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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 D can be found below.

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Terms D

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

A high boron content glass made especially for laminates requiring a precisely controlled dielectric constant. See:

damage tolerance
A design measure of crack growth rate. Cracks in damage tolerant designed structures are not permitted to grow to critical size during expected service life.

The decay with time of the amplitude of free vibrations of a specimen. See also hysteresis and attenuation

The distance, in the open position, between the moving and fixed tables or the platens of a hydraulic press. In the case of a multiplaten press, daylight is the distance between adjacent platens. Daylight provides space for removal of the moulded part from the mould.

A deliberate separation of a bonded joint or interface, usually for repair or rework purposes. Also, an unbonded or nonadhered region; a separation at the fibre-matrix interface due to strain incompatibility. In the United Kingdom, the term often refers to accidental damage. See also disbond and delamination

Compacting of a thick laminate under moderate heat and pressure and/or vacuum to remove most of the air, to ensure seating on the tool, and to prevent wrinkles.

deep-draw mould
A mould having a core that is long in relation to the wall thickness.

A finishing technique used to remove the flash (excess, unwanted material) on a plastic moulding.

deflection temperature under load
The temperature at which a simple cantilever beam deflects a given amount under load. Formerly called heat distortion temperature.

deformation under load
The dimensional change of a material under load for a specified time following the instantaneous elastic deformation caused by the initial application of the load. See also cold flow and creep

See: breathing

A deleterious change in the chemical structure, physical properties, or appearance of a plastic.

degree of polymerisation
Number of structural units, or mers, in the average polymer molecule in a sample measure of molecular weight.

Separation of the-layers of material in a laminate, either local or covering a wide area. Can occur in the cure or subsequent life.

A yarn and filament numbering system in which the yarn number is numerically equal to the weight in grams of 9000 meters. Used for continuous filaments. The lower the denier, the finer the yarn.

densification process
Consolidation of a loose or bulky material.

The process of applying a material to a base by means of vacuum, electrical, chemical, screening, or valour methods, often with the assistance of a temperature and pressure container.

design allowables
Statistically defined (by a test program) material property allowable strengths, usually referring to stress or strain. See:

The process of eliminating sizing, which is generally starch, from gray (also greige) goods before applying special finishes or bleaches (for yarn such as glass or cotton). Also, removing lubricant size following weaving of a cloth.

A process in which an absorbed material is released from another material. Desorption is the reverse of absorption, adsorption, or both.

The formation of crystals (seeds) in a glass melt, usually occurring when the melt is too cold. These crystals can appear as defects in glass fibres.

Tolerance of diameter of part, given in inches.

dielectric constant
The ratio of the capacitance of an assembly of two electrodes separated solely by a plastic insulating material to its capacitance when the electrodes are separated by air. See: complex dielectric constant

dielectric curing
The curing of a synthetic thermosetting resin by the passage of an electric charge (produced from a high frequency generator) through the resin.

dielectric heating
The heating of materials by dielectric loss in a high-frequency electrostatic field.

dielectric loss
A loss of energy evidenced by the rise in heat of a dielectric placed in an alternating electric field.

dielectric monitoring
A means of tracking the cure of thermosets by changes in their electrical properties during material processing.

dielectric strength
The property of an insulating material that enables it to withstand electric stress. The average potential per unit thickness at which failure of the dielectric material occurs.

A non-conductor of electricity. The ability of a material to resist the flow of an electrical current.

Use of electrical techniques to measure the changes in loss factor (dissipation) and in capacitance during cure of the resin in a laminate.

differential scanning calorimetry (DSC)
Measurement of the energy absorbed (endotherm) or produced (exotherm) as a resin system is cured. Also detects loss of solvents and other volatiles.

differential thermal analysis (DTA)
An experimental analysis technique in which a specimen and a control are heated simultaneously and the difference in their temperatures is monitored. The difference in temperature provides information on relative heat capacities, presence of solvents, changes in structure (that is, phase changes, such as melting of one component in a resin system), and chemical reactions. See above: differential scanning calorimetry

dimensional stability
Ability of a plastic part to retain the precise shape to which it was moulded, cast, or otherwise fabricated.

dipole groups (polar groups) of polymeric material
Molecules such as epoxide or hydroxyl groups in which electron pairs are unequally shared in the covalent bonds.

An area within a bonded interface between two adherents in which an adhesion failure or separation has occurred. Also, colloquially, an area of separation between two laminae in the finished laminate (in this case, the term delamination is normally preferred). See debond and delamination

displacement angle
In filament winding, the advancement distance of the winding ribbon on the equator after one complete circuit.

dissipation factor, electrical
See: electrical dissipation factor

In fabric, the displacement of fill fibre from the 90°ree; angle (right angle) relative to the warp fibre. In a laminate, the displacement of the fibres (especially at radii), relative to their idealised location, due to motion during lay-up and cure.

doctor blade or bar
A straight piece of material used to spread resin, as in application of 3 thin film of resin for use in hot melt prepregging or for use as an adhesive film. Also called paste metering blade.

In filament winding, the planar reinforcement applied to a local area between windings to provide extra strength in an area where a cut-out is to be made, for example, port openings. Usually placed at the knuckle joints of cylinder to dome.

In filament winding, the portion of a cylindrical container that forms the spherical or elliptical shell ends of the container.

In filament winding, a local area with extra wound or fabric reinforcement, wound integrally with the part, or wound separately and fastened to the part.

draft angle
The angle of a taper on a mandrel or mould that facilitates removal of the finished part.

The taper or slope of the vertical surfaces of a mould designed to facilitate removal of moulded parts.

The ability of a fabric or prepreg to conform to a contoured surface.

drawn fibre
Fibre with a certain amount of orientation imparted by the drawing process by which it was formed.

dry laminate
A laminate containing insufficient resin for complete bonding of the reinforcement. See: resin-starved area

dry lay-up
Construction of a laminate by the layering of pre-impregnated reinforcement (partly cured resin) in a female mould or on a male mould, usually followed by bag moulding or autoclave moulding.

dry winding
A term used to describe filament winding using pre-impregnated roving, as differentiated from wet winding, where un-impregnated roving is pulled through a resin bath just before being wound onto a mandrel. See: wet winding

See: differential scanning calorimetry (DSC)

See: differential thermal analysis

The amount of plastic strain that a material can withstand before fracture. Also, the ability of a material to deform plastically before fracturing.

A pause in the application of pressure or temperature to a mould, made just before it is completely closed, to allow the escape of gas from the moulding material.

In filament winding, the time that the traverse mechanism is stationary while the mandrel continues to rotate to the appropriate point for the traverse to begin a new pass. In a standard autoclave cure cycle, an intermediate step in which the resin matrix is held at a temperature below the cure temperature for a specified period of time sufficient to produce a desired degree of staging. Used primarily to control resin flow.

dynamic modulus
The ratio of stress to strain under vibratory conditions (calculated from data obtained from either free or forced vibration tests, in shear, compression, or elongation)

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