Koichi Akizono

Some crystal boundary phenomena in aluminum bicrystals

Abstract The authors have found that in the melt growth of aluminum bicrystals under certain conditions, the crystal boundary rotates about the direction of heat flow during progressive solidification, even though the crystal boundary area increases. This crystal boundary phenomenon may not be analogous to that found by Chalmers in tin and lead. It is suggested that the former occurs in the bicrystals the boundaries of which have twist components, and in which a cellular substructure grows appreciably so that there will be a variation in the thermal conductivity for different directions. In the high purity aluminum bicrystals this boundary phenomenon does not occur.

On building diagnostic expert system for ultrosonic testing.

Diagnostic expert system for an ultrasonic testing was built upon based on Method of Ultrasonic Angle Beam Testing and Classification of Test Results for Butt Welds in Steel Plates, WES2021-1987. In the present expert system, it may be advantage to use a production role and a backward inference when knowledge presentation was done. The diagnostic time could be reduced because the inference process become evident. Non-destructive inspection engineers can use this expert system on a general microcomputer. In order to confirm the expert system, the ultrasonic testing, which was diagnosed by the present expert system, and the radiographic testing were performed on butt welded joints in steel plate. Results of ultrasonic testing were almost coincident with those of radiographic testing. Therefore, it has been confirmed that the expert system was available on inferring method of ultrasonic testing.

The effects of strain-induced martensitic transformation and temperature on impact fatigue crack propagation behavior of SUS 304 at low temperature.

The fatigue crack propagation behavior in fatigue impact at room temperature and 103K was investigated by means of fracture mechanics, X-ray diffraction analysis and fractography for an austenitic stainless steel, SUS 304. The crack growth rate in fatigue impact decreased with decreasing temperature. The crack growth rate at room temperature was scarcely influenced by the microstructure, while at low temperature it was markedly influenced by the microstructure. The effects of microstructure and temperature on the crack growth rate were closely related to the strain-induced martensitic transformation. The martensitic transformation was influenced by the microstructure, the temperature, the fracture morphology and the stress intensity level and resulted in a decrease in crack growth rate with increasing crack opening level.

The influence of vacuum on near-threshold fatigue crack growth behavior in 60-40 brass.

The influence of vacuum environments on near-threshold crack growth behavior in an annealed 60-40 brass have been studied by means of fracture mechanics and fractography. In vacuum, the crack growth rate was smaller than that in air and decreased with decreasing vacuum pressure. When the R ratio and ΔK level increased, the crack growth rate in vacuum approached that in air. The near-threshold crack growth behavior in vacuum was markedly influenced by a fracture roughness, which resulted from a crystalline fracture mode, in addition to a plastic induced crack closure.

An explanation for near-threshold fatigue crack propagation behavior in welded residual stress fields by crack closure phenomenon.

Fatigue crack growth rates and threshold for crack propagation were determined for CCT and SEN specimens taken from the butt welded joints in 600 MPa grade steel. The crack opening stress has also been determined by using relation between the elastic compliance and loads. The compressive residual stresses resulted in the decrease of fatigue crack growth rates and the increase of threshold values. These behavior strongly depended on the stress ratio. While, the tensile residual stresses resulted in the increase of fatigue crack growth rates and the decrease of threshold values. These behavior scarcely depended on the stress ratio. The effects of welded residual stresses and stress ratio can be correlated by using the effective stress intensity range concept.