed through the image analysis of visualized images, obtained from 2D scanning measurements of surface transient displacements, of ultrasonic wave propagation. The displacements induced by the ultrasonic wave on a 2D surface have been measured and visualized by scanning surfaces of opaque media using a laser system. The ultrasonic propagation was analyzed by extracting the characteristic lines by processing the visualized images. The scattering, diffraction and mode conversion of ultrasonic waves around artificial defects of various shapes are observed using the visualization method. The visualization system provides various kinds of visualized images, such as the propagation image, amplitude image, arrival time image, velocity image, and a series of successive images as an animation of the wave propagation. The proposed method is well suited to non-destructive inspection

Inhomogeneity Response Function of Particulate Metal Matrix Composite

In a former report, we proposed a probabilistic theory of propagation of ultrasonic waves in particulate metal matrix composite (MMC). That theory is based on the assumption that when ultrasonic rays impinge on a dispersed particle, they transmit by 100% through the particle. However, in practice, a percentage of impinging rays are considered to creep around the particle. In this report, using a theoretical model in which both transmitting and creeping rays exist, ultrasonic waves propagating in particulate MMC are analyzed. Fairly good agreement is seen between analyzed results and experimental results. Using this theory, the relationship equation between particle parameters (volume fraction, size) and ultrasonic parameters (arrival time, pulse width, amplitude) are derived.

A Probabilistic Analysis of Propagation of Ultrasonic Waves in Metal Matrix Composite for the Measurement of Dispersed Particles.

The propagation of ultrasonic waves in ceramics-dispersed aluminum alloy composite was investigated for the purpose of developing a nondestructive method for inspecting ceramic particles. From the results of ultrasonic tests, the following important laws of ultrasonic waves were revealed. Propagation time decreases with an increase in SiC volume fraction; and (2) pulse width increases with an increase in SiC particle size. We studied these phenomena based on a probabilistic method, and derived formulas for the relationship between ultrasonic waves (propagation time and pulse width) and dispersed particles (volume fraction and mean size).

Fracture mode changes according to the progress of hydrogen attack in high-carbon steel and its acoustic emission characteristics.

Hydrogen damage or attack is produced in steels exposed to a high-pressure hydrogen environment at high temperatures. This study was done to investigate the dynamic fracture processes of hydrogen-attacked steel. Some samples of high-carbon steel with differet hydrogen exposure times were prepared, and acoustic emission signals during fracture toughness testiness were detected, located and analyzed. The acoustic emissions showed the different characteristics according to the progress of the hydrogen attack. The fracture sources were quantitatively characterized in terms of crack size, crack formation speed and fracture mode.

Monitoring of crack growth and crack closure behavior by a simulated acoustic emission technique.

A new nondestructive method using a simulated acoustic emission (AE) technique is proposed for the monitoring of crack growth and crack closure behavior. Simulated AE signals, which propagated through a crack, were detected and the waveform changes with the crack growth were examined. It became clear that the amplitudes of the first peak of the waveforms have a strong correlation with the crack length and the state of crack closure. The numerical simulation by a finite differential method showed that about ±10mm of crack length can be measured with a pair of AE transducers, and the correlation curve between crack length and amplitude of the simulated AE shows little change with the materials. These results suggest that the simulated AE technique is applicable to the evaluation of both crack propagation and crack closure behavior.