Self Healing Materials

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Self Healing Materials

• Nick Strandwitz
• E MCH 597A
• Structural Health Monitoring

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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Self Healing Concept

• Sensing and actuation with no human intervention.
• Material should gain some fraction of the initial
  strength after healing.
• Bonus Sensing and actuation also provide means
  for detection. (not required)

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Living Systems

• A common goal in self healing materials is the
  modeling and mimicking of the human body and
  other living systems.
• The human body and other living systems have
  amazing potential for self healing which we hope
  to bring to these new materials.

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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Microsphere Embedment

• Microshpere capsules are embedded in material
  along with a catalyst
• Sensing is done by microspheres
• Actuation is chemical release

White, S.R., et al., Autonomic healing of polymer
composites. Nature, 2001. 409 p. 794-797.
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Microsphere Healing

• The contents of the microspheres interacts with
  the catalyst, forming a glue like bond
• Crack inducing stress must be relieved for the
  healing to take place
• Process usually takes 24-48 hours

SEM image of broken microsphere
White, S.R., et al., Autonomic healing of polymer
composites. Nature, 2001. 409 p. 794-797.
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Results of microsphere embedment
Figure 4. Stress strain curve for virgin and
healed woven composite
Figure 5. Multiple healings shown in a stress
strain curve.
Kessler, M.R. and S.R. White, Self-activated
healing of delamination damage in woven
composites. Composites Part A, 2000. 32 p.
683-699.
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Conclusions Microsphere Embeddment

• Average healing efficiency of only about 12
• Catalyst, and microsphere clustering causes
  less polymerization
• Manufacturing of material is very difficult and
  expensive
• More research is required before real world
  applications are exercised

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Materials With Potential for Microsphere
Embeddment

• Composites
• Woven Glass Fibers
• Reinforced Unidirectional
• Polymers
• Polymer Composites

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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Tube Embedment

• Very similar to microsphere embedment
• Sensing/Actuation the same Tubes crack when a
  crack develops, releasing chemical to seal the
  crack

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Healing of ECC

• Engineered Cementitious Composite
• Concrete that displays some yield strength
• Normal concrete would need large diameter glass
  fibers, which would change the mechanical
  properties
• Glass fiber filled with Superglue, an air curing
  sealant

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Glass Fiber Embedment

• Embedded fiber and concrete were cracked using
  method shown, as well as a cyclic flexural method

Li, V.C., Y.M. Lim, and Y.-W. Chan, Feasiblilty
study of a passive smart self-healing
cementitious composite. Composites Part B, 1998.
29B p. 819-827.
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Glass Fiber Embedment

• More realistically, fibers were uniformly
  deposited throughout the ECC and tested
• Different volume fractions were tested as shown

Li, V.C., Y.M. Lim, and Y.-W. Chan, Feasiblilty
study of a passive smart self-healing
cementitious composite. Composites Part B, 1998.
29B p. 819-827.
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Results Fiber Embedment

• All samples exhibited maintained stiffness
• Specimens suffered stiffness degradation of
  10-40

Li, V.C., Y.M. Lim, and Y.-W. Chan, Feasiblilty
study of a passive smart self-healing
cementitious composite. Composites Part B, 1998.
29B p. 819-827.
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Conclusions Fiber Embedment

• Glass fiber embedment exhibits potential for self
  healing
• Further development must be done
• Testing of sealing capability
• Methods to fill and seal fibers
• Different sealing agents (such as those used in
  microspheres)

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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Electrohydrodynamics

• Voltage applied across inner and outer tube
• Damage causes an increase in current density at
  the location of the damage
• Increased current density causes particle
  coagulation at damage site

Slowik, M.A., Research Self-Healing Materials
Using Electrohydrodynamics. 2002, Princeton
University.
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Electrohydrodynamics

• Colliodal (polystyrene) particals do not
  completely fill cracks
• NiSO4 can be dispersed as well to
  electrochemically deposit in small voids

Slowik, M.A., Research Self-Healing Materials
Using Electrohydrodynamics. 2002, Princeton
University.
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Damage Detection

• Electrohydrodynamics can be very valuable for
  monitoring purposes
• Voltage or current can be monitored for changes
  that occur during damage

Slowik, M.A., Research Self-Healing Materials
Using Electrohydrodynamics. 2002, Princeton
University.
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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Shape Memory Alloys

• Shape memory alloys such as Nitinol
  (nickel-titanium) exhibit the self healing effect
  when heated
• Before heating the material tends to have low
  yeild strength
• After heating to a certain temperature the
  material returns to the original state
• In returning to the original state, large forces
  can be generated

Ni, W., Y.-T. Cheng, and D.S. Grummon, Recovery
of microindents in a nickel-titanium shape memory
alloy A "self healing" effect. Applied Physics
Letters, 2002. 80(18) p. 3310-3313.
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Applications of SMAs

• Forces created in returning to original shape can
  be large, making SMAs useful as actuators (most
  frequent use)
• Any material prone to moderate damage, that
  cannot be reached for repair
• Aerospace latching mechanisms
• Microvalves
• Skin simulators

http//www.memory-metalle.de/html/01_start/index_o
uter_frame.htm
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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Healing Agents

• A very important part of self healing materials
  is the healing agent
• Microspheres relied on a Grubbs catalyst and DCP
  (dicyclopentadiene)
• This process utilized ROMP (ring opening
  metathesis polymerization)
• Useful because of high reactivity and high degree
  of cross-linking (high strength)

Rule, J.D. and J.S. Moore, ROMP Reactivity of
endo- and exo-Dicyclopentadiene. Macromolecules,
2002. 35 p. 7878-7882.
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Healing Agents

• Fiber embedment method shown used Superglue
  (thermoplastic monomer) for its air curing
  capabilities
• This was merely used to show potential and better
  healing agents should be developed and tested

Rule, J.D. and J.S. Moore, ROMP Reactivity of
endo- and exo-Dicyclopentadiene. Macromolecules,
2002. 35 p. 7878-7882.
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Healing Agents - Problems

• Inappropriate mixing during actuation
• Heterogeneous dispersion of catalyst
• Exhausted polymer supply
• Crack propagation occurs in region of little
  polymer/catalyst
• Temperature must be below 200 F, but too low
  temperature slows reaction
• Polymer has already reacted
• Occasionally air cured polymers will have already
  reacted before actuation (cracking)

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Healing Agents

• Much research is being done on polymers/monomers
  with potential for applications in self healing
  materials
• More research is currently being done on
  different matrix materials, dispersion methods,
  and healing agents

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Potential Applications of Self Healing Materials

• Civil Structures (cementitious composite)
• Composite materials for
• Aerospace applications
• High quality sporting equipment
• Anything that cannot be reached for repair at the
  moment of damage
• Microelectronics
• Medical uses
• To detect a breech in a glove, gown, etc., using
  electrohydrodynamic technology
• Tools (Nitinol)

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Future of Self Healing Materials

• Healing particles from micro to nano scale
• Develop more re-healing capable polymers
• High strength
• High reactivity only when desired
• Micro-channels, modeled after the circulatory
  system
• Material could use a system of veins to
  distribute healing agent intelligently

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Self Healing Materials

• Self Healing Concept
• Microsphere embedment
• Tube embedment
• Electrohydrodynamics
• Shape memory alloys
• Polymer role
• Future uses and developments

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Sources Self Healing Materials