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Composites Terminology Database

This glossary is not an exhaustive list, however it does contain the majority of terms used in the composites industry and as part of the management of our website, it is updated on a continual basis.

The terms are accessed by clicking on the appropriate letter below, all the terms beginning with the letter G can be found below.

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Terms G

Click on a term and it will take you to the coresponding explanation.

Modulus of rigidity, see modulus of rigidity
"modulus of rigidity"

gage length
Length over which deformation is measured, for a tensile or compressive test specimen. The deformation over the gage length divided by the gage length determines the strain.

gap-filling adhesive
An adhesive subject to low shrinkage in setting, used as sealant.

In filament winding, the space between successive windings, which windings are usually intended to lay next to each other. Separations between fibres within a filament winding band. The distance between adjacent plies in a lay-up of unidirectional tape materials.

gel coat
A quick setting resin applied to the surface of a mould and gelled before lay-up. The gel coat becomes an integral part of the finished laminate, and is usually used to improve surface appearance and bonding.

gel permeation chromatography (GPC)
A form of liquid chromatography in which the polymer molecules are separated by their ability or inability to penetrate the material in the separation column.

gel point
The stage at which a liquid begins to exhibit pseudoelastic properties. This stage may be conveniently observed from the inflection point on a viscosity time plot.

The initial jelly-like solid phase that develops during the formation of a resin from a liquid. A semisolid system consisting of a network of solid aggregates in which liquid is held.

gelation time
That interval of time, in connection with the use of synthetic thermosetting resins, extending from the introduction of a catalyst into a liquid adhesive system until the start of gel formation. Also, the time under application of load for a resin to reach a solid state.

The point in a resin cure when the resin viscosity has increased to a point such that it barely moves when probed with a sharp instrument.

geodesic ovaloid
A contour for end domes, the fibres forming a geodesic line: the shortest distance between two points on a surface of revolution. The forces exerted by the filaments are proportioned to meet hoop and meridional stresses at any point.

geodesic-isotensoid contour
In filament wound reinforced plastic pressure vessels, a dome contour in which the filaments are placed on geodesic paths so that the filaments will exhibit uniform tensions throughout their length under pressure loading.

The shortest distance between two points on a surface. Geodesic isotensoid. Constant stress level in any given filament at all points in its path.

glass cloth
Conventionally woven glass fibre material. See also scrim

glass fibre
A fibre spun from an inorganic product of fusion that has cooled to a rigid condition without crystallising.

glass filament bushing
The unit through which molten glass is drawn in making glass filaments.

glass filament
A form of glass that has been drawn to a small diameter and extreme length. Most filaments are less than 0.15 mm (0.005 in.) in diameter.

glass finish
A material applied to the surface of a glass reinforcement to improve the bond between the glass and the plastic resin matrix.

glass flake
Thin, irregularly shaped flakes of glass, typically made by shattering a thinwalled tube of glass.

glass former
An oxide that forms a glass easily. Also, one which contributes to the network of silica glass when added to it.

glass stress
In a filament wound part, usually a pressure vessel, the stress calculated using the load and the cross-sectional area of the reinforcement only.

glass transition temperature (Tg)
The approximate midpoint of the temperature range over which the glass transition takes place; glass and silica fibre exhibit a phase change at approximately 955 degree C (1750 degree F) and carbon/graphite fibres at 2205 to 2760 degree C (4000 to 5000 degree F).

The temperature at which increased molecular mobility results in significant changes in the properties of a cured resin system. Also, the inflection point on a plot of modulus versus temperature. The measured value of Tg depends to some extent on the method of test.

glass transition
The reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from, or to, a viscous or rubbery condition to, or from, a hard and relatively brittle one.

glass, percent by volume
The product of the specific gravity of a laminate and the percent glass by weight, divided by the specific gravity of the glass.

An inorganic product of fusion that has cooled to a rigid condition without crystallising. Glass is typically hard and relatively brittle, and has a conchoidal fracture.

graphite fibre
A fibre made from a precursor by oxidation, carbonisation, and graphitisation process (which provides a graphitic structure). See also carbon fibre
"carbon fibre"

The crystalline allotropic form of carbon.

The process of pyrolysation in an inert atmosphere at temperatures in excess of 1925 degree C (3500 degree F), usually as high as 2480 degree C (4500 degree F), and sometimes as high as 9750 degree C (5400 degree F), converting carbon to its crystalline allotropic form. Temperature depends on precursor and properties desired.

green strength
The ability of the material (such as a urethane elastomer), while not completely cured, to undergo removal from the mould and handling without tearing or permanent distortion.

greige, gray goods
Any fabric before finishing, as well as any yarn or fibre before bleaching or dyeing; therefore, fabric with no finish or size.

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