Hajime Hatano

An application of ultrasonic vibration to the deep drawing process

Abstract An experimental apparatus with the blank-holder or die plate vibrated in a radial mode was constructed in order to make the apparatus compact. The application of 20 and 28 kHz oscillation increases the LDR from 2.68 to 3.01, from 2.58 to 2.94 and from 2.38 to 2.77 respectively, in the case of cold rolled steel for deep drawing, cold rolled steel and 304 stainless steel. greater accuracy and deeper cups can be formed by stopping the oscillation after the maximum punch load rather than applying the oscillation throughout the deep drawing process. The radial vibration induces the axial vibration in the blank-holder or die plate and the axial vibration contributes strongly to the rise in the limiting drawing ratio (LDR) rather than the radial one. When one of the blank-holder and die plates is vibrated, the vibration in anti-phase is induced in the other. This means that both the blank-holder and the die plate should be simultaneously vibrated in anti-phase. Seasoning cracks of drawn cups can be avoided when the vibration is applied to the deep drawing process of 304 stainless steel sheets.

Quantitative measurements of acoustic emission related to its microscopic mechanisms

A method for the quantitative measurements of the acoustic emission is worked out. Its performance is analyzed with regard to the transducer loss and the ultrasonic attenuation in the specimen. This method is actually applied to the tension tests of pure aluminium specimens. The power spectrum of the acoustic emission is obtained over a wide range of 100 kHz to 4 MHz. The total power attains a peak of 5 pW at the beginning of the plastic deformation and decreases to 0.3 pW with the increase of the deformation. The autocorrelation function for the acoustic emission is given as a monotonically decreasing function. This result reveals that the elastic energy of the acoustic emission is radiated not oscillatorily but in the form of random pulses. Mean value of the pulse widths is estimated to change from 0.6 to 0.2 μsec in the early stages of the deformation. This change is shown to be attributable to the increase of the density of dislocations in the material.Subject Classification: 35.10.

Acoustic‐emission transducer and its absolute calibration

A new method is developed for absolute calibration of acoustic‐emission transducers using a reciprocity technique in a Rayleigh‐wave sound field. It is applied to practical transducers, and their sensitivity is obtained over a frequency range of 100 kHz to 1 MHz. The result is compared with frequency spectrum of an actual acoustic emission signal from a large structure detected by an identical transducer. It is shown that practical characteristics of transducers can be estimated with ease and repeatability in an acoustical environment similar to that of structures such as pressure vessel walls.Subject Classification: [43]40.42; [43]85.40.

Reciprocity calibration of impulse responses of acoustic emission transducers

By means of reciprocity calibration in Rayleigh-wave and longitudinal-wave sound fields, frequency characteristics of amplitude and phase of absolute sensitivity of acoustic emission transducers were measured on the basis of the newly derived complex reciprocity parameters, and the impulse responses were obtained through inverse Fourier transform. Calibration results were confirmed with supplemental experiments in which the fracturing of a pencil lead was utilized for the source of elastic waves. Impulse responses of acoustic emission transducers to both the Rayleigh-wave and longitudinal-wave displacement velocities were determined by means of purely electrical measurements without the use of mechanical sound sources or reference transducers.

Reciprocity calibration of acoustic emission transducers in Rayleigh-wave and longitudinal-wave sound fields

A new system was developed for the reciprocity calibration of acoustic emission transducers in Rayleigh-wave and longitudinal-wave sound fields. In order to reduce interference from spurious waves due to reflections and mode conversions, a large cylindrical block of forged steel was prepared for the transfer medium, and direct and spurious waves were discriminated between on the basis of their arrival times. Frequency characteristics of velocity sensitivity to both the Rayleigh wave and longitudinal wave were determined in the range of 50 kHz–1 MHz by means of electrical measurements without the use of mechanical sound sources or reference transducers.

High-frequency ultrasonic cleaning tank utilizing oblique incidence

Transmission characteristics of a double-structured tank, used for high-frequency (1 MHz range) ultrasonic cleaning of semiconductor wafers and substrates, were improved by utilizing oblique incidence of ultrasonic waves. As the sound transmittivity through a plate in water varies with the angle of incidence, the bottom of the Pyrex glass inner container was slanted at the angle where strong transmission occurred. In the slant-bottom container, an intensive and uniform sound pressure distribution was measured with a polyvinylidene fluoride (PVDF) hydrophone probe. In comparison with the conventional horizontal-bottom container, it was shown that the distributions as well as amplitude of sound pressure were remarkably improved by slanting the bottom of the inner container at the proper angle.

Axisymmetric analysis of a tube-type acoustic levitator by a finite element method

A finite element approach was taken for the study of the sound field and positioning force in a tube-type acoustic levitator. An axisymmetric model, where a rigid sphere is suspended on the tube axis, was introduced to model a cylindrical chamber of a levitation tube furnace. Distributions of velocity potential, magnitudes of positioning force, and resonance frequency shifts of the chamber due to the presence of the sphere were numerically estimated in relation to the spheres position and diameter. Experiments were additionally made to compare with the simulation. The finite element method proved to be a useful tool for analyzing and designing the tube-type levitator.<<ETX>>

Calibration of acoustic emission transducers

This paper reviews the state of the art on the calibration of acoustic emission transducers, which is essential to establish the basis for the standardization of acoustic emission technology. For this purpose, absolute sensitivity should be determined quantitatively in a sound field similar to that of actual acoustic emission waves. Many attempts were made to characterize acoustic emission transducers. However in most cases, only relative response was measured since the magnitude and frequency distribution of the sound source used were not clear. We developed a new calibration method using a reciprocity technique, and absolute sensitivity was obtained with ease and repeatability [H. Hatano and E. Mori, J. Acoust. Soc. Am. 59, 344–349 (1976)]. Besides a longitudinal sound field, a Rayleigh‐wave sound field was employed to estimate practical characteristics of transducers in a structure such as a pressure vessel wall. An automatic calibration system was constructed as a primary standard, where a large hamme...

Absolute measurements of acoustic emission

The present paper summarizes and reviews the current understanding of the absolute measurements of the amount, frequency spectra, and wave forms of the elastic energy which is rapidly released during acoustic emission events. Quantitative emission measurements are essential both for basic research and for practical applications, but many problems are left to be resolved. In general, the absolute measurement involves two fundamental problems: the absolute calibration of the transducer and the estimation of the transmission characteristics of the propagation path from the source to the transducer. For the first problem, the reciprocity technique can be employed, when the wave mode of the acoustic emission signals is identical to what is employed in the calibration. The second is a problem of greater difficulty. A few attempts have been made only under comparatively simple conditions. In practice, the wide frequency distribution and low energy levels of most acoustic emission signals complicate the measureme...