Flaw Imaging Technique for Plate-Like Structures Using Scanning Laser Source Actuation

Changgil Lee,Seunghee Park

doi:10.1155/2014/725030

Abstract

Recently, the longitudinal, shear, and surface waves have been very widely used as ultrasonic wave-based exploration methods to identify internal defects of host structures. In this context, a noncontact nondestructive testing (NDT) method is proposed to detect the damage of plate-like structures and to identify the location of the damage. To achieve this goal, a scanning laser source actuation technique is utilized to generate a guided wave and scans a specific area to find damage location more precisely. The ND:YAG pulsed laser is used to generate Lamb wave and a piezoelectric sensor is installed to measure the structural responses. The measured responses are analyzed using 3-dimensional Fourier transformation (3D FT). The damage-sensitive features are extracted by wavenumber filtering based on the 3D FT. Then, flaw imaging techniques of a plate-like structure are conducted using the damage-sensitive features. Finally, the plates with notches are investigated to verify the effectiveness and the robustness of the proposed NDT approach.

Highlights

There have been increasing demands on structural 2 health monitoring (SHM) and nondestructive testing (NDT)in the fields of civil, mechanical, and aerospace engineering and so on to prevent losses of life and property by continuously monitoring the systems
A lot of researches based on acoustic and ultrasonic technologies have been proposed using laser interferometry, laser vibrometer, pulsed laser, and so on because the ultrasonic waves are sensitive to the mechanical properties of structures, while the wave responses are hardly affected by radiation [5]
The performance of the laser Doppler vibrometry is improved in terms of scan angles and automatic focusing [7], it has still disadvantage that retroreflective film should be attached on target surfaces to improve signal-to-noise ratio when a scanning head is located far from the target [8,9,10]

Summary

Introduction

There have been increasing demands on structural 2 health monitoring (SHM) and nondestructive testing (NDT). SHM/NDT methods must be intuitive so that inspection results can be understandable and must have high throughput [5] To tackle this issue, a lot of researches based on acoustic and ultrasonic technologies have been proposed using laser interferometry, laser vibrometer, pulsed laser, and so on because the ultrasonic waves are sensitive to the mechanical properties of structures, while the wave responses are hardly affected by radiation [5]. Laser interferometry, which senses vibration responses of target structures, works well without the retroreflective film, but its performance has not been proved when the distance between scanning head and target surface is greater than 0.5 m [11, 12] To overcome these drawbacks, a laser beam pulse can be used to generate ultrasonic waves. Investigated to verify the effectiveness and the robustness of the proposed NDT approach

Ultrasonic Wave Propagation

Experimental Study

Conclusion