COMPOSITE TERMINOLOGY

COMPOSITES terminology is essential in understanding all the processes and the materials required in this technology.

Adhesive
A thermoset resin (e.g., epoxy, phenolic or BMI) in the form of a thin film or paste, cured under heat and pressure to bond a wide range of composite, metallic and honeycomb surfaces.

Aramid
A high strength, high stiffness fiber derived from polymid. Kevlar(tm) and Nomex(tm) are examples of aramids.

Carbon Fiber
Fiber produced by carbonizing precursor fibers based on PAN (polyacrylonitrile), rayon or pitch. The term is often used interchangeably with graphite. However, carbon fibers and graphite fibers are made and heat treated at different temperatures and have different carbon contents.

Composite Material
Product made by combining two or more dissimilar materials such as fibers and resins to create a product with exceptional structural properties not present in the original materials.

Cowls or Cowling
The outside protective shell of a jet engine, traditionally made out of metal. Cowls mainly provide the engine with protection from the elements and with structural support.

Engineered Core
The forming, shaping, machining or bonding of sheets or blocks of honeycomb into profiled and complex shapes for use as semi-finished components in the fabrication of composite parts and structures.

Engineered Products
Completed composite components that typically are manufactured from prepregs, honeycomb, adhesives and assembled hardware. These parts are ready for direct attachment to a structure (e.g., aircraft) or to sub-assemblies. Emerging manufacturing processes allow the fabrication of engineered products directly from reinforcing fibers/fabrics and matrix resins.

Fairing
A secondary structure of an airplane providing enhanced aerodynamics. Typically, fairings are found where the wing meets the body or at various locations on the leading or trailing edge of the wing.

Fiberglass
Filaments made by drawing molten glass. Woven by Hexcel into fabrics and commonly used as a composite reinforcement.

Filament Winding
A process to manufacture composite materials components such as rocket casings and cylinders. Fiber filaments are impregnated in a resin matrix and then wound in a predetermined pattern over a form of the desired component.

Honeycomb
A unique, lightweight, cellular structure made from either metallic sheet materials or non-metallic materials (e.g., resin-impregnated paper or woven fabric) and formed into hexagonal nested cells, similar in appearance to a cross-section of beehive.

Inlet Ducts
  Intake passages or tubes that confine and conduct air. They are usually located at the upstream end of an airplane engine on the engine cowling and aid in propulsion and engine cooling.

Interiors
Finished internal aircraft components, such as overhead stowage compartments, lavatories, sidewalls, floor panels and ceilings.

Kevlar(tm)
An aramid fiber from DuPont. Woven Kevlar(tm) fabrics are used in both ballistic and composite materials applications.

Modulus of Elasticity
The physical measurement of stiffness in a material. A high modulus indicates a stiff material.

Nacelle
The protective shell of a jet engine housed within the cowling, usually made from honeycomb. Provides noise absorption, insulation, structural support and can aid heat dissipation.

Nomex(tm)
DuPont's registered trade name for its high temperature resistant aramid papers, pressboard, staple fibers and filament yarns. Nomex(tm) aramid paper is used in the manufacture of honeycomb.

PAN (Polyacrylonitrile)
A polymer which when spun into fiber is used as a precursor material in the manufacture of certain carbon fibers.

Precursor
The PAN, rayon or pitch fibers from which carbon or graphite fibers are derived.

Prepreg (Pre-impregnated)
A composite material made from combining high performance reinforcement fibers or fabrics with a thermoset or thermoplastic resin matrix. When cured under high temperature and pressure, exceptional structural properties are achieved.

Primary Structure
A critical load-bearing structure on an aircraft. If this structure is severely damaged, the aircraft cannot fly.

Radome
  The housing which protects the aircraft radar system from the elements while allowing transmission of radar signals. Often the radome is in the nose of an aircraft but can be found at other locations on the aircraft, as well.

Reinforcement
A strong material which when combined with a resin matrix forms a composite material. Reinforcements are usually continuous fibers, which may be woven. Fiberglass, aramid and carbon fibers are typical reinforcements.

Reinforcement Fabrics
Woven fiberglass, carbon or aramid fabrics used in production of prepregs and honeycomb.

Resin Matrix
In reinforced fiber composites, a formulated polymeric substrate.

Sandwich Panels
A stiff and lightweight panel consisting of thin sheets such as aluminum or cured prepreg laminate bonded to a low density, rigid core material (e.g., foam or honeycomb).

Spectra(tm)
A high strength polyolefin fiber from Allied Signal. Woven Spectra(tm) fabrics are very strong and lightweight and are used in both ballistic and composite materials applications.

Structures
Finished components for aircraft and industrial applications. For aircraft, these may be for primary or secondary external structures. Truck applications include chassis fairings and floors.

Composite  A material created by the synthetic combination of  two or more dissimilar materials to obtain specific properties more desirable that the properties of the individual constituent materials. In FRP composites, the structural fiber is held together by a resin matrix, much the same as structural rebar is held in place by concrete.  Most often differentiation in composite materials is designated by the structural fiber used.  It can be carbon fiber, Kevlar, fiberglass(E-glass or S-Glass).  

CFRP  -- Carbon fiber reinforced plastic (or Carbon fiber reinforced polymer) is a very strong, light weight composite  in which Carbon  constitutes the reinforcing fibers.   The matrix resin system will usually be epoxy, polyester, vinyl ester or nylon.

GFRP -- Glass Fiber Reinforced Plastic uses fiber glass material  with an appropriate matrix resin system.

Matrix – The material in which the reinforcing fabric of a composite is embedded.  Matrix materials include thermosetting and thermoplastic polymers, metal and ceramic compounds.  In advanced development of composite material, the focus on the next generation has shifted from the structural fiber to the resin matrix..  

Mandrel – A rigid male form which can be used as a base for composite production of a part around which the material can be wound or laid up.  It is generally removed after the composite material has cured.

Master Plug  -- Once a composite part has been designed and captured in a digital format, the CAD program  can be used to create a master plug by using a CNC mill.  The master plug should be carefully scanned and inspected to ensure congruency with the original design.  The master plug then becomes the physical standard for production.  It is used to fabricate production molds  which are in turn used to  fabricate the parts.  The master plug must be controlled and stored because as parts are produced the molds witll experience normal wear.  Though molds can be maintained and repaired, they will at some point in repeated production use have to be replaced.  At that time the master plug will be used to produce a replacement mold.

Male Mold --  Male mold  generally describes a form which is convex in overall shape and will be used to fabricate a part with a concave finished surface.   To be able to remove the mold after the part is cured the mold must have sufficient draft to permit the mold to be removed. Since the 'finished' surface of the composite part is that which is next to the mold,  during fabrication the fiber laminate is build out from the mold surface.  The outside surface is the material is then compressed against the mold during cure.

Female Mold -- Generally a concave mold which will produce a composite component with a smooth surface on the outside of the curve.

Closed-Molding- A molding process that uses two matched molds.  This method of fabricating reinforced plastic provides a finished inside and outside surface.  It is more expensive than open mold tooling but can result in lower production costs because is reduces the need for labor to vacuum bag the molded component.

Peel Ply – A layer of tightly woven fabric  which is applied directly to the surface of a prepreg  lay-up.  The peel ply (which is removed after component curing) helps produce a clean surface texture and minimized surface preparation for bonding.

Prepreg refers to the material produced by  the practice of mixing resin and fiber reinforcement and effecting a partial cure before use.  The prepreg material  is slightly tacky to the touch, but allows the lay-up technician to work with a ‘dry’ fabric.  Generally, the resulting laminate is cured under vacuum bag pressure in a curing oven at a temperature and time profile dictated by the prepreg manufacturer.
 
Resin transfer molding  (RTM)  - A closed mold process in which catalyzed resin is drawn or injected into a double sided mold to impregnate a pre-formed fiber reinforcement structure.  The resin and mold may or may not be heated during this process.  If vacuum is used to increase the resin transfer the procedure is sometimes called Vacuum  Assisted Resin Transfer Molding (VARTM).   RTM is exacts less wear on the molds and is often used for larger structure fabrication.

Wet Lay-up , a process where the technician impregnates the resin into the fabric by hand. This is usually accomplished by rollers or brushes.  Laminates are left to cure under standard atmospheric conditions.  Some resin systems utilizing wet lay-up may be vacuum bagged to remove trapped air during the cure cycle.  This can be used with a male or female mold which will determine which side of the part will be the finished surface.

 

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