EXTRUSION: Conversion of a billet into lengths of uniform cross section by forcing the plastic metal through a die
orifice of the desired cross-sectional outline.
EXTRUSION DEFECT: A defect of flow in extruded products caused by the oxidized outer surface of the billet flowing
into the center of the extrusion. It normally occurs in the last 10 to 20% of the extruded bar. Also called pipe or
EXUDED (PT): To ooze out slowly in small drops through openings; to flow slowly out.
EYE DOSE EQUIVALENT: applies to the external exposure of the lens of the eye and is taken as the dose equivalent
at a tissue depth of 0.3 centimeters (300-mg/ cm2).
f: Symbol for frequency.
FALSE INDICATIONS: See NON-RELEVANT INDICATIONS.
FALSE INDICATIONS (MT): An indication of magnetic particles on the part held by gravity or surface roughness. It
is neither caused nor held in place by leakage field.
FAMILY CONCEPT (PT): See SYSTEM CONCEPT. The term Family Concept has been changed to System
Concept to comply with DOD standardization requirements. The two terms have the same meaning.
FAMILY (PT): A family of materials refers to the entire series of materials supplied by one manufacturer, necessary to
perform a specific type or process of inspection.
FAR FIELD (UT): Sound beam zone in which equal reflectors give signals of exponentially decreasing amplitude with
increasing distance; zone beyond the near field; also known as the FRAUNHOFER ZONE.
FAST FILM: Radiographic film that has inherent graininess characteristics of a coarse nature intended to increase the
relative film speed.
FATIGUE: The progressive fracture of a material that begins at a defect and increases under repeated cycles of stress.
Fatigue fractures are progressive, beginning as minute cracks that grow under the action of the fluctuating stress.
FATIGUE CRACKS: See CRACKS, FATIGUE.
FATIGUE LIFE: The number of cycles of stress than can be sustained prior to failure for a stated test condition.
FATIGUE LIMIT: The maximum stress below which a material can presumably endure an infinite number of stress
cycles. If the stress is not completely reversed, the value of the mean stress, the minimum stress or the stress ratio
should be stated.
FATIGUE RATIO: The ratio of the fatigue limit for cycles of reversed flexural stress to the tensile strength.
FATIGUE STRENGTH: Maximum stress that a metal will withstand without failure for a specified number of cycles of
FATIGUE STRENGTH REDUCTION FACTOR (Kf): The ratio of the fatigue strength of a member or specimen with
no stress concentration to the fatigue strength with stress concentration. Kf has no meaning unless the geometry, size
and material of the member or specimen and stress range are stated.