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MODELING ULTRASONIC STRUCTURAL NOISE

BASED ON THE MICROSTRUCTURAL PROPERTIES

OF METALS IN THE CONTEXT OF NON

DESTRUCTIVE EVALUATION

NDCM 2013

V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

2013 International Congress on Ultrasonics | V. Dorval, L. Ducousso-Ganjehi, S. Chatillon, F. Jenson

APPLICATION CASES

FOCUS ON COMPLEX NUCLEAR COMPONENTS

20 mm 1 mm

O.D.

I.D.

Thickness of large bands: 5 to 8 mm

Pressurizer

Steam generatorPump

Reactor

Nuclear power plant Cast Stainless Steel (CASS) components


APPLICATION CASES

FOCUS ON COMPLEX AERONAUTIC COMPONENTS

Superalloys turbine blades


NON DESTRUCTIVE TESTING OF COMPLEX MATERIALS

Homogeneousmedium

Scatteringmedium

t

x

Structural noise and attenuation

These phenomena can cause significant loss in ultrasonic non destructive evaluation of highly scattering materials.

A part of the energy is scattered in all direction by the microstructure

STRUCTURAL NOISE


EXAMPLE: UT NOISE IN TITANIUM ALLOY BILLETS

Focused transducerFocal length F = 406.2 mmDiameter = 25.4 mmCenter frequency f0 = 10 MHz

70 mm

ImmersionNormal incidence

The waterpath was chosen such thatthe beam was focused in the half depthof the block

LONGITUDINAL WAVES IN TI ALLOY

Measurement setup


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-40

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-10

0

Time (µs)

Mea

n no

ise

leve

l (dB

) and

sta

ndar

d de

viat

ion

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-30

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-10

0

Time (µs)

Mea

n no

ise

leve

l (dB

) and

sta

ndar

d de

viat

ion

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-40

-30

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0

Time (µs)

Mea

n no

ise

leve

l (dB

) and

sta

ndar

d de

viat

ion

Z205 Face R1

Z205 Face R2

Z205 Face Z1

»Envelopes of the signal are measured for each probe position

»Envelopes are averaged over probe positions

»Expressed in dBs compared to the amplitude of the echo of a reference FBH echo

Cscan

1- Cscan 2- Bscan

3- Mean noise level

UT NOISE IN TITANIUM ALLOY BILLETS



UT NOISE IN TITANIUM ALLOY BILLETS

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Time (µs)

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n no

ise

leve

l (dB

) and

sta

ndar

d de

viat

ion

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0

Time (µs)

Mea

n no

ise

leve

l (dB

) and

sta

ndar

d de

viat

ion

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0

Time (µs)

Mea

n no

ise

leve

l (dB

) and

sta

ndar

d de

viat

ion

Z205 Face R1

Z205 Face R2

Z205 Face Z1

Time (µs)

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0

Time (µs)

Mea

n no

ise

leve

l (dB

) an

d st

anda

rd d

evia

tion

Z205 Face Z1 Face Z1

Time (µs)

Z1

R1

R2

R1

R2

Z1

Z1

R1

R2

R1

R2

Z1

Face Z1

Face R1 Face R1Macrograph Micrograph

Ti alloy

70 mm

Biphasic structure with equiaxed macrograins

Biphasic structure with elongated macrograins

Biphasic structure with elongated macrograins

Z205 Face R1

Noise level anisotropy depends strongly on the metallurgical structure



ORIGIN OF THE PHENOMENON

In case of a monophasic medium, scattering is due to acoustic impedance fluctuations of grains

• Mono-phasic medium, random, homogeneous and isotropic (statistically)

• Single scattering (Born approximation)• Plane wave(far field)

rCCrC ijklijklijkl

0

ijklijkl CC 0with

r

rkiB

r

rkiAru

s

t

m

s

l

m

s

m

exp,

exp,,

Spatial correlation function:Shape and size of grainsElastic constants variation

skkisWsdCCrr

kksiOrlj

ssil

sl

expˆˆ4

33333

,22

26

2iA

2iB

skisWsdCCk

ilLL

2exp4

3333322

8

In case of LL and θ = 180°

STRUCTURAL NOISE SIMULATION


In case of biphasic medium, scattering is due to acoustic impedance fluctuations of grains and contrast between phases

- Random crystallographic orientation of macrograins- Crystallographic orientation relationships between phases: each variant occurs with equal probability- Individual crystallites are too small to make a significant contribution to the grain noise

gCCfCCk CCMMlLL

333333333333333322

8

4

skisWsWsdg CM 2exp

skisWsdf M 2exp

In case of LL and θ = 180°

Averaged over all macrograins orientation

Averaged over all colonies orientation

ORIGIN OF THE PHENOMENON



Higher scattering coefficients are obtained for transverse waves than for longitudinalwaves. In both cases, the backscattering coefficient for two phases case has a frequency dependencysimilar to the macrograin coefficient for low frequencies and to the colonies coefficient for the higher frequencies.

0 1 2 3 4 5-50

-40

-30

-20

-10

0

Frequency (MHz)

(1

80

°)LL

(d

B)

DuplexMacrograinsColonies

0 1 2 3 4 5-50

-40

-30

-20

-10

0

Frequency (MHz)

(1

80

°)T

T (

dB

)


It confirms that it is necessary to take into account both scales of the material structurein order to be able to properly model the scattering at all frequencies.

BACKSCATTERING COEFFICIENT



For both L and T waves, the attenuation coefficient for the two-phases structure is somewhereinbetween the attenuation for macrograins and that for colonies.

For the case of L waves, it is very close to the attenuation due to colonies, but this is not a general behavior, as it is strongly dependent on the material properties .

1 2 3 4 50

0.5

1

1.5

Frequency (MHz)

L (d

B/m

m)


1 2 3 4 50

0.5

1

1.5

Frequency (MHz)

T (

dB

/mm

)


L T

ATTENUATION COEFFICIENT



SUMMARY OF THE COMPUTATION METHOD

Properties of the microstructure

Properties of the probe and the part

Input parameters

Determination of a sufficient number of

scatterers

Scattering coefficient

Computation of the emission and the

reception by the probe

Distribution of scatterers

Simulated B-Scan

Tim

e

Position


Objective: To predict the influence of the metallic alloys microstructure on the inspection performances

(see presentation LUT-10 Session D5 – Laser ultrasound – Thursday at 5:40 PM)


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Time(µs)

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ise

leve

l (dB

)

Experimental resultCIVA result

Face Z1- Biphasic structure- Equiaxed Macrograin = 100 µm-Colony = 2 µm -Elastic constants (bibliography)

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Time (µs)

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n no

ise

leve

l (dB

)

Experimental resultCIVA result

Face R1- Biphasic structure- Ellipsoidal macrograin = 100 µmwith L/l = 5.5-Colony = 25 µm-Elastic constants (bibliography)

Very good agreement between experimental and CIVA results

COMPARISONS BETWEEN EXPERIMENTAL AND NUMERICAL RESULTS


Face R1

Face Z1

TI ALLOY


Structural noise

Echo defect(notche)

Echo Defect(end of block)

Structural noise

Echo defect(notche) Echo

Defect(end of block)

ExperienceSimulation

Time (µs)

LONGITUDINAL WAVES IN STEEL ALLOY

Input data in CIVA software

Elastic constants of biphasic medium

Percentage of colony 85 %

Macrograin size 4 mm

Colony size 1 mm

Macrograin shape Equiaxe

Colony shape Equiaxe (?)

COMPARISONS BETWEEN EXPERIMENTAL AND NUMERICAL RESULTS

STEEL ALLOY

SHEAR WAVES IN SMALL GRAIN AUSTENITIC STEEL


Simulated B-ScanMeasured B-Scan

Tim

e

Tim

e

Position Position

12 14 16 18 20 22 24 26 28 30

-36

-34

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-30

-28

-26

-24

-22

-20

-18

Time (s)

Env

elop

e/R

efer

ence

(dB

)Shear 45° 2.25MHz

Measurement

Computation

Constructive interferences near the

backwall of the part are correctly simulated

• Comparison of noise levels by plotting the average envelope as a function of time

• Evolution of the noise correctly simulated, but underestimation by 5 dBs

Inspection with shear wave at 45° at 2.25MHz on a sample of austenitic steel

with ≈120μm grains

SHEAR WAVES IN STEEL ALLOY

CONCLUSION


• Structural noise can be simulated using a random distribution of scatterers with properties that are related to properties of the microstructure

• Correct prediction of the evolution of the noise level in several cases (Titanium and steel alloys)

• Limitations of the method:• Multiple scattering not taken into account• Underestimation of the noise for austenitic steel inspected with shear waves

PERSPECTIVES

• Simulation of multiple scattering (presentation concerning the work of T. Bedetti)• Amelioration of the accuracy of the simulation:

• Possible explanation for the underestimation for austenitic steel with shear waves: inaccuracy of the Born approximation due to the important variations of elastic properties in this material with shear waves

• Development of a more accurate scattering model in the SIMPOSIUM European project with IZFP (S. Hirsekorn)

• Experimental Determination of elastic properties in collaboration with LAUM (Session D5 at 5:40 PM)


Thank you for your attention

[email protected]

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