intro to shearography

1Xxxxxx Titre xxxx © NDT expertDate © NDT expert - The ultimate control2003

Shearography - NDT Capabilities


The basic principles of the measurement method are interferometry and correlation techniques

Interferometry is determination of fractional relative phase difference between light waves traversing different paths. Phenomena which can be measured are those which influence the phase of the light beams. In practice this is e. g. surface deformation


The basic principles of the measurement method are interferometry and correlation techniques

Digital Image Correlation is a data analysis method, which uses a proprietary mathematical correlation method to analyse digital image data taken while samples are subjected to mechanical stresses. Consecutive image captures taken during the testing phase will “show” a change in surface characteristics as the specimen is effected by the mechanical stresses imposed upon it.


Non-destructive testing is the common use of shearography. The defects become visible on measuring their inhomogeneous deformation gradients. Depending on the spatial distribution of deformation the defect or the structure itself can be characterised. The rotor measurements show a dis-bond (left), a crack (right) and a structural transition (centre). Compare fringe density and distribution.


Dynamic excitation is a special technique of isi-sys for non destructive testing. During the sweep the vibration modes are visible in real-time. The example (left) shows selected images of C-Si-C composite (sweep 1-20kHz) with an in service dis-bond in the middle. Further data processing enables determination the mechanical properties of the defect area.


Impact defect detection in carbon fibre composites (CFRP) by dynamic excitation

The examples shows carbon fibre panel with impacts prepared by Airbus, Bremen. Similar carbon composites are used for the new Airbus A380.


Impact defect detection in carbon fibre composites (CFRP) by dynamic excitation

The defects are prepared by impacts of different energies. The defects become visible by dynamic excitation at their natural frequencies as show below.

Defect visible at 17.873Hz

Evaluated vibration mode


Example of NDT by dynamic excitation applied on GLAREThe examples shows a glare panel (size 500x500, see below) with de-bondings (Ø60mm) prepared by Airbus Bremen. Glare is a combination of Aluminium plates with composite layers used for the new Airbus A380F.The defects (dis-bonds or delaminations) are prepared in different depth between the aluminum plates. The defects become visible by dynamic excitation at their natural frequencies as show below by the supperposed measurement results.


Illuminated

object

Birefringent

element Polarizer

Lens

CCDImage processing

Loading:

Thermal

Vacuum – pressure

Vibration

Mechanical

Shearography principle recall


Comparaison : TV-Holographie and Shearographie

Typical shearographic result

- - - Initial position

_____ After-stress position

Measured value

x Shear length

Typical TV-holography result13-02-2001 19:37:20

Deslocamento [µm]

PV= 30.614

LOME/INEGI

-5.5

-2.1

1.3

4.7

8.1

11.5

14.9

18.3

21.7

25.1

3.1 27.0 52.1 76.0 100.7 124.6 149.7 173.6 198.3 222.2 247.3

91.9

73.7

55.9

37.7

20.2

13-02-2001 19:37:20

Deformação [µm/shear]

PV= 2.497

LOME/INEGI

X=11.0

Y=59.6

32.9

59.6

55.6

59.6

78.8

59.6

101.9

59.6

124.6

60.2

147.7

60.2

170.8

60.2

193.6

60.2

216.7

60.2

239.4

61.0

-1.301

-1.052

-0.802

-0.552

-0.303

-0.053

0.197

0.446

0.696

0.946

1.195

13-02-2001 19:49:40

Deslocamento [µm]

PV= 30.925

LOME/INEGI

X= 9.8

Y=59.6

32.9

59.6

55.6

60.2

78.8

60.2

101.9

61.0

124.6

61.6

147.7

61.6

170.8

62.2

193.6

62.2

216.7

63.1

239.4

63.6

-5.54

-2.45

0.64

3.74

6.83

9.92

13.01

16.11

19.20

22.29

25.38

11-12-2000 10:56:13

Deformation [µm/shear]

PV= 3.301

NDT Expert

3-grad.TFD

-1.75

-1.38

-1.01

-0.65

-0.28

0.09

0.45

0.82

1.19

1.55

6.9 31.5 57.3 82.3 107.8 132.8 158.6 183.2 209.1 233.7 259.5

138.6

108.2

78.8

48.9

19.5

Shearography principle recall


REPORTING

SIZING

LOCALIZATION

Monitoring on Optical disc – useful on serialised parts

FOLLOW UP

Shearography - Capabilities


13-02-2001 18:23:41

Deformation [µm]

PV= 6.332

Dr. Ettemeyer GmbH & Co.

-4.08

-3.38

-2.67

-1.97

-1.26

-0.56

0.14

0.85

1.55

2.25

33.1 57.3 80.7 104.9 128.3 152.5 176.0 200.1 223.6 247.8

99.2

78.8

59.5

39.1

19.8

13-02-2001 18:23:41

Deformation [µm]

PV= 3.203


-1.62

-1.27

-0.91

-0.55

-0.20

0.16

0.51

0.87

1.23

1.58

33.1 57.3 80.7 104.9 128.3 152.5 176.0 200.1 223.6 247.8

99.2

78.8

59.5

39.1

19.8

13-02-2001 18:20:31

Deformation [µm]

PV= 5.434


X9.86

57.44105.02

152.60200.19

247.77

Y

158.09

118.45

78.81

39.17

-0.47

-40.11

Z

-3.77

-2.69

-1.60

-0.51

0.57

1.66

13-02-2001 18:20:31

Deformation [µm]

PV= 2.502


X9.86

57.44105.02

152.60200.19

247.77

Y

158.09

118.45

78.81

39.17

-0.47

-40.11

Z

-1.30

-0.80

-0.30

0.20

0.70

1.20


Example of images obtained with thermal Loading


X-ray result Shearographic Images with two perpendicular shear directions

DAMAGE TYPE DETECTED – Honey comb junctions dislocation



unbounding

DAMAGE TYPE DETECTED – Metal/metal edges unbounding

Top view

Profile view



ON CONCORDE

Positioning and sizing tool



DAMAGE TYPE DETECTED – Adhesive craking under impact

Cross section Adhesive cracks Honeycomb

Skin

Top view

Visible impacted area

Multiple adhesive cracks




Example of vacuum loading


Liquid ingress

unbound

DAMAGE TYPE DETECTED – Water or liquid ingress



US-Laser System

Shearographic system

Thermographic system

Comparative tests



Thermography Lock-InShearography immediate(t)

Shearography after 15 sc. (t’)

US-Laser (Amplitude)

US-Laser (time base)

Results of Comparative tests



US C-ScanImpacted Monolithc

(CFRP)Displacement field

Corrosion Detection

Aluminium Alloys

CF C-ScanDisplacement field



MIRA pressure vessel Filamentary wounded (Al-

GFRP)

Ageing control

Delamination detection

Old New

Procedure Control – Diagram of the part to be inspected

Shearography - CapabilitiesPressurized material control


Benefits:

Contact less

Global method,

Good sensitivity,

Real time inspection,

Quicker than most of the NDI methods,

Working on all type of materials and structures,

Numerical acquisition give rise to efficient follow up,

New type of damage are now detectable without opening the structure…

The keys of the efficiency are in the selection of the loading and the implementation

Conclusions


intro to shearography

Documents

carbon fibre

impact defect

measurement

dynamic excitation

image processing

basic principles

comparative

natural frequencies