Electromagnetic Materials State Awareness Monitoring

1. Electromagnetic Materials State Awareness Monitoring Peter B. Nagy Department of Aerospace Engineering University of Cincinnati Cincinnati, Ohio 45221-0070

2. Past and Present Goals Health 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

3. What can we predict? What can we monitor? Is there a sufficient finite set of parameters? prognostics community monitoring community Can a specific set of parameters be determined? Future Goals: Materials State Awareness Prognosis of Aircraft and Space Devices, Components, and Systems (Discovery Challenge Thrust, AFOSR, 2008) Problem Determine in real time the current stateso 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

4. What can we monitor? 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. What can we predict? Is there a sufficient finite set of parameters? prognostics community monitoring community Can a specific set of parameters be determined?

5. sensitivity selectivity What Can We Monitor? by electromagnetic means (measuring electric signals produced by electric, magnetic, or thermal stimulus) • ● microstructure • ● phase transformation • ● plastic strain • ● elastic strain • ● hardening • ● embrittlement • ● creep damage • ● fatigue damage • etc. • ● crack initiation • ● crack growth • ● impact damage • ● erosion • ● corrosion • etc. • ● electric conductivity • ● magnetic permeability • ● thermal conductivity • ● thermoelectric power • ● material state • ● component state • ● structure state • ● system state • ● service loads • ● environment • etc. • ● electric conductance • ● magnetic conductance • ● thermal conductance

6. NAC1 NAC2 NAF1 NAF2 NACF1 NACF2 NAT 15 3.0 10+0 . . 10-1 10 2.5 10-2 Magnetic Susceptibility Thermoelectric Power [μV/°C] AECC [%IACS] 5 2.0 10-3 0 1.5 10-4 -5 1.0 10-5 Alloy Designation Alloy Designation Alloy Designation • ● microstructure evolution • ● phase transformation • ● hardening • ● embrittlement • ● elastic strain • etc. • ● electric conductivity • ● magnetic permeability • ● thermoelectric power • ● material state Example I: Microstructure Evolution seven different nickel-base powder-metallurgy alloys (Ni, Al, Cr, Fe) after five different heat temper

7. ● microstructure evolution • ● phase transformation • ● hardening • ● embrittlement • ● elastic strain • etc. • ● electric conductivity • ● material state Example I: Microstructure Evolution NAF1-1 nickel-base powder-metallurgy alloy (70.5% Ni, 24.5% Al, 0% Cr, 5% Fe) room temperature

8. ● microstructure evolution • ● phase transformation • ● hardening • ● embrittlement • ● elastic strain • etc. • ● electric conductivity • ● material state Example I: Microstructure Evolution NAC2-1 nickel-base powder-metallurgy alloy (65.5% Ni, 24.5% Al, 10% Cr, 0% Fe) room temperature

9. 1500 1000 500 6 4 8 2 10 10 10 10 with opposite residual stress 0 service load Alternating Stress [MPa] • ● elastic strain • ● plastic strain • ● microstructure evolution • ● phase transformation • ● hardening • etc. without residual stress • ● material state • ● component state endurance limit • ● electric conductivity natural life time increased life time Fatigue Life [cycles] Example II: Elastic Strain residual stress assessment in surface-treated nickel-base superalloys

10. Al 2024 Al 7075 0.004 0.004 0.004 0.004 0.004 0.004 Ti-6Al-4V parallel parallel normal normal parallel 0.002 0.002 0.002 0.002 0.002 0.002 normal Δσ / σ0 Δσ / σ0 Δσ / σ0 Δσ / σ0 Δσ / σ0 Δσ / σ0 0 0 0 0 0 0 -0.002 -0.002 -0.002 -0.002 -0.002 -0.002 -0.004 -0.004 -0.004 -0.004 -0.004 -0.004 -0.002 -0.001 -0.001 -0.001 -0.002 -0.002 0 0 0 0 0 0 0.002 0.002 0.001 0.001 0.002 0.001 0.004 0.004 0.002 0.002 0.004 0.002 τua/ E τua/ E τua/ E τua / E τua / E τua/ E IN718 Waspaloy Copper parallel parallel parallel normal normal normal • ● material state • ● electric conductivity • ● elastic strain Example II: Elastic Strain electric conductivity versus uniaxial elastic strain in various metals

11. 200 0 -200 -400 -600 Residual Stress [MPa] -800 -1000 -1200 Almen 4A Almen 8A -1400 Almen 12A -1600 -1800 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Depth [mm] • ● elastic strain • ● plastic strain • ● microstructure • ● electric conductivity • ● material state Example II: Elastic Strain eddy current spectroscopy in shot-peened IN100 eddy current– solid circles, XRD – open squares κip = -1.06 (+33% “empirical” correction of AECC data)

12. 1.001 1.05 2 . static IN718 IN718 IN100 Waspaloy IN718 Waspaloy IN100 Waspaloy Normalized Electro-Elastic Coefficient Normalized Bulk Electrical Conductivity 1.000 1.00 1 Normalized Magnetic Permeability 0.999 0.95 0 Cold Work [%] Cold Work [%] Cold Work [%] 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 • ● piezoelectricity • ● magnetic permeability • ● electric conductivity • ● material state • ● plastic strain Example III: Plastic Strain effect of uniaxial plastic strain in various nickel-base superalloys at room temperature 300 kHz 500 kHz

13. 2.70 0.004 2.68 0.003 | 2.66 0.002 2.64 Magnetic Susceptibility AECC [%IACS] 0.001 2.62 2.60 0.000 RT RT 50ºC 50ºC 100ºC 100ºC 150ºC 150ºC 200ºC 200ºC 250ºC 250ºC intact intact • ● magnetic permeability • ● electric conductivity • ● material state • ● plastic strain Example III: Plastic Strain 304 austenitic stainless steel, 15% plastic strain

14. 1.6 0.6 intact 0.5 300 °C 350 °C 400 °C homogenized 450 °C 0.4 1.5 as-forged inhomogeneous 500 °C 550 °C 600 °C 0.3 650 °C 700 °C Conductivity [%IACS] Conductivity (AECC) Change [% ] 750 °C 0.2 1.4 800 °C 850 °C 900 °C 0.1 0 1.3 0.1 0.16 0.25 0.4 0.63 1 1.6 2.5 4 6.3 10 Frequency [MHz] Exposure Temperature [ºC] intact 300 350 400 450 500 550 600 650 700 750 800 850 1.2 • ● microstructure • ● elastic strain • ● electric conductivity • ● material state Example IV: Thermal Exposure microstructure evolution thirty-two as-forged Waspaloy specimens subsequent heat treatments of 24 hours thermal relaxation Waspaloy, Almen 8A, repeated 24-hour heat treatments at increasing temperatures

15. 25 20 8 15 series 1 (intact) series 2 (intact) 7 10 series1 (565 °C) series 2 (675 °C) 6 5 Magnetic Signature [nT] Magnetic Signature [nT] 5 0 before relaxation 0 2 4 6 8 10 12 14 16 4 relaxation at 235 ºC relaxation at 275 ºC relaxation at 315 °C 3 2nd relaxation at 315 °C 0 4 8 12 16 3rd relaxation at 460 °C Almen Intensity (A) Almen Intensity (A) 2 recrystallization at 600 °C • ● elastic strain • ● plastic strain • ● microstructure evolution • ● phase transformation • ● hardening • etc. 1 0 • ● thermoelectric power • ● material state Example VI: Thermal Relaxation noncontacting thermoelectric inspection shot-peened C11000 Copper shot-peened IN100

16. ● microstructure evolution • ● phase transformation • ● hardening • ● embrittlement • ● elastic strain • etc. • ● thermoelectric power • ● material state Example V: Microstructure Evolution A503 ferritic steel, thermal embrittlement (β = 0.00123 ºC-1)

17. erosion events • ● crack growth • ● corrosion • ● erosion • etc. • ● electric resistance • ● component state Example VI: Corrosion and Erosion ½”-thick 304 austenitic stainless steel, thermal embrittlement (β = 0.00117 ºC-1)

18. 1.5 directionally solidified GTD-111 1.4 intact material 1.3 Conductivity [%IACS] 1.2 1.1 1 coarse grained GTD-111 1.02 2% 3% 2% 3% 1% 1% 3% 3% 2% 2% 1% 1% 1% 0.5% 0.5% 0.5% 0.25% 0.25% 0.25% 0.25% 1.01 Anisotropy Factor 1 0.99 0 0 2 2 2 1 1 0.5 0.5 0.5 0.6 0.9 0.25 0.25 0.25 Creep Strain [%] • ● microstructure • ● plastic strain • ● electric anisotropy • ● material state Example VII: Creep Damage

19. 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.

20. Thank You!