120228 composites expo 2012

EXPANDING THE LIFETIME OF EPOXY COMPOSITES

FIBRE REINFORCED EPOXY COMPOSITE MATERIALS ARE USED IN A WIDE VARIETY OFHIGH DEMANDING INDUSTRIAL APPLICATIONS. THE COMPOSITE STRUCTURES BASED ONEPOXY RESIN BINDER SYSTEMS EXCEL THROUGH SUPERIOR CHEMICAL AND MECHANICALPROPERTIES VERSUS OTHER BINDER SYSTEMS. LONG TERM AND REPEATED EXPOSURETO CHANGING TEMPERATURES OR MECHANICAL STRESSES CAN HOWEVER INDUCEMICRO-CRACKING AND SUBSEQUENT EARLY BREAK OR LEAKAGE. THREE DIFFERENTTECHNOLOGIES WILL BE DESCRIBED THAT CAN HELP TO OVERCOME PREMATUREFAILURE THROUGH ABSORPTION OF CRACK ENERGY USING DUAL PHASE SYSTEMS.

Composite-Expo - 20125th International Specialized Exhibitionon composite materials and technologiesMoscow, RussiaToine Dinnissen, February 28th 2012

Toine Dinnissen, February 28th 2012

Outline

Epoxy Products in Fibre Reinforced PlasticsFailure & Mechanical Properties and Fracture

TheoryDuctility (Toughness) and How to enhance?

• Change Conditions• Change Network• Change Type of Stress

Dow Epoxy Toughening Platform• Rubber modification• Co-polymer modification• Core-shell rubber modification

http://upload.wikimedia.org/wikipedia/commons/2/28/STS-107_launch.jpg


D.E.R.™ Epoxy Resin in Composites

Features:• Excellent adhesion to many (difficult) substrates• Low shrinkage upon cure• Excellent Chemical Resistance• Excellent Mechanical Properties• Good Heat Resistance• …

Often used to produce light weight composite parts that can replace metal articles.e.g. FRP pipes, automotive parts, storage tanks, wind-mill blades, ….

™ Trademark of The Dow Chemical Company


Fibre Reinforced Plastics Primary Failure Modes

25%

14%

7%4%

15%

8%

6%

21% Environmental Stress Cracking

Notched Static Rupture

Chemical Attack

Thermal Degradation

Dynamic Fatigue

Creep/relaxation

UV Attack

Others

Material Causes

http://www.rapra.net/consultancy/product-design-and-manufacture-plastic-design-and-material-selection.asp

45%

20%

20%

15%

Human Causes

Data ex. Smithers Rapra

http://www.rapra.net/consultancy/product-design-and-manufacture-plastic-design-and-material-selection.asp


Mechanical PropertiesTensile Strength and Stiffness

Room temperature cured Epoxy = 20-30% stronger than Polyester. After post-cure the difference becomes even bigger. Polyester boats typically are not post-cured whereas epoxy boats are. Polyester boats often “post-cure” in service

Consequences;• Initial almost double strength of post-cured epoxy boats versus non PC PE• Cosmetics;

•Volume shrinkage epoxy about 2 % immediately•PE volume shrinkage up to 7% over longer period, “print through” effect


Micro-cracking / Fatigue Resistance

Maximum Strength is not the sole criteria, such load is seldom applied to for instance a hull. Micro-cracking occurs well before reaching ultimate strength.Loss of adhesion between binder and fibers and cracking away from the fibers into the binder.The Strain that a composite article can take before micro-cracking will depend on the adhesion binder-to-fiber and the toughness of the binderSuperior ability to withstand cyclic loading (Fatigue Resistance) is THE main advantage of Epoxy binder systems over Polyester or other binder system. This is the reason that in high demanding application predominantly epoxy binders are used.

Typical binder Stress/Strain curves(Post-cured for 5 hours at 80 °C)


Brittle Materials

Glassy thermosets, e.g. highly cross linked epoxy resins• Glass transition temperature is well above operating temperature• Brittle, catastrophic failure

Elastomeric thermosets• Tg is below operating temperature• No yielding; toughness due to stretching of molecules


Fracture Toughness

In material science Fracture Toughness is a property which describes the ability of a material containing a crack to resist fracture, and is one of the most important properties of any material for virtually all design applications.The fracture toughness is determined by the Stress Intensity Factor at which a thin crack in the material begins to growFracture toughness is a quantitative way of expressing a material's resistance to brittle fracture when a crack is present. If a material has much fracture toughness it will probably undergo ductile fracture. Brittle fracture is very characteristic of materials with less fracture toughness

KIc dimension Pa √ m


Ductile Materials

Ductility is a solid material's ability to deform under tensile stress, is an aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture.

Toughness is a balance of strength and ductility and is the ability to absorb mechanical (or kinetic) energy up to failure. It is the area under the stress –strain curve.


How to Enhance Ductility in Thermosets ?

Change the conditions• Temperature (operating Temperature versus Tg)• Strain Rate (how quickly do we apply the force)

Change the “Network”• Crosslink Density

Change the “stress-type”


Change Temperature / Strain Rate


Change the Polymer Network

Reduce the Crosslink Density:• Plasticisers

– Phthalates– Pine Oil– Hydrocarbon resins

• Flexibilisers– Flexible Epoxy Resin (e.g. XZ 92466.00 / D.E.R.™ 3913 epoxy resin)– Blocked Isocyanate pre-polymers– Acrylate functional urethane resins

• (Reactive-) Diluents– Mono-functional aliphatic (e.g. Polypox® R-24 / D.E.R. 721 epoxy resin)– Mono-functional aromatic (e.g. Polypox R-6 / D.E.R. 723 epoxy resin)– Bi-functional (e.g. D.E.R. 732P epoxy resin)– Multi (3/4) –functional (e.g. Polypox R-20 / D.E.R. 742 epoxy resin)



Change the Stress Type

Crack due to impact

or

Minor crack due to

repeated uses

brittle fractures have a distinctive fracture surface. The fracture surface of a brittle failure is usually reasonably smooth. The crack propagates through the material by a process called cleavage.The images on the right show the fracture surface of a steel that failed in a brittle manner

The ductility of the steel varies depending on the alloying constituents. Increasing levels of carbon decreases ductility (harder, stronger more brittle).

Rigid Matrix


Change the Stress type. How ?Toughening (increase ductility) of brittle Chromium (Vickers Hardness 1060 MPa)

by inclusion of Copper (Vickers Hardness 369 MPa)

The crack, propagating from left to right, has to deform the copper particle and to re-nucleate afterwards.The crack propagation energy is dissipated in the copper particle in all directions and has to re-concentrate before the cracking can continue

add Toughening agent


Dual / Secondary Phase Toughening

Secondary Phase Toughening; Properties of modifier Concentration Interfacial strength Particle size Poly-dispersity

Large crack due to impact

or

Minor crack due to repeated uses


FORTEGRA™ 201 Toughened Epoxy Resin

Carboxyl-Terminated Butadiene acrylo-Nitril copolymer (CTBN) – Liquid Epoxy Resin adduct technology

Reactive induced phase separation “process”Epoxy groups drive phase separation and lock in place the domains

FORTEGRA 201 vs. pure CTBN Chemical modification in Fortegra drives phase separationSmaller, more uniforms domains are formed

Toughness is increased more consistently

OO

CTBN rubber CTBN-LER rubber

2 µm




20-30% Free Liquid Epoxy Resin40% Elastomer ContentEEW: 320 – 360 gr/eqViscosity: 150,000 – 230,000 mPa.s @ 25°C




8 layer E-glass (7 hours at 70°C) Reference Sample

Glass Transition temperature [°C] 86 85

Fracture Energy GIc [J/m2 ]ASTM D-5528

820-1060 1970-2350

Fatigue See Graph

Shear Modulus (GPa)Straight Edge, ± 45° laminate

7.8 8.1

Clear Casting (7 hours at 70°C Reference Sample

Formulated Epoxy Resin 76.3 63.4

Formulated Amine Curing Agent 23.7 24.1

FORTEGRA 201 Toughened Epoxy 0 12.5

Resin Viscosity 1400 2800


Fracture toughness KIc [Pa √ m ]ASTM D-5045

0.75-0.85 2.8-3.2




220K760K



FORTEGRA™ 100 Epoxy Toughener

Block copolymer technology

Self-assembly “process”• Dependant upon

- the formulation e.g. type of curing agent, amount of fillers etc. - the curing conditions e.g. temperature, time etc.

“epoxyphilic”“epoxyphobic” Addition in epoxy

formulation and curing




100% ToughenerEEW: NAViscosity: 3,000 – 4,000 mPa.s @ 25°C

Clear Casting (2 hours @ 90°C plus 4 hours @ 150°C)

Reference Sample

D.E.R.™ 330 Epoxy Resin 43.1 49.3

Anhydride Curing Agent 45.9 44.7

FORTEGRA 100 Toughener 0 5




0.61-0.77 1.57




6 layer E-glass (24 hours @ 90°C) Reference Sample


Amine Curing Agent 23.7 21.9

FORTEGRA 100 Toughener 0 5




Fatigue See Graph


7.8 7.4



FORTEGRA™ 301 Toughened Epoxy ResinCore-shell rubber technology

Mono-dispersed (single) secondary particles are formed from the start

Dow’s unique dispersion technology

Pre-fabricated




8 layer E-glass (7 hours at 70°C) Reference Sample



820-1060 1360-1620

Fatigue See Graph


7.8 7.3

Clear Casting (7 hours at 70°C) Reference Sample


Amine Curing Agent 23.7 22.5

FORTEGRA 301 Toughened Epoxy 0 33.3




0.75-0.85 3.4-3.7

85% Free Liquid Epoxy Resin15% Core Shell Rubber (CSR)EEW: 206 – 216 gr/eqViscosity: 68,000 – 72,000 mPa.s @ 25°C

3,000 – 4,000 mPa.s @ 50°C



FORTEGRA™ Epoxy Toughening

OO

FORTEGRA ™ 100 series

Self-assembled block copolymer

FORTEGRA ™ 201

CTBN-LER adduct

FORTEGRA ™ 301

Core-shell rubber

During cure

PreformedDuring cure

20 – 100 nm 1 – 2 µm 300 nm

Viscosity 1600 2800 2240Ref resin is 1400

More “Forgiving” (easier to use)



Portfolio

FORTEGRA ™ 100 series

(block copolymer - BCP)

FORTEGRA 100 100% BCP FORTEGRA 100

FORTEGRA 102 50% BCP in LER FORTEGRA 383-50

FORTEGRA 104 12% BCP in SER FORTEGRA 664-12

FORTEGRA 200 series

(CTBN-LER adduct)

FORTEGRA 201 40% CTBN (in adduct) N/A

FORTEGRA 300 series

(Core-shell rubber - CSR)

FORTEGRA 301 15% CSR in LER N/A

5 – 10% toughener, NOT toughening agentWhat does this mean? FORTEGRA 100 5% by weight in the formulationFORTEGRA 201 12.5% - 25% by weight in the formulationFORTEGRA 301 33% - 66% by weight in the formulation


3 families of toughening agents• Based on three different technologies• Varying degree of robustness• Varying impact on viscosity

Can be used in; Composites,(Powder) Coatings,CastingsFloorings

FORTEGRA™ in Epoxy CompositesReliability and Durability is Increased !!!Resistance to (sudden) impact

• Fracture Toughness KIc

Resistance to long-term changing load• Fatigue Resistance



Контакты

ЗАО "НЕО Кемикал"Юлия Ташкинова

[email protected](8313) 32-06-74, 33-68-68, 32-59-63

Дау Юроп, Московское ПредставительствоДмитрий Белобородов[email protected]

Dow Europe GmbHToine Dinnissen

[email protected]

mailto:[email protected]




Mechanical Properties ComparisonBlack Steel Stainless Steel

316Hastelloy® C GRP

(Mat & Roving)Density [gr/cm3] 7.8 7.9 8.9 1.5Tensile Modulus [GPa] 207 193 180 10-15

Tensile Strength [MPa] 450 590 550 120-250

Heat Conductivity [W/mºC] 46 15 12 0.2

Thermal Expansion Coefficient [mm/mm ºC]x10-6

12 16 12 23

PE PP PVC PVDF GRPDensity [gr/cm3] 0.95 0.90 1.4 1.75 1.5Tensile Modulus [MPa] 80 80-130 300-350 1200 10,000-15,000

Tensile Strength [MPa] 30 30 60 50 120-250

Heat DistortionTemperature [ºC]

40 45 75-100 90 100-200

All data are typical data and not to be construed as specifications


Fibre Reinforced Composites

Property Epoxy Unsaturated Polyester (UPR) and Epoxy Vinyl Ester Resin (EVER)

Phenolic

Cure mechanism Polymerization of resin plus hardener

Catalytic copolymerization

CondensationPolymerization

(produces water)Wet impregnation, typical

systemLiquid resins plus amine

or other hardenersStyrene-modified resins plus peroxide

catalystsLiquid phenolics plus acid

catalystsCure temperature (°C) 25-150 25-100 25-170

Typical cure time (min) 60-180 10-60 60-180Stability of resin (alone) Excellent Fair Poor

Cure-shrinkage of system Low (2-3%) High (6-8%) High

Adhesion to metal Excellent Fair Fair

Physical properties of cured laminate

Excellent Excellent Excellent/Bad (best heat resistance, most brittle)

All data are typical data and not to be construed as specifications


Fatigue Testing

1. Run standard tensile testing and determine the stress at break (SBREAK)

2. Run fatigue test series at a fraction of the maximum stress the specimen could withstand (S)• Sinusoidal loading in tension-tension• R = min. load / max. load = 0.1/1 = 0.1• Test Frequency = 5 Hz• 4” gauge length

Record the amount of cycles after which the specimen fails

Max load

min load

1 cycle

X

X

X


Back-up Fracture-modes

Schematic appearance of round metal bars after tensile testing.(a) Brittle fracture(b) Ductile fracture after local necking(c) Completely ductile fracture


Compact Tension Testing of Epoxies

ASTM Standard D 5045)

fracture

)W/a(fBWPK 2/1

maxc1 =

Pnax = load at failureB = sample thicknessW = lengtha = crack lengthf(a/w) is geometry dependentStrain energy release rate

21

1 (1 )cc

KGE

ν 2= −

(plane strain)

Stress intensity factor

proportional to fracture toughness (J/m2)


Amphiphilic block co-polymer self-assembly

+ Epoxy

Epoxy Miscible Block Epoxy Immiscible Block

Vesicle+ Epoxy Matrix

Amphiphilic block copolymer toughening phase

Spherical micelle

Wormlike micelle

120228 composites expo 2012

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