Peter B. Nagy

Department of Aerospace Engineering

University of Cincinnati

Cincinnati, Ohio 45221-0070

Electromagnetic Materials State Awareness Monitoring

Past and Present GoalsHealth Monitoring and Materials Damage Prognosis for

Metallic Aerospace Propulsion and Structural Systems

(FY06 DoD MURI BAA, AFOSR)

Integrated with Structure

● enables real-time monitoring

● in-situ interrogation, reduces costly tear-down

● integrated with autonomic logistic methods

Integrated with Prognosis

● sensitive to microstructural change and damage evolution

● quantitative probabilistic life prediction rather than warning

● integrated with physics-based materials damage models

Future Goals: Materials State AwarenessPrognosis of Aircraft and Space Devices, Components, and Systems

(Discovery Challenge Thrust, AFOSR, 2008)

Problem

Determine in real time the current state so that the remaining capabilities of the system or component can be predicted with a high degree of accuracy and known level of confidence

● for any material systems and material processing ● operational environments, component usage history ● failure or material/structure/system degradation mode

monitoringcommunity

prognosticscommunity

Is there a sufficientfinite set of parameters?

Can a specific set of parametersbe determined?

What can we monitor? What can we predict?

Technology Challenges(Discovery Challenge Thrust, AFOSR, 2008)

● Assess early and progressive changes in material state associated with operational usage and exposure.

● Predict the real-time physical, chemical or electronic state at any location for complex systems subject service loads and environmental exposure over time.

● Relate the current and evolving state of microstructure and damage processes to enable probabilistic prognosis modeling of the material/structural/system state.

monitoringcommunity

prognosticscommunity

Is there a sufficientfinite set of parameters?

Can a specific set of parametersbe determined?

What can we monitor? What can we predict?

What Can We Monitor?

● microstructure● phase transformation● plastic strain● elastic strain● hardening● embrittlement● creep damage ● fatigue damage etc.

● crack initiation ● crack growth● impact damage● erosion● corrosion etc.

by electromagnetic means

(measuring electric signals produced by electric, magnetic, or thermal stimulus)

● material state● component state● structure state● system state● service loads● environment etc.

● electric conductivity● magnetic permeability● thermal conductivity● thermoelectric power

● electric conductance● magnetic conductance● thermal conductance

sensitivityselectivity

Example I: Microstructure Evolutionseven different nickel-base powder-metallurgy alloys (Ni, Al, Cr, Fe) after five different heat temper

NAC1 NAC2 NAF1 NAF2 NACF1 NATNACF2

10-5

10-4

10-3

10-2

10-1

10+0

Alloy Designation

Mag

netic

Sus

cept

ibili

ty .

.

1.0

1.5

2.0

2.5

3.0

Alloy Designation

AEC

C [%

IAC

S]

-5

0

5

10

15

Alloy Designation

Ther

moe

lect

ric P

ower

[μV

/°C

]

● material state● electric conductivity● magnetic permeability● thermoelectric power

● microstructure evolution● phase transformation● hardening● embrittlement● elastic strain etc.

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 200 400 600 800 1000 1200Temperature [ºC]

Res

istan

ce [m

Ω] .

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 50 100 150 200 250Time [hour]

Res

istan

ce [m

Ω] .

0

200

400

600

800

1000

1200

1400

Tem

pera

ture

[ºC

] .

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 200 400 600 800 1000 1200Temperature [ºC]

Res

istan

ce [m

Ω] .

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 50 100 150 200 250Time [hour]

Res

istan

ce [m

Ω] .

0

200

400

600

800

1000

1200

1400

Tem

pera

ture

[ºC

] .

Example I: Microstructure EvolutionNAF1-1 nickel-base powder-metallurgy alloy (70.5% Ni, 24.5% Al, 0% Cr, 5% Fe) room temperature

● material state ● electric conductivity

● microstructure evolution● phase transformation● hardening● embrittlement● elastic strain etc.

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 50 100 150 200 250Time [hour]

Res

istan

ce [m

Ω] .

0

200

400

600

800

1000

1200

1400

Tem

pera

ture

[ºC

] .

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 200 400 600 800 1000 1200Temperature [ºC]

Res

istan

ce [m

Ω] .

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 50 100 150 200 250Time [hour]

Res

istan

ce [m

Ω] .

0

200

400

600

800

1000

1200

1400

Tem

pera

ture

[ºC

] .

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 200 400 600 800 1000 1200Temperature [ºC]

Res

istan

ce [m

Ω] .

Example I: Microstructure EvolutionNAC2-1 nickel-base powder-metallurgy alloy (65.5% Ni, 24.5% Al, 10% Cr, 0% Fe) room temperature

● material state ● electric conductivity

● microstructure evolution● phase transformation● hardening● embrittlement● elastic strain etc.

Example II: Elastic Strainresidual stress assessment in surface-treated nickel-base superalloys

106102

withoutresidual stress

with oppositeresidual stress

Fatigue Life [cycles]104 108

0

500

1000

1500

endurancelimit

serviceload

naturallife time

increasedlife time

Alte

rnat

ing

Stre

ss [M

Pa]

● material state● component state

● electric conductivity

● elastic strain● plastic strain● microstructure evolution● phase transformation● hardening etc.

Example II: Elastic Strainelectric conductivity versus uniaxial elastic strain in various metals

● electric conductivity● material state ● elastic strain

parallel

-0.004

-0.002

0

0.002

0.004

-0.001 0 0.001 0.002

τua / E

Δσ

/ σ0

normal

Copper

Ti-6Al-4V

parallel

-0.004

-0.002

0

0.002

0.004

-0.002 0 0.002 0.004

τua / E

Δσ

/ σ 0

normalparallel

-0.004

-0.002

0

0.002

0.004

-0.001 0 0.001 0.002

τua / E

Δσ /

σ 0

normal

Al 2024

parallel

-0.004

-0.002

0

0.002

0.004

-0.001 0 0.001 0.002

τua / E

Δσ

/ σ 0

normal

Al 7075

Waspaloy

parallel

-0.004

-0.002

0

0.002

0.004

-0.002 0 0.002 0.004

τua / E

Δσ

/ σ 0

normal

IN718

parallel

-0.004

-0.002

0

0.002

0.004

-0.002 0 0.002 0.004

τua / E

Δσ

/ σ 0

normal

● elastic strain● plastic strain● microstructure

● material state ● electric conductivity

Example II: Elastic Straineddy current spectroscopy in shot-peened IN100

eddy current– solid circles, XRD – open squares

κip = -1.06 (+33% “empirical” correction of AECC data)

-1800

-1600-1400

-1200

-1000

-800-600

-400

-2000

200

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Depth [mm]

Res

idua

l Stre

ss [M

Pa]

Almen 4AAlmen 8AAlmen 12A

Example III: Plastic Straineffect of uniaxial plastic strain in various nickel-base superalloys at room temperature

static

0.999

1.000

1.001

0 10 20 30 40 50Cold Work [%]

Nor

mal

ized

Mag

netic

Per

mea

bilit

y

IN718 IN100 Waspaloy

500 kHz

0.95

1.00

1.05

0 10 20 30 40 50Cold Work [%]

Nor

mal

ized

Bul

k El

ectri

cal C

ondu

ctiv

ity

.

IN718 IN100 Waspaloy

Nor

mal

ized

Ele

ctro

-Ela

stic

Coe

ffic

ient

0

1

2

0 10 20 30 40 50Cold Work [%]

IN718 Waspaloy

300 kHz

● piezoelectricity● magnetic permeability● electric conductivity

● material state ● plastic strain

Example III: Plastic Strain304 austenitic stainless steel, 15% plastic strain

● magnetic permeability● electric conductivity

● material state ● plastic strain

0.000

0.001

0.002

0.003

0.004

RT50

ºC10

0ºC15

0ºC20

0ºC25

0ºC intact

Mag

netic

Sus

cept

ibili

ty

2.60

2.62

2.64

2.66

2.68

2.70

AEC

C [%

IAC

S]

|

RT50

ºC10

0ºC15

0ºC20

0ºC25

0ºC intact

Example IV: Thermal Exposuremicrostructure evolution

thirty-two as-forged Waspaloy specimenssubsequent heat treatments of 24 hours

1.2

1.3

1.4

1.5

1.6

intact 300 350 400 450 500 550 600 650 700 750 800 850Exposure Temperature [ºC]

Con

duct

ivity

[%IA

CS]

as-forgedinhomogeneous

homogenized

0.1 0.16 0.25 0.4 0.63 1 1.6 2.5 4 6.3 10Frequency [MHz]

0

0.1

0.2

0.3

0.4

0.5

0.6

Con

duct

ivity

(AEC

C) C

hang

e [%

] intact 300 °C 350 °C 400 °C 450 °C 500 °C 550 °C 600 °C 650 °C 700 °C 750 °C 800 °C 850 °C 900 °C

thermal relaxation

Waspaloy, Almen 8A, repeated 24-hour heat treatments at increasing temperatures

● microstructure● elastic strain

● material state ● electric conductivity

Example VI: Thermal Relaxation

● material state ● thermoelectric power

● elastic strain● plastic strain● microstructure evolution● phase transformation● hardening etc.

before relaxationrelaxation at 235 ºCrelaxation at 275 ºCrelaxation at 315 °C2nd relaxation at 315 °C3rd relaxation at 460 °Crecrystallization at 600 °C

0

5

10

15

20

25

0 2 4 6 8 10 12 14 16Almen Intensity (A)

Mag

netic

Sig

natu

re [n

T]

0 4 8 12 16Almen Intensity (A)

0

1

2

3

4

5

6

7

8

Mag

netic

Sig

natu

re [n

T]

series 1 (intact)

series 2 (intact)

series 1 (565 °C)

series 2 (675 °C)

shot-peened C11000 Copper

noncontacting thermoelectric inspection

shot-peened IN100

Example V: Microstructure EvolutionA503 ferritic steel, thermal embrittlement (β = 0.00123 ºC-1)

● material state ● thermoelectric power

● microstructure evolution● phase transformation● hardening● embrittlement● elastic strain etc.

6.4

6.6

6.8

7.0

7.2

7.4

0 1 2 3 4 5 6 7 8 9 10 11 12Time [day]

Abs

olut

e Th

erm

oele

ctric

Pow

er [μ

V/ºC

] .

32

34

36

38

40

42

Tepm

erat

ure

[ºC] .

Absolute TEP Temperature

3 weeks at 450ºC

6.8

6.9

7.0

7.1

7.2

7.3

33 34 35 36 37Temperature [ºC]

Abs

olut

e Th

erm

oele

ctric

Pow

er [μ

V/ºC

] .

Example VI: Corrosion and Erosion½”-thick 304 austenitic stainless steel, thermal embrittlement (β = 0.00117 ºC-1)

● electric resistance● component state

● crack growth● corrosion● erosion etc.

32.0

32.2

32.4

32.6

32.8

33.0

0 5 10 15 20Time [day]

Res

istan

ce [µ

Ω] .

20

21

22

23

24

25

Tem

pera

ture

[ºC

] .32.0

32.2

32.4

32.6

32.8

33.0

0 5 10 15 20Time [day]

Res

istan

ce [µ

Ω] .

erosion events

Example VII: Creep Damage

1

1.1

1.2

1.3

1.4

1.5

2%0.

25% 2%

0.5%

0.25

% 1%0.

5% 1% 2%0.

25% 3% 1%

0.25

% 2% 3%0.

5% 1% 1% 3% 3%

Con

duct

ivity

[%IA

CS]

intact material

directionally solidified GTD-111

coarse grained GTD-111

● microstructure● plastic strain

● material state ● electric anisotropy

0.99

1

1.01

1.02

0 00.2

50.2

50.2

5

0.5 0.5

0.5 0.6 0.9 1 1 2 2 2

Creep Strain [%]

Ani

sotro

py F

acto

r

Conclusions

Electromagnetic methods offer unique opportunities for materials state awareness monitoring.

A variety of sensors can be built based on electric, magnetic, electromagnetic, and thermoelectric principles. These very simple and robust sensors can detect and quantitatively characterize subtle environmentally-assisted and/or service-related changes in the state of metals, such as microstructural evolution, phase transformation, plastic deformation, hardening, residual stress relaxation, increasing dislocation density, etc.

In most cases, the detection sensitivity is sufficiently high for the purposes materials state awareness monitoring and the feasibility of the sensing method is mainly determined by its selectivity, or the lack of it, to a particular type of damage mechanism.

Thank You!