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Tensile Strength Of Epoxies
Santa Rosa Junior College
Engineering 45
Peter Breyfogle, Michael Eddy, Ben Valdovinos, Ibrahim Mansour
9 December 2009
History of Epoxies
www.axminster.co.uk/images/products/ZPOX5_l.jpg
• The word epoxy is derived from two Greek prefixes - epi,
which means "upon" and oxy, which means
"sharp/acidic".
• The first commercial attempts to prepare resins from
epichlorohydrin were made in 1927 in the United States.
Credit for the first synthesis of bisphenol-A-based epoxy
resins is shared by Dr. Pierre Casta of Switzerland and Dr.
S.O. Greenlee of the United States in 1936.
History
• Dr. Castan's work was licensed
by Ciba, Ltd. of Switzerland,
which went on to become one
of the three major epoxy resin
producers worldwide.
• Ciba's epoxy business was spun
off and later sold in the late
1990s and is now the advanced
materials business uni of
Huntsman Corporation of the
United States.
Applications
•
•
•
•
•
•
•
Paints and coatings
Adhesives
Industrial tooling and composites
Electrical systems and electronics
Consumer and marine applications
Aerospace applications
Art
Epoxy-Paintings and Coatings
• "2 part waterborne epoxy coatings"
are used as ambient cure epoxy
coatings.
• These non-hazardous, two-part epoxy
coatings are developed for heavy duty
service on metal substrates and use
less energy than heat-cured power
coatings.
• The coating dries quickly providing a
tough, UV resistant, protective coating
with excellent ultimate hardness, and
good mar and abrasion resistance.
• They are designed for rapid dry
protective coating applications.
www.prestwich.ndirect.co.uk/.../epoxyresin.jpg
Epoxy-Paintings and Coatings
• Low volatility and water clean up.
– factory cast iron
– cast steel
– cast aluminum applications
• For automobile and industrial uses
• Polyester epoxies are used as powder coating
for washers, driers and other "white goods".
• Epoxy coatings are also widely used as primer.
– improve the adhesion of automotive and
marine paints
– Metal cans and containers are often
coated with epoxy to prevent rusting.
product-image.tradeindia.com/.../Epoxy-Paint.jpg
Epoxy-Adhesive
http://www.made-in-china.com/showroom/magpow/productdetailDoBxteiJOEYF/China-Super-Strong-Epoxy-Adhesive-Glue-.html
• Epoxy adhesives are a major part of the
class of adhesives called "structural
adhesives" or "engineering adhesives"
• Exceptional adhesives for wood, metal,
glass, stone, and some plastics
• Can be made flexible or rigid,
transparent or opaque/colored, fast
setting or extremely slow setting
• Some epoxies are cured by exposure to
ultraviolet light. Such epoxies are
commonly used in optics, fiber optics,
optoelectronics and dentistry.
• Used in the construction of aircraft,
automobiles, bicycles, boats, golf clubs,
skis, snow boards,.
– and other applications where high
strength bonds are required
Epoxy-Industrial Tooling and Composites
• Used in producing fiber-reinforced or composite parts.
• This "plastic tooling" replaces metal, wood and other traditional
materials, and generally improves the efficiency.
• Lowers the overall cost
• Shortens the lead-time for many industrial processes
• Epoxy systems are used in industrial tooling applications.
– Produce:
• Molds
• master models
• Laminates
• castings
• Fixtures
• and other industrial production aids.
Epoxy-Industrial tooling and composites
http://www.directindustry.com/prod/master-bond/epoxy-casting-resin-17407198115.html
http://esciencenews.com/files/images/200903261308930.jpg
Epoxy-Electrical Systems and Electronics
• employed in motors, generators,
transformers, switchgear, bushings, and
insulators
• epoxy resins are the primary resin used
in overmolding integrated circuits,
transistors and hybrid circuits, and
making printed circuit boards.
• Flexible epoxy resins are used for potting
transformers and inductors.
• The cured epoxy is an electrical insulator
and a much better conductor of heat
than air.
• Transformer and inductor hot spots are
greatly reduced, giving the component a
stable and longer life than unpotted
product.
http://www.robotroom.com/Flashing-Sneakers/Epoxy-Encapsoluted-CircuitWith-Coin-Cell.jpg
Epoxy-Consumer and marine applications
• Amateur building projects including
aircraft and boats
• Epoxy materials tend to harden
somewhat more gradually, while
polyester materials tend to harden
quickly.
• Epoxies are used for commercial
manufacture of components where a
high strength/weight ratio is required
• Polyester thermosets typically use a ratio
of at least 10:1 of resin to hardener (or
"catalyst"), while epoxy materials
typically use a lower ratio of between 5:1
and 1:1.
• Used during boat repair and assembly
• Sold as:
– separate resin and hardener
– repair resins for marine applications
http://www.morrison-marine.com/service_and_repair_
project_pages/epoxy_current/epoxy2.jpg
Chemistry of Epoxy
•Epoxies consist of two components
•Part A consists of an epoxide (resin)
•Part B is the curing agent (hardener)
•A chemical reaction occurs between the two
parts generating heat and hardening the mixture
into a hard inert plastic.
Part A: Resin
• Most epoxy resins are produced from a reaction between
epichlorohydrin and bisphenol.
• When epichlorohydrin and bisphenol-A mix together to form
a covalent bond, the resulting polymer is rigid and strong.
• Also used for protective coatings, high performance
composites, and adhesives.
Part B: Hardener
• Hardeners consist of Polyamine monomers
• Play a major role in:
–
–
–
–
–
Tensile Strength
Compression
Gel Time
Viscosity
Demolding Time
Mix
• Most epoxies mix at a 1-1 ratio
• Allows consumers to measure by eye-balling.
• Measure by either volume or weight, depending on
the epoxy.
• Extra resin or hardener weakens the epoxy.
• Other specialized epoxies require other ratios and
more careful measuring.
Mix
• After being mixed together the epoxy goes through a
curing process.
• Process can be controlled through temperature and
choices of resin and hardener compounds.
• The curing process can take minutes to hours.
• Some formulations benefit from heating during
curing.
• Others simply require time, and ambient
temperatures.
Epoxy
• Epoxy adhesion is due to the strong polar bond the
epoxy makes with the surface.
• After the two epoxy parts are combined there is a
working time (pot life) during which the epoxy can be
applied or used.
• The pot life will be anywhere from minutes to one
hour or longer.
Facts
• After cured, epoxies can handle temperatures well
below freezing.
• They mostly soften at about 140°F, but will harden
when cooled.
Our Project
• Our purpose was to test the tensile strength of six different
types of epoxy
– In addition to the base epoxies, two epoxy-carbon fiber
composite samples were tested
• To contrast the behavior of epoxies under tension, we tested a
sample of Nylon 101
Procedure
1. Cast a mold in the shape required by the
tensile strength testing machine.
2. Use this mold to cast the epoxies into tensile
specimens.
3. Test to find the yield and tensile strengths, as
well as Young’s Modulus of Elasticity for each
epoxy.
Making the Mold
•The mold was made using a Silicone
RTV system.
•This system is a TAP plastics
proprietary two-part silicone that
need to be mixed together.
• After mixing, the solution was
poured into a rectangular column
with the original standing upright in
the middle
• After 48 hours, the silicone solution
sets in the desired shape
Casting the Tensile Specimens
• Six epoxies were tested for this experiment
• Devcon 5-minute
• Shafting Epoxy
• System 3
• Devcon 5-minute gel
• Devcon 2-ton with carbon fiber strips
• Devcon 2-ton with chopped carbon fibers
The four Devcon epoxies were generously donated by the
Devcon company.
http://www.devcon.com
Devcon 5-Minute
Tensile Yield Strength: 1860 PSI
Ultimate Tensile Strength: 1860 PSI
Modulus of Elasticity: 179,977 PSI
Devcon 5-min
2000
1800
Stress (PSI)
1600
1400
1200
1000
800
600
400
200
0
0
0.002
0.004
0.006
Strain
0.008
0.01
0.012
0.014
Shafting Epoxy
Tensile Yield Strength: 1504 PSI
Ultimate Tensile Strength: 1504 PSI
Modulus of Elasticity: 108,169 PSI
Shafting Epoxy
1600
1400
Stress PSI
1200
1000
800
600
400
200
0
0
0.002
0.004
0.006
Strain
0.008
0.01
0.012
0.014
System 3
Tensile Yield Strength: 1310 PSI
Ultimate Tensile Strength: 1540 PSI
Modulus of Elasticity: 67,874 PSI
System 3
1800
1600
Stress (PSI)
1400
1200
1000
800
600
400
200
0
0
0.02
0.04
0.06
0.08
Strain
0.1
0.12
0.14
Devcon 5-Minute Gel
Tensile Yield Strength: 300 PSI
Ultimate Tensile Strength: 598 PSI
Modulus of Elasticity: 57,622 PSI
5-Min Gel
700
600
Stress (PSI)
500
400
300
200
100
0
0
0.01
0.02
0.03
0.04
Strain
0.05
0.06
0.07
Devcon 2-ton with Carbon Fiber
Strands
Tensile Yield Strength: 1774 PSI
Ultimate Tensile Strength: 1774 PSI
Modulus of Elasticity: 223,899 PSI
Devcon 2-ton w/CF
2000
1800
1600
Stress (PSI)
1400
1200
1000
800
600
400
200
0
-0.002
0
0.002
0.004
Strain
0.006
0.008
0.01
Devcon 2-ton with Chopped Carbon
Fibers
Due to a sizable air bubble running throughout the length of the tube,
the Devcon 2-ton with chopped carbon fibers failed before any
meaningful data could be collected.
Nylon 101 and Silicon
Tensile Yield Strength: 1184 PSI
Ultimate Tensile Strength: 3774 PSI
Modulus of Elasticity: 161,724 PSI
Nylon 101
4000
3500
Stress (PSI)
3000
2500
2000
1500
1000
500
0
0
0.02
0.04
0.06
0.08
0.1
Strain
0.12
0.14
0.16
0.18
0.2
Tensile Strength of Epoxies
Comparitive Stress Strain Curves for all Samples
4000
3500
3000
Stress (PSI)
Nylon 101
Devcon 2-ton
w/CF
5-Min gel
2500
2000
System 3
Tennis Club
1500
Devcon 5min
1000
500
0
-0.02
0
0.02
0.04
0.06
0.08
0.1
Strain
0.12
0.14
0.16
0.18
0.2
Tensile Strength of Epoxies (Zoomed)
Comparitive Stress Strain Curves for all Samples
2500
2000
Stress (PSI)
Nylon 101
Devcon 2-ton
w/CF
5-Min gel
1500
System 3
Tennis Club
1000
Devcon 5min
500
-0.005
0
1E-17
0.005
0.01
Strain
0.015
0.02
Conclusion
• Tensile Strengths
The epoxy with the highest yield strength was the Devcon 5minute epoxy, which tested at a maximum of 1860 PSI, and a
Young’s Modulus of 179,977 PSI
The Devcon 2-ton with the addition of carbon fiber strands
came in second place, with a maximum tensile strength of
1774 PSI, and a Young’s Modulus of 223,899 PSI
The System 3 epoxy yielded the third highest tensile strength of
1540 PSI, and a Young’s Modulus of 67,874 PSI, followed
closely by the Shafting Epoxy, which failed at a maximum
tensile strength of 1504 PSI, and a Young’s Modulus of
108,169.
The quick-set 5 minute epoxy failed at a tensile strength of 598
PSI, and a Young’s Modulus of 57,622 PSI resulting in the
lowest maximum tensile strength and Young’s Modulus.
Errors and Oversights
1. Air Bubbles
Air bubbles presented a major issue throughout this experiment. Since the epoxy was being
poured into the mold lengthwise, it was almost impossible to completely eliminate bubbles
from the tensile specimens, no matter how slowly and carefully the epoxy was poured.
Air bubbles seemed to be the leading cause of most of the failures.
Only the System 3 epoxy failed at the most narrow point, which means that
defects acted as stress raisers.
Examination of the break-surface of the other specimens showed the failure radiated
from the imperfection
To try and eliminate the amount of air bubbles
in the shafts, we could have elevated the
temperature at which the epoxy was poured,
cast it in a vacuum, or had a different mold setup.
Image from Materials
Science and
Engineering: An
Introduction
By Callister, 7th ed
2. Surface Defects
A surface defect (probably due an air bubble) on the surface of the Devcon 5minute Gel caused the failure to happen at a considerable distance from the
expected break point
Works Cited
•Materials Science and Engineering: An Introduction
By Callister, 7th ed
•http://en.wikipedia.org/wiki/Epoxy
•http://www.epotek.com/
•http://www.hempel.com/Internet/InecorporateC.nsf/vHEMPELDOC/085E68EB4DA0
1C29C1256EBB0034D1C1?OpenDocument&1
•http://www.absoluteastronomy.com/topics/Epoxy
•http://www.epoxyandepoxyflooring.com/epoxyresins/epoxyresins.htm
•http://www.epoxyproducts.com/25points4u.html