Identification of structural damage using multifunctional Bragg grating sensors: I. Theory and implementation

Abstract

Structural health monitoring has become a respected and established discipline in engineering. Health monitoring involves the development of autonomous systems for continuous monitoring, inspection and damage detection of structures with minimum involvement of labour. The ultimate goal of structural health monitoring is to increase reliability, improve safety, enable light-weight design and reduce maintenance costs for all kinds of structures. The identification of structural damage is therefore a key issue in structural health monitoring. The scope of this paper is to present the results of testing a system for the identification of structural damage based on fibre Bragg grating sensors. The basic idea is to use fibre Bragg gratings as acoustic receivers of ultrasonic Lamb waves. The layout of such a damage identification system is introduced and its theoretical limits are studied numerically and experimentally. The set-up for damage identification experiments is described and the results of initial experiments introducing damage detection based on the analysis of Lamb wave signals are presented. The results for the Bragg grating sensors are then compared to the results of established technology for Lamb wave detection using piezoceramic transducers.

Strain Wave Acquisition by a Fiber Optic Coherent Sensor for Impact Monitoring

“…compared to Fiber Bragg Gratings (FBG), is the possibility to be tailored for the specific application. Focusing on high frequency dynamics, several works related to FBG acquisition have shown that a key parameter affecting the grating response is the ratio between the ultrasonic wavelength and the grating length [15][16][17]. The same considerations reasonably hold for interferometric sensors, which perform a spatial integration over the sensing length of the ultrasonic signals: if an excessive sensing length is chosen, the overall integration may drastically degrade the sensor sensitivity.…”

Acousto-Ultrasonic Optical Fiber Sensors: Overview and State-of-the-Art

“…A similar FBG sensing method was also presented by Betz et al [108], [109], [110]. Their system is intended to monitor and detect Lamb waves, and was implemented in a Perspex plate.…”

Advanced fiber-optic acoustic sensors

“…As the acquisition rate of wavelength interrogators increased, the first dynamic study appeared. Betz et al used FBGs for the monitoring and detection of Lamb waves [32][33][34], while other groups investigated the possibility of using FBGs for dynamic strain sensing [35][36][37]. In 2009, Seo et al studied the sensitivity enhancement of FBG sensors for acoustic emission detection [38].…”