デジタル信号処理を用いた超音波による非破壊材料特性評価・劣化診断
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概要
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A digital ultrasonic measurement system has been developed for nondestructive material characterization and diagnosis of material degradation. Different from the conventional analog systems, the digital system records the whole echo wave forms into a digital memory with high S/N ratio by averaging. Then several features, e.g., velocity , dispersion, attenuation, of the wave form are extracted through the digital signal processing. These features can be evaluated through only single measurement. In particular, the zero crossing, cross correlation and phase spectral techniques are implemented for precise velocity measurement. Several application of the digital system have been demonstrated for material characterization as well as diagnosis of material degradation: thermal degradation of steel with velocity change and variation of the backscattered noise, identification of anisotropic elastic constants of fiber reinforced composites with measurement of the quasi-longitudinal and -transverse velocities, simultaneous measurement of the leaky Rayleigh, surface SV and creeping waves by focused PVDF sensors, evaluation of
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