Transcript EPE 2004

Applications of the SMART project to structural monitoring in military
aeronautics
Andrea Cusano and Antonello Cutolo
Michele Giordano
Giovanni Breglio
Antonio Concilio
Optoelectronic Group
Department of Engineering
Università del Sannio, Corso Garibaldi, Benevento (Italy)
Istituto dei Materiali Compositi e Biomateriali
Piazzale Tecchio 80, Napoli (Italy)
Dipartimento di Elettronica e delle Telecomunicazioni
Via Claudio 21, 80125 Napoli (Italy)
Centro Italiano di Ricerche Aerospaziali
Via Maiorise, Capua (Italy)
S.C.p.A.
CENTRO
ITALIANO
RICERCHE
AEROSPAZIALI
SUMMARY
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.
N°4 FBGs Embedded within Spar, Parallel to Wing’s Axis
29 Excitation Points for Experimental Measures
N°4 Uni – Axial Accelerometers Bonded to Wing’s Surface
II Strain Bending Mode Shape
II Dispalcement Bending Shape
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Experimental Data
Interpolating Polynomial
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Experimental Data
Interpolating Polynomial
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Arbitrary Units [ A. U. ]
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Arbitrary Units [ A. U. ]
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.
Modal Analysis Tests on a
Composite Aircraft Model Wing
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FBG Output
Accelerometer
Simulation
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Excitation Point Position [cm]
Excitation Point Position [cm]
Vibration Control for
Aeronautic Structures
Co-Collocated SensorActuator Syatem
Vpp
Optic Fiber 1
B1
Coating
PZT
PTZ
Sensor-Actuator
System for
Vibration Control
Coating
Straingages
B2
SMART AND MULTIFUNCTION
SENSORS
STRUCTURAL HEALTH
MONITORING
PROCESS
MONITORING
CURE MONITORING, GLASS
TRANSITION TEMPERATURE
DETECTION, RELAXATION
MONITORING. PHASE
TRANSITION IDENTIFICATION
Optic Fiber 2
Aluminium
Cushion
Adaptive close
loop Control
Approach
MULTIFUNCTION SENSING STATIC STRAIN MAPPING,
TEMPERATURE DISTRIBUTION,
SYSTEM
DYNAMIC STRAIN MEASUREMENTS
Damage Detection Tests
High quality
Crack detection
Advanced materials
Damage identification
Damage 2
FBG
Cost reduction
Safety Improvement
Smart Processing
Maintenance cost reduction
Damage 1
FBG +
Accelerometer
Piezoelectric Patch
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Amplitude [A.U.]
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Frequency [Hz]
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No Damage
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Amplitude *10 [A.U.]
• 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
1 Damage
2 Damages
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Amplitude [A.U.]
Fiber Bragg Gratings
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No Damage
1 Damage
2 Damages
Accelerometer
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Frequency [Hz]
FBG
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Frequency [Hz]
Different fields of Application
Railway track monitoring
Bragg = 2n 
Ultrasound Wave Detection in Fluids
Packaged FBG for
Enhanced Performances
Narrow Band
Laser
Photodiode
patent filed with Alenia WASS
fsound:7KHz Filter:Not Applied
Embedded Sensors
in Composite Materials
Bragg Signal [V]
Optical Fiber with
FBG along the railway
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Ultrasounds
Source
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Experimental Results
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BraggReference
Signal Signal
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Time [msec]
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Time Excitation Signal
(Piezoelectric Element)
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TimeFilter:Not
[msec] Applied
fsound:7KHz
Multipoint Monitoring system into
the Railway Control Cabin
Signal
[V]Signal [V]
ReferenceReference
Bragg
Signal [V]
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Time [msec]
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FBG response
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Time [msec]
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Time [msec]