Advαnced materials:

Self diagnosis & Self

healing

ΠΜΣ ΠΡΟΗΓΜΕΝΑ ΥΛΙΚΑ

Α. ΠΑΪΠΕΤΗΣ

Smart Materials &

Structures

Smart materials are designed

materials that have one or

more properties that can be

significantly changed in a

controlled fashion by external

stimuli, such

as stress, temperature, moisture, pH, electric or

magneticfields.

From Wikipedia, the free encyclopedia

Smart Materials &

Structures

Smart Materials respond in some way when an external effect such as light or temperature. The response can be reversed when the external effect is removed.

.

Piezoelectric materials are

materials that produce a voltage

when stress is applied. Since this

effect also applies in the reverse manner, a voltage across the

sample will produce stress within

the sample. Suitably designed

structures made from these

materials can therefore be made that bend, expand or contract

when a voltage is applied.

Smart Materials

Smart Materials

Shape-memory alloys and

shape-memory polymers are

materials in which large

deformation can be induced and recovered through

temperature changes or

stress changes

(pseudoelasticity). The shape

memory effect results due to respectively martensitic

phase change and induced

elasticity at higher

temperatures.

Magnetostrictive materials exhibit change in

shape under the influence of magnetic field and

also exhibit change in their magnetization under the influence of mechanical stress.

Magnetic shape memory alloys are materials that

change their shape in response to a significant

change in the magnetic field.

Magnetocaloric materials are compounds that

undergo a reversible change in temperature

upon exposure to a changing magnetic field.

Ferrofluid is a liquid that becomes strongly

magnetized in the presence of a magnetic field.

Smart Materials

pH-sensitive polymers are materials that change in

volume when the pH of the surrounding medium

changes.

Temperature-responsive polymers are materials

which undergo changes upon temperature.

Halochromic materials are commonly used

materials that change their colour as a result of

changing acidity.

Chromogenic systems change colour in response

to electrical, optical or thermal changes.

Smart Materials

Photomechanical materials change shape under exposure to light.

Polycaprolactone (polymorph) can be molded by immersion in hot water.

Self-healing materials have the intrinsic ability to repair damage due to normal usage, thus expanding the material's lifetime

Dielectric elastomers (DEs) are smart material systems which produce large strains (up to 300%) under the influence of an external electric field.

Thermoelectric materials are used to build devices that convert temperature differences into electricity and vice versa.

Smart Materials

The term “smart structures” is commonly used for

structures which have the ability to adapt to

environmental conditions according to the design

requirements. As a rule, the adjustments are

designed and performed in order to increase the

efficiency or safety of the structure.

Smart Structures

Combining “smart structures” with the

“sophistication” achieved in materials science,

information technology, measurement science, sensors, actuators, signal processing,

nanotechnology, cybernetics, artificial

intelligence, and biomimetics,[1] one can talk

about Smart Intelligent Structures.

Structures which are able to sense their

environment, self-diagnose their condition and

adapt in such a way so as to make the design

more useful and efficient.

Smart Structures

Morphing structures

Structural health

monitoring

SHM: Fibre Bragg Gratings

SHM: Fibre Bragg Gratings

SHM: Piezoelectric sensors

an active transmit

piezoelectric (PZT)

transducer sensor is

used to assess

damage, by transmission of a

guided wave and

reception of

reflections.

http://www.engineering.

leeds.ac.uk/ultrasound

SHM: Piezoelectric sensors

http://www.engineering.leeds.ac.uk/ultrasound

Self-diagnosis

Intrinsic property changes lead

to information about structural

integrity

Multifunctional materials

A multifunctional material is typically a composite or hybrid of several distinct material phases

each phase performs a different but necessary function, such as structure, transport, logic, or energy storage.

Because each phase of the material performs an essential function, and because there is little or no parasitic weight or volume,

multifunctional materials promise more weight-efficient, volume-efficient performance flexibility and potentially less maintenance than traditional multicomponent brass-board systems.

https://www.nae.edu/

HYBRID MULTISCALE

COMPOSITES

Nano-scaled fillers offer:

high axial elastic modulus

high aspect ratio

large surface area

excellent thermal and electrical

properties

Actuating capabilities

CarbonNanofibers

Multi-wallCarbon

Nanotubes

Single-wallCarbon

Nanotubes

HYBRID MULTISCALE

COMPOSITES

However, it is difficult to:

induce anisotropy with Nano-scale fillers

achieve high volume content

Instead the use of Hybrid Compositesmay:

exploit the excellent properties of nanoreinforcement

maintain all the advantages of traditional composites

CarbonNanofibers

Multi-wallCarbon

Nanotubes

Single-wallCarbon

Nanotubes

The goal…

Automotive/Aerospace Structures with

Improved Toughness & Fatigue properties

Integral Health monitoring Abilities

via

the incorporation of carbon nanotubes in the

composite matrix

The principle…

TOUGHNESS & FATIGUE LIFE ENHANCEMENT

The incorporation of a carbon nanotube network in the composite matrix may offer additional

energy dissipation mechanisms via

Increase of the interfacial area

Fibre debonding, bridging & pull out at

nanoscale

Crack bifurcation and arrest at the loci of failure

The principle…HEALTH MONITORING ABILITIES

The incorporation of a carbon nanotube network in the composite matrix may offer damage detection

abilities.

This network:

deforms according to the strain state of the composite

is interrupted at a the locus of any flaw created during

the loading of the composite

The mechanisms (i)CONCEPT OF STRAIN/ DAMAGE DETECTION

Introduction of CNTs in the matrix as sensors for matrix failure

R

Resistance Monitoring during Mechanical Loading

The mechanisms (i)Resistance vs. Strain for SWNTs

Armchair SWCNTs exhibit small resistance changes with strain

SWCNTs with lower symmetries exhibit more resistance sensitivity with strain, as the global strain leads to band gap changes

Experiments have shown larger resistance dependence with strain than theoretically expected

(Jien Cao et. Al., Phys. Rev. Lett., 90(15), 2003)

What is the situation with MWCNTs?

The mechanisms (i)Strain dependence of the CNT network

Filler Volume Fraction [%]

Ele

ctr

ica

l C

on

du

cti

vit

y [

S/c

m]

Percolation Threshold

The mechanisms (i)Strain dependence of the CNT network

Filler Volume Fraction [%]

Ele

ctr

ica

l C

on

du

cti

vit

y [

S/c

m]

The CNTs are 2 to 3 order of magnitude stiffer than the matrix

Far field matrix strain will result in the reduction of contacts/ breeching of the conductive paths

In the elastic region, these contacts will be reestablished

In the case of irreversible changes (yielding and /or cracking) these breeching will result to irreversible resistance increase

The mechanisms (ii)

Toughening mechanisms• Increase of the

interfacial area• Fibre

debonding, bridging & pull out at nanoscale

• Crack bifurcation

• Crack arrest at the loci of failure

• What is the toughening mechanism?• How does the increase in the interfacial area lead

to toughening?Drawings reproduced from: Matthews & Rawlings, Composite Materials

Engineering and Science, Woodhead Pub;ishers, Cambridge, England, 1999.

The mechanisms (ii)

Toughening mechanismsWhat is the toughening effect for CNTs that comprise

the same volume as a single carbon fibre?

Assumption: A Carbon Fibre and CNTs of the same volume are bridging the crack

The mechanisms (ii)

Toughening mechanisms

Wichtmann et al, Composites Science and Technology 68, 329–331, 2008

The mechanisms (ii)

Toughening mechanisms

•The CNT strength can be up to two orders of magnitude larger than that of the carbon fiber•substantial toughening can be attained by very small loadings

•1% CNT loading in the matrix of a typical composite would be responsible for almost twice the pull out energy than that attributed to the main reinforcement i.e. the carbon fibers, for a crack propagating perpendicular to the reinforcement.

(i) mechanical properties

FRACTURE TOUGHNESS

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25 30 35 40 45

Displacement (mm)

Lo

ad

(N

)

Epoxy

CNT 1%

0

0.1

0.2

0.3

0.4

0.5

0.6

Epoxy CNT 1% CNT 0.5% CNT 0.1%

GIc

(k

J/m

2)

Modified Beam Theory

Areas Method

Proof of concept

(i) mechanical propertiesFATIGUE

Proof of concept

(i) mechanical propertiesIMPACT

Proof of concept

(ii) damage sensing: Cyclic loading

TENSILE LOADING -

UNLOADING

-200 0 200 400 600 800 1000 1200 1400 1600-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

DISPLACEMENT

LO

AD

(K

Nt)

DIS

PL

AC

EM

EN

T (

mm

)

TIME (sec)

-200 0 200 400 600 800 1000 1200 1400 1600

-3

0

3

6

9

12

15

18

21

24

27

30

33

LOAD

0 250 500 750 1000 1250 1500 1750

200000

225000

250000

275000

300000

325000

350000

375000

400000

425000

RESISTANCE

RE

SIS

TA

NC

E (

Oh

m)

TIME (sec)

Proof of concept

(ii) damage sensing (cyclic loading)

TENSILE LOADING -

UNLOADING

0 10 20 30 40 50 60 70 80 90 100 1100.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

CNT DOPED

E/E

0

% OF MAXIMUM LOAD

0 20 40 60 80 100

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

1.05

0 10 20 30

75

80

85

90

95

100

% O

F IN

ITIA

L M

OD

UL

US

REMAINING RESISTANCE

(% OF INITIAL)

Proof of concept

(ii) damage sensing (Fatigue loading)

Proof of concept

(ii) damage sensing (Fatigue loading)

0.0 0.1 0.2 0.3 0.4 0.5

0.00

0.25

0.50

0.75

1.00

1.25

1.50Doped CFRP

Neat CFRP

R

/R [1]

W/W [%]

0.0 0.5 1.0 1.5 2.0-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

R

/R [

1]

W/W [%]

Doped Resin 0.3%

Doped Resin 0.5%

Doped Resin 1.0%

Proof of concept

(ii) Damage sensing (hydrothermal loading)

•The resistance change vs. weight gain is non monotonic.

•This reversal phenomenon is matrix dominated as it corresponds to approximately 1 % weight gain for the matrix (with or without carbon fibre reinforcement).

•There is a synergistic effect from the Carbon fibres and the CNTs that eliminates the phenomenon

SUMMARY

A new generation of hybrid composites is providing promising results for

Enhanced damage tolerance

Life cycle monitoring abilities

The hybrid composites incorporate CNTs in the matrix which is

improving toughness properties via the triggering of energy dissipation mechanisms at the nanoscale

Acting as an internal damage sensor through the creation of the percolated conductive network

Experimental results reveal

Spectacular improvement in fracture toughness

Enhanced fatigue properties

Enhanced impact and after impact properties

2

1

3

5

7

6

8

9

16

15

141312

11

10

4

I

V

PC-data acquisition

Digital multimeter

DC power supplyflaw

Image

constructionMatlab

42

# # # # # #

# # # # # # # # # #

# # # # # # # # # # # #

# # # # # # # # # # # # # #

# # # # # # # # # # # # # #

# # # # # # # # # # # # # # # #

# # # # # # # # # # # # # # # #

# # # # # # # # # # # # # # # #

# # # # # # # # # # # # # # # #

# # # # # # # # # # # # # # # #

# # # # # # # # # # # # # # # #

# # # # # # # # # # # # # #

# # # # # # # # # # # # # #

# # # # # # # # # # # #

# # # # # # # # # #

# # # # # #

ELECTRICAL POTENTIAL MAPPING: EPM

43

Induced impact damageEPM

Surface electrical measurementsBulk electrical measurements

2

1

3

5

7

6

8

9

16

15

141312

11

10

4

V

I

2

1

35

76

8

9

16

15141312

11

10

4

V I

44

EPM implementation

Bulk EPM

Surface EPMElectrical contacts via

Copper electrochemical plating

Electrical contacts via 1) Silver paint and 2) silver paste

45

EPM imaging

0 %

100 %

0 %

100 %

Bulk EPMSurface EPM

C-scan

Bulk EPMSurface EPM

C-scan

3 Joule LVI 5 Joule LVI

46Augusta-pzl SW - 4Application

47SW4 Tailwing testingOn site…

Artificial crack

48IR camera

stabilizer

patch

P2

P1

P2

P1

patch

IR camera

SW4 Tailwing testingOn site…

49

(a) – 480 kcycles

(b) –final image (561

kcycles)

ExperimentalOn-line

Self-healingFrom principles to applications

Why Self-healing?

• All matter is subject to thermal or mechanical destruction as well as chemical

degradation during its active lifetime

• The formation of damage is not problematic as long as it is counteracted by a

subsequent autonomous process of “removing” or “healing” the damage

• The healing potential of living organisms and the repair strategies in natural

materials is increasingly of interest to designers seeking lower mass structures with

increased service life, who wish to progress from a conventional damagetolerance philosophy

The principle

The ability to substantially return to an initial, proper operating state or

condition prior exposure to a dynamic environment by making the necessary

adjustments to restore normality and/or the ability to resist the formation of

irregularities and/or defects1.

Major characteristics of a self-healing system

Sense Respond Indicate

1Hartmut Fischer, Self-repairing material systems―a dream or a reality?, Natural Science 2 (2010) 873-901

Self-healing approaches

1Janet Sinn-Harion, Scott White, Ben Blaiszik, University of Illinois 2Image by Piyush Thakre, Alex Jerez, Ryan Durdle and Jeremy Miller, Beckman Institute3University of north Carolina at chapel hill

Capsule based Vascular Intrinsic

• Differ in healing mechanism

• Each have advantages and disadvantages

Capsule based

The Idea...Capsule-based model developed by Scott White

of the Beckman Institute, University of Illinois in 2001.

Capsule-based self-healing materials sequester the healing agent in discrete

capsules.

When the capsules are ruptured by damage, the self-healing mechanism is

triggered through the release and reaction of the healing agent in the region of

damage.

After release, the local healing agent is depleted, leading to a local healing event.

1H. Magnus Andersson and Gerald Wilson, Self-Healing Systems for High-Performance Coatings, 2011 Journal of Protective Coatings & Linings

Capsule based

Capsule based self-healing systems consist of (usually) two components:

• Monomer - 1

• Polymerizer/Catalyst - 2

Sequestration concepts

Encapsulated healing agentand a dispersed catalyst phase

Multicapsule systems, both healingagent and catalyst are encapsulated

Functional groups within the matrixphase that react with an encapsulatedhealing agent

Capsule based

The materials…

Microcapsule

1. Wall material2. Core material

• Urea-formaldehyde (UF)

• melamine-formaldehyde (MF)

• Melamine-urea formaldehyde (MUF)

• Polyurethane (PU)

• Poly-methyl methacrylate (PMMA)

• Epoxy resins

• Polydimethylsiloxane (PDMS)

3. Catalyst phase

(dispersed or encapsulated)

• Grubbs' catalyst

• Hexachloride (WCl6)

• Dimethyldineodecanoate tin (DMDNT)

Capsule based

Methods for preparing microcapsules

Emulsification Polymerization

√ High strength capsule shell walls with narrow size distribution

√ Large scale synthesis

X Difficult to encapsulate aqueous core

Layer-by-Layer Assembly

√ Compatible with aqueous or organic cores

X Poor structural integrity

Coacervation

√ Simple fabrication

X Low strength shell wall formation

Internal Phase Separation

√ Carbon rich polymers can be used

X Limited core/shell polymer combination

Capsule based

The design…

1. Encapsulation process 2. Integration 3. Characterization

4. Triggering 5. Healing evaluation

VascularThe Idea...

Inspired by the autonomous healing processes of living organisms

Network of refillable interconnected capillaries or hollow channels filled with

healing agent

Capillary ruptures, releases healing agent and heals damage site

Healing agent flows through channels (can be refilled externally)

J. F. Patrick, K. R. Hart, B. P. Krull, C. E. Diesendruck, J. S. Moore, S. R. White, and N. R. Sottos, Advanced materials, 2014

Based on the connectivity of the vascular network, there are two categories

of vascular self-healing material:

Vascular

1-D Networks

Easy to produce No inter-channel connectivity Empty channels created with

hollow glass fibers

Channels filled with healing agent

More connection points Decreased channel blockage Easier refilling after depletion Larger accessible reservoir for healing agent

2-D and 3-D Networks

Vascular

The materials…

Vascular based self-healing systems consist of (usually) two components:

• Monomer – 1

• Polymerizer/Catalyst - 2 } Matrix material = Healing agent

1. Monomer 2. Polymerizer

Image courtesy of Beckman Institute for Advanced Science and Technology

Vascular

Methods for preparing network structures

Hollow glass fibers (HGFs)

√ Easy to produce

√ Compatible with many standard polymer matrices

√ Inert to many popular self-healing agents

√ Use in composites due to their similar size and shape*

X Restricted to 1D connectivity

Direct-ink writing of a fugitive ink scaffold

√ Provides control over network shape and connectivity

√ Production of 2-D and 3-D networks

X Restricts the choice of matrix to materials that can be

formed around the fugitive scaffold

*In the case of carbon reinforced polymers, the integration of HGFs leads to a significant

reduction of mechanical properties.

Vascular

The design…

1. Development

4. Healing evaluation

2. Characterization

3. Triggering

Intrinsic

The Idea...

Matrix material acts as the healing agent

Repair is achieved though inherent reversibility of bonding of the matrix polymer

Healing at the molecular level

IntrinsicCategories:

• Self-healing polymers based on reversible reactionsTransformation from the monomeric state to the cross-linked polymeric state through

the addition of external energy.

• Self-healing from dispersed thermoplastic polymers

Self-healing in thermoset materials can be achieved by incorporating a meltable

thermoplastic additive.

• Ionomeric self-healing materialsIonic segments that can form clusters that act as reversible cross-links

• Supramolecular self-healing materials

Polymers capable of forming strong end group and/or side-group associations via

multiple complementary, reversible hydrogen bonds, resulting in a self-healing

elastomeric polymer

• Self-healing via molecular diffusionHealing is achieved via void closure, surface interaction and molecular

entanglement between the damaged surfaces

Intrinsic

Self-healing polymers based on reversible reactions

The most widely used reaction scheme for remendable self-healing

materials is based on the Diels-Alder (DA) and retro-Diels-Alder (rDA)

reactions

The Diels-Alder reaction is reversible. The equilibrium lies by far toward the

Diels-Alder adduct at lower temperatures and toward the diene and the

dienophile side at higher temperatures.

IntrinsicSelf-healing polymers based on reversible reactions

1. Polymer experiences damage1

2

33. Bond breakage and re-forming,

mends the damage

2. Heat is applied, polymer bonds are

broken and reformed

ΔΕ

Diels-Adler Reaction

Intrinsic

Ionomeric Copolymers

Material with ionic segments that can cluster and form cross-links

Much like reversible bonding method, but with ionic bonds

Requires ultraviolet radiation from external source from damage

itself to activate ionic segments

Intrinsic

Supramolecular self-healing materials

• Use of noncovalent, transient bonds to

generate networks

• Pull apart and reattach

• Requires no external stimulus

Advantages Vs Disadvantages

+

-

Capsules Vascular Intrinsic

• Easily integrated in most polymer systems

• Healing is triggered at damage site

• Freedom to use any healing agent

• Endless supply of healing agent

• Capable of healing large damage volumes

• Any site can be healed multiple times

• Does not require healing agent supply

• Some require only heat, some are 100% automatic

• Healing on a molecular level

• One healing cycle (healing agent is depleted upon a single damage event)

• Not sustainable• Agglomerations

• Requires external supply of healing agent

• Not completely automatic

• The integration in existing material systems is difficult

• Limited to small damage volumes

• External stimulus is required

Successful completion of the self healing process presents a complex

set of requirements on:

• Stable storage of liquid healing agent

• Mechanical triggering

• Release and transport of the healing agent

• Chemical triggering

• Polymerization

• Recovery of mechanical toughness

All the aforementioned requirements must occur without significantly

impacting the inherent properties of the material

Requirements for successful

Self healing process

Healing Efficiency

If “f” is the property of interest, healing efficiency (η) can be

defined as a ratio of changes* in the material property “f”:

Mechanical Characterization

• The ultimate goal is to demonstrate functional recovery in some

fashion

• Significant efforts have been made to develop a set of experimental

protocols that may be used to evaluate self healing materials in both

static and dynamic fracture conditions.

Static Fracture Testing

Fatigue Testing

Impact Testing

Methods based on:

Mechanical Characterization

Static Fracture Testing

For quasi-static fracture conditions, healing efficiency is defined in terms

of the recovery of fracture toughness 𝐾𝐼𝐶 :

1. Healing evaluation begins with a virgin fracture test of an undamaged specimen

2. The crack is then closed and allowed to heal3. After healing, the sample is loaded again until

failure (same loading conditions)4. At the end of the test, healing efficiency can

be calculated using the following equation:

Mechanical Characterization

Specimen geometries for such tests include:

Rectangular shaped specimens

Dog bone specimens

Single Lap shear

Tapered Double cantilever beam (TDCB)

Double cantilever beam (DCB)

Mechanical CharacterizationFatigue Testing

For dynamic fracture conditions, healing efficiency is defined in terms

of the life extension factor.

N is the number of fatigue cycles to failure

Crack length vs. fatigue cycles of in situ sample tested to failurein high-cycle fatigue regime

Mechanical Characterization

Impact Testing

Impact events can result in massive damage volume from several failure modes

such as puncture, delamination and mixed-mode cracking

Healing has been quantified by restoration of compressive strength (σ) by

compression-after-impact (CAI) testing

Compression after impact fixture

Self healing composites

Highway to…structure

Material

Matrix

Structure

Composite

Self healing composites

Materials Functionality

The self-healing strategy

Which type of healing material will be used? Type of damage needs to be healed?

Self healing composites

• Damage modes in composites are far more complex than those of pure

polymer systems

• Healing not only of the matrix material, but also of the interface between

the reinforcement and matrix

• Selection of appropriate healing approach (capsules, vascular, intrinsic)

• Embedment of healing agent into the polymeric matrix

Main considerations

A great many natural materials are themselves self healing composite materials!

Capsule based self healing composites

Self healing composites

The three types of specimens tested. (a) Reference specimen inwhich the healing agent is manually catalyzed and theninjected into the delamination. (b) Self-activated specimenwhere the catalyst is embedded within the polymer matrix andthe healing agent is manually injected into the delamination. (c)Self-healing specimen in which microcapsules of the healingagent and the catalyst are embedded into the polymer matrixand healing is autonomic.

• Microencapsulated healing agent and a solidchemical catalyst are dispersed within thepolymer matrix phase

• Healing is triggered by crack propagationthrough the microcapsules, which then releasethe healing agent into the crack plane

• Exposure of the healing agent to the chemicalcatalyst initiates polymerization and bonding ofthe crack faces

Typical loading curves for virgin

and healed reference specimens

M.R. Kesslera, N.R. Sottosc, S.R. White, Self-healing structural composite materials, Composites: Part A 34 (2003) 743–753

Self healing compositesCapsule based self healing composites

Benjamin J. Blaiszik , Marta Baginska , Scott R. White , and Nancy R. Sottos, Autonomic Recovery of Fiber/Matrix Interfacial Bond Strength in a Model Composite,

• Fibers destined to reinforce a composite material are coated with capsules that act as a repair system

• The capsules are filled with a liquid healing agent that spills out when a crack ruptures them

• The healing efficiency ( η ) is defined as the ratio of healed and virgin (interface shear strength) IFSS values Fibers coated with capsules

Schematic side view of a microbond

specimen with a self healing

functionalized fiber.

Load vs displacement for the virgin

and the healed specimenHealing efficiency

Self healing composites

Vascular self healing composites

Double cantilever beam (DCB) Mode I specimen

geometry. Note: all dimensions in mm; dashed lines

represent internal features

• Bio-inspired series of vascules incorporated into an FRP composite material facilitates the delivery of SHAs to exposed fractured crack planes

• Healing is effected by ring-opening polymerization (ROP) of an epoxy resin using novel metal triflate catalysts injected after Mode I crack opening displacement

• Strong adhesive compatibility with the host matrix confers full recovery of mechanical properties (>99% healing)

Tim S. Coope, Duncan F. Wass, Richard S. Trask, Ian P. Bond, Metal Triflates as Catalytic Curing Agents in Self-Healing Fibre Reinforced Polymer Composite

Materials, Macromol. Mater. Eng. 2014, 299, 208–218

Self healing compositesVascular self healing composites

(a) Hollow glass fibers; (b) hollow glass fibers

embedded in carbon fibre-reinforced

composite laminate; (c) damage visual

enhancement in composite laminate by

the bleeding action of a fluorescent dye

from hollow glass fibers

Initially, key failure interfaces were identified

Hollow fibre self healing network was designed for a

specific composite component and application

The self healing mechanism was found to restore 100% of the strength

a

b

c

Location of resin and hardener self-healing filaments intermingled

within an E-glass ply in the 16-ply stacking sequence of the

composite laminate

• Gap-filling scaffolds are created through a two-stagepolymer chemistry that initially forms a shape-conforming dynamic gel but later polymerizes to asolid structural polymer with robust mechanicalproperties

• Impacted regions that exceed 35 mm in diameterhave been healed within 20 min and restoredmechanical function within 3 hours

• After restoration of impact damage, 62% of the totalabsorbed energy was recovered in comparison withthat in initial impact tests

S. R. White, J. S. Moore, N. R. Sottos, B. P. Krull, W. A. Santa Cruz, R. C. R. Gergely, Restoration of Large Damage Volumes

in Polymers, SCIENCE VOL 344 9 MAY 2014

Self healing compositesIntrinsic self healing composites

Optical micrographs of a glass fibre

composite subjected to two impact and

heal cycles showing the closure of

damage in a healable matrix composite

(a) non-healed and (b) after healing.

• Optimized self-healing resin system used as a matrixfor high volume fraction glass fibre-reinforcedcomposites

• Healing in composites was determined by analyzingthe growth of delaminations following repeatedimpacts with or without a healing cycle

• The optimized resin system displays a healingefficiency of 65% after the first healing cycle,dropping to 35 and 30% after the second and thirdhealing cycles, respectively.

S. A. Hayes, W. Zhang, M. Branthwaite and F. R. Jones, Self-healing of damage in fibre-reinforced polymer-matrix composites, J. R.

Soc. Interface (2007)

Self healing compositesIntrinsic self healing composites

Interfacial healing concept. Maleimide functionalization

(blue triangles) of glass fiber within a furan-functionalized

(red notched trapezoids) polymer network will result in a

thermoreversible, and healable, fiber–network interface

• Reversible Diels–Alder reaction between afuran-functionalized epoxy-aminethermosetting matrix with a maleimide-functionalized glass fiber was used to impartremendability at the glass fiber reinforcedpolymeric composite

• Healing of the interface was investigated withsingle fiber microdroplet pull-out testing

• Following complete failure of this interface,significant healing was observed, with somespecimens recovering over 100% of the initialproperties

• Up to five healing cycles were successfullyachieved

Amy M. Peterson, Robert E. Jensen , Giuseppe R. Palmese, Thermoreversible and remendable glass–polymer interface for fiber-reinforced composites,

Composites Science and Technology 71 (2011) 586–592

Applications

Transportation: Cracks in the structure orcomponents of automobiles, airplanes, andspacecraft shorten vehicle life and cancompromise passenger safety.

Sporting Goods: Many consumers are willing to pay top dollar for high-quality fishing equipment, tennis rackets, helmets and other protective gear, boats and surfboards, skis, and other sports equipment.

Medicine: Once implanted in the body, prosthetics and other medical devices are difficult to monitor and access for repair.

Car painted with “Scratch Guard Coat”, NISSAN 2008

New scratches

One week later

Applications

Electronics: Polymer composite circuit boards and electronic components can suffer from mechanical and electrical failures if microcracks progress unabated.

Paints, Coatings, and Adhesives: Used in a wide variety of products, paints, coatings, and adhesives are subject to scratches, cracks and deterioration.

Schematic showing the reflow effect of self-

healing clear coats [Bayern, 2008]

Scratching

Heating

60-700C