METHOD AND DEVICE FOR DETECTING MATERIAL DEFECT WITH HAMMERING METHOD

PURPOSE:To check the generation of an unwanted high frequency component and to determine the existence of a minute defect in material by measuring the oscillation generated in the measured material and making the Fourier transform synchronizing a window function to the zero cross point of the oscillatory wave form. CONSTITUTION:An outer portion of an alumina plate 1 whose one end is fixed is given a blow with a microhammer 2 to be excited. This oscillation is detected by a sensor 3 and the output is amplified to the size suited for a data processing and made a digital sampling 4. This sampling data, to which a window function by a window function setting measure 5 is synchronized and multiplied in a zero cross synchronization measure 6, is led into a high speed Fourier transform measure 7 by a digital computer. Frequency spectra on oscillation of the alumina plate 1 from this measure 7 are recorded and indicated in a record and display unit 8. Thus, a minute defect inside material can be detected from the spectra because of the conversion at a wave form as close to the original wave form as possible by the synchronization of the oscillation and the window function in the Fourier transform.