Question:
What are composite materials?
COMPOSITES by the literal meaning of the word are something made
from a collection of parts or elements. In the case of the racing car or
aerospace industry the term is applied generally to two categories of
materials. Metals as in things like metal matrix composites
-- and fiber/ resin combinations like polyester resin and glass fibers (commonly
called fiber glass) or epoxy resin and carbon fibers (commonly called
carbon fiber).
Most of the time when composites are talked about it is the
resin fiber stuff that is the center of the discussion.
The background of this technology can be explained a few different
ways the method we will use a comparative analogy to something that occurs
in nature combined with a simplification of some physics. One of the
materials that is relatively light and strong and occurs in nature is wood.
Wood has for a long time been one of our (human for most of us) species
most versatile engineering material. We have constructed everything from
vehicles that float fly and drive to houses, bridges and weapons out of
wood. Wood is basically a collection of cellulose fibers that are
intertwined and bonded together with the resins that the plant makes as it
grows. The next factor to consider is that materials generally fail due to
flaws in the surface that make inclusions into the atomic structure
creating stress concentrations when loads are applied. If you create a
sample of material without flaws you get the material in its strongest
form, so a chain created of one atom joined to the next in a long line,
like in a fiber, is the strongest form you can get of the base material.
Of course it isn't a perfect world so a single atomic chain is tough to
build so we do the next best thing and make thin fibers of the material
that give us something close to the optimum atomic chain arrangement. If
these fibers can be fastened together into a structure (something like wood) we get a strong light weight engineering material.
So we have two components to composite materials, the fiber material
and the binding resin. If we go a step further and closely match the yield
strength of both fiber and resin then we have optimized the materials
strength properties. Sounds simple - - so what's all the hype about
composites --- Well if you get the right fibers ( CARBON ) and the right
resin (High Strength Epoxy ) in combination you can get an order of
magnitude strength of about 7 times that of steel with about half the
weight of aluminum.
Sounds like the perfect high performance material to
build race cars out of. In fact it is a terrific material to build things
like jet fighter aircraft race cars aerospace products etc. There is of
course a catch - - like any other exotic material cost is right in there
with the performance aspect of the material "high".
At this point in time most of the methods used in the manufacture of
structures from these materials tend to be either labour intensive and/or
require elaborate high tech machines. The other additional factor is that
the process cannot be hurried --- the many stages to the process plus the
atomic cross-linking that takes place in the resin system when it cures
takes a certain amount of time, trying to rush the process usually
compromises the integrity of the part.
Having said all of this, new resins
and processes are developed daily and by the time you read this a cost
effective quick curing resin may be a reality, but at this point in time
the above is the reason that these materials don't make it into the
construction of commodity parts
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