STRESS: Force per unit area, often thought of as force acting through a small area within a plane.
STRESS CONCENTRATION FACTOR (Kt): The ratio of the greatest stress, in the region of a notch or other stress
raiser as determined by advanced theory, photo-elasticity or direct measurement of elastic strain, to the corresponding
STRESS-CORROSION CRACKING: Failure by cracking under combined action of corrosion and stress, either
external (applied) or internal (residual). Cracking may be either intergranular or transgranular, depending on metal
and corrosive medium.
STRESS RAISERS: Changes in contour of discontinuities in structure that cause local increases in stress.
STRESS RELIEVING: Heating to a suitable temperature, holding long enough to reduce residual stresses and then
cooling slowly enough to minimize the development of new residual stresses. See TEMPER.
STRESS RUPTURE TEST: A tension test performed at constant load and constant temperature, the load being held at
such a level as to cause rupture. Also known as creep-rupture test.
STRETCH FORMING: Shaping of a sheet or part, usually of uniform cross-section, by first applying suitable tension or
stretch and then wrapping it around a die of the desired shape.
STRETCHER LEVELING: Leveling where a piece of metal is gripped at each end and subjected to a stress higher than
its yield strength to remove warp and distortion. Sometimes called patent leveling.
STRETCHER STRAIGHTENING: A process for straightening rod, tubing and shapes by the application of tension at
the ends of the stock. The products are elongated a definite amount to remove warpage.
STRETCHER STRAINS: Elongated markings that appear on the surface of some materials when deformed just past
the yield point. These markings lie approximately parallel to the direction of maximum shear stress and are the result
of localized yielding. Same as Luders Lines.
STRIKING: Electrodepositing, under special conditions, a very thin film of metal which will facilitate further plating
with another metal or with the same metal under different conditions.
STRINGER: In wrought materials, an elongated configuration of microconstituents or foreign material aligned in the
direction of working. Commonly, the term is associated with elongated oxide or sulfide inclusions in steel.
STRIPPING EMULSION (RT): A photographic emulsion, for use in autoradiography, which can be removed from its
base and placed in contact with a specimen containing radioactive material.
SUBJECT CONTRAST: See CONTRAST, SUBJECT.
SUBJECT CONTRAST (RT): The ratio (or the logarithm of the ratio) of the radiation intensities transmitted by
selected portions of the specimen.
SUBJECT RANGE (RT): The range of thickness or radiation opacity of material in a specimen.
SUBJECTIVE CONTRAST (RT): A qualitative estimate of the contrast in a radiograph or fluorescent screen
SUBSTITUTIONAL SOLID SOLUTION: An alloy composed of two or more chemical elements in which both metals
are randomly distributed at equivalent lattice positions throughout the metal.
SUBSTRATE: Layer of metal underlying a coating, regardless of whether the layer is basis metal.