A-stage

An early stage of polymerization of thermosetting resins in which the material is still soluble in certain liquids and fusible. (See also B-stage, C-stage.)

Ablative

Describes a material that absorbs heat through a decomposition process called pyrolysis at or near the exposed surface.

Accelerator

A chemical additive that hastens cure or chemical reaction (see also catalyst).

Addition

Polymerization reaction in which no byproducts are formed.

Additive

An ingredient mixed into resin to improve properties (e.g., plasticizers, initiators, light stabilizers and flame retardants).

Adhesive

Substance applied to mating surfaces to bond them together by surface attachment.

Adhesive film

A thin plastic film onto which premixed adhesives are cast.

Aliphatic

Designates a large class of organic compounds having open-chain structures, (e.g., isopropyl alcohol).

Amorphous

Describes polymers with no crystalline component.

Angle-ply laminate

Any balanced laminate consisting of plies at angles of plus and minus theta, where theta is an acute angle with the principal laminate axis.

Anisotropic

Not isotropic. Exhibiting different properties when tested along axes in different directions within the material.

Aramid

Aromatic polyamide fibers in which at least 85 percent of the amide linkages are directly attached to two aromatic rings, giving hight tensile strength characteristics. (Often referred to as Kevlar, DuPont's trademark.)

Areal weight

Weight of a fiber reinforcement per unit area (width times length) of tape or fabric.

Aspect ratio

Ratio of the length to the diameter of a fiber.

Autoclave

Closed vessel for applying fluid pressure, with or without heat, to an enclosed object (see consolidation).

Autoclave molding

Molding technique in which an entire assembly (layup and tooling) is placed into an autoclave and subjected to heat and elevated pressure for consolidation and/or curing while removing entrapped air and volatiles.

Automated tape laying

Fabrication process in which a structure is formed by laying prepreg material, typically unidirectional tape, across the surface of a mold in multiple layers and directions by using an automated tape-application machine.

Axial winding

Filament winding wherein the filaments are parallel to or at a small angle to the axis of rotation (x-axis).