| Observed value |
The particular value of a characteristic determined as a result of a test or measurement. |
| Octane number |
(octane rating) A measure of the anti-knock properties of a fuel taken as the percentage by volume of iso-octane in the fuel. |
| Offset |
The distance along the strain coordinate between the initial portion of a stress-strain curve and a line parallel to the initial portion that intersects the stress-strain curve at a value of stress (commonly 0.2%) that is used as a measure of the yield strength. Used for materials that have no obvious yield point. |
| Offset modulus |
The ratio of the offset yield stress to the extension at the offset point (plastics). |
| Offset yield strength |
The stress at which the strain exceeds by a specified amount (the offset) an extension of the initial proportional portion of the stress-strain curve. Expressed in force per unit area. |
| Oil hardening |
The formation of martensite before tempering by quenching suitable steels in oil at lower cooling rates than given by water quenching, thus reducing the likelihood of component fracture or severe residual stresses. |
| Oil hardening |
Quench-hardening treatment involving cooling in oil. |
| Oil quenching |
Hardening of carbon steel in an oil bath. Oils are categorized as conventional, fast, martempering, or hot quenching. |
| Oil-cooled |
A term for a machine that uses circulating oil to remove heat. |
| Oldham coupling |
(double-slider coupling) A device for connecting a pair of misaligned parallel shafts, on the end of each of which are flanges having diametral tenons (tongues) that engage with matching slots spaced at 90° in an intermediate disc. As the coupling rotates, the disc compensates for shaft offset by sliding along each tenon in turn. Low-friction surfaces are requisite and the disc is often made of a polymer. An alternative arrangement has the slots in the flanges and the tenons on the disc. |
| Olsen cup test |
A cupping test in which a piece of sheet metal, restrained except at the center, is deformed by a standard steel ball until fracture occurs. The height of the cup at time of fracture is a measure of the ductility. |
| Orange peel |
A surface roughening in the form of a pebble-grained pattern where a metal of unusually coarse grain is stressed beyond its elastic limit. Also known as pebbles and alligator skin. |
| O-ring (O-ring seal) |
A toroidal ring of synthetic rubber seated in a groove machined into a flat or cylindrical surface to act as a seal. |
| Outside diameter (Unit m) |
(external diameter, OD) The diameter of a circular cylindrical tube or a sphere measured between opposite points on the external surface. |
| Overaging |
Aging under conditions of time and temperature greater than those required to obtain maximum change in a certain property, so that the property is altered in the direction of the initial value. |
| Overheating |
Heating a metal or alloy to such a high temperature that its properties are impaired. When the original properties cannot be restored by further heat treating, by mechanical working, or by a combination of working and heat treating, the overheating is known as burning. |
| Oxidation |
(1) A reaction in which there is an increase in valence resulting from a loss of electrons. (2) A corrosion reaction in which the corroded metal forms an oxide; usually applied to reaction with a gas containing elemental oxygen, such as air. |
| Oxidative wear |
A type of wear resulting from the sliding action between two metallic components that generates oxide films on the metal surfaces. These oxide films prevent the formation of a metallic bond between the sliding surfaces, resulting in fine wear debris and low wear rates. |
| Oxidized surface (on steel) |
Surface having a thin, tightly adhering, oxidized skin (from straw to blue in color), extending in from the edge of a coil or sheet. Sometimes called annealing border. |
| Oxidizing agent |
A compound that causes oxidation, thereby itself becoming reduced. |
| Oxidizing flame |
A gas flame produced with excess oxygen in the inner flame. |
| Oxygen probe |
An atmosphere-monitoring device that electronically measures the difference between the partial pressure of oxygen in a furnace or furnace supply atmosphere and the external air. |
