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Applications of the SMART project to structural monitoring in military aeronautics
In the last years, Fiber Bragg grating (FBG) based devices have been widely exploited in applications ranging from sensing to telecommunications. Based on this technology, with unrivaled performances compared with other optoelectronic devices, a strong cooperation between different institutions has lead to a number of novel configurations which noticeably increased the performance and miniaturization of systems. This innovation has generated a number of applications in the following fields: structural health monitoring, aerospace, aeronautic, railway, electrical plants, ultrasonic diagnostics, high speed optical communications, GHz e.m. beam forming, microwave photonics. This is evident in light of several industrial research projects in cooperation with Italian Aerospace Research Center (CIRA), Alenia and Circumvesuviana and in the creation of a Spin Off company involved in smart applications. In particular, the SMART project, just arrived at the end of the second year, is finalized to integrate advanced materials, sensing and actuator systems in order to develop smart components able to:
•perform auto diagnosis on the health state during the operative life •change their structural features such as stiffness, shape and so on.
The critical points in the development of a true structural health monitoring in practical applications are related to the development of resident sensing systems able to retrieve all the required information in order to recovery the health state of the structure and its dependence on the working conditions. To this aim, a great effort has been spent to develop innovative interrogation techniques of fiber optic sensors based on grating technology, enabling a full integration of the entire measurement apparatus in such a way that the stuff mounted outside the fiber and capable to simultaneously interrogate many gratings on the same fiber can be made smaller than a few cubic inches. In addition, our system is able to fully exploit the dynamic response of the grating in such a way it is able to measure mechanical vibrations and acoustic fields with frequencies higher than 1 MHz. This capability is instrumental in acoustic emission detection and ultrasonic investigations aimed to localize and identify damages within the structure. This ability can be exploited in many fields especially in the case of military aircrafts where over limit performances pose severe problems in structural health monitoring. Many prototypes have been exploited in industrial applications in industrial sectors such as civil, aeronautic and aerospace. The same technology will be implemented for in flight tests within the European Project Ahmos 2, with the objective to monitor the structural state of the aircraft.In addition, the integration with actuating systems would enable the possibility to change the structural properties of the components through the modulation of the mechanical and the geometrical properties. In passing we note that our sensors systems can be easily mounted on the same optical fiber normally used for data transmission. In aeronautic applications, this last property can results in the use of the same optical fiber circuits for structure monitoring and fly by light simultaneously.
SUMMARY
SMART AND MULTIFUNCTION SENSORS
Vibration Control for Aeronautic Structures
Fiber Bragg Gratings
Andrea Cusano and Antonello CutoloOptoelectronic Group
Department of Engineering
Università del Sannio, Corso Garibaldi, Benevento (Italy)
Michele GiordanoIstituto dei Materiali Compositi e Biomateriali
Piazzale Tecchio 80, Napoli (Italy)
Giovanni BreglioDipartimento di Elettronica e delle Telecomunicazioni
Via Claudio 21, 80125 Napoli (Italy)
Antonio ConcilioCentro Italiano di Ricerche Aerospaziali
Via Maiorise, Capua (Italy)
CENTROITALIANO
RICERCHEAEROSPAZIALI
S.C.p.A.
CURE MONITORING, GLASS TRANSITION TEMPERATURE
DETECTION, RELAXATION MONITORING. PHASE
TRANSITION IDENTIFICATION
PROCESS MONITORING
STATIC STRAIN MAPPING, TEMPERATURE DISTRIBUTION,
DYNAMIC STRAIN MEASUREMENTS
STRUCTURAL HEALTH MONITORING
Cost reduction
Smart Processing
Safety Improvement
Maintenance cost reduction
High quality
Advanced materials
Crack detection
Damage identification
MULTIFUNCTION SENSING SYSTEM
Bragg = 2n
• One dimensional grating in a fiber– Reflect light in fiber– Change modes in fiber
• n index variation in fiber core• Strength of grating is proportional to refractive index
modulation depth
N°4 FBGs Embedded within Spar, Parallel to Wing’s Axis
N°4 Uni – Axial Accelerometers Bonded to Wing’s Surface
29 Excitation Points for Experimental Measures
20 40 60 80 100 120 140
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Excitation Point Position [cm]
Arb
itra
ry U
nit
s [
A.
U.
]
II Dispalcement Bending Shape
Experimental Data Interpolating Polynomial
20 40 60 80 100 120 140
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Excitation Point Position [cm]
Arb
itra
ry U
nit
s [
A.
U.
]
II Strain Bending Mode Shape
Experimental Data Interpolating Polynomial
AccelerometerAccelerometer FBG OutputFBG OutputSimulationSimulation
Modal Analysis Tests on a Composite Aircraft Model Wing
Co-Collocated Sensor-Co-Collocated Sensor-
Actuator SyatemActuator Syatem
Aluminium Cushion
PTZ
PZT
VppOptic Fiber 1
Coating
Optic Fiber 2
CoatingStraingages
Sensor-Actuator Sensor-Actuator
System for System for
Vibration ControlVibration Control
Embedded Sensors in Composite Materials
Embedded Sensors in Composite Materials
FBG + Accelerometer
Damage 1
Damage 2
FBG + Accelerometer
Damage 1
Damage 2
2000 2050 2100 21500
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
Frequency [Hz]
Am
plitu
de [
A.U
.]
No Damage1 Damage2 Damages
2079.5 2080 2080.5 2081 2081.5 2082 2082.5 2083 2083.5 2084
1.59
1.6
1.61
1.62
1.63
1.64
Frequency [Hz]
Am
plitu
de [
A.U
.]
1 Damage2 Damages
AccelerometerAccelerometer2000 2050 2100 21500
1
2
3
4
5
6
7
8
9
Frequency [Hz]
Am
pli
tud
e *
10
3 [A
.U.]
No Damage1 Damage2 Damages
FBGFBG
FBG
Piezoelectric Patch
Damage Detection Tests
Adaptive close
loop Control
Approach
Different fields of Application Railway track monitoring Ultrasound Wave Detection in Fluids
Narrow Band Laser
FBG Ultrasounds Source
Photodiode Narrow Band Laser
FBG Ultrasounds Source
Photodiode
Packaged FBG for Enhanced Performances
pat
ent
file
d w
ith
Ale
nia
WA
SS
pat
ent
file
d w
ith
Ale
nia
WA
SS
Experimental ResultsExperimental Results
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-0.2
-0.1
0
0.1
0.2fsound:7KHz Filter:Not Applied
Bra
gg
S
igna
l [V
]
Time [msec]
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Re
fere
nce S
ign
al [V
]
Time [msec]
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-0.2
-0.1
0
0.1
0.2fsound:7KHz Filter:Not Applied
Bra
gg
S
ign
al [V
]
Time [msec]
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Re
fe
re
nc
e S
ign
al
[V
]
Time [msec]
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-0.2
-0.1
0
0.1
0.2
fsound:7KHz Filter:Not Applied
Bra
gg
S
ig
na
l [V
]
Time [msec]
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Re
fere
nce S
ig
nal [V
]
Time [msec]
Time Excitation Signal (Piezoelectric Element)
FBG responseFBG response
Optical Fiber with FBG along the railway
Multipoint Monitoring system into the Railway Control Cabin