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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 L can be found below.

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Terms L

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

The ribbon direction, that is, the direction of the continuous sheets of honeycomb.

Plural of lamina.

laminate co-ordinates
A reference co-ordinate system (used to describe the properties of a laminate), generally in the direction of principal axes, when they exist.

laminate orientation
The configuration of a cross-plied composite laminate with regard to the angles of cross-plying, the number of laminae at each angle, and the exact sequence of the lamina lay-up.

laminate ply
One fabric-resin or fibre-resin layer of a product that is bonded to adjacent layers in the curing process.

To unite laminae with a bonding material, usually with pressure and heat (normally used with reference to flat sheets, but also rods and tubes). A product made by such bonding. See also bi-directional laminate and unidirectional laminate.
(("bi-directional laminate" "bi-directional laminate") ("unidirectional laminate" "unidirectional laminate"))

lap joint
A joint made by placing one adherend partly over another and bonding the overlapped portions.

In filament winding, the amount of overlay between successive windings, usually intended to minimise gapping. In bonding, the distance one adherend covers another adherend.

The reinforcing material placed in position in the mould. The process of placing the reinforcing material in position in the mould. The resin-impregnated reinforcement. A description of the component materials, geometry, and so forth, of a laminate.

Length of constant cross section, given in inches. "pultrusion size"

level winding
See circumferential winding.
(("circumferential ("circ") winding" "circumferential ("circ") winding"))

linear expansion
The increase of a given dimension, measured by the expansion or contraction of a specimen or component subject to a thermal gradient or changing temperature. See also coefficient of thermal expansion
"coefficient of thermal expansion"

In a filament-wound pressure vessel, the continuous, usually flexible coating on the inside surface of the vessel, used to protect the laminate from chemical attack or to prevent leakage under stress.

liquid crystal polymer
A newer thermoplastic polymer that is melt processable and develops high orientation in moulding, with resultant tensile strength and high-temperature capability that is notably improved. First commercial availability was as an aromatic polyester. With or without fibre reinforcement.

liquid metal infiltration
Process for immersion of metal fibres in a molten metal bath to achieve a metal matrix composite; for example, graphite fibres in molten aluminium.

liquid shim
Material used to position components in an assembly where dimensional alignment is critical. For example, epoxy adhesive is introduced into gaps after the assembly is placed in the desired configuration.

load-deflection curve
A curve in which the increasing tension, compression, or flexural loads are plotted on the ordinate axis and the deflections caused by those loads are plotted on the abscissa axis.

Longitudinal Insert
Insert such as antenna wire, plywood, foam, which can be moulded along the length of the part. Many pultruded parts, such as fibre optic cable, contain this type of insert. This is not be confused with metal inserts which are used for fastening, etc. "wire insert"

Low angle helical or longitudinal windings.

loop tenacity
The tenacity or strength value obtained by pulling two loops, as two links in a chain, against each other in order to demonstrate the susceptibility that a fibrous material has for cutting or crushing itself; loop strength.

loss factor
The product of the dissipation factor and the dielectric constant of a dielectric material.
(("electrical dissipation factor" "electrical dissipation factor") ("dielectric constant" "dielectric constant"))

loss modulus
A damping term describing the dissipation of energy into heat when a material is deformed.

loss on ignition
Weight loss, usually expressed as percent of total, after burning off an organic sizing from glass fibres, or an organic resin from a glass fibre laminate.

loss tangent
See electrical dissipation factor. A specific amount of material produced at one time using the same process and the same conditions of manufacture, and offered for sale as a unit quantity.

low-pressure laminates
In general, laminates moulded and cured in the range of pressures from 2760 kPa (400 psi) down to and including pressure obtained by the mere contact of the plies.

A material added to most sizings to improve the handling and processing properties of textile strands, especially during weaving.

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