THICKNESS-MEASURING METHOD OF ELASTIC BODY, THICKNESS CHANGE BOUNDARY POINT DETECTING METHOD, CAVITY DETECTION AND MEASURING METHOD OF DEPTH TO CAVITY OF ELASTIC BODY, AND SOUNDNESS INSPECTING APPARATUS FOR ELASTIC BODY

摘要

PROBLEM TO BE SOLVED: To provide a measuring method which can easily measure the thickness of an elastic body with high precision. ;SOLUTION: When an arbitrary hammering point P_o of a concrete board 2 as an elastic body is hammered several times, a compound elastic wave (c) is generated at every hammering. Each of the compound elastic waves (c) is detected at a first detection point P₁, and the total value of power spectrum of a value to which power spectrum is normalized is obtained. By measuring a frequency for which the total value becomes large, a candidate of the resonance frequency f_o is obtained. A compound elastic wave (c) generated by percussion with a pulse width shorter than the period of a reflected wave P, out of the respective compound elastic waves (c) is detected at the first detection point P₁ and a second detection point P₂, and the phase difference of the compound elastic waves (c) is obtained. By obtaining a range showing the minimum of the phase difference, a frequency range containing the resonance frequency f_o is obtained. The resonance frequency f_o is determined by superposing the candidate of the resonance frequency f_o and the frequency range containing the resonance frequency f_o. The thickness of the concrete board 2 is operated by using the reflected wave velocity together with the resonance frequency f_o.;COPYRIGHT: (C)1999,JPO