Structural Damage Location with Fiber Bragg Grating Rosettes and Lamb Waves

Abstract

The aim of this study is to present the results of testing a damage detection and damage localization system based on fiber Bragg grating sensors. The objective of the system is to detect and locate damage in structures such as those found in aerospace applications. The damage identification system involves Bragg gratings for sensing ultrasound by detecting the linear strain component produced by Lamb waves. A tuneable laser is used for the interrogation of the Bragg gratings to achieve high sensitivity detection of ultrasound. The interaction of Lamb waves with damage, e.g., the reflection of the waves at defects, allows the detection of damage in structures by monitoring the Lamb wave propagation characteristics. As the reflected waves produce additional components within the original signal, most of the information about the damage can be found in the differential signal of the reference and the damage signal. Making use of the directional properties of the Bragg grating the direction of the reflected acoustic waves can be determined by mounting three of the gratings in a rosette configuration. Two suitably spaced rosettes are used to locate the source of the reflection, i.e., the damage, by taking the intersection of the directions given by each rosette. A genetic algorithm (GA) can be used to calculate that intersection and to account for any ambiguities from the Lamb wave measurements. The performance of the GA has been studied and optimized with respect to the localization task. Initial experiments are carried out on an aluminum structure, where holes were drilled to simulate the presence of damage. The results show very good agreement between the calculated and actual positions of the damage.

Wavefront Integrating Fiber Sensors for Ultrasonic Detection

“…For the Bragg grating, the most efficient approach to couple between the ultrasound and the reflection wavelength of the grating is to propagate an ultrasonic wave with a wavelength much longer than the grating in a direction parallel to the optical fiber in which the grating has been fabricated. This produces a longitudinal strain that is linearly related to the ultrasonic wave, which results in a very specific polar response, experimentally verified in [7]. All fiber interferometers in contrast respond to changes in pressure and are typically configured to be much longer in wavelength than the ultrasonic radiation.…”

Global overview on advances in structural health monitoring platforms

“…The sensors development and monitoring techniques had been improved and the inclusion of the durability parameters has been an upgrade, to promote a better damage characterization and an accurate structural lifetime prediction [97]. A significantly quantity of optical sensors has been developed and implemented, motivated by the better signal to noise ratio, good sensitivity, electromagnetic interference immunity, multiplexing possibility, low size and weight, robustness, low attenuation on remote monitoring, and no electrical power needed at the measuring point, among other advantages [52,98,99]. Thus, such sensors can potentially provide an optimized sensing system with higher performance.…”

Instrumentation of integrally stiffened composite panel with fiber Bragg grating sensors for vibration measurements

“…The first is the use of strain anomalies to detect buckling of the stiffened panel, a critical failure mode in skinstiffener airframe structures [1,2,[4][5][6][7]. The second approach is to measure the FBG strain due to an acoustic signal in the composite due to propagating Lamb waves, for example, through acoustic emission or active actuation of the structure with piezo-electric (PZT) elements [15]. Such information can then be applied for damage detection and identification within the airframe.…”