Governed by resin's chemistry. Determines the
compatibility between a resin and fiber or between a
resin and a fiber's surface treatment. Poor adhesion
leads to poor fatigue properties and premature
Determines ratio between first microcracks in matrix
and ultimate failure of laminate. (I.e.
Polyester/glass woven roving begins cracking at .2%
elongation, but fails at 2%. This means the designer
can only use 10% of the ultimate strength of the
laminate.) Resin microcracks lead to shorter lifetime
by accelerating delamination and exposing fabric to
Shrinkage While Curing
Affects dimensional stability of a component. Also
dictates level of residual stress left in a part due
to manufacturing (higher % reduction in volume
results in higher internal compressive stresses).
Some matrices experience dramatic changes in material
properties as a result of hydrolysis. I.e. Polyester
when soaked in water for 1 year exhibited only 65% of
its original strength.
Matrix should withstand exposure to harsh chemicals
like gasoline, lubricants, and various cleaning
solutions while retaining almost all of its original
Affects how easy it is to "wet out" a material. Lower
viscosity resins tend to be easier to work with.
Discussion of Researched Resin Types
Impacts if used on Racecar
Polyesters are low viscosity resins based on
unsaturated polyesters dissolved in a reactive
monomer, generally styrene. They generally cure in
the presence of heat and a catalyst through a cross
linking process. They typically have "tailorable"
properties (i.e. excellent UV resistance when used
with a styrene-MMA blended monomer, effective flame
retardancy when incorporating halogens, etc...). As a
general rule, they are lacking in dimensional
stability while curing (shrinkage of up to 8%) and
have low mechanical properties (strength of adhesion,
bulk material strength, elastic modulus, etc...). In
addition, polyesters exhibit decreased strength in
the presence of water due to the high tenancy of of
ester groups to be hydrolyzed. Nonetheless, polyester
is a very popular resin due to its low cost, ease of
manufacturing (low viscosity makes lay-up easier),
and ability to have custom tailored properties.
Positive impacts on racecar would be lower cost and
easier manufacturing procedures. Almost all other
facets of performance would be less than desirable.
Poor adhesive properties and less than ideal behavior
in wet environments would result in decreased part
life and possible unsafe behavior in the very likely
event of a high-speed cone impact.
Vinyl ester is similar chemically to polyester, but
has reactive sites primarily at the ends of molecular
chains (like epoxy). This difference increases the
toughness/resiliency of vinylester as the whole
length of the molecular chain is used to disperse
shock loadings. Also, vinyl has fewer ester groups,
making it less susceptible to degredation by water
than polyester. Unfortunately, vinylesters usually
require elevated temperature post-cure to obtain full
mechanical properties. Like polyester, dimensional
instability while curing is still an issue (shrinkage
of up to 8%). Regardless, vinylester is an excellent
intermediate step in between polyester and epoxy in
terms of mechanical properties, ease of application,
Vinylester would yield slightly reduced performance
relative to epoxy in fatigue, damage tolerance, and
stability in varying environmental conditions, but
would result in lower overall system cost.
Epoxy has very good adhesive properties, strength,
toughness, and resistance to environmental
degredation. Ring groups at the centers of molecules
enable epoxy to endure both mechanical and thermal
stresses better than resins that use linear groups.
Toughness is increased by locating reactive sites at
the end of molecular chains, like vinylester, but
Ethylene Oxide groups are used instead of esters.
This also contributes greatly to its resistance to
water. Epoxy also exhibits low shrinkage during
curing (1.2-4% by volume). However, since curing of
epoxy is an additive process (one in which hardener
is attached, or "added" to the ends of epoxy
molecules), it requires that extra attention be paid
to the mixture ratio. Any "unused" amine or epoxy
molecules will never cure. This is in contrast to
ester based resins which undergo a "catalyzed"
cross-linking in order to cure. Finally, epoxy's
relatively high viscosity also increases the
difficulty in manufacturing.
Racecar components would see increased fatigue life,
toughness, strength, stiffness, and resistance to
creep if epoxy were used as a matrix. In addition,
components would be rugged enough for use in the
presence of water, gasoline, oil, etc.. Primary
downsides would be increased manufacturing effort and