Kiyoshi Sakamaki

Effect of transient stress on acoustic emission behaviour during firing of dental porcelain

Acoustic emission activity was measured in the glass transition range of dental porcelain during firing. Transient and residual stresses in porcelain during cooling from a temperature higher than porcelain sag point and during re-heating of the tempered porcelain were calculated by computer simulation using a viscoelastic stress analysis. The detected acoustic emission event was discussed with the relative rules of the simulated transient stresses. High acoustic emission activity was detected at the temperature where the internal stress faded away for heating and build up for cooling. The low-level acoustic emission pulses were only detected in the following conditions: (1) in the temperature range where porcelain behaved like an elastic solid; (2) at temperatures higher than the deformation point of porcelain; (3) with a re-heating process of the porcelain without tempered stress. From these results, it was concluded that elastic energy is released related to transient stress in porcelain during viscoelastic deformation and can be detected by the acoustic emission method. The acoustic emission method is considered to be helpful in non-destructive testing in order to understand transient stress due to viscoelastic deformation of glassy materials in heat treatment.

Acoustic emission behavior during tensile deformation of Ni3Al intermetallic compound

Abstract Acoustic emission behavior during tensile deformation of single crystals and unidirectionally solidified specimens of Ni 3 Al intermetallic compound was studied. Mobile dislocation behavior in single crystals was investigated by measuring acoustic emission rms voltage. Using unidirectionally solidified specimens, effects of grain boundaries parallel to tensile axis on the acoustic emission behavior during tensile deformation of Ni 3 Al was examined. It was made clear that blocking dislocations at grain boundaries and microcracking along grain boundaries are acoustic emission sources.

The effects of lamellar structure in the TiAl intermetallic compound on its acoustic emission behavior during tensile deformation

Abstract The dynamic behavior of TiAl intermetallic compounds during tensile deformation has been determined by the different appearance of the (α2 + γ) lamellar structure using the acoustic emission (AE) method. The AE events of these materials are obviously different. There is, however, no effectively direct evidence to prove the relationship between the microstructure of these TiAl alloys and the AE behavior. In this paper, the effect of the interfaces on the transmitted wave are calculated quantitatively. According to these results, the effects of the microstructure of TiAl alloys on the AE behavior have been clarified.

Mechanical Properties and AE Behavior of Particle-Dispersed Nickel-Base Alloys Prepared by Powder Metallurgy.

This paper discusses the tensile properties and acoustic emission behavior of Ni-NiO alloys and Ni-Al2O3 alloys prepared by means of the PM method. The mechanical properties of these materials were changed by their manufacturing process conditions. In the case of Ni-NiO alloys, the sintering time of 3.6ks along with repressing and resintering processes may be effective. On the other hand, the best conditions for Ni-Al2O3 alloys are the sintering time of 10. 7ks with neither repressing nor resintering. The AE characteristics of Ni-NiO alloys became highly apparent. It appeared that the AE events generated in the region of 5-40% strain were related to the decohesion of the matrix / dispersoid interface. The AE events with high energy and high peak amplitude before fracture of the Ni-NiO specimen were produced by intergranular cracking. The AE activity of Ni-Al2O3 alloys was weaker than that of Ni-NiO alloys ; that is, the peak amplitude distribution of AE events generated in Ni-Al2O3 alloys became narrow and most AE events had low energy.