Papers by Author: Yosiyuki Okuda

Abstract: Lotus-type porous magnesium was fabricated by unidirectional solidification of the melt dissolving hydrogen in a high-pressure mixture gas of hydrogen and argon. The damping constant
of porous magnesium with various porosities was measured by the hanging excitation method. The damping constant was defined as α=log (xn/xn+1)/
T, where xn and xn+1 are the successive amplitude values of the damping wave, and
T is the damping time. The frequency-amplitude dependence curve was obtained by Fast Fourier Transform analysis. The damping time of the lotus-type porous magnesium was observed to be shortened greatly compared with non-porous metals and porous copper. Moreover, the damping constant of the lotus-type porous magnesium was calculated by the damping amplitude.

Abstract: Lotus-type porous magnesium with a large number of unidirectional cylindrical pores was fabricated by unidirectional solidification of melt dissolving hydrogen in a pressurized hydrogen atmosphere. The vibration-damping capacity of the lotus-type porous magnesium plate which has many open pores was measured in this work. The attenuation coefficients of the free vibration of lotus-type porous magnesium were measured by hammering-vibration-damping test, which revealed that the attenuation coefficients increase with increase in porosity; the damping capacity of lotus magnesium is higher than that of non-porous magnesium. The mechanism for high damping capacity was analyzed on the basis of the Fourier transform technique, which indicates that various vibration modes of high frequency are observed. The excited vibrations of high frequency enhance the damping capacity of lotus-type porous magnesium.

Abstract: Lotus-type porous magnesium whose long cylindrical pores were aligned in one direction was fabricated by unidirectional solidification of the melt dissolving hydrogen in a pressurized hydrogen atmosphere. The sound absorption coefficient of porous magnesium whose specimen face has many open pores was measured by standing-wave method in the range up to the frequency of sound of 4 kHz. The relationship between absorption coefficient and pore structure of porous magnesium was studied. The absorption coefficient increases with decrease of the pore size, while it increases with increase of the porosity. Moreover, the peak value with high absorption coefficient is shifted toward higher frequency of sound when the thickness of the porous magnesium specimen decreases.