What are composites?
By the broadest definition, a composite material is one in which
two or more materials that are different are combined to form a
single structure with an identifiable interface. The properties
of that new structure are dependant upon the properties of the
constituent materials as well as the properties of the interface.
In the more familiar world of metals, the mixing of different
materials typically forms bonds at the atomic level (alloys),
composites typically form molecular bonds in which the original
materials retain their identity and mechanical properties.
Additionally, where metal alloys (steel, copper bronze, etc.)
have isotropic characteristics (the same in all directions),
composites can have very selective directional properties to
meet specific application needs. Thus, composites are typically
highly engineered materials targeted at specific applications.
Note: Throughout this web site, we will frequently refer to
"structures" as the larger, purposeful structure created to
meet an application need. Thus we refer to
sonar domes, ship hulls,
etc. as structures.
History of Composites
One of the earliest known composite materials is adobe brick in
which straw (a fibrous material) is mixed with mud or clay
(an adhesive with strong compressive strength). The straw
allows the water in the clay to evaporate and distributes cracks
in the clay uniformly, greatly improving the strength of this
early building material. Another form of a composite material
is the ubiquitous construction material we call plywood.
Plywood uses natural materials (thin slabs of wood) held
together by a strong adhesive, making the structure stronger
than just the wood itself. In nature, bamboo is often cited
as an example of a wood composite structure, combining a
cellulose fiber and lignin, with the lignin providing the
adhesive to hold the fibers together. Of course, you probably
drive a car across a composite highway every day. Reinforced
concrete is a combination of two remarkable materials,
concrete (a composite by itself) and steel that takes
advantage of the strengths of each material to overcome
their individual limitations in each. Steel has very high
tensile strength, while concrete has very high compressive
strength. In combination, they make a superior material for
road and bridge construction.
Today, when we speak of composite materials, or just
"composites", we are referring to the highly engineered
combinations of polymer resins and reinforcing materials such
as glass fibers. A fiberglass composite structure is a
combination of glass fibers of various lengths and resins
such as vinyl ester or polyester. The term FRP is often used,
meaning Fiber Reinforced Plastic. FRP is a very general term
for many different combinations of reinforcement materials and
bonding resins. Thus, the term "composites" is used extremely
broadly to describe many materials with many different
properties targeted at an even larger number of applications.
To show how composites have changed our world, look no further
than under the hood of a modern car and realize that most of
what you can see are components made of composite materials.
If the car is a Corvette, the entire body is made of fiberglass
or carbon reinforced composite materials. At Goodrich Engineered
Polymer Products, our similar composite applications are for
huge Sonar Domes for
Navy ships and submarines.
Goodrich Corporation began as a maker of rubber products in
the 1800's. You may have known us as the BFGoodrich Tire
Company. Tires are a composite of rubber and a reinforcing
material such as steel or nylon. The BFGoodrich tire business
and brand were sold to Michelin in the 1980's. The current
Goodrich Corporation is a multi-billion dollar aerospace and
defense business. We continue to manufacture modern composite
materials throughout our businesses to serve the demanding
needs of our customers. At Goodrich’s Engineered Polymer
Products (EPP) division, our specialty is composite materials
for marine applications, or just Marine Composites.
Benefits of Composites
Composites offer many advantages over other materials. Within
aerospace and marine markets, where exceptional performance is
required but weight is critical, composites continue to grow in
importance. The many advantages of composites may be summarized
as:
- Stronger and stiffer than metals on a density basis
- For the same strength, lighter than steel by 80% and aluminum by 60%
- Superior stiffness-to-weight ratios
- Capable of high continuous operating temperatures
- Up to 250°F in many composites
- Up to 2000°F with FyreRoc composites, Goodrich's new inorganic resin
- Highly corrosion resistant
- Essentially inert in the most corrosive environments
- Electrically insulating properties are inherent in most composites (depending on reinforcement selected).
- Yet composites can be made conducting or selectively conducting as needed.
- Tailorable thermal expansion properties
- Can be compounded to closely match surrounding structures to minimize thermal stresses
- Tunable energy management characteristics
- Exceptional formability
- Composites can be formed into many complex shapes during fabrication, even providing finished, styled surfaces in the process.
- Outstanding durability
- Well-designed composites have exhibited apparent infinite life characteristics, even in extremely harsh environments
- Low investment in fabrication equipment
- The inherent characteristics of composites typically allow production to be established for a small fraction of the cost that would be required in metallic fabrication.
- Reduced Part Counts
- Parts that were formerly assembled out of several smaller metallic components can be fabricated into a larger single part. This reduces manufacturing and assembly labor and time.
- Corrosion Resistance
- The non-reactive nature of many resins and reinforcements can be custom selected to resist degradation by many common materials and in corrosive environments.
- Benefits include lower maintenance and replacement costs.
- Low Observable
- Radar works by sending out directional radio waves (electromagnetic radiation) through the air, then listening for a reflected return from an airplane or other object. Composites are normally transparent to electromagnetic radiation, but can be “seeded” with appropriate materials to absorb such radiation and divert its energy away from the source. This low observability is called “stealth” in the popular press, and is a vitally important capability to our war fighters.
- Composite materials can also be used to reduce transmitted mechanical noise from a ship or submarine to the surrounding water, thus making it more difficult to detect vessels using acoustic means. This capability is of particular importance in Anti-Submarine Warfare (ASW)
Composite Applications
Each year, composites find their way into hundreds of new
applications, from golf clubs and tennis rackets to jet skis,
aircraft, missiles and spacecraft. Composite materials offer
designers an increasing array of as a material and system
solution. At the same time, composite cost trends are highly
favorable, especially when the total cost of fabrication is
considered. Processes such as pultrusion offer the means to
convert composite materials into finished products in a single
trip through the machinery. Composite sheet molding compounds
allow the formation of complete automobile skin panels in a
single stroke of a press.
At Goodrich, composites are used in numerous aerospace and
marine applications where weight reduction is the primary
driver. As aircraft designers look to increase the performance
of aircraft, composites are playing an ever-larger role.
Marine Composites Applications
One of the earliest and largest uses for composites was in the
manufacturing of pleasure boats. Once, nearly all boats were
wood, and any old-timer can tell you that keeping a wooden boat
in shape is a lot of work. By the 1950's, boat builders began
the transition to fiberglass hulls. Such designs were easier
to build and significantly lower in cost because complex shapes
were easily formed in fiberglass when compared to wood or
metal. Boat buyers got attractive new styles that were lower
cost, easier to transport, extremely durable and easy to
maintain, since fiberglass does not rust like steel nor rot
like wood. With less need to scrape and paint, owners were left
with more time to enjoy their boats. Despite the nostalgia for
the beauty of wood in ship hulls, such construction has been
left to the few purists of ship ownership. Fiberglass
composites rule the boat world today.
In the Defense world, marine composites offer similar
advantages. Navy ships have historically been made of steel,
an ideal material for ship construction, being both durable and
cost effective. But steel ships rust, requiring constant
maintenance. While the cost of such maintenance has always
been accommodated in defense budgets in the past, today there
is significant emphasis on eliminating such costs. Further,
the loss of ship availability, due to this type of maintenance,
is considered a major cost penalty, because other ships must
be added to the fleet to assure availability. The heavy weight
of steel ships also places limits on their speed and increases
fuel consumption: heavy ships take a lot of fuel to move.
Because warships often have to worry about explosive mines,
the magnetic signature of ships is a concern to all sailors.
Composites are non-magnetic and make an ideal material for any
ship expected to face mine warfare conditions. Expect to see
more composites in Navy ships of the future, such as the new
Littoral Combat Ship (LCS),
an important new concept for future war fighters.
