T.O. 33B-1-1
Glossary 18
CRACKS, FATIGUE: Progressive cracks which develop in the surface caused by the repeated loading and unloading of
the part, or by what is called reverse bending.
CRACKS, FORGING: Cracks developed in the forging operation due to forging at too low a temperature, resulting in
rupturing of the steel.
CRACKS, GRINDING: Thermal cracks due to local over-heating of the surface being ground, generally caused by lack
of coolant, improper coolant, dull wheel, too rapid a feed, or too heavy a cut.
CRACKS, HEAT TREATING: See CRACKS, QUENCHING.
CRACKS, HOT: Same as CRACKS, COLD, but developing before the casting has completely cooled.
CRACKS, MACHINING: A surface defect generally called machining tear and caused by too heavy a cut, a dull tool,
chatter, or dragging the tool over the metal when not cutting cleanly.
CRACKS, NOT OPEN: Indications which are difficult to discern or prove upon the use of contrast penetrant inspection
techniques.
CRACKS, OPEN: Those flaws which can be detected by contrast penetrant inspection techniques.
CRACKS, PICKLING: Cracks caused by the release of internal stresses due to metal removal by immersion in acid or
chemical solutions.
CRACKS, PLATING: A crack developed by the plating process, usually occurring in parts having high internal
stresses.
CRACKS, QUENCHING: Ruptures produced in the tempering of metal, due to uneven cooling and contracting of one
portion of a part.
CRACKS, SERVICE: Ruptures that occur on a part after all fabrication has been completed and the part placed in-
service. Failure may be due to fatigue, corrosion, overstressing, or undetected processing discontinuities.
CRATER:
(1)
In machining, a depression in a cutting tool face eroded by chip contact.
(2)
In arc welding, depressions at the termination of a bead or in the weld pool beneath the electrode.
CREEP: Time-dependent strain occurring under stress. The creep strain occurring at a diminishing rate is called
primary creep; that occurring at a minimum and almost constant rate, secondary creep; that occurring at an
accelerating rate, tertiary creep.
CREEP STRENGTH:
(1)
The constant nominal stress that will cause a specified quantity of creep in a given time at constant
temperature.
(2)
The constant nominal stress that will cause a specified creep rate at constant temperature.
CREVICE CORROSION: A type of concentration cell corrosion; corrosion of a metal that is caused by the
concentration of dissolved salts, metal ions, oxygen or other gases, and such, in crevices or pockets remote from the
principal fluid stream, with a resultant building up of differential cells that ultimately cause deep pitting.
