Definitions /Dictionary/Glossary - nptel

Dielectric: A nonconductor of electricity. It is the material’s ability to resist the flow of electrical
current.
Dielectric Constant: An assembly’s ratio of capacitance when its two electrodes are separated
solely by a plastic insulating material to its capacitance when the electrodes are separated by air.
Dielectric Heating: Heating materials by dielectric loss in a high-frequency electrostatic field.
Dielectric Strength: An electrical property indicating how well a material acts as an electrical
insulator. It describes how much of an electrical voltage can be built up on one side of the
material before it is communicated to the other side. Units are measured in volts per mil of
thickness (volts/mil). Higher numbers indicate materials with better insulation properties. C
means that the material conducts electricity and therefore has no dielectric strength.
Dimensional Stability: A plastic part’s ability to retain the precise shape to which it was
molded, cast, or otherwise fabricated.
Direct-Sized Yarn: Specially formulated sizing on textile yarns that allows them to be resin
compatible.
Dispersion: Degree to which roving separates into discrete bundles after being chopped. Good
dispersion is characterized by a bed of bundles uniform in width. Poor dispersion is characterized
by a wide distribution in the widths of various bundles in the bed. Poor dispersion can cause poor
wet-through and wet-out.
Distortion: Change in shape from that which is intended. Symptomatic of laminating
difficulties, curing problems, tooling problems or resin shrinkage.
Doctor Blade or Bar: A straight piece of material used to spread resin, as applying a thin film of
resin for use in hot melt prepreg or as an adhesive film. It is also called paste metering blade.
Doff: see Roving Doff
Doff Collapse: the failures of the roving doff to maintain its shape and stability during run-out or
storage. Doff collapse generally occurs when there is only a 1/2" to 1/4" ring of roving left from
the original doff.
Draft: The taper or slope of a mold’s vertical surface allowing molded parts to be removed.
Drape: The ability of pre-impregnated broad goods to conform to an irregular shape; textile
conformity.
Dry Loft: Height of the bed of chopped fibers.
Dry Spot: Area of incomplete surface film on laminated plastics; in laminated glass, an area
over which the interlayer and the glass have not become bonded.