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

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Excitation Point Position [cm]

Arb

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nit

s [

A.

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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

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1

1.2

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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

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A.U

.]

1 Damage2 Damages

AccelerometerAccelerometer2000 2050 2100 21500

1

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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

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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

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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