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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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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)
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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.
Toine Dinnissen, February 28th 2012
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”
Toine Dinnissen, February 28th 2012
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)
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 201 Toughened Epoxy Resin
20-30% Free Liquid Epoxy Resin40% Elastomer ContentEEW: 320 – 360 gr/eqViscosity: 150,000 – 230,000 mPa.s @ 25°C
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 201 Toughened Epoxy Resin
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
Glass Transition temperature [°C] 93 91
Fracture toughness KIc [Pa √ m ]ASTM D-5045
0.75-0.85 2.8-3.2
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 201 Toughened Epoxy Resin
220K760K
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
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
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 100 Epoxy Toughener
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
Resin Viscosity 9000 8000
Glass Transition temperature [°C] 142 140
Fracture toughness KIc [Pa √ m ]ASTM D-5045
0.61-0.77 1.57
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 100 Epoxy Toughener
6 layer E-glass (24 hours @ 90°C) Reference Sample
Formulated Epoxy Resin 76.3 73.1
Amine Curing Agent 23.7 21.9
FORTEGRA 100 Toughener 0 5
Resin Viscosity 1400 1600
Glass Transition temperature [°C] 86 84
Fracture Energy GIc [J/m2 ]ASTM D-5528
Fatigue See Graph
Shear Modulus (GPa)Straight Edge, ± 45° laminate
7.8 7.4
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 100 Epoxy Toughener
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
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
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 301 Toughened Epoxy Resin
8 layer E-glass (7 hours at 70°C) Reference Sample
Glass Transition temperature [°C] 86 80
Fracture Energy GIc [J/m2 ]ASTM D-5528
820-1060 1360-1620
Fatigue See Graph
Shear Modulus (GPa)Straight Edge, ± 45° laminate
7.8 7.3
Clear Casting (7 hours at 70°C) Reference Sample
Formulated Epoxy Resin 76.3 39.2
Amine Curing Agent 23.7 22.5
FORTEGRA 301 Toughened Epoxy 0 33.3
Resin Viscosity 1400 2200
Glass Transition temperature [°C] 93 82
Fracture toughness KIc [Pa √ m ]ASTM D-5045
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
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
FORTEGRA™ 301 Toughened Epoxy Resin
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
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)
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
™ Trademark of The Dow Chemical Company
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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
Toine Dinnissen, February 28th 2012
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)