Detection Method Using Laser Differential Interferometer under Environmental Vibration for Inner Defect in Concrete Structure

Abstract

We performed simulation experiments to detect defects in a vibrating concrete structure by running loads using a laser differential interferometer. In laser interferometry, it is difficult to acquire vibration information when the amplitude of the out-of-plane vibration is big enough in comparison to the working wave length because the interference signals repeat bright and dark as different frequencies of actual vibrations. In this paper, we performed interference measurements using scattered light from an inspected object as a signal and a reference beam to reduce the relative displacement. Our results show that artificial inner defects in samples under environmental vibration can be detected.

Flash-lamp-pumped 4 J, 50 Hz Nd:YAG nanosecond laser system for mobile and transportable equipment

“…1) The laser hammering method (LHM) is a LRS procedure that can replace the hammer impact test for detecting defects inside concrete. [1][2][3][4][5] The basic idea behind the LHM is that a high energy pulse of an impact laser system is irradiated on the concrete surface to generate panel vibrations by laser ablation and=or thermal stress, 6) acting thus as a hammer, and after that, a laser interferometer detects the generated vibrations in the audible range, similar to a human ear. In recent years, we have demonstrated the LHM (in the laboratory) using a laser system with a pulse energy of 1 J and a repetition rate of 25 Hz.…”

“…[18] Ref. [4] Target area therefore, it is a tool for compensating the thermally induced wavefront distortion or the presence of some poor-quality components. 13) On the other hand, cryogenic laser systems also constitute an effective approach to reduce the thermal effects, and the performance of the laser is improved under cryogenic conditions as well.…”