vith international workshop ndt in progress october 10 12, 2011… · 2011-12-29 · 11/25/2011...

ELECTROMECHANICAL IMPEDANCE FOR STRUCTURAL HEALTH MONITORING

V.Pavelko, I. Ozolinsh, S. Kuznetsov, I.Pavelko

( Aviation Institute of Riga Technical University, Latvia)

11/25/2011 1

VIth International Workshop NDT in Progress

October 10 – 12, 2011,

Hotel and Congress center Floret, Prague,

Czech Republic

11/25/2011 2 VIth International Workshop NDT in Progress, October 10 – 12, 2011, Hotel and Congress center

Floret, Prague, Czech Republic

Structural Health Monitoring of Aircraft Structure by Method of

Electromechanical Impedance V.Pavelko, I. Ozolinsh, S. Kuznetsov , I.Pavelko


Contents

Introduction

Test results: damage of a sheet; pre-loading of a bolt-joint

Problem of EMI prediction

The electromechanical impedance of constrained transducer

General model of EMI

Discussion and conclusions

The beam has the form of the truncated cone with a length of 5485 mm, i.e. the length of the beam. The base diameters are 1000 and 550 mm respectively.

Intention: To create experimental SHM system (ESHM) for the tail beam and estimation of its reliability and technical and economical efficiency.

Introduction

11/25/2011 3 10th International Conference on Fracture and Damage Mechanics

19-21 September 2011 Dubrovnik, Croatia




SEVENTH FRAMEWORK PROGRAMME

AIRCRAFT INTEGRATED STRUCTURAL HEALTH ASSESSMENT II

a) b)

Typical points of the stress concentration in structural

elements of the MI8 helicopter tail beam skeleton (a) and

the bolt-joints with others components of aircraft (b).

11/25/2011 4

Typical elements of a skeleton and the bolt-joints




VIth International Workshop NDT in Progress, October 10 – 12, 2011, Hotel and

Congress center Floret, Prague, Czech Republic

Fatigue damage of the bolt-joints

a) b)

A view of the frame 17 in zone of cracking (a) and the fatigue cracks

in frame at fatigue test (b, view in a direction against flight)

11/25/2011 5






Hot spots of structure. Here also there is a problem of damage detection

near known points of a structure.

a) b)

Examples of the typical “hot spots” of the MI8 helicopter tail beam.

Technological cut in skin forced by riveted overlay (a), the fatigue

crack in zone of a hot spot (b)

11/25/2011 6 VIth International Workshop NDT in Progress, October 10 – 12, 2011, Hotel and Congress

center Floret, Prague, Czech Republic




E/m impedance for the near field damages detecting

Mechanical properties cause the changes

of electromechanical impedance

oStiffness

oAttenuation

11/25/2011 7






I

UZ

11/25/2011 8






10

50 mm 80

80

1 mm

Sensor local stiffness increase (a) and decrease (b) effect on EMI experimental investigation

(a) (b)

The effect of local stiffness of a sheet

The PI Ceramic PIC 151 piezoceramic sensor sized

0.5x10x50mm was glued on Al alloy 2024-T3 1x80x80 mm plate

11/25/2011 9






The first resonance of a constrained sensor (local stiffness increase)


10

50 mm 80

80

1 mm

Sensor local stiffness increase

(a)

(b)

11/25/2011 10






Local stiffness effects on the first resonance frequency


11/25/2011 11






The effect of holes 1

ZRe

ZReR

0

51

6 2

7 3

8 4

a ) b) The scheme of holes in a plate near PZT (a) and smoothed real part of EMI relative increasing in frequency band near resonance (b)

11/25/2011 12






Bolt material: Hihg strength steel

Initil stress: 300MPa

Sensor: Pz27 Plate 6.35 x 6.35 x 1 mm

(Ferroperm Piezoceramics A/S)

Pre-loading of a bolt-joint

Electromechanical impedance for SHM of a bolt-joint

11/25/2011 13






The relative increment of real part of EMI of the transducer T1 in resonance frequency band as a result of loosing of bolt preload.

Test results: Pre-loading of a bolt-joint

11/25/2011 14






Figure 8. The relative increment of real part of EMI of the transducer T2 in resonance frequency band as a result of loosing of bolt preload.


11/25/2011 15






Figure 9. The relative increment of real part of EMI of the transducer T3 in resonance frequency band as a result of loosing of bolt preload.


11/25/2011 16 VIth International Workshop NDT in Progress, October 10 – 12, 2011, Hotel and





Computational Simulation

11/25/2011 18






The electromechanical impedance of

constrained transducer

11/25/2011 19

331

112

31

011

1

Ed

UlUk

CiZ

21

010

01

222

2

2

1

2

2

2

2

212

2

2

21

020

02

111

1

2

2

1

2

2

2

1

2

uuDG

G2

A1

bc

x

uc

t

u

uuDG

G2

A1

bc

x

uc

t

u

2

11

11











The first resonance of sensor with decreasing local stiffness

10

50 mm 80

80

1 mm

Sensor local stiffness decrease effect on EMI

11/25/2011 21






General model of EMI of conservative

elastic system

tz,y,xWt,z,y,xw k

1k

k

ttMtM kk

2

kkkk

dVz,y,xWz,y,xM2

k

W

k dV)z,y,x(Wt,z,y,xFt k

W

k

ti

22

kk

k0k eM

z,y,xWt,z,y,xw

0k

S

k0k dS)z,y,x(Wz,y,xQ

11/25/2011 22






l

T

T

σ

σ

σ

σ

a ) b) The views of the system ‘structural element-ultrasound transducer’ (a) and the simplified scheme of interaction of a transducer with structural element (b)

ti

22

2m

2

m

2

m

2

0mti

22

1k

1

k

1

k

1

0k eM

z,y,xWe

M

z,y,xW

S

i

k

ii

k dS)z,y,x(Wt,z,y,xFt

tiiiez,y,xFt,z,y,xF

S

i

k

i

0

i

0k dS)z,y,x(Wz,y,xF tii

0k

i

k et

z,y,xFz,y,xF2

0

1

0

blWF1dS)z,y,x(Wz,y,xF

i

k

i

0

i

S

i

k

i

0

i

0k

General model of EMI of conservative elastic system

11/25/2011 23






The crack in the thin plate (top) and approximate simulation of its effect to

stiffness (bottom)

L

L1

2c 2B

0 x

a dAK

E

1KK

E

-1

Q

2

S

2

III

2

II

2

I

2

2

j

j

,B/ccB/ccA

FK I

,9063.03554.00248.01 32

dEA

B2d

EA

tB4dcK

EAF

t4B/c

0

2

c

0

2

2

2c

0

2

I22

d

L

B2B/c

0

2

0

11/25/2011 24






22

2m

2

m

22

m

22

1k

1

k

21

k

M

W

M

W

1

k

22

m

2

m

21

k

2

1k

1

k

22

m

2

2m

2

m

21

k2

MWMW

MWMW

331

*

11331111111 EdSEdTsS 2331

*

11 wlEdww

lEdM

FW

M

FW33122

1k

1

k

0

21

k

22

2m

2

m

0

22

m

22

1k

1

k

21

k

22

2m

2

m

22

m

331

0

M

W

M

W

lEdF

22

2m

2

m

22

m

22

1k

1

k

21

k

22

2m

2

m

22

m

331

21M

W

M

W

M

W

lEdww

22

1k

1

k

21

k

22

2m

2

m

22

m

22

2m

2

m

22

m

2

31

M

W

M

W

M

W

1k1Ci

1Z

11/25/2011 25






The relative additional compliance of plate as a function of crack half-length

11/25/2011 26






1

11

1

E

b

2

b

xcosW

b

0b

1

1

2

btldx

b

xcosltM 1

b

0

2

1

1

1

0kLcoskLsinkLcoskLsinkLcos

kLcoskLcoskLsinkLsinkLcoskLkLsin

111

1111

2

Lx if ,xksinxkcosC

2

Lx if ,xksinC

xW

mm3

m22

m

1LktanLktanC 1mm2 LktanC m3 1m2m2

x

xm2l

2

m xksinxksinCxksinCW2

1

11/25/2011 27






The natural frequencies of the plate as functions of half-length of a crack

11/25/2011 28






Magnitude of EMI of system in narrow frequency band lower than the first natural frequency of transducer

11/25/2011 29






Magnitude of EMI of system in narrow frequency band close to the first natural frequency of transducer

11/25/2011 30






Magnitude of EMI of system in narrow frequency band higher than the first natural frequency of transducer

Conclusions

The effect of structural damage is associated with the changes of dynamic properties of a

structure and can be effectively defined at ultrasonic frequencies by identification of EMI of

system „sensor-structural element‟.

The developed 1-D model of constrained PZT can be used for analysis of the elastic and

geometrical parameters effect to properties of piezoceramics transducer, and for structural

health monitoring of element with possible damage.

The key problem of increase of efficiency of EMI inspection is development of acceptable

methods of prediction of effect of damage to the impedance.

The simple method of estimation was developed. This method uses the effect of natural

frequency changing as a result of PZT and structural element coupling. The effect of a

crack is approximately estimated as a function of elastic compliance of a plate using the

energetic approach of fracture mechanics.

The model of constrained piezoceramics transducer can be also used for creation of a

type of pre-stressed one protected from effect of mechanical fatigue and environmental

degradation.

11/25/2011 VIth International Workshop NDT in Progress, October 10 – 12, 2011, Hotel and


31




Thanks you for your attention!

11/25/2011 32 VIth International Workshop NDT in Progress, October 10 – 12, 2011, Hotel

and Congress center Floret, Prague, Czech Republic

vith international workshop ndt in progress october 10 12, 2011… · 2011-12-29 · 11/25/2011...

Documents