T.O. 33B-1-1
Glossary 91
TEMPORARY MAGNETS: A body of normally soft steel or piece iron which is readily magnetized but retains only a
very small field after the active power of the external magnetic field is removed.
TENSILE STRENGTH: The maximum stress that a material is capable of withstanding without breaking under a
gradually and uniformity applied load. Other terms commonly used to express the same thing are ultimate tensile
strength and, less accurately, breaking strength.
TENTH-VALUE LAYER (TVL) (RT): The thickness of the layer of a specified substance which, when introduced into
the path of a given narrow beam of radiation, reduces the intensity of this radiation to one-tenth the original value.
TEST BLOCK: See REFERENCE STANDARD.
TEST FREQUENCY: The number of complete input cycles per unit time of a periodic quantity such as alternating
current employed for a specified inspection. The test frequency is always considered to be the fundamental whenever
harmonics are generated in the process of testing certain materials such as ferromagnetic materials.
TEST PART: A part, material, or assembly being inspected.
TEST SURFACE: The test part surface through which the ultrasonic energy used for inspection initially enters the test
part.
THERMAL ANALYSIS: A method for determining transformations in a metal by noting the temperatures at which
thermal arrests occur. These arrests are manifested by changes in slope of the plotted or mechanically traced heating
and cooling curves. When such data are secured under nearly equilibrium conditions of heating and cooling, the
method is commonly used for determining certain critical temperatures required for the construction of equilibrium
diagrams.
THERMAL CAPACITY: A measure of the amount of heat that can be obtained in a given mass of material.
THERMAL FATIGUE: Fracture resulting from the presence of temperature gradients which vary with time in such a
manner as to produce cyclic stresses in a structure.
THERMAL FOCUS (RT): That part of the anode of an X-ray tube submitted to direct heating by the electron beam.
THERMAL SHOCK: The development of a steep temperature gradient and accompanying high stresses within a
structure.
THERMAL STRESSES: Stresses in metal, resulting from non-uniform temperature distribution.
THERMIONIC EMISSION (RT): The emission of electrons from the surface of a heated material by virtue of their
thermal energy.
THERMOLUMINESCENCE (RT): The property possessed by certain crystals, of emitting light when heated after
having been exposed to ionizing radiation.
THERMOLUMINESCENCE DOSIMETER (TLD) (RT): A dosimeter, commonly used as a personnel monitor that
uses thermoluminescent material. The total amount of light emitted upon heating of the material is proportional to the
amount of radiation energy absorbed.
THETA (0): Symbol for the half angle of beam spread; the Greek letter Theta.
THORIATED TUNGSTEN FILAMENT (RT): A vacuum-tube filament consisting of tungsten mixed with thorium
oxide to give improved electron emission. Also known as thoriated emitter.
