TIME REVERSAL SIGNAL PROCESSING IN ACOUSTIC EMISSION

11 ECNDT 2014 Prague, 6-10 October 2014

TIME REVERSAL SIGNAL PROCESSING IN ACOUSTIC EMISSION

Zdenek PREVOROVSKY1, Josef KROFTA1,Milan CHLADA1, Jan KOBER1,

and Serge DOS SANTOS2

1 - Institute of Thermomechanics Academy of Sciences CR, Prague, Czech Republic

www.it.cas.cz, E-mail: [email protected]

2 - INSA , Université François Rabelaise, Blois, France

1

mailto:[email protected]�

OUTLINE

1. AE Source Location and Identification using Time Reversal

2. TR AE Signal Deconvolution (TRAED)

3. Transfer of AE signal and the source reconstruction on

similar body without AE source

4. Conclusions for AE signal analysis on remote objects

Z. Prevorovsky, J. Krofta, M. Chlada1, Z. Farova, V. Kus:

Progressive Approaches to Localization and Identification of AE Sources.

30 EWGAE / 7 ICAE 2012, Granada, Spain, 12-15 Sept. 2012, http://www.ndt.net/EWGAE-ICAE2012

11 ECNDT 2014 Prague, 6-10 October 2014 2

AE SOURCE IDENTIFICATION IN COMPLEX STRUCTURES

Troubles: • Large and geometrically complex objects (reflections, dispersion,...)

• Remote (large distance) AE detection w/o direct access to tested structure

• Lack of information (noisy and incomplete data)

PROBLEMS:

1. Precise AE source location (variations of elastic wave propagation velocity)

2. Signal deconvolution using Time Reversal signal processing - 2 inverse

problems : Green’s function (TRAED), and sensor transfer function (TR

calibration - TRC)

Possible solution:Transfer of detected AE signals onto a model of tested structure and perform precise source location and deconvolution on the modelusing TRAED procedure

.311 ECNDT 2014

Prague, 6-10 October 2014

B. E.. Anderson, M. Griffa, C. Larmat, T.J. Ulrich, P.A. Johnson: Time Reversal(Acoustics Today, Volume 4, Issue 1, January 2008)

2 implementations of TR:

source emission

a) standard TR

b) reciprocal TR

steps in TR

Time Reversal Mirrors (TRM)

- Improvement of S/N ratio- Space focusing of waves

- Source signal reconstruction


Based on the fact that solution of acoustic wave equation in non-dissipative medium is invariant with respect to TR operation.

Theory of TRM

TR operation is described as a transformation t → T − tand the new sources can be expressed

Resulting TR field has the form


AE Signal Deconvolution using Time Reversal Mirrors

A point source function s(t) at the position r0 and a receiver at position ri. The signal detected at ri on time t arises from two convolutions:SG(t)

Detected AE signal is then time reversed and rebroadcast from the position ri to r0.

Resulting TR signal is expressed as multiple convolution:

Which is in the frequency domain

After inverse FT we obtain the TR signal reconstructed at the source


Schema of the experimental deconvolution principle

!! ResultingTR signal is proportional to the original one emitted by the source !!!

This is very important for AE source location and further analysis:

In the standard AE measurements we mostly analyze signals, which are notdirectly related with the originally emitted waves, but are influenced by travelingthrough the structure and by characteristics of AE sensors and recordingdevices.

JOURNAL OF APPLIED PHYSICS 106, 113504 2009


Experimental TR AE Deconvolution (TRAED)

4 sensors (T1-T4) 5 “sources” (S1-S5)

PMMA block 100x100x40 Steel plate 500x500x45


8

TR AE Source Location

T1+t1=T, T2+t2=T, T3+t3=T11 ECNDT 2014

Prague, 6-10 October 2014

PERFECT SYNCHRONIZATION OF TR ARRIVAL TIMES AT THE SOURCE

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EFFECT OF INACCURATE SOURCE LOCATIONSURFACE SCANNING a) by LASER interferometer, b) AE sensor (reciprocal TR)

2.95 3 3.05

x 104

-10

-5

0

5

10

2.98 2.99 3 3.01 3.02 3.03

x 104

-3

-2

-1

0

1

2

3

4

RECEIVER SHIFTS

SUMMATION OF TR SIGNAS

0 mm 10 mm 20 mm

Emitted signal (85 kHz)


10

AE IN FATIGUE TESTS OF AIRCRAFT WING FLANGE

date/time: 12081800 used sensors: 1 3 4 5 7 9

50 100 150 200 250 300

100

200

300

400

500

600

700

800

900

date/time: 12091400 used sensors: 1 3 4 5 7 9

50 100 150 200 250 300

100

200

300

400

500

600

700

800

900


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AE SOURCESdetected on "FLY"

TR-NEWS CRACK LOCALIZATION

C5

Final fracture

Comparison of the AE and TR-NEWS detection


12

TYPICAL AE SOURCESARE CRACKS AT RIVETS

TRAED EXPERIMENTAL SETUP


13

3-D NUMERICAL MODELING OF WAVE PROPAGATIONIN THE FLANGE CUTOFF

AE SOURCE (Ricker pulse)


14

SIGNALS IN 10 POINTS

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-5

0

5

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-1

-0.5

0

0.5

1

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-2

-1

0

1

2

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-2

-1

0

1

2

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-2

-1

0

1

2

6 6.05 6.1 6.15 6.2

x 104

-20

0

20

6 6.05 6.1 6.15 6.2

x 104

-20

0

20

6.05 6.1 6.15 6.2

x 104

-20

0

20

6 6.05 6.1 6.15 6.2

x 104

-20

0

20

6 6.05 6.1 6.15 6.2

x 104

-20

0

20

Source S1AE signals from T1-T4

T1

T2

T3

T4

LASER

TIME REVERSALRECONSTRUCTION


TRAED TESTING OF THE WING FLANGE5 PEN-TEST SOURCES (S1-S5)

4 AE TRANSDUCERS (T1-T4)

LASER

15

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-2

0

2

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-2

0

2

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200

-2

0

2

6200 6400 6600 6800 7000 7200 7400 7600 7800 8000 8200-2

0

2

6 6.05 6.1 6.15 6.2

x 104

-2

0

2

6 6.05 6.1 6.15 6.2

x 104

-1

0

1

2

6 6.05 6.1 6.15 6.2

x 104

-1

0

1

2

6 6.05 6.1 6.15 6.2

x 104

-2

0

2

6 6.05 6.1 6.15 6.2

x 104

-1

0

1

2

6 6.02 6.04 6.06 6.08 6.1

x 104

-2

0

2

6 6.02 6.04 6.06 6.08 6.1

x 104

-1

0

1

6 6.02 6.04 6.06 6.08 6.1

x 104

-2

0

2

6 6.02 6.04 6.06 6.08 6.1

x 104

-2

0

2

6 6.02 6.04 6.06 6.08 6.1

x 104

-1

0

1

2

PEN –Test on the flange rivet (S5)

T1

T2

T3

T4

AVERAGEFROM 4

TRANSDUCERS

TR – SIGNAL RECONSTRUCTION OF S5


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INFLUENCE OF THE SOURCE LOCATION INACCURACY ON SIGNAL RECONSTRUCTION'LINEAR SCANNING ON THE FLANGE RIB'

PEN TESTat S4

020

Reconstruction shifts

-505

10

-505

10-505

-505

-2

0

2

0 150-5

0

5

TR of S4

0

4

8

12

16

20


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AE SOURCE LOCATION ACCURACYFocusing of TR signal at the source

'LINEAR SCANNING ON THE FLANGE RIB'


amplitude

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PEN – TESTS ON THE ONE FLANGE (SOURCE SAMPLE) ARE RECONSTRUCTED ON

OTHER (REFERENCE SAMPLE) of SIMILAR GEOMETRY AND

THE SAME SENSORS PLACEMENT.

IT CAN BE USEFUL e.g.ON FLYING AIRCRAFT OR SATELITE PARTS, HAVING

THEIR 'GROUND COPY'

TRANSFER OF TR AE DATA ONTO A SIMILAR PART3 BROKEN PARTS OF THE AIRCRAFT WING FLANGES P1, P2, P3


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TESTING OF TR SOURCE SIGNALTRANSFER FROM THE FLANGE # P2 ONTO # P3 Source location and reconstruction is performed on the reference sample

PEN-TEST

20

Flanges # P3 and # P2are "SIMILAR"

P3 P2

Sample # P1

Sample # P3


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P1

P3

DIFFERENCES BETWEEN FLANGES # P1 and # P3 or # P2TR signal transfer P1 P3, P2 failed

Big rivet holes lead toadditional reflections,

which influences resultingTR signal composition

Tr 1Tr 2

Tr 3

Tr 4

yx


Tr 1

Tr 3

Tr 2

Tr 4

SOURCE SAMPLE# P2

REFERENCE SAMPLE# P3

3 mm MESH # M1 (9x9 points = 27x27 mm)

3 mm MESH # M2 (9x9 )

M1'

M2'

FLANGE# P2

FLANGE# P3

part of riveted wing skin

S1

S2

S2'

S1'

PEN-TEST SIGNAL TRANSFER AND LOCATION ON RECTANGULAR MESH 24x24 mm

22


SCANNING OF TRANSFER MESHES USING LASER INTERFEROMETERMOUNTED ON 3-D ULTRASONIC SCANNER

by 3 mm steps in both directions

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TR Pen-Test signals were transmitted by transducers T1-T4 and maximal TR amplitude received by interferometer indicates precise original source position


24

TR PEN -TEST SIGNALS ON MESH # M1 NODES (9x9)Pen-Test source is in the mesh center

TR scan of mesh M1 on the flange P2 - T1 emits TR signal. Source location is in the center

TR scan of flange P2, mesh M1 – emitter T2


25

RESULTS OF MESH M1 SCANNING ON THE FLANGE # P2



y1 y2 y3 y4 y5 y6 y7 y8 y9

TR signal sample(time)

x- mesh steps

y1..y9 y- mesh steps

colors...TR signalamplitudes

(spline interpolated)


26

3-D MAPPING OF THE SOURCE RECONSTRUCTION ON THE FLANGE # P2 MESHES

Reconstruction on the Mesh # M1

Reconstruction on the Mesh # M2

TR signal source T1 T2 T3 T4


27

PLANE PROJECTIONS OF SIGNAL RECONSTRUCTION AMPLITUDES ON MESH M1 AND M2 IN THE FLANGE P1

AND OF SIGNAL TRANSFER FROM FLANGE P1 TO P2

P1 / M1

P1 / M2

Transfer P1 to P2

Transfer is reconstructed only in 5x5 inner mesh points

(15x15 mm)


28

TESTING OF TRAED RECONSTRUCTION USING DIFFERENT TRANSDUCERS(useful for reciprocal TR)

-10

0

10

-0.50

0.51

-200

20

0 300-505

SAMPLE P1 to P1

P2 to P2

P1 to P2

P2 to P3

AE SOURCE RECONSTRUCTION ON REFERENCE SAMPLES


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SHM - 2 ultrasonic NDT methods combined

1. AE - Enables real-time source detection

2. TR- NEWS - AE source verification

Advantages :- Both methods use the same array of piezoelectric transducers

- Common devices are used (NEWS needs additional AWG, MUX, and Power Amplifier – all are used also in AE calibration)

- Both can localize arising defects AE - needs structure stimulationNEWS – applied without stimulation but needs structure excitation

Using of both methods is highly effective


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CONCLUDING REMARKS AND RUNNING WORK

- Study of influences on transferred signal reconstruction (small geometry differences, differences of transducers, length of TR signal, ...)

- Development of large numerical models including more details

- Reconstruction of AE sources detected during performed loading tests

- Surface scanning with non-contact ultrasonic signal sources (reciprocal TR)

- Regularization of amplitudes and energy (corrections on attenuation)

- Design of new signal parameters for better identification of sources after TRAED


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• TRM techniques are very effective tools for highly accurate AE source location and AE signal reconstruction (deconvolution). Procedure is performed off-line but needs only a very short time

• TRAED procedure enables better AE source recognition. It can be easy realized either experimentally or by the help of computer simulation model (procedure can be also performed 'reciprocally')

AE sources may be reconstructed on a similar body. Performed experiment showed robustness of TR method with respect to transferring results from one specimen to another

• Conjunction of AE with TR-NEWS method in SHM systems is highly effective as both methods are complementary and localized AE sources correspond well with damage zones detected by TR-NEWS

CONCLUSIONS


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THANK YOU

FOR YOUR KIND ATTENTION


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TIME REVERSAL SIGNAL PROCESSING IN ACOUSTIC EMISSION