Research on improvement of defect detection accuracy by resonance judgment for noncontact acoustic inspection method by acoustic irradiation-induced vibration

Abstract

Noncontact acoustic inspection methods using acoustic irradiation induced vibration and laser Doppler vibrometer that can perform defect exploration from a distance are being studied. This method has the feature that it can measure a wide range of measurement objects such as composite materials used for aerospace as well as concrete structures such as tunnels and bridges without contact. From the experimental results, it was found that the increase in noise level due to the decrease in the return light of the laser due to the condition of the measurement surface causes a decrease in the estimation accuracy of defect exploration. Therefore, it has been clarified that the detection accuracy of the defect position can be improved by devising a resonance judgement process for discriminating the signal and noise due to the resonance of the defect portion.

Study on movement measurement for internal defects in concrete structures by noncontact acoustic inspection method using correlation processing

“…25,26) Furthermore, spatial spectral entropy (SSE) 22,27) can distinguish between resonance phenomena caused by internal defects and resonance phenomena of the LDV itself by using the planar vibration velocity distribution. A resonance judgment process 28) has also been devised to determine whether the emitted signal caused vibration.…”

Feasibility of nondestructive testing using transient vibrations excited by acoustic radiation force

“…Vibrations can be also excited on an object by ultrasonic irradiation from a fluid such as air or water. [3][4][5][6][7] By measuring the vibration velocity of the object's surface, e.g. with a laser Doppler vibrometer, internal defects can be detected without contact with a tested object.…”

Pulse compression of guided wave by airborne ultrasound excitation for improving defect detection accuracy in concrete

“…The methods use laser ultrasound, 12,13) electromagnetic ultrasound, 14,15) and air-coupled ultrasound. [16][17][18][19][20][21][22][23][24][25][26] Among them, the method using laser ultrasound is the most practical for long-distance irradiation, and in recent years, a technique has been developed for imaging defects in structures by using a scanning laser source. [27][28][29] In this method, a relatively lowfrequency pulse laser is irradiated from a distance to generate sound waves on the target.…”