FOIL: Metal in sheet from less than 0.006 inches in thickness.
FOLD: See LAP.
FOREIGN MATERIALS: They may appear as isolated, irregular, or elongated variations of film density not
corresponding to variations in thickness of material or to cavities. May be sand, slag, oxide or dross, or metal of
different density, included in the material being examined.
FORGING: Working metal into a desired shape by hammer, upsetting, or pressing, either hot or cold, or by a
combination of these processes.
FORGING CRACKS: See CRACKS, FORGING.
FORGING RANGE: Temperature range in which a metal can be forged successfully.
FORGING STRAIN: Internal strains in the metal set up by the forging operation.
FORGE WELD: Uniting metal by heat and pressure during forging.
FORMABILITY: The relative ease with which a metal can be shaped through plastic deformation.
FORMING: Making a change, with the exception of shearing or blanking, in the shape or contour of a metal part
without intentionally altering the thickness.
FORWARD SCATTER: Radiation scattered in approximately the same direction of the primary beam.
FOUNDRY: A commercial establishment or building where metal castings are produced.
FRACTOGRAPHY: Descriptive treatment of fracture, especially in metals, with specific reference to photographs of
the fracture surface. Macrofractography involves photographs at low magnification; microfractography, at high
FRACTURE: A break, rupture, or crack large enough to cause a full or partial partition of a casting.
The maximum principal true stress at fracture. Usually refers to unnotched tensile specimens.
The (hypothetical) true stress which will cause fracture without further deformation at any given strain.
FRACTURE TEST: Breaking a specimen and examining the fractured surface with the unaided eye or with a low-
power microscope to determine such things as composition, grain size, case depth, soundness, or presence of defects.
FRAGMENTATION: The subdivision of a grain into small discrete crystallites outlined by a heavily deformed network
or intersecting slip as a result of cold working. These small crystals or fragments differ from one another in orientation
and tend to rotate to a stable orientation determined by the slip systems.
FRAUNHOFER ZONE (UT): See FAR FIELD.
FREE CARBON: The part of the total carbon in steel or cast iron that is present in the elemental form as graphite or
FREQUENCY: Frequency in uniform circular motion or in any periodic motion is the number of revolutions or cycles
completed in unit time. The International Systems of Units expresses frequency in Hertz (1 Hz = 1 cycle per second).