A-glass: corrosive-resistant boron-free glass.

Ablative Plastic: material that absorbs heat (with low material loss and char rate) through a decomposition process (pyrolysis) that takes place at or near the surface exposed to the heat.

Abrasion: wearing away by friction. Glass is highly resistant to abrasion by other materials, but can be damaged through contact with itself.

Accelerated test: procedure in which conditions are increased in magnitude to reduce the time required to obtain a result. To reproduce in a short time the deteriorating effect obtained under normal service conditions.

Accelerator: material that, when mixed with a catalyst or a resin, will speed the chemical reaction between the catalyst and the resin. Also called promoter.

Acetone: ketone group solvent that is used to dissolve polyester resins. Used to a large extent for clean up of tools in fiberglass operations.

Acoustic emission: measure of integrity of a material, as determined by sound emission when a material is stressed. Ideally, emissions can be correlated with defects and/or incipient failure.

Acrylic: thermoplastic polymer made by the polymerization of esters of acrylic acid and its derivatives.

Activator: see Accelerator.

Addition polymerization: chemical reaction in which simple molecules (monomers) are added to each other to form long-chain molecules (polymers) without forming by-products.

Additive: any number of materials used to modify the properties of polymer resins, such as plasticizers, initiators, light stabilizers and flame retardants.

Adhesive: substance capable of holding two materials together by surface attachment. Adhesive can be in film, liquid, or paste form.

Admixture: addition and homogeneous dispersion of discrete components, before cure.

Afterbake: see Postcure.

Aggregate: hard, coarse material usually of mineral origins in composite tools. Also used in flooring or as a surface medium.

Aging: effect on materials of exposure to the environment. The process of exposing materials to an environment for an interval of time.

Air-bubble: void air entrapment within and between plies of reinforcement or within a bondline or encapsulated area; localized, noninterconnected, spherical in shape.

Air vent: small outlet to prevent entrapment of gases in a molding or tooling fixture.

Alligatoring: visible cosmetic defect in exposed gel coat which looks like wrinkled or alligator skin.

Alloy: in plastics, a blend of polymers or copolymers with other polymers or elastomers under selected conditions.

Ambient: surrounding environmental conditions, such as pressure, temperature, or relative humidity.

Angle-ply laminate: laminate having fibers of adjacent plies oriented at alternating angles.

Anisotropic: exhibiting different properties when tested along axes in different directions. see also Anisotropic laminate and Isotropic.

Anisotropic laminate: one in which the properties are different in different directions.

Antioxidant: substance that, when added in small quantities to resin, prevents oxidative degradation and contributes to the maintenance of its properties.

Antistatic agents: agents that, when added to a molding material or applied to the surface of a molded object, make it more conducting, thus hindering the fixation of dust or the buildup of electrical charge.

Aramid: type of highly oriented organic material derived from polyamide but incorporating aromatic ring structure. Used primarily as a high-strength, high-modulus fiber. Kevlar and Nomex are example of aramids.

Arc resistance: ability to withstand exposure to an electric voltage. The total time in seconds that an intermittent arc may play across a plastic surface without rendering the surface conductive.

Ash content: proportion of the solid residue remaining after a reinforcing substance has been incinerated (charred or intensely heated).

Aspect ratio: ratio of length to diameter of a fiber.

A-Stage: early stage in the polymerization reaction of certain thermosetting resins (especially phenolic) in which the material, after application to the reinforcement, is still soluble in certain liquids and is fusible. Also called resole. see also B-Stage and C-Stage.

Autoclave: closed vessel for conducting and completing a chemical reaction or other operation, under pressure and heat.

Autoclave Molding: process in which, after lay-up, winding, or wrapping, and entire assembly is placed in a heated autoclave, usually 50 to 200 psi. Additional pressure permits higher density and improved removal of volatiles from the resin. Lay-up usually vacuum bagged with a bleeder and release cloth.

Axial Winding: in filament-wound reinforced plastics, a winding with the filaments parallel or at a small angle to the axis (0 helix angle).

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