| Budget Amount *help |
¥3,040,000 (Direct Cost: ¥2,800,000、Indirect Cost: ¥240,000)
Fiscal Year 2007: ¥1,040,000 (Direct Cost: ¥800,000、Indirect Cost: ¥240,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
The characteristic of ultrasonic called "nonlinear ultrasonic" has been reported in recent years. The characteristic has a possibility of early detection of unclear cracks and slight delaminations, which are difficult to detect with a conventional technique. However, it takes high voltage and continuous pulses, and thus, a special equipment to generate such pulses is required. The detectable nonlinearity pertaining to the crack and delamination is relatively large, and it is easily detected even in the ultrasonic waveform. The purpose of this study is an enhancement of the detection of the nonlinear ultrasonic. In this study, the technique to detect a small modulation of the ultrasonic frequency, which is a kind of nonlinear ultrasonic with a harmonic wavelet transform is devised.
Firstly, the harmonic wavelet transform with modified time-frequency plane is applied to the ultrasonic waveform. An object of experiment is a glued acrylic plate. Some objects were prepared and gluing conditions are different from other. However, it was difficult to distinguish the gluing condition for lack of the voltage.
On one hand, it was estimated that the information discriminating the gluing condition appeared as a slight variation around the basic frequency of the ultrasonic. In order to capture the slight variation, a newly continuous wavelet transform was devised. The harmonic wavelet was segmentally used in the proposed technique for the sake of numerical stability. It was found that the variation of the ultrasonic frequency which passed the glue layer was different according to the gluing conditions. The gluing condition was discriminated by the degree of the frequency variation. This phenomenon seems to be a kind of nonlinear ultrasonic. It shows the possibility that a small abnormality inside the object becomes detectable, even if ordinary low voltage ultrasonic is used.
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