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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 V can be found below.

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Terms V

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

vacuum bag moulding
A process in which a sheet of flexible transparent material plus bleeder cloth and release film are placed over the lay-up on the mould and sealed at the edges.

A vacuum is applied between the sheet and the lay-up. The entrapped air is mechanically worked out of the lay-up and removed by the vacuum, and the part is cured with temperature, pressure, and time. Also called bag moulding.

vacuum hot pressing (VHP)
A method of processing materials (especially powders) at elevated temperatures and consolidation pressures, and low atmospheric pressures.

vapour-liquid-solid (VLS) process
A process utilising vapour feed gases and a liquid catalyst, and producing solid crystalline whisker growth. Used to produce silicon carbide whiskers.

An ultrathin mat similar to a surface mat, often composed of organic fibres as well as glass fibres.

vent cloth
A layer or layers of open-weave cloth used to provide a path for vacuum to "reach" the area over a laminate being cured, such that volatiles and air can be removed. Also causes the pressure differential that results in application of pressure to the part being cured. Also called breather cloth.

A small hole or shallow channel in a mould that allows air or gas to exit as the moulding material enters.

In autoclave curing of a part or assembly, turning off the vacuum source and venting the vacuum bag to the atmosphere. The pressure on the part is then the difference between pressure in the clave and atmospheric pressure.

A granular material mixed with resin to form a filler of relatively high compressive strength.

See vacuum hot pressing
"vacuum hot pressing"

vinyl esters
A class of thermosetting resins containing esters of acrylic and/or methacrylic acids, many of which have been made from epoxy resin. Cure is accomplished as with unsaturated polyesters by copolymerisation with other vinyl monomers, such as styrene.

virgin filament
An individual filament that has not been in contact with any other fibre or any other hard material.

A property involving a combination of elastic and viscous behaviour in the application of which a material is considered to combine the features of a perfectly elastic solid and a perfect fluid. Phenomenon of time-dependent, in addition to elastic, deformation (or recovery) in response to load.

The property of resistance to flow exhibited within the body of a material, expressed in terms of relationship between applied shearing stress and resulting rate of strain in shear.

Viscosity is usually taken to mean Newtonian viscosity, in which case the ration of shearing stress to the rate of shearing strain is constant. In non-Newtonian behaviour, which is the usually case with plastics, the ratio varies with the shearing stress. Such ratios are often called the apparent viscosities at the corresponding shearing stresses.

Viscosity is measured in terms of flow with water as the base standard. The higher the number, the less flow.

VLS process
See vapour liquid solid process
"vapour-liquid-solid process"

void content
Volume percentage of voids, usually less than 1% in a properly cured composite. The experimental determination is indirect; that is, calculated from the measured density of a cured laminate and the "theoretical" density of the starting material.

Air or gas that has been trapped and cured into a laminate. Porosity is an aggregation of microvoids. Voids are essentially incapable of transmitting structural stresses or nonradiative energy fields.

volatile content
The percent of volatiles that are driven off as a vapour from a plastic or an impregnated reinforcement.

Materials, such as water and alcohol, in a sizing or a resin formulation, that are capable of being driven off as a vapour at room temperature or at a lightly elevated temperature.

volume fraction
Fraction of a constituent material based on its volume.

volume resistance
The volume resistance between two electrodes in contact with or embedded in a specimen is the ratio between the direct voltage applied to them and that portion of the current between them that is distributed through the volume of the specimen. Also, the electrical resistance between opposite faces of a 1-cm (0.40 in.) cube of insulating material. Also called specific insulation resistance.

A chemical reaction in which a rubber is cured by reaction with sulfur or other suitable agents.

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