Aircraft Composite Terminology

Plastic	The term plastic is a commonly used term to denote any of the thermoplastic or thermosetting polymers used in aircraft construction.
Fibre	Material in a form which has a high length to thickness ratio and is characterized by flexibility and fineness.
Filament	A single fiber.
Tow	An untwisted loose bundle of filaments.
Strand	An untwisted compact bundle of filaments.
Roving	An untwisted assembly of strands.
Yarn	A twisted strand of continuous or discontinuous filaments suitable for weaving into fabric.
Denier	The weight in grams of 9000 metres of roving, tow, yarn or strand.
Tex	The weight in grams of 1000 metres of roving, tow, yarn or strand.
Lamina, Ply	A single layer of resin impregnated reinforcement.
Laminate	A molded assembly of laminae (plies).
Lay-Up	The description of the components and arrangement of reinforcement in a laminate.
Matrix	The component of a composite which surrounds the reinforcement, protects it from damage and transfers loads to and between reinforcing fibers.
De-Lamination	The failure of a laminate due to separation of the layers (laminae).
Prepreg	(Pre-impregnated Reinforcement).  A combination of reinforcement with the correct quantity of resin for moulding, usually partially cured (to the B-stage) and capable of shipment and handling but having a limited storage life.  A B-stage cure is the partial cure of a resin.  The resin remains flexible but can no longer glow.
Tack	The stickiness of the partially cured resin in a prepreg.
Flow	The movement of the resin during molding.
Splice	A join in a tow, roving or yard made by an adhesive bonded lap joint rather than by a knot.
Catalyst (Hardener)	An active reagent which causes the resin to cure.
Accelerator	A material which is added to a mixture of resin and catalyst to speed up the curing reaction.
Fabric	A manufactured assembly of fibers or yarns with sufficient mechanical strength to hold the assembly together when handled.
End	An individual roving, tow, thread, yarn or mono-filament, especially in the warp direction.
Pick	An end in the weft direction.
Warp	The end running lengthwise in a woven fabric.
Weft (Fill)	The end running across the width of a woven fabric.
Catenary	A defect in a roving or tow caused by uneven tension in the component filaments or strands resulting in some fibers hanging in a loop below the remainder when the tow or roving is stretched horizontally.
Drape	The ability of a woven fabric or prepreg to conform to an irregular shape especially a double curvature.
Size	A compound applied to the reinforcement which bonds the filaments lightly together for ease of handling and may provide improved properties in the laminate.
Composite	A material consisting of two or more different constituents which retain their identity combined together to provide properties unobtainable with either constituent separately.
Cure	To irreversibly change the properties of a thermosetting resin by chemical reaction with a suitable agent with or without heat.
Post Cure	The additional processing of a laminate at elevated temperatures to improve the properties or complete the cure of the resin.
Pot Life	The length of time a resin system comprising the mixed resin catalyst and accelerator retains a viscosity low enough to be used satisfactorily in the molding process.

Isotropic	Having uniform properties in all directions.
Anisotropic	Not isotropic, having different properties along axes in different directions.
Modulus	A measure of the stiffness or rigidity of a material which is independent of the geometrical shape of the component.  the numerical value is obtained by dividing the stress by the strain when a specimen is loaded within the elastic limit.
Specific	Modulus value divided by specific gravity or density in consistent
Modulus	Units.
Specific	Ultimate tensile strength (UTS) divided by specific gravity or
Strength	Density in consistent units.
Eight Harness Satin	A type of fabric weave.  It looks different on one side than on the other.  The fabric has a seven by one weave pattern in which a weft thread passes over seven warp threads and then under one.  This weave is more pliable than any of the others and is especially adaptable to forming around compound curves such as radomes.
Shelf Life	The shelf life of a resin system or prepreg is the length of time that it can be stored before the flow and tack properties of the liquid resin or the mechanical properties of the cured resin deteriorate too far for the material to be used.  An average shelf life for epoxy resins is 3 to 6 months.  Storage at –18oC will increase shelf life.
Gel Coat	A gel coat is a polyester resin which is used during the manufacturing of the part.  The mold is coated with a color coat of polyester resin.  The plies are laid down into the surface of the colored gel coat and impregnated with epoxy resin.  After curing, the gel coat is on the outside surface and provides a smooth finish.
Bolt	A term used to describe a roll of fabric.