| Waist |
The joint in a robot corresponding to the human waist, i.e. providing rotation about a vertical axis. In an articulated robot, the first joint mounted at the base frame. |
| Wallner lines |
A distinct pattern of intersecting sets of parallel lines, usually producing a set of V-shaped lines, sometimes observed when viewing brittle fracture surfaces at high magnification in an electron microscope. Wallner lines are attributed to interaction between a shock wave and a brittle crack front propagating at high velocity. Sometimes Wallner lines are misinterpreted as fatigue striations. |
| Washer |
An annular disc of metal, rubber, plastic, ceramic, etc., placed between two surfaces in contact either to spread the load (for example, between a surface and a tightened nut or a bolt head), to provide a seal, or to separate or align components. |
| Waste heat |
1. Heat generated by internal-combustion engines, gas turbines, electrical generators, electrical equipment, and industrial processes that is not used directly but is expelled to the environment, often in hot flue or exhaust gases. 2. Heat generated from waste |
| Waste-heat recovery |
The recovery of thermal energy from flue and exhaust gases, or from liquids heated in industrial processes. Recovery devices include pre-heaters, recuperators, regenerators, and waste-heat boilers. |
| Water column |
Water in a tube, which may be vertical or inclined. If the tube is open to the atmosphere, the vertical height h from a datum level to the water surface is a measure of the water static pressure p at the datum level given by p − B = ρgh where B is the barometric pressure, ρ denotes the water density, and g is the acceleration due to gravity. |
| Water hammer |
The reflected pressure surge that occurs in a liquid flowing through a pipe, usually as a consequence of sudden closure of a valve. The surge may cause the pipe to vibrate and a hammering noise to be heard. Key factors affecting the surge amplitude are the compressibility of the liquid (especially if it contains undissolved gas) and the elasticity of the pipe wall. |
| Water jacket |
A casing, typically of sheet metal, surrounding a machine, such as an engine, that requires cooling. Water is circulated through the jacket and a heat exchanger where the heat is removed. |
| Water quenching |
A quench in which water is the quenching medium. The major disadvantage of water quenching is its poor efficiency at the beginning or hot stage of the quenching process. |
| Water-jet cutting |
Cutting of materials such as rock by means of a high-speed jet of water containing abrasive particles. |
| Wave spring |
A type of compression spring, similar to a coil spring, but made of strip shaped into waves around the circumference. |
| Waviness |
Waviness is periodic deviations from geometric surface, often sinusoidal in form and often determined by low-level oscillations of the machine-tool-workpiece system during machining. Typically, wavelengths range from 1 to 10 mm (0.04 to 0.4 in.) and wave heights from a few to several hundred micrometers. |
| Wear |
Damage to a solid surface, generally involving progressive loss of material, due to relative motion between that surface and a contacting surface or substance. |
| Wear |
The deterioration of a component or structure with time and usage, often impairing the function for which it was designed, owing to abrasion, corrosion, fatigue, friction, etc. during relative motion of parts. The wear factor (K), with unit mm3/N.m, is an empirical dimensional factor that quantifies surface wear due to mechanical frictional contact, and defined by K = /Fs where is the worn volume (in mm3), F is the contact load (in N), and s is the sliding distance (in m). |
| Wear rate |
The rate of material removal or dimensional change due to wear per unit of exposure parameter—for example, quantity of material removed(mass, volume, thickness) in unit distance of sliding or unit time. |
| Wedge |
A short triangular prism whose major surfaces subtend an acute angle, that can be driven between two objects or parts of an object to split, tighten, or secure them, or to widen an opening or raise a heavy object. The acute angle gives a high mechanical advantage. |
| Weight |
The force of attraction on a body due to gravity. A body’s weight is the product of its mass and the gravitational field strength at that point. Mass remains constant, but weight depends on the object’s position on the Earth’s surface, decreasing with increasing altitude. |
| Weight (W) (Unit N) |
If g is the acceleration due to gravity, the weight of a mass m is given by W = mg. On Earth, the acceleration due to gravity is approximately 9.81 m/s2, so that the weight of a 1 kg mass is 9.81 N. More generally, the weight is the force exerted on the mass of a body when in the gravitational field of another body. |
| Weld penetration |
It is the depth below the surfaces, as revealed in microstructural sections of joined metals, which is melted during welding. |
| Welding |
In tribology, the bonding between metallic surfaces in direct contact, at any temperature. |
| Welding |
A joining process in which the mating surfaces are at least softened, or more usually melted, unlike soldering and brazing. In solid-state (non-melting) welding, similar or dissimilar metals or thermoplastics may be joined by applying pressure to hot interfaces. In forge welding, joining is achieved by compression across the join between pre-heated workpieces. In friction welding (spin welding) one of the contacting surfaces is rotated rapidly before being loaded against the other. On contact, heat generated by friction softens the materials and permits severe plastic deformation that seals the joint. In friction stir welding, a wear-resistant tool is rotated rapidly, indents the surfaces and is traversed to form a join line. Resistance welding involves simultaneous pressure and electrically-generated heat, as in spot welding where a heavy electric current is passed for a short time through metal sheets which are pressed together between electrodes. |
| Wheel |
A solid disc, or a circular ring with spokes radiating from a central hub, either attached to an axle around which it revolves or which revolves with a rotating axle. |
| Widmanstätten structure |
A structure characterized by a geometrical pattern resulting from the formation of a new phase along certain crystallographic planes of the parent solid solution. The orientation of the lattice in the new phase is related crystallographically to the orientation of the lattice in the parent phase. The structure is readily produced in many alloys by appropriate heat treatment. |
| Width across flats |
A principal dimension of nuts, or of bolt heads. Work hardening The slight increase in hardness and strength produced when a body is loaded past its yield point. Also called strain hardening. |
| Wind energy (Unit kJ) |
The kinetic energy associated with wind that can be converted by a wind energy conversion system (WECS) into electrical or mechanical power by a rotor, such as a multi-bladed propeller, exposed to the wind. If the air density is ρ and the wind speed is V, then the kinetic energy flux is ρV3/2. The actual wind power that can be extracted by a wind turbine intercepting a cross section of wind A is CPρAV3/2 where CP is an empirical efficiency factor termed the power coefficient. The wind-energy distribution is a histogram of the calculated wind power that can be generated annually from the windspeed frequency distribution at a given location. A windmill generates mechanical power whereas a wind turbine (wind generator) generates electrical power. The largest wind turbine, manufactured by MHI Vestas, has a power rating of 9.5 MW, a rotor diameter of 164 m, and a hub height of 105 m (the highest wind turbines have heights in the region of 190 m). A wind farm is an array of wind turbines, typically ten to several hundred, at a single location, either onshore or offshore. Energy derived from wind is a major contributor to sustainable energy generation. The largest operational offshore wind farm, located in the Irish Sea, has 87 turbines and a total generating capacity of 659 MW. The largest onshore wind farm is in Kern County, California with some 586 turbines and a total capacity of 1 550 MW. |
| Wind pressure (Unit Pa) |
The dynamic pressure associated with the wind. The static pressure of the wind is the atmospheric pressure. |
| Wind pump |
A pump driven directly by a windmill on a tower. Widely used in remote locations. |
| Wind tunnel |
A duct in which a controlled flow of air is used for testing and research. Types include blow down, closed circuit, open return, and open section. Closed-circuit tunnels may be pressurized or evacuated. The working section is usually situated immediately downstream of the flow-conditioning elements, which may include a plenum chamber, honeycomb, screens, turbulence grids, and a contraction. Immediately downstream there is usually a diffuser. For basic research the usual requirement is for uniform steady flow in the working section with low swirl and turbulence intensity. For some applications the flow may be density stratified, sheared, unsteady, or of high turbulence intensity. |
| Wind velocity (Unit m/s) |
1. In the Earth’s atmosphere, a vector quantity that quantifies both the magnitude of the wind speed and its direction at a given altitude and location, conveniently represented in the hodograph plane. For convenience, the unit kph is often used. It could in principle also include information about large- and small-scale unsteadiness. Spatial variation in wind velocity, either with altitude or in a horizontal plane, is termed wind shear. 2. The airspeed in the working section of a wind tunnel. |
| Wing |
A relatively long and thin body with a cross section designed to produce lift when there is motion relative to a fluid. The principal applications are to aircraft and highperformance motor vehicles. |
| Wing nut |
A nut having two opposite protruding wings to permit hand tightening. |
| Wire rope |
A type of cable formed from individual strands of wire with a helical twist. |
| Work ratio |
The ratio of the net work out to the actual work out for a thermodynamic cycle. |
| Working fluid |
In thermodynamics, the fluid contained within the boundary of a system that experiences changes in its properties during any fluid dynamic or thermodynamic process. |
| Working load |
The tension in a bolt in use; tension produced by a combination of Residual preload and a portion (usually) of any External load. The Joint diagram is usually used to predict the approximate working load a fastener will see in service. |
| Working load (Unit N) |
The load under which a component or structure is designed to operate under normal conditions. |
| Working pressure (Unit Pa) |
The pressure at which a pressure vessel, such as a boiler, is designed to operate under normal conditions. |
| Working section |
That part of a wind tunnel in which models are placed for testing, or where detailed measurements are performed. |
| Working stress (Unit Pa) |
The stress under which a component or structure is designed to operate under normal conditions. |
| Workspace (Unit m3) |
(working-space volume) The volume around the base frame of a robot, defined by the reach of the robot. The robot can thus only perform tasks within this volume. |
| Wrap-around bend |
The bend obtained when a specimen is wrapped in a closed helix around a cylindrical mandrel. This term is sometimes applied to a semiguided bend of 180° or less. |
| Wrinkling |
A wavy condition obtained in deep drawing of sheet metal, in the area of the metal between the edge of the flange and the draw radius. Wrinkling may also occur in other forming operations when unbalanced compressive forces are set up. |
| Wrist |
The final three joints on a robot which simulate rotations provided by the human wrist and thus allow orientation of the end effector to which it is attached by the wrist socket. |
| Wrist pin |
A stud projecting from a crank as an attachment for a connecting rod. wrought alloys Metal alloys that are initially cast and then shaped into final form by processes such as extrusion, forging, or rolling. |
| Wrought iron |
A highly ductile (but anisotropic) type of iron containing elongated slag fibres that resulted from the method of manufacture in which excess carbon in pig iron was burnt and worked out. The yield strength is some 200 MPa, tensile strength 320 MPa, and reduction of area on a 50-mm gauge length up to 35%. Now replaced by steel. |
