This document summarizes self-healing composite materials. It discusses various self-healing strategies such as microencapsulation of healing agents, hollow glass fibers to transport agents, and microvascular networks for distribution. Microencapsulation and hollow glass fibers are described in more detail. Applications include reducing maintenance costs for civil structures and improved durability of composite materials for aerospace and sports equipment. While progress has been made, full strength recovery has not been achieved and manufacturing of self-healing composites remains challenging.

1. SELF HEALING OF COMPOSITE
MATERIAL
By
LAKSHI NANDAN BORAH
Mechanical department
Material and Manufacturing Technology
2017-22-404
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2. INTRODUCTION
• Self-healing materials
• are artificial or synthetically-created substances that have the built-in ability
to automatically repair damage to themselves without any external diagnosis
of the problem or human intervention.
• A material with the ability to heal itself automatically.
• Proposed in 1980s as a means of healing invisible micro cracks.
• COMPOSITE MATERIAL
• Also called a composition material or shortened to composite.
• It is a material made from two or more constituent materials with significantly
different physical or chemical properties that, when combined, produce a
material with characteristics different from the individual components.
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3. Why self-healing?
• Traditional repairs are expensive!
• to design (never two the same)
• to implement (removal from service or in-situ repair)
• to certify & monitor (additional inspection often required) throughout
remaining operational life.
• Sense and respond to damage, restore performance without affecting
inherent properties.
• No human intervention required.
• Provide early means of detection of damage.
• It is like modelling and mimicking of the human body and other living
systems which have the ability to self heal.
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4. NEED OF SELF HEALING MATERIALS
• Built in capability to substantially recover their load transferring
ability after damage.
• Contribute greatly to the safety and durability of polymeric
components.
• Capable of continuously sensing and responding to damage over the
lifetime.
• Restoring the material performance.
• Offers great opportunities for broadening the applications.
• Refer to the recovery of properties such as fracture toughness, tensile
strength.
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5. Strategies of self healing materials
• Microencapsulated healing agent.
• Micro vascular network.
• Hollow fibre approach.
• Dissolved thermoplastics.
• Reversible chemical reactions
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6. STRATEGIES OF SELF HEALING MATERIALS
• Extrinsic self-healing mechanism
• microcapsule self-healing mechanism,
• vascular network self-healing mechanism.
• Intrinsic self-healing mechanism
• Presence of healing agent and catalyst are not requisite.
• Molecular level due to the low Tg of thermoplastic polymers.
• The heating and cooling process will lead to molecular inter-diffusion,
randomisation, recombination of chain ends, etc.
• More competitive in terms of end products manufacturing and
applications.
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7. Microencapsulation of healing agent
A microencapsulated healing agent is embedded in a
composite matrix containing a catalyst capable of
polymerizing the healing agent.
1. Cracks form in the matrix wherever damage occurs.
2. The crack ruptures the microcapsules, releasing the
healing agent into the crack plane through capillary
action.
3. The healing agent contacts the catalyst triggering
polymerization that bonds the crack faces closed.
4. Also possible at Nano scale
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8. 11-02-2018 8
(Source: Self-healing flexible
laminates for resealing of puncture
damage, smart materials and
structures, 2009.)

9. Materials used
There are several constituent materials which, when combined
function as self healing material system:
• Healing Agent: Dicyclopentadiene (DCPD)
• Microcapsule shell: Urea–formaldehyde (UF) (mean 166µm diameter)
• Chemical Catalyst: Bis(tricyclohexylphosphine) bensylidine ruthenium (IV)
• Flexiblizer: Heloxy 71, Shell Chemical Company used to improve
toughness and crack growth stability.
• Polymer Matrix: Epoxy Polymer Matrix EPON 828
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10. MICROCAPSULE SELF-HEALING MECHANISM
• Dual capsule self-healing system
• Instead of having polymer resin filled capsules and catalyst,
• Encompasses monomer and polymerizer/hardener,
• Encapsulated separately and embedded into composite.
• The crack forms and ruptures the capsules, the monomer will be polymerized
when it comes into contact with hardener and eventually heal the cracks.
• Mono capsule self-healing system
• Using solvents such as methanol and ethanol in healing the cracks of
thermoplastic polymers.
• Using the same healing concept, only solvent filled capsules into
thermoset polymer matrix.
• The solvent worked as a wetting agent on the polymer surface, causing
the bulk polymer material to swell which led to reptation & interlocking
of the chains across the crack plane
• Finally, liquid solvent will then fill up the cracks and healing is achieved.
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11. ADVANTAGES OF CAPSULATION
• A key advantage of the microencapsulation self-healing approach is
the ease with which they can be incorporated within a bulk polymer
material.
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DISADVANTAGES
• Need for microcapsule fracture and the need for the resin to
encounter the catalyst.
• Limited amount of healing agent.

12. Hollow glass fibre repair mechanism
12
• This is very important for thermosetting
composite matrices.
• Hollow fibres filled with a reactive fluid.
• Same as microcapsules.
• This system used two sets of HGFs
embedded at varying layer intervals
within a fiber reinforced laminate.
• Each set of hollow fibers was filled with
one part of a two-part resin-hardener
system.
• Each part of the healing chemistry was
diluted with a solvent.
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13. ADVANTAGES OF HGF
• The fibres can be located to match the orientation of the surrounding
reinforcing fibres thereby minimising Poisson ratio effects.
• higher volume of healing agent is available to repair damage
• different resin can be used.
• visual inspection of the damaged site is feasible.
• hollow fibers can easily be mixed and tailored with the conventional
reinforcing fibers.
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DISADVANTAGES
• Fibers must be broken to release the healing agent
• Low-viscosity resin must be used to facilitate fiber infiltration
• use of hollow glass fibers in carbon fiber-reinforced composites will lead to CTE
(coefficient of thermal expansion) mismatch.
• multistep fabrication is required.

14. Vascular network self-healing mechanism
• One-dimensional vascular network self-healing system
• Two- and three-dimensional network self-healing system
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15. Micro vascular network
• Material could use a system of veins
to distribute healing agent
intelligently.
• This approach relies on a centralized
network (microvascular network) for
distribution of healing agents into
polymeric systems in a continuous
pathway.
• The bio-inspired design delivers
healing agent to cracks in a polymer
coating via a three-dimensional
micro-vascular network embedded
in the material. Crack damage is thus
healed repeatedly. This can also
ensure continuous delivery of
healing agents for self-repair from a
additional reservoir.
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16. DISADVANTAGES
• Fabrication process is complex
• It is very difficult to achieve synthetic materials with such networks
for practical applications.
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• This technique can be applied to highly crosslinked thermosets.
• Numerous different healing chemistries and encapsulation techniques
make the healing mechanism tunable and hence, suitable for
different matrices.
ADVANTAGES

17. Dissolved thermoplastics
• Thermally activated self-healing approach.
• Dissolved in the polymer matrix, resulting in a homogeneous system.
• Triggered by a rise in temperature and pressure so that the
thermoplastic healing agent can move and fill the cracks.
• Need for external pressure to heal the cracks.
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(SOURCE:Iee Lee Hia “Self-Healing Polymer Composites”)

18. Reversible chemical reactions
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• Demonstrated self-healing properties of furanemaleimide polymers.
• Bis-maleimide tetrafuran can be used.
• Using a DA reaction and electrical resistive heating of carbon fibres.
• 100% strength recovery under certain conditions.
• Heating was achieved using resistivity of carbon fibres.

19. Electrohydro-dynamics
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NiSO4 can be electrochemically dispersed into the small voids present in the
system.
Voltage applied across inner and outer surfaces.
Damage causes an increase in current density at the location of the damage
Increased current density causes particle coagulation at damage site

20. Design of self-repair materials
1. The material must be subjected to gradual deterioration, for
example by dynamic loading that induces micro cracks;
2. The fibre must contain self-repair fluid;
3. The fibres require a stimulus to release the repairing chemical;
4. A coating or fibre wall must be removed in response to the
stimulus; and
5. The fluid must promote healing of the composite damage.
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21. Mechanical properties recovery
• Fracture property
• Impact property
• Fatigue property
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22. Potential Applications of Self Healing Materials
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• Civil Structures (Engineered cementitious composite)
• Tools (Nitinol)
• Space applications
• Self healing coatings for steel structure
• Composite materials for:
Aerospace applications
High quality sporting equipment
Microelectronics
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23. Results & Shortcomings
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• The Maximum strength recoverable till date is about 75-80%.
• 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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24. CONCLUSION
• The problem of damage initiation, propagation & tolerance has
limited the acceptance of composite materials in all engg. disciplines.
• Nature has developed materials with healing potential over years.
• Self healing approaches applied in composite materials to-date are
primarily bio-inspired.
• More recent advance is the study of natural healing to allow
biomimetic self-healing.
• Reinforcements extend the concept of healing beyond repair of
matrix dominated failure modes.
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25. REFERENCES
• First published as an Advance Article on the web 10th January 2008 By Richard P. Wool
“Self-healing materials: a review”.
• M.R. Kessler, N.R. Sottos, S.R. White, 2008 “Self-healing structural composite materials”.
• R. Das, C. Melchior, K.M. Karumbaiah, University of Auckland, Auckland, New Zealand;
2National Polytechnic Institute of Chemical Engineering and Technology (INP-ENSIACET),
Toulouse, France“Self-healing composites for aerospace applications”.
• Guoqiang Li and Harper Meng, Woodhead Publishing Series in Composites Science and
Engineering: Number 58 “Recent Advances in Smart Self-healing Polymers and
Composites”.
• R.S Trask, H R Williams & I P Bond 2007 SELF HEALING POLYMER COMPOSITES:
Mimicking nature to enhance performance U.K: University Of Bristol, Bristol. BS8 1TR
Department of Aerospace Engineering.
• Rajesh Purohit, Neelesh Kumar Gupta, Murli Raj Purohit, Akshat Patil,R.K.Bharilya,
Swadesh “An Investigation on manufacturing of self-healing materials”.
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26. REFERENCE CONTINUE…
• Carrere, P., Lamon, J., 2003. Creep behaviour of a SiC/Si-B-C composite with a
self-healing multilayered matrix. Journal of the European Ceramic Society 23 (7),
1105-1114.
• Chunlin, C., Kara, P., Yulong, L., 2013. Self-healing sandwich structures
incorporating an interfacial layer with vascular network. Smart Materials and
Structures 22 (2), 025-031.
• Dry, C., Sottos, N.R., 1993. Passive smart self-repair. In: Varadan, V.K. (Ed.),
Polymer Matrix Composite-Materials. Smart Materials: Smart Structures and
Materials 1993, vol. 1916, pp. 438-444.
• Deng, G., Tang, C., Li, F., Jiang, H., Chen, Y., 2010. Covalent cross-linked polymer
gels with reversible sol-gel transition and self-healing properties. Macromolecules
43 (3), 1191-1194.
• Espinosa, L.M., Fiore, G.L., Weder, C., Johan Foster, E., Simon, Y.C., 2015. Healable
supramolecular polymer solids. Progress in Polymer Science 49-50.
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