Method and system for structural health monitoring with frequency synchronization

Patent metadata

Field	Value
Publication number	US-10024756-B2
Application number	US-201414526226-A
Country	US
Kind code	B2
Filing date	Oct 28, 2014
Priority date	Oct 28, 2014
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

Structural health monitoring (“SHM”) methods, apparatus and techniques involve building deformation fields maps (amplitude and phase related to excitation) on the surface of the structural component under monitoring based on a network of strain measurements by fiber Bragg grating sensors.

First claim

The invention claimed is:

1. A method for monitoring the structural health (SHM) of a structural component of a type that has plural fiber Bragg grating (FBG) sensors distributed in a network of FBG sensors attached to a surface of the structural component, the method comprising:
a) with at least one actuator, exciting the structural component using CW (continuous waves) across a predetermined frequency range to generate a dynamic deformation field thereby imposing sinusoidally defined variation at the same frequency of a potential difference on plural fiber Bragg grating (FBG) sensors distributed in the network of FBG sensors attached to the surface of the structural component;
b) sensing a deformation field using the plural fiber Bragg grating (FBG) sensors distributed in the network of FBG sensors attached to the surface of the structural component, including synchronizing actuation of said at least one actuator with sensing using the plural fiber Bragg grating sensors to obtain in-phase and out-of-phase measurement resolution for strain measurements using the plural fiber Bragg gratings;
c) filtering the sensed deformation field to select only that portion of the sensed deformation field associated with the sinusoidal actuation generated by the at least one actuator;
d) in response at least in part to the filtered sensed deformation field, generating a two-dimensional deformation field map indicating the amplitudes and phases of surface strains, said deformation field map being based on the amplitude and phase sensed by the plural sensors;
e) repeating steps (a)-(d) for multiple excitation frequencies of the at least one actuator to provide additional corresponding two-dimensional deformation field map(s);
f) comparing the two-dimensional deformation field maps obtained by the different excitation frequencies to detect structural damage; and
g) performing computational analysis of the two-dimensional field deformation field maps with the aid of pattern recognition to identify structural damage.

2. The method according to claim 1 , wherein the frequency of actuation is different based on frequency ranges associated with primary and secondary loads as well as based on temperature variations in the said structural component.

3. The method according to claim 1 , wherein said filtering excludes not only the amplitude but also phase, and selects only a specific frequency of a sinusoidal signal used in the feeding of the at least one actuator.

4. The method according to claim 1 , wherein the method further includes obtaining a baseline two-dimensional deformation field map for comparison when the structural component under monitoring is free from defects or bears known defects.

5. The method according to claim 1 , wherein the method is substantially unaffected by changes in structural component temperature.

6. A system for the structural health monitoring (SHM) of a structural component, comprising:
a computer configured to (i) control inspections by executing software; and (ii) analyze deformation signals to obtain deformation field maps and compare the deformation field maps with a reference map, for detecting, locating and quantifying damage in the structural component or monitoring growth of some previously detected damage;
a set of at least two Bragg gratings written along at least one optical fiber, the Bragg gratings forming sensors, the sensors being longitudinally positioned on the said structural component under monitoring, the Bragg gratings being attached to a surface of the structural component and configured to effect monitoring, and to provide strain measurements;
a set of piezoelectric actuators comprising at least one actuator, attached to the surface of the structural component or embedded in the structure of the structural component and fed by a CW signal;
a tunable laser used as a narrow band light source for interrogating the optical fiber sensors, the laser being configured to sweep a wide band of wavelengths to interrogate the Bragg grating sensors installed in the component under monitoring;
an optical circulator providing at least first and second outputs, the first output sending a light signal emitted by the tunable laser towards the Bragg grating sensors, the second output sending the signal reflected by the sensors to a photo detector;
a lock-in amplifier configured to perform a double function: (i) to use its own reference signal to provide a harmonic signal for excitations of the set of piezoelectric actuators; and (ii) to recover the amplitude and phase of the sinusoidal strain signals, at the same frequency component, produced by the harmonically excited piezoelectric actuators;
a power amplifier configured to increase the excitation signal provided by the lock-in amplifier;
a multiplexer configured to control the distribution of the excitation harmonic signal (phase and amplitude) by the piezoelectric actuators;
the photo detector configured to detect the light signal reflected by the optical fiber sensors, turning the detected light signal into an electrical signal and conveying the signal to the lock-in amplifier; and
an optical fiber multiplexer structured to access more than one optical fiber in the case the sensors are distributed on more than one optical fiber.

7. A system for monitoring the structural health (SHM) of a structural component of a type that has plural fiber Bragg grating (FBG) sensors distributed in a network of FBG sensors attached to a surface of the structural component, the system comprising:
at least one actuator coupled to the structural component, the actuator exciting the structural component using CW (continuous waves) across a predetermined frequency range to generate a dynamic deformation field thereby imposing sinusoidally defined variation at the same frequency of a potential difference on the plural fiber Bragg grating (FBG) sensors distributed in the network of FBG sensors attached to the surface of the structural component;
a detector that is coupled to the plural fiber Bragg grating sensors, the detector being configured to detect a deformation field using the plural fiber Bragg grating sensors in a manner that synchronizes detection by said plural fiber Bragg grating sensors with actuation of said at least one actuator to obtain in-phase and out-of-phase measurement resolution for strain measurements using the plural fiber Bragg gratings;
a filter configured to filter the detected deformation field to select only that portion of the detected deformation field associated with the sinusoidal actuation generated by the at least one actuator;
a map generator configured to generate, in response at least in part to the filtered detected deformation field, a two-dimensional deformation field map indicating the amplitudes and phases of surface strains, said two-dimensional deformation field map being based on the amplitude and phase sensed by the plural sensors;
the at least one actuator, the detector, the filter and the map generator cooperating to use multiple frequencies to provide additional corresponding two-dimensional deformation field map(s); and
at least one processor comparing the two-dimensional deformation field maps obtained by the different excitation frequencies to detect structural damage;
the at least one processor operatively coupled to the comparator and the map generator, the at least one processor performing computational analysis of the two-dimensional field deformation maps with the aid of pattern recognition in order to identify structural damage.

8. The system according to claim 7 , wherein the frequency of actuation is different based on frequency ranges associated with primary and secondary loads as well as based on temperature variations in the said stru

Assignees

• Embraer Sa
• Puc Rio
• Puc Rio Pontificia Univ Catolica Do Rio De Janeiro

Inventors

• Da Silva Paulo Anchieta
• Dotta Fernando
• De Moraes Da Costa Laudier Jacques
• Braga Arhur Martins Barbosa
• Valente Luiz Carlos Guedes
• Louzada Daniel Ramos
• Salvini Leonardo
• De Gouvêa Paula Medeiros Proença

Classifications

• G01N29/11

  by measuring attenuation of acoustic waves · CPC title

• G01L1/246

  using integrated gratings, e.g. Bragg gratings · CPC title

• G01N29/345

  continuous waves · CPC title

• G01N29/4436

  with a reference signal (amplitude comparison G01N29/48) · CPC title

• G01M5/0033 Primary

  by determining damage, crack or wear · CPC title