RESIDUAL STRESS: Internal stress remaining in a piece of metal following some processing operation, such as
hardening, cold working, etc.
RESISTANCE: The opposition to the flow of an electrical current through a conductor or circuit that does not include
inductive or capacitive elements. It can be expressed as the ratio of the applied voltage to the current.
RESOLUTION, DEFECT: A property of a test system that enables the separation of indication due to defects in a test
specimen that are located in close proximity to each other.
RESONANCE METHOD: A method that varies the frequency of continuous ultrasonic waves to excite standing waves
in a body generally used for thickness measurement.
RETENTIVITY (MT): The ability of a material to retain magnetism after the current has been removed.
RETICULATION (RT): The swelling of film emulsion because of sudden change of temperature, in excess of 15F
REVERSAL (RT): The production of a positive instead of a negative image in an emulsion or vice versa.
RF DISPLAY (UT): A CRT signal display that is not rectified. Displayed signals are both above and below the sweep
or base line.
RHM (RT): See ROENTGENS PER HOUR AT ONE METER. rhr: Abbreviation for roughness height rating.
RIGGING: The engineering design, layout, and fabrication of pattern equipment for producing castings; including a
study of the casting solidification program, feeding and gating, risering, skimmers, and fitting flasks.
RIMMED STEEL: A low-carbon steel containing sufficient iron oxide to give a continuous evolution of carbon
monoxide while the ingot is solidifying, resulting in a case or rim of metal virtually free of voids. Sheet and strip
products made from the ingot have very good surface quality.
RINGING METHOD (UT): A bonded structure inspection method in which unbonds are indicated by increased
amplitude ringing signals.
RINGING SIGNALS (UT): Closely spaced multiple signals can be caused by multiple reflections in a thin material or
continued vibration of a transducer element.
RINGING TIME (UT): The time that the mechanical vibrations of a transducer element continue after the electrical
pulse has stopped.
RIPPLE (RT): The periodic variation in the potential differences between the cathode and anode of an X-ray tube,
resulting from rectification of an alternating current. As the ripple is decreased by the use of filtering circuits, a
constant potential is more nearly approached.
RINSE (PT): In penetrant inspection, the operation by which the excess surface penetrant is removed from the part.
Sometimes also referred to as the WASH.
RISER: A reservoir of molten metal connected to the casting to provide additional metal to the casting, required as the
result of shrinkage before and during solidification.
R-METER: An ionization-type instrument designed to measure radiation dose.
ROCKWELL HARDNESS TEST: A test for determining the hardness of a material based upon the depth of
penetration of a specified penetrator into the specimen under certain arbitrarily fixed conditions of test.