Tadao Mori

Improved ultrasonic testing by phased array technique and its application

Abstract The phased array ultrasonic testing method is available for beam steering and focusing, and then the focused beam divergence angle can be narrowed and the sound level can be intensified at the focused region. In the present study, two examples of phased array application which are the linear scanning mode operation and the sector scanning mode operation, were conducted in order to establish the availability of this technique as an actual NDT technique. As the result of the experiments, it was recognized that both types of scanning mode had the capability for defect detection and successful estimation of the defect size. Furthermore, it was well realized that the real time B-scope display without mechanical scanning was effective to reduce the operating time of inspection.

Size effect and crack propagation of turbine-generator rotor steel under torsional loading.

The fatigue strength of large and small-scale smooth specimens of a turbine-generator rotor steel was examined under torsional loading. Shear strain behaviour and axial crack growth of Mode II on smooth specimens and notched specimens were investigated in relation to size effect of the rotor steel. Elastic-plastic shear stress-strain characteristics at notch root were analyzied by finite element method. The main conclusions are as follows; (1) Size effect factor defined by the ratio of fatigue limits between 100 and 10 mm diameters was 0.78 and agreed the value of JSME recomendation (2) Shear stress-strain of notch root under large scale yielding condition can be estimated by expanded Neubers rule, using inelastic nominal stress-strain relationship. (3) Using the modified parameter √(EJIIa), Mode II axial crack growth rate of smooth and notched specimens, in both elastic and plastic shear strain fields, was successfully expressed by linear regression lines.

Relationship between S-N curve and fracture pattern under impact loading (In the case of JIS. S45C steel plain bars of different hardness)

A series of impact fatigue tests were conducted for structural carbon steel JIS. S45C of different hardness ranging from HV 166 to HV 534. In order to investigate the S-N characteristics over a wide range of stress cycle, two types of impact fatigue testing machines were used; one is an impact cylinder falling type with the loading rate of about 0.5 Hz, and the other is a vibro-motor type with the loading rate of about 60 Hz.Discussions were made on the configuration of S-N curves, the fracture pattern and the effect of the difference in impact stress pattern on the fatigue life in relation to the hardness of each specimen. The main results are summarized as follows; firstly, the fatigue strength under a triangular stress pattern applied in this study was higher than that under a rectangular stress pattern with duration of the peak stress of about 0.8msec. Secondly, the S-N curve had an obvious transitional number of the stress cycle and fracture surface patterns were found to be entirely different between in front and in rear of the transition point, that is, the ductile fatigue fracture appeared in the low cycle region and the ordinary one in the high cycle region. Besides, this transition point had a tendency to transfer from the high cycle region to the low cycle region as the hardness increased.

Evaluating Methods of J-Integral and Scatterings of Fracture Toughness

In recent work of fracture mechanics, the J-integral has been shown to be effective as a fracture criterion, and some experimental evaluating procedures of the J-integral have been proposed for fracture toughness testing. However, a number of important problems remained to be resolved for accuracy and the applicable range of the proposed evaluating procedures.