| Gage length |
The original length of the portion of a specimen over which strain, change of length, or other characteristics are determined. |
| Galilean transformation |
In steady fluid flow, the addition or subtraction of a constant velocity to the entire flowfield, e.g. so that flow can be considered relative to a moving object or flow feature, such as a shock wave. |
| Galling |
An extreme form of adhesive wear, in which large chunks of one part stick to the mating part (during sliding contact). |
| Galvanic protection |
The coating on a fastener is said to provide galvanic protection if it is more anodic than the fastener and will, therefore, be destroyed instead of the fastener. Zinc plate (galvanizing) provides galvanic protection to steel fasteners, for example. |
| Gamma iron |
The face-centered cubic form of pure iron, stable from 910 to 1400 °C (1670 to 2550 °F). |
| Gas compressor |
A machine which draws in a gas at low pressure and delivers it at high pressure, usually accompanied by a temperature increase. Compressor designs include axial, centrifugal, diaphragm, reciprocating, and rotary (including the blade compressor). |
| Gasket factors |
Experimentally derived ‘‘constants’’ used to define the behavior of a gasket or the assembly and in-service conditions required for acceptable behavior. |
| Gasket m-factor |
For a gasketed joint of area A in which the clamping force is F, the factor m is defined by F ≥ mpA where p is the pressure that would separate the two halves of the joint and m > 1. |
| Gasket stress |
The contact stress exerted on the gasket by the joint members. |
| Gauge |
1. Any instrument for measuring or checking dimensions, including adjustable gauges such as a micrometer and non-adjustable gauges such as go/no-go limit gauges that indicate the maximum and minimum dimensions allowable in a component during manufacture. 2. A term often used to mean an instrument, e.g. pressure gauge. 3. The diameter of a wire or thickness of a sheet according to a standard. 4. The distance between the rails of a railway track. |
| Gauge pressure (Unit Pa) |
The level of static pressure above the ambient pressure. |
| Gear motor |
Essentially a gear pump run in reverse, in which high-pressure fluid supplied to one side of the casing causes the gears to rotate. |
| Gear pump |
A positive-displacement pump in which fluid is pumped by meshing gears, one driven and the other an idler gear, on parallel axes within a closed casing. |
| Gear ratio |
For two gears in contact, the ratio of the number of teeth on the driving gear to that on the driven gear. |
| Gear wheel |
Any form of toothed wheel, particularly those having conjugate teeth employed in the transmission of motion and power. |
| Gearbox |
A mechanism consisting of meshing gears which transmit power and torque to an output shaft from an input shaft directly connected to an engine. The mechanism is normally contained within a casing filled with lubricating oil. The diagram shows a simple four-speed sliding-mesh gearbox in which gears with different numbers of teeth are slid along parallel splined shafts within the gearbox to mesh with each other and change the ratio of output to input speed (gear ratio). |
| generator |
1. A machine for converting mechanical energy to electrical energy. 2. (generatrix) A point, line, or surface regarded as moving and so forming a line, a surface, or a volume, respectively. |
| GGas turbine |
An engine in which air, compressed by a multi-stage axial compressor and/or one or more centrifugal compressors, flows into a combustion chamber (or chambers) where fuel is burned and the hot gases then drive an axial turbine which powers the compressor. |
| Gibbs–Dalton law |
An extension of Dalton’s law of additive pressures to include the statement that the internal energy, enthalpy, and entropy of a mixture of gases are equal to the sum of the internal energies, enthalpies, and entropies the individual constituents would have if each existed alone at the same temperature and volume. Gibbs rule is that part of the law pertaining to entropy. |
| Graham’s laws |
The laws stating that the rates of diffusion and effusion of a gas are inversely proportional to the square root of its density. |
| Grain |
1. An individual crystal in a polycrystalline solid. Most engineering materials such as metals and ceramics are used in polycrystalline form. 2. (gr) A non-SI unit of mass. The conversion to SI is 1 gr = 6.479 891 × 10−5 kg. |
| Grain coarsening |
A heat treatment that produces excessively large austenitic grains. |
| Grain growth |
An increase in the average size of the grains in polycrystalline metal, usually as a result of heating at elevated temperature. |
| Grain growth |
An increase in the average size of the grains in polycrystalline metal, usually as a result of heating at elevated temperature. |
| Grain refiner |
A material added to a molten metal to induce a finer-than-normal grain size in the final structure. |
| Grain size |
A measure of the areas or volumes of grains in a polycrystalline metal, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, the grain size refers to that of the matrix unless otherwise specified. |
| Grain size |
For metals, a measure of the areas or volumes of grains in a polycrystalline material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, the grain size refers to that of the matrix unless otherwise specified. Grain sizes are reported in terms of number of grains per unit area or volume, average diameter, or as a grainsize number derived from area measurements. |
| Grain-boundary liquation |
An advanced stage of overheating in which material in the region of austenitic grain boundaries melts. |
| Granular fracture |
A type of irregular surface produced when metal is broken that is characterized by a rough, grainlike appearance, rather than a smooth or fibrous one. It can be subclassified as transgranular or intergranular. |
| Graphitic carbon |
Free carbon in steel or cast iron. |
| Graphitization |
Formation of graphite in iron or steel. Where graphite is formed during solidification, the phenomenon is called primary graphitization; where formed later by heat treatment, secondary graphitization. |
| Graphitizing |
Annealing a ferrous alloy in such a way that some or all of the carbon is precipitated as graphite. |
| Gravity |
The attractive force by which bodies are drawn towards the centre of Earth or other celestial object. Its intensity is measured by the acceleration produced. |
| Gravity |
The gravitational force of attraction at the surface of a planet or other celestial body. The Earth’s gravity produces an acceleration of around 9.8m / s2 for any unsupported body. |
| Grinding |
1. A process of high-speed multiple scratching of surfaces by a wheel formed from hard grits and a binder which are progressively exposed as the binder wears away. It is a process of micromachining employed particularly in accurate finishing operations on hard materials. 2. A form of comminution. |
| Grinding stress (Unit Pa) |
The residual stresses left in the surface of a component after grinding, owing to non-uniform cooling from the high surface temperatures produced. |
| Grip length |
Combined thickness of all the things clamped together by the bolt and nut, including washers, gaskets, and joint members. |
| Grub screw |
A short headless screw with a recess at one end to receive a screw driver or key. |
| Guided bend |
The bend obtained by use of a plunger to force the specimen into a die in order to produce the desired contour of the outside and inside surfaces of the specimen. |
| Guided-bend test |
A test in which the specimen is bent to a definite shape by means of a punch (mandrel) and a bottom block. |
