Stretching a relatively small, shallow indentation into sheet metal.
In aircraft, stretching metal into a conical flange for the use of a countersunk head rivet.
DIP RINSE (PT): A means of removing excess penetrant in which the test parts are dipped into an agitated tank of
water or remover.
DIRECT CURRENT: Electric current flowing continuously in one direction through a conductor. Such current is
frequently referred to as DC.
DIRECT FILM (RT): See non-screen film.
DIRECTIONAL PROPERTIES: Properties whose magnitude varies depending on the relation of the test axis to the
specific direction within the metal. The variation results from preferred orientation or from fibering of constituents or
DISCERNABLE IMAGE: Image capable of being recognized by sight without the aid of magnification; corrected
DISCONTINUITY: An interruption in the normal physical structure or configuration of a part such as cracks, laps,
seams, inclusions, porosity. A discontinuity may or may not affect the usefulness of a part. See DEFECT.
DISINTEGRATION, NUCLEAR: A spontaneous nuclear transformation (radioactivity) characterized by the emission
of energy and/or mass from the nucleus.
DISLOCATION: A linear defect in a crystal or lattice of a material. The two basic types are edge and screw.
DISPERSANT (PT): A substance for promoting the formation and stabilization of dispersed particles of one substance
DISPERSION, SOUND: Scattering of rays of an ultrasonic beam as a result of reflection from a highly irregular
incident surface above that normally associated with a particular transducer.
DISTANCE AMPLITUDE CORRECTION (UT): Compensation for variance in amplitude from equal reflectors at
different sound travel distances. The abbreviation is DAC. Also used to denote electronic change of amplification to
provide equal amplitude from equal reflectors at different sound travel distances. Other designations for this electronic
change of amplification are Swept Gain (SG), Time Corrected Gain (TCG), Time Variable Gain (TVG) and Sensitivity
Time Control (STC).
DISTORTED FIELD (MT): The direction of a magnetic field in a symmetrical object will be substantially uniform if
produced by a uniformly applied magnetizing force, as in the case of a bar magnetized in a solenoid. But if the piece
being magnetized is irregular in shape, the field is distorted and does not follow a straight path or have a uniform
DOSE OR RADIATION DOSE: A generic term that means absorbed dose, dose equivalent, etc. And represents the
total amount of radiation received during the applicable period of exposure.
DOSE EQUIVALENT: The product of the absorbed dose in tissue, quality factor, and all other necessary modifying
factors at the location of interest. The units of dose equivalent are the rem and Sievert (Sv).
DROSS: The scum that forms on the surface of molten metals largely because of oxidation but sometimes because of
the rising of impurities to the surface.
DRY DEVELOPER (PT): A developer powder that is applied as a dust without a liquid carrier.