Imaging in Non-Destructive Testing

Imaging in Non-Destructive Testing

W. Arnold, M. Kröning, and F. WalteFraunhofer-Institute for Non-Destructive Testing

Bldg. E 3.1, UniversityD-66123 Saarbrücken, Germany

1929: Sokolov (Russia) notices that with ultrasound defect can be detected in metals. He calls this signal on the scope a reflectogram.

1945: Delano (Sperry Inc. USA) names this reflectogram an A-scan A- Scan.

Reflectogram of a defect in a steel shaft

Source: L. Bergmann, Ultraschall 1954

Imaging in Non-Destructive Testing: A-Scan

1935: Sokolov (Russia) andPohlmann (Germany)develop the first ultrasonic imaging system.



Ultrasonic imaging system after Sokolov/Pohlmann

UV- light

Electrostatic lens

Magnetic lens

Piezoelectriccrystal

Object with defect

Lens Piezoelectric plate with photoelectric layer = Cathode of the image converter

Source: L. Bergmann, Ultraschall1954


Two with screws joined metallic blocs

Frequency = 7 MHz


Ultrasonic imaging system after Sokolov/Pohlmann


Amplitude Scan: A- Scan

xz

A

BWE

DE

y

Defect

z

1945: Delano (Sperry Inc., USA)calls the reflectogram A-scanas an abbreviation for amplitude-scan


1954: Leksell (USA) 1. Ultrasonic B-scans in medical imaging. A- scans are added in analog fashion and defect-echoes are depicted as amplitude modulated images.

B-scans stands for Brightness Image.

Source: Geschichte der Ultraschall- Diagnostik. Ultraschall Museum im Deutschen Röntgen-Museum


Brightness Scan: B- Scan

xz

A

BWE

DE

y

Defect

z

x

DE

BWEz

Amplitude Scan: A- Scan

Brightness-scan = B-scan in NDT

The amplitude is color coded in a typical B- Scan in a modern NDT imaging system


1957: Michalskie (Germany/Röchling, Saarland) carries out one the first B-scans tests in NDT.

Images of inclusions in a steel shaft

Source: Chronik der zfP. U. Richter, DVS- Verlag 1999


Acoustic signal(Tone-burst)

Reference signal

Plane wave

Object wave

Object Reference wave

Acoustic Holography

1954: Greguss, Hungary develops in analogy to optical holography acoustical holography.


Object signal Reference signal

Multiplication

Digital storage

Analog storage

Storage on PC

Photodiode

Storage on hologram plate

1976: Holosonics (USA) constructs the first commercially availableholographic system with analog recording and optical reconstruction.

1979: Schmitz (IZFP) and Kutzner(BAM) develop holographic systems with digital recording and numericalreconstruction.


LASER

Aperture Mirror

Mirror

TV- CameraHologram plate

Display

Acoustical holography withoptical reconstruction


Digitally storedsignal

PC Holography algorithm(Back-propagation)

Display

Acoustical holography with numerical reconstruction

∫ ∫= ηρλ

dderizuu ikr

212


x – y plane at z1

Holography

Result: ultrasound amplitude distribution in y-x plane

Rekonstruktion using backpropagationA

xz

y

Defectz 1

zo

Measurement:Real- and imaginary partof ultrasound in x-y plane at zo

A

t

Real

Imag


Holography in tandem – and pulse-echo mode

Specimen with flat-bottom holeswith different orientation

Optical reconstruction

Pulse Echo Tandem Quelle: V. Schmitz and M Wosnitza, Erfahrungen der Ultraschallholographie mit numerischer und optischer Rekonstruktion


Holography in pulse-echo and pitch-catch mode

Specimen with a side-drilled hole

Numerical reconstruction

Source: J. Kutzner, H. Wüstenberg BAM- Berlin


1979: Holography system (IZFP) based on the unit from Holosonics Inc. USA


Specimen with slag inclusions

0ptical reconstruction Numerical reconstruction for line A-A

A A

Application of acoustical holography in the inspection of welds

Source: V. Schmitz, M. Wosnitza. Erfahrungen der Ultraschallholographie mit numerischer und optischer Rekonstruktion


x

yz

C - Scanx

y

1955: Projection of the ultrasonic amplitude as projection on the area scanned: C- Scan.


FV

SV

TVFV: Front viewTV: Top view

SV: Side view

1973: Based on C-scans Lund & Jensen (Denmark) develop the P-Scan technique (projection-scan)


15 mm

15 mm

3 mm 2 mm

UT- Probe: 2 MHz, 70 ° P- wave

1985: C- scan technique (IZFP/CPSN) for austenitic welds seams.The double indications originate from the direct P-wave and the mode converted signal SPP.


Ultraschallfront

Fokus

FokussierungWinkeleinschallung

θ

1968: First proposal of a phased array testing system in the USA


Control Unit

Timedelay

Timedelay

Timedelay

T T TR R R

α

Dd

α

Time delay D = d sin α

D

Variable insonification angle

Block model ofphased-array system


1 2 N3

Digitizer

Multiplexer

Preamplifier

Phased-Array Electronics Computer

Phased-Array Probe

Transmitter device32 channels

Max. time delay = 8 μs

Bandwidth 0.5- 8 MHz

Receiver device

32 channel analog multiplexer

100 MHz digitizer

Computer At- 386 / 33 MHz

1979: Gebhardt (IZFP)carries out the first measurements in NDT using a Phased-Array in Germany


1 m

1/2 m

1980: IZFP phased array-system “ARGUSS“


xz

y

Defect

y1

α

COMPOUND- Scanwith

Phased Arrays

Measurement:

Sector-Scans (A, z, a )

Reconstruction by superposition of video-signals in x- z plane at y1

Result: Amplitude distribution in the x-z plane at y1

1980: Gebhardt (IZFP) develops the COMPOUND-Scan in NDT


32 °

20 mm φ

130 mm 100 mm

Phased Array COMPOUND- Scan

Application of a COMPOUND- Scans

Source: W. Gebhardt. F. Bonitz, H. Woll, V. Schmitz. Beam Forming and Defect Characterization by Phased Array Systems. 9. World Conf. on NDT


xz

y

Defect

y1

Atm1

t m2tm3

t

1978: Barbian (IZFP) develops ALOKAmplitude and time-of-flight LOCUS Curve

Measurement:of time of flight (t) for each (A max) of all RF-signals in x-z plane at y1

Reconstruction by points of intersection in x- z plane at y1

Result:Reflection points in x-z plane at y1


Inspection of RPV- NozzleALOK- reconstruction

of notches (saw cuts) in the nozzle corner

notch


1987: ALOK-3 unit (IZFP)For ndt of components of the primary circuit of nuclear power plants


Ultrasonic Inspection for 40 – 56‘‘Pipelines

Insertion into a 40‘‘pipeline

Transducer made ofpiezoelectric material


Abb. 1.2.4.1 Synthetisierung der Apertur durch Abtasten des Prüfobjekts

1972: Based on radar technology Prine (USA) develops the “Synthetic Aperture Focus Technique“ (SAFT).

By scanning a small transducer on the component to be tested, a synthetic aperture is built. All rf-signals are stored and their origin is numerically calculated and the source displayed as defect.


xz

y

Defect

y1

A

t

SAFTSynthetic Aperture Focusing Technique

Measurement of all RF wave-forms on the line y1

Reconstruction by circles with time depending summation of all RF- amplitudes

Result: SAFT- B- Scan for x-zplane at y1


SAFT- reconstruction of a crack in a circumferential weld, wall thickness 30 mm

70° insonification of a transverse wave


Austenitic weld UT- probe 2.25 MHz, 60°, P-

Wave

Hot crack 50 mm

Crack tip; Direct echo

Back wall

Angle mirror effect (Sv- P- Sv)

Test of austenitic weld using SAFT


xz

yy1

A

t

Defect

Reconstruction: B- Scan in x- z plane at y1

Measurement of allRF- waveforms

Two transducers in pitch-catch mode

1975: Silk (GB)Time-of-FlightDiffraction TechniqueTOFDT


Time-of-Flight Diffraction Technique TOFDT

Side drill holes

TOFDT- B- Scan

Source: J.P. Charlesworth, J.A.G. Temple: Ultrasonic Time-of-Flight Diffraction: John Wiley & Sons Inc. 1989


α

A11 A12 A13 A14A21 A22 A23 A24A31 A32 A33 A34A41 A42 A43 A44

Σi2Σi1 Σi3 Σi4

i

j

1 2 3 4

Pixel-field

ΣΑij

Transmitter Elements

Receiver Elements

Transmitter time-delay

Receiver time-delay

2005: Using the powerful computers available now, Andrei Boulavinov (IZFP)develops the sampling phased array (SPA) whose basic principle has been formulated by various groups previouslyP. Wilcox et al, Bristol, Chiao and Thomas,GE Schenectady, Ozaki et al, Mitshubishi

Conventional Phased Array:With N elements one obtains only a sub-number of the matrix based on n signals

The functions Ultrasonic beam sweepingFocusingSectors-canSAFT- reconstructionCOMPOUND- scan

must be carried out consecutively by acquiring new data

Conventional Phased Array


Sampling Phased Array (SPA)

a

A11A12A13A14A21A22A23A24A31A32A33A34A41A42A43A44

i

j

1 2 3 4

A11A21

A31A41

A14A24

A34A44

Pixel-field

ΣΑij

Transmitter elements

Receiver elements

i): First element transmits, all elements receiveii): Second elements transmits, all elements receive

Filling up the complete matrix with N elements, oneobtains N2 data, allowing one

Beam sweepingFocusingSector-scanSAFT reconstructionCOMPOUND-scan

All functions can be realized in one test.

Data matrix of information


Electronics

Gruppenstrahler 16 Elemente

Mobiler PC

Sampling Phased Array (IZFP)

Phased array transducer with 16 elements

Laptop PC Specifications:

Synthetic transmitting channels:16 - 1024

No. of channels: 16 - 64Dynamic range: 110 dBSignal depth ADC: 14 BitMaximal digitization rate: 80 MHzMaximal IFF: q0 kHz


Crack

Angle mirror Backwall

Application: Sampling Phased Array SynFo- reconstruction

Corresponds to SAFT- reconstruction based on a stationary probe position with redundant data acquisition

+/- 65°

Stationary SAFT- Inspection (manual)

50 mm

25 mm

P-wave

Phased Array Probe16 Elements

Isotropic material

Natural crack


Sampling Phased ArrayComplete Information Matrix

Inspection Volume

Phased Array Probe Phased Array Probe

COMPOUND- Scan with SPA


Inspection of turbine axleusing SPA- COMPOUND- scan

0°21° - 21°

7°14°

Side-drilled holes 3 mm φ

0°7°14°- 21°21°


Test flaw 1

Test flaw 2

Test flaw 3

Test flaw 4

Reconstruction without depth compensation

Application: Sampling Phased Array

Specimen with 4 side-drilled holes2 mm φ


SF-phased array without focusing

Back-wall signal

Artificial defect

GT- phased-array with inverse phase-matching

Phased-array probe on component

Back-wall signalArtificial defect

SPA: First Application on anisotropic composite materials


30 30

84

114

24θ1

θ2

134

θ3

θ4

Nr. 3

Nr. 4

R2R3

R4

R2’’

BWER3’’

Nr. 2

Nr. 1

R5 (edge)

θ5

Application: SPAsector-scan


•Acoustic Microscopy (SAM)

•Atomic Force Acoustic Microscopy (AFAM)

Imaging in Non-Destructive Testing: Surface Characterization

Imaging in Non-Destructive Testing: Acoustic Microscopy

07.11.01

Electronics Image Processing

(a), (b): Scanning directions of the lens

TransducerSurface Acoustic Wave

Geometrical Focus

SurfaceSapphire

4

5 8

2

1

109

6

7

3

20μm

SAM Image of a Rock Sample

20 μm

Frequency 1 GHz

Measurement of Acoustic Impedance with the SAM

Cu

Al

Epoxy

Ni

Mg

Si

W

Acoustic impedanceZ = ρ × v

Calibration curve for acoustic impedance

acoustic image of sandstone with clay cement: what is contact stiffness?

Contact Zone in Sandstone

quartz

pore space

clay cement

500 µm 62.5 µmAcoustic images of a sandstone with clay cement made at 1 GHz. Impedances in the AM image is coded by gray shades: black = low impedance pore space, and light gray to white = high impedance quartz grains. The gray scale in the image extends from 45 Mrayls (white) to about 3 Mrayls (black). The right image show details of the clay contact zone with significantly lower impedance that the quartz.

Rayleigh wave velocity in Al2O3 from V(z) measurements

High-Resolution Testing of Piezoelectric Ceramics by Atomic Force Acoustic Microscopy Techniques

Atomic-Force Microscope

Deflection

Sample

Sensor tip

Micro-fabricatedcantilever

230 μm

*mk

f2 C00 =π⋅=ω

Harmonic oscillator model:

Typical values:Resonance frequency f0: 10 - 300 kHzSpring constant kC: 0.1 - 50 N/m

Torsion

AFAM Set-Up

Laser diode

Cantilever

Sample

Ultrasonictransducer

Sound wave

Computer

Spectrum

Lock-in-amplifier

Heterodynedown-converter

Signalgenerator

Ultrasonicimage

Reference

Signal

Electricalexcitation

Topo-graphyAFAM

Imaging using AFAM

Topography AFAM image

Area of higher stiffness; It appears as a bright one when imaged at (b) frequency

Soft area: Here one is out of resonance frequency and the amplitude of cantilever vibrations is small

Courtesy by NT-MDT, Zelenograd

Excitation of Contact Resonance Frequencies

AFAM and Ultrasonic Piezomode Images of PTC Samples Annealed at Different Temperatures; Image Size 2 μm x 2 μm.

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

Silicon

2000 2050 2100 2150 2200 2250 2300

0.07 0.13 0.20 0.34 0.51 0.68 1.02 1.36

Surface amplitude [Å] PIC 151

Frequency [kHz]

Can

tile

ver

vib

ratio

n a

ngle

[ º

]

Contact Resonance Curves, First and Second Mode

0.0000

0.0004

0.0008

0.0012

0.0016

0.0020

0.0000

0.0004

0.0008

0.0012

0.0016

0.0020

0.07 0.14 0.21 0.28 0.36 0.72 1.08

Surface amplitude [Å] Silicon

700 750 800 850

PIC 151

Frequency [kHz]

Can

tile

ver

vib

ratio

n a

ngl

e [ º

]C

antil

ever

vib

ratio

n an

gle

Piezoelectricceramic

Piezoelectricceramic

Silicon Silicon

Transmission of Ultrasound in Macroscopic Experiments:Interface with Mesoscopic Contacts

Frequency f0

Harmonics f0, f1, f2, f3, …

Ultrasonictransducer

Sample withdamagecracksdelaminationsinternal interfaces

• Space Probe

consisting of an orbiter & the landerPHILAE

• Target67P/Churyumov-Gerasimenko

• Time schedule

Start: 2. März 2004

Approach: August 2014

Landing: November 2014

End of mission: December 2014

Rosetta-Mission

Weight on Earth: ~ 830 NWeight on the comet: ~120 mN

Stabilization of the lander on thecomet by a harpoon and icescrews

Three-leg landing-gear each legwith two soles

On the lander there are 10experiments designed to examinethe structure and the compositionof the comet nucleus.

MPAe, Katlenburg-Lindau

≈ 2,50m

15 cm

Philae Landing Gear

• Transmitter and receivers

Piezoelectric transmitters Fraunhofer-Institute for Non-Destructive Testing;Piezoelectric accelerometerBrüel & Kjaer, Naerum, Denmark

• Operation modus

Passive: inactive transmitter Active: active transmitter

CASSE: Cometary Acoustic Surface Sounding Experiment

1. Resolution of imaging determined by wavelength2. Near-field imaging by antenna size

For data reconstruction there are still many things to do


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Imaging in Non-Destructive Testing