A complex material, such as wood or fiberglass, in which two or more distinct structurally complementary substances, especially metals, ceramics, glasses, and polymers, combine to produce structural or functional properties not present in any individual component. -The American Heritage Dictionary
For the purpose of our review, the combination of fibers and resins to produce a single component or structure, is the basis for advanced composite construction.
What is Fiber?
Fiber is a natural or synthetic material filament that is spun into a larger strand such as rope or thread. Fibers used in the composite industry come in many forms, examples are: glass fiber, carbon fiber, arimid fiber, quartz fiber, and various other types of fiber, each with it’s own unique structural properties. Each fiber can even have several different structural properties to choose from, such as: e-glass, s-glass, standard, intermediate, and high modulus carbon fiber, quartz etc. Fiber can be purchased in many forms as well. The most common form is woven fabric which is woven in specific patterns to maximize ease of use or maximize structural properties.
What is Resin?
Resin is a natural or synthetic compound, usually in liquid form, which, when combined with another compound, such as a hardener or oxygen, changes it’s state from a liquid to a solid. These resins are generally referred to as “thermoset” resins. When combined with fiber, resin binds the fiber, which is the structural material, in the shape of the finished component. Resin comes in many forms. Examples are: polyester, epoxy, vinylester and phenolic. But other systems, using different combinations of compounds, have been designed and formulated for very specific purposes. Generally, polyester resins are used for applications which have low temperatures requirements such as bath tubs, HVAC ducts and cowlings. Epoxies can be used for a very wide range of applications with temperature ranges beyond 400°F and very high structural properties. Phenolic resins are used for fire and smoke applications such as heat shields and aircraft interiors or ductwork as well as carbon/carbon processes. Vinylester resins are more suitable for applications where moderate heat is an issue such as engine cowlings and boats. Other resin systems such as cyanate ester, polyimide or bismaleimide, have been developed to perform better in very specific situations such as: extreme heat, radar absorption, radar transparency, and fire and smoke inhibitors.
What is the best combination for my project?
You must first consider the desired result of your project. Is weight a factor? Is it cost sensitive? Is temperature a factor? Is it a structural or cosmetic part? Are you building one part or a thousand? These are only some of the issues that must be considered.
Fact or Fiction?
1. Myth: Composites are very expensive and only applicable for aerospace or other highly technical applications.
Fact: In general, composite components are similar in cost to similar metal components. Breakthroughs in manufacturing processes and materials for composite components have made it more cost effective, in many cases, to use composites rather than metals or other materials. Composite components are used everyday in hi-tech and lo-tech applications from aerospace to playground equipment to recreational equipment and even electronic equipment.
2. Myth: Metal is more suitable for “high-volume” manufacturing.
Fact: Composite components can be and are being manufactured in high volumes every day throughout the world. Because many steps of the manufacturing process can be incorporated into a single step and because many components can be made in a single piece as compared to requiring many steps and the combining of many pieces for the same metal part, use of composites can provide significant savings in labor and manufacturing costs.
3. Myth: Aluminum is lighter and stronger than composites
Fact: Aluminum and steel have the same strength to weight ratio. While some composite materials have a lower strength to weight ratio than aluminum or steel, carbon fiber is pound for pound 5 times stronger than steel or aluminum. This means you can build a structure 5 times lighter or up to 5 times stronger using carbon fiber components rather than steel ar aluminum. In the aviation industry, this adds up to incredible fuel conservancy and greater performance. Composite components can also be designed for strength. By adding core materials such as honeycomb or foam core, or by using complex shapes to add strength, even materials that have lower strength to weight ratios, like fiber glass, can be used for structural components that are lighter than similar metal components.
4. Myth: Composites are not suitable for structural components.
Fact: Composites are being used more and more each day as structural and non-structural components. Presently there are several all composite aircraft fuselages in service, some are pressurized and some are not. The fact is that composites are more suitable for some aerospace structural parts than metal. For example, a typical metal fuselage is comprised of hundreds of pieces that must be cut, shaped, drilled, riveted, and welded in order to assemble an outer fuselage. A composite fuselage can be made in a few pieces and bonded together to form an entire fuselage including the tail. Fewer parts means greater integrity and less assembly time and less chance for mistakes in the manufacturing process. Structural uses are not limited to aerospace applications only. Other uses include architectural columns, arches and mezzanines, bridges / roads, pipes / tubes, marine yacht hulls and masts, automotive fenders and ballistic armoring applications.
5. Myth: Metal is easier to repair than composites.
Fact: As in metal, processes have been developed specifically for the repair of composite materials. Composites are not susceptible to the same types of corrosion associated with metals exposed to oxygen and moisture (yes, even aluminum is susceptible to corrosion), so, composites are more durable in most environments and don’t need repairs unless physically damaged.
6. Myth: Metal is easier to create contoured exotic shapes.
Fact: Composites are significantly more functional in developing lightweight, strong components of exotic shapes and sizes than any other material. Manufacturing methods and material weaving can allow for components of virtually any shape in a manner much more efficient than metal.
7. Myth: Tooling costs to build composite components makes it prohibitive.
Fact: Tooling, or molds, are used to create the shape of the composite components.Tooling comes in many different styles. If the production run is small, short term or temporary tooling can be made from wood, plaster, foam or other inexpensive materials. Longer runs use permanent molds or tooling which are made from other composite materials or metal. Long term tooling varies in price depending on the materials used and the process used to make them, but on average cost between 5-15 times the cost of the part. In most cases, tooling for metal production is similar in cost to that of composite production. In some cases, tooling for composite production is not necessary.
8. Myth: Injection Molded plastics and composites are the same.
Fact: Injection molding is a process where thermoplastic pellets are heated to melting point and injected into a metal cavity mold to form the finished part. Composites use thermoset resins (see What is Resin? above) combined with various types of fibers (see What is Fiber? above)to form parts. The two processes are used for completely different applications and achieve separate results.
9. Myth: It takes longer to build composite components than metal components.
Fact: With metal assemblies, many pieces and manufacturing steps must be used to complete the assembly. With composite assemblies, many of those pieces and steps can be incorporated into one piece and one step, thus eliminating manufacturing times and labor. Some one piece metal components that don’t require machining or assembly can be cheaper than composites, but complex shaped components are less expensive because they can be made quicker than similar metal components.
Copyright © 2002 Contour Composites, Inc.