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Thermo-mechanical evaluation of self-healing metallic structures for aerospace

vehicles utilizing shape memory alloys

Investigators:

M. Clara Wright, NASA KSC1

Michele Manuel, University of Florida2

Terryl Wallace, NASA LaRC3

Team members: Charles Fisher2, Glenn Bean2, Oscar Figueroa III2,3,

Jeff Sampson1, Thad Johnson1, Roy King1, Peter Marciniak1,

Andy Newman3

NASA Aeronautics Research Institute FY12 Seedling Phase I Technical Seminar

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Outline

•The innovation: SMASH technology

•Liquid-assisted self-healing approach

•Impact of the innovation

•Results of the Seedling Phase I effort

•Distribution/dissemination

•Future work

July 9-11, 2013 NASA Aeronautics Research Institute FY12 Seedling Phase I Technical Seminar 2

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Shape Memory Alloy Self-Healing(SMASH) Technology

• Designing and testing an aeronauticallightweight structural alloy with self-repairing capabilities

– Materials system can self-repair cm-longcracks

• Investigation focused on self-repair of fatiguecracks

– Aluminum alloy matrix reinforced with high-strength shape memory alloy (SMA) elements

– Thermodynamic approach to design matrixalloy with pre-determined fraction of lowmelting eutectic phase

July 9-11, 2013 NASA Aeronautics Mission Directorate FY12 Seedling Phase I Technical Seminar 3

Catastrophic failure of theforward fuselage of an A-10aircraft test article during

fatigue testing

M. Creps et. Al., IncorporatingAluminum Hybrid Materials to

Facilitate Life Extension inLegacy Aircraft, Airworthiness

2012 proceedings

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Liquid-Based Self-Healing of Metal-MetalComposites


• Clamping force from the SMA wires

• Partial liquefaction of the matrix

Manuel, M.V, Principles of Self-Healing in Metals and Alloys: An Introduction, Chapter in Self-Healing Materials: Fundamentals,Design Strategies and Applications, Ghosh, S. K., Ed. Wiley: 2008;.

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Manuel, et al, “Design Considerations for Matrix Compositions in Self-Healing Metal Matrix Composites.”3rd International Conference on Self-Healing Materials; June 27-29, 2011; Bath, England.

• Healing of cm-long cracks has been achieved in aproof-of-concept Sn-Bi matrix reinforced with Ni-TiSMA wires

Liquid-Based Healing History


169ºC

Sn-21wt% Bi

– Healing treatment: 20%liquid in matrix

– Post heal: 95% strengthrecovery (UTS)

Virgin

Post-heal

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Knowledge Gap

• POC material showed liquid-assisted self-repair of overload cracks

– Will self-healing work with a higher strengthstructural material?

– Will liquid-assisted self-repair work for repairingfatigue cracks?

– How is fatigue life affected by this technology?


McDanels et al, NASA KSCFailure Analysis and Materials Evaluation

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Heinimann et al, Alcoa, “Advanced Metallic and Hybrid Structural Solutions for Light-Weight, Long-Lived Aerospace StructuresAircraft Airworthiness & Sustainment Conference 2012

Applications

• Aerospace-grade aluminum materials subject to cyclic loading aresusceptible to fatigue failure, sometimes catastrophic, at loadswell below yield strength.

• Wrought and cast Al alloys used throughout aircraft:


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Impact of Innovation

• Improve damage tolerance and fatigue life of metalsat critical structural locations

• Alternative to conventional repair techniques offatigued structures

– Mechanically fastened, bonded, etc.

• Integrated self-repairing approach would improvedurability and sustainability of the aerospacematerial to ensure vehicle safety


Implications could revolutionize theindustry and other NASA programs

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Technical Approach

• The principal objectives of Phase I:

1. Fabricate a high specific strength aluminum-based metalmatrix composite that can repair cracks using liquid-assistedself healing

a. Targeting specific microstructural constituents based onthermodynamics and kinetics of the system.

b. Testing various fabrication techniques for optimal performance

2. Characterize the mechanical behavior of the novel aluminummatrix constituent and composite before and after healing

a. Primarily tensile and fatigue testing

3. Explore and optimize the reinforcement architecture forcomposites reinforced in a uniaxial and cross-ply orientation.


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Phase I Results

• Fabricated, tested, and healed overload and fatigue cracks inproof-of-concept tin-bismuth (Sn-Bi) composite.

• Proved self-healing in a cast binary Al-Si matrix alloy with pre-determined eutectic phase and 2 vol% Ni-Ti SMA wires.

• Fatigue tested the self-healing binary Al-Si alloy to create a stresslife (S-N) curve.

• Fabricated two Al-Cu alloys with a pre-determined eutecticphase for self-healing: binary Al-Cu & ternary Al-Cu-Si.

• Fabricated multi-ply test samples of Al-Cu-Si alloys byisostatically hot pressing thin slices of the matrix andsandwiching SMA reinforcements at the interface.


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Results: POC Material

• Fatigue tested proof-of-concept tin-bismuth (Sn-Bi)material to establish use of technology for cyclicallyloaded applications.


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Healing Fatigue Crack in POC


Proved healing of fatigue crack in POC

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Systematic Alloy Design

• Thermodynamicapproach usedto design binaryalloy.

– Castability

– Eutectic Temp

– Strength

• Samples werecast in graphitemold


Manuel et al, “Design Methodology for Liquid-Assisted Self-Healing Materials”4th International Conference on Self-Healing Materials, Ghent, Belgium, June 2013

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Healing in Al-Si alloy

• Binary Al-3Si cast at750

oC;

– 2 vol% NiTi SMA wires

– Microstructuralstabilization heattreatment

– Tensile tested, healingtreatment, tensiletested again


Proved self-healing with over 90% UTSrecovered

0.5 cm

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Results: Healing in Al-Si

• Microstructure showed uniform eutectic phasedistribution and adequate wire bonding.

– Eutectic phase distribution ideal for liquid-assisted healing


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Results: Al-Si Fatigue Behavior

• Fatigue tested theself-healing binary Al-Si alloy to create a S-Ncurve.

– Significant variability indata due to porosityfrom fabricationtechnique

– No effect of fatigueloading on SMA wires


Cast binary alloy fatigue behavior was determined

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Results: Al-Si Fatigue Behavior

• Conducted fatigue crack growth tests on middle tension M(T) andsingle edge notch tension ESE(T) specimens to grow and heal asmall fatigue crack.– Cracking occurs preferentially through eutectic along grain boundaries both

pre- and post- healing.


Healed binary Al alloy fatigue crack

500μm 500μm 500μm

• Healing of micron-scale fatigue cracks, as well as macro-scale machined notches achieved

• Fatigue crack growth rate decreased after healing;dotted line represents healing treatment

VirginFatigued Healed Re-Fatigued

Pre-heal Post-heal

200μm

Inter-granularEutectic

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Results: Al-Cu alloys

• Fabricated two Al-Cu alloys with a pre-determinedeutectic phase for self-healing:

– Binary Al-Cu & ternary Al-Cu-Si.


0

20

40

60

80

100

120

140

0 0.01 0.02 0.03 0.04 0.05

Str

es

s(M

Pa

)

Strain

Al-9Cu-2Si

Al-10Cu

Al-3Si

• Al-Cu alloys more brittle than the Al-3wt%Si in tension

• Little healing was evident in either Al-Cu or Al-Cu-Si alloys.

• It is theorized that the lack of ductilitydid not allow for themartensiteaustenite transitionwithin the SMA wire, and thereforeno closure force was put on thematrix from the SMA wire.

• Without a clamping force to close thefracture faces, healing was unable tooccur.

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Results: Diffusion Bonding Fabrication

• Fabricated multi-ply test samples of Al-Cu-Si alloys byisostatically hot pressing thin slices of the matrix andsandwiching SMA reinforcements at the interface fordiffusion bonding.

– Eliminates casting defects

– Potential for improved strength and ductility

– Composites with more complex wire geometries can befabricated


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Multi-ply Specimens


• Up to four plies with three reinforcement layers atthe interfaces were successfully fabricated.

Viable fabrication technique for multi-ply specimenswas established

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Distribution/Dissemination

• Submitted for NASA New Technology Report for futurepatent application.

• International Conference of Self Healing Materials, Ghent,June 2013, Design Methodology for Liquid-Assisted Self-Healing Metals.

• Team will also continue to present results at relevanttechnical presentations (MS&T 2013, TMS 2014), write atleast one peer-reviewed journal article, and be submittedfor inclusion in NASA technical publications such as TechBriefs.

• The technology will be showcased at KSC’s nextinnovation day.


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Next Steps

• Phase II research will include:

– Full development and characterization of the fatigue lifebehavior of the Al-Cu base alloys fabricated withunidirectional, multi-ply SMA reinforcements.

– Modeling of the multi-ply specimens to determineoptimal wire reinforcement and SMA clamping forces forhealing using SMA-specific finite element analysis (FEA).

– Fabrication of multi-ply specimens with optimal wirereinforcement and heat treatment to demonstratemulti-axis crack closure and healing of tensile andfatigue cracks.


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Optional Funding

• Design, model, andfabricate a small scaleprototype with morecomplex geometry basedon vehicle parts that haveshown a history of fatiguecracking in the field.


Team is requesting the additional $75K to create a self-repairing prototype and bring TRL to 4.

Aluminum alloy 7075-T73 landing-gear

torque-arm assemblythat was redesigned to

eliminate fatiguefracture at a lubrication

hole.

Nose wheel forkfailed whenplane was in

service.

ASM Failure Analysis Center, Case Histories in FailureAnalysis, 2024-T3

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Phase II Team

• KSC – project management, fatigue testing,characterization

• LaRC – specimen fabrication, healing

• University of Florida – master alloy creation,fabrication, testing, healing of tested specimens

• Northwestern University – FEA models


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