| Tab washer (lock washer) |
A washer with one or more protruding tabs which can be bent in such a way that a nut or bolt head is prevented from becoming loose. |
| Tangent modulus |
The slope of the stress-strain curve at any specified stress or strain. See also modulus of elasticity. |
| Tangent screw |
A worm screw used to adjust measuring instruments such as sextants and vernier callipers. |
| Tangential load (Unit N) |
The component of load applied to an object, such as a gear, that tends to cause or resist rotation. |
| Tap |
1. A threaded hard metal plug for cutting screw threads in holes. It has longitudinal grooves for the clearance of chips while cutting. Progressive cutting is achieved by using three taps in succession: taper, second, and plug. First and second taps have tapers to help start the thread along the axis of the hole; the plug tap has no taper and is used on the final cut in a blind hole. 2. A valve in, or at the end of, a pipeline. |
| Tap wrench |
A lever with an adjustable square hole at its centre into which is fitted the shank of a tap so that torque can be applied to cut a thread. |
| Taper |
A gradual, often linear, reduction in cross section or shape. |
| Taper |
A shaft or hole that gets gradually smaller toward one end. |
| Taper key |
A key with parallel sides but tapering cross section along its length. |
| Taper pin |
A pin or peg of circular cross section that tapers along its length. |
| Taper pins |
Steel pins used for locating and holding the machine parts in position on a shaft. |
| Tare weight (Unit N) |
The weight of an empty container. |
| T-bolt |
A threaded bolt having a square or rectangular end which fits into the T slot of a machine table for clamping workpieces. |
| Tear strength (Unit N/m) |
The tensile force divided by the sheet thickness required to tear a pre-split sheet material at a specified rate. Particularly used for plastics, rubber, fabrics, and elastomers. Since the units are not those of stress but equivalent to J/m2, the units of toughness, the term ‘strength’ is strictly incorrect. |
| Teeth |
The projecting elements on gears, cutting tools, etc. |
| Temper |
(1) In heat treatment, reheating hardened steel or hardened cast iron to some temperature below the eutectoid temperature for the purpose of decreasing hardness and increasing toughness. The process also is sometimes applied to normalized steel. (2) In tool steels, temper is sometimes used, but inadvisedly, to denote the carbon content. (3) In nonferrous alloys and in some ferrous alloys (steels that cannot be hardened by heat treatment), the hardness and strength produced by mechanical or thermal treatment, or both, and characterized by a certain structure, mechanical properties, or reduction in area during cold working. |
| Temper color |
A thin, tightly adhering oxide skin that forms when steel is tempered at a low temperature, or for a short time, in air or a mildly oxidizing atmosphere. The color, which ranges from straw to blue depending on the thickness of the oxide skin, varies with both tempering time and temperature. |
| Temper embrittlement |
Brittleness that results when certain steels are held within, or are cooled slowly through, a certain range of temperature below the transformation range. The brittleness is manifested as an upward shift in ductile-to-brittle transition temperature but only rarely produces a low value of reduction in area in a smooth-bar tension test of the embrittled material. |
| Temper embrittlement |
The anomalous reduction in toughness of martensitic stainless steels when tempered in the range 370–600°C. |
| Temper embrittlement |
Embrittlement of alloy steels caused by holding within or cooling slowly through a temperature range just below the transformation range. Embrittlement is the result of the segregation at grain boundaries of impurities such as arsenic, antimony, phosphorus, and tin; it is usually manifested as an upward shift in ductile-to-brittle transition temperature. Temper embrittlement can be reversed by retempering above the critical temperature range, then cooling rapidly. |
| Temperature (Unit K or °C) |
A quantitative measure of the molecular kinetic energy of a substance and so how hot or cold it is. |
| Temperature factor |
A calibration constant used in ultrasonic measurement of bolt stress or strain. Accounts for the effects of thermal expansion and the temperature-induced change in the velocity of sound. |
| Tempered martensite embrittlement |
Embrittlement of ultrahigh-strength steels caused by tempering in the temperature range of 205 to 400 °C (400 to 750 °F); also called 350 °C or 500 °F embrittlement. Tempered martensite embrittlement is thought to result from the combined effects of cementite precipitation on prioraustenite grain boundaries or interlath boundaries and the segregation of impurities at prioraustenite grain boundaries. |
| Temporal decomposition |
The splitting of a control problem into parts with relatively short and long time constant so that different controllers may be used for the different parts. |
| Tensile strength |
In tension testing, the ratio of maximum load to original cross-sectional area. Also known as ultimate strength. |
| Tensile strength |
The resistance that a material offers to tensile stress. It is defined as the smallest tensile stress required to break the body. |
| Tensile strength (Unit Pa) |
(ultimate strength, ultimate tensile strength, UTS, Rm, Rm) The nominal or engineering stress given by the maximum load in a tension test divided by the original cross-sectional area of the specimen. The maximum load could be the fracture load for a brittle material, but for a ductile material it is usually taken as the load at which necking begins, beyond which the load falls. |
| Tensile stress |
A stress that causes two parts of an elastic body, on either side of a typical stress plane, to pull apart. |
| Tensile stress (Unit Pa) |
A stress that tends to stretch a component, or local region of a component, when under load. In simple tension it results from the applied axial load, but tensile stresses occur in bending, torsion and other forms of loading. |
| Tensile test (tension test) |
A test in which a precisely-machined tensile specimen (tensile testpiece), typically circular or rectangular in cross section with large end sections that are gripped in the testing machine, is subjected to an increasing tensile load, usually to the point of fracture, to produce a stress–strain curve from which such material properties as modulus of elasticity, limit of proportionality, proof stress, yield point, and ultimate tensile stress can be determined. The relevant standard is ISO 6892-1. |
| Tensiometer |
An instrument used to measure surface tension. |
| Tension |
The force or load that produces elongation. |
| Tension |
1. The condition in a bar, belt, cable, spring, string, wire, etc. that is being pulled from either end. 2. (tensile force) (unit N) The force associated with tension as in (1). It is measured by a tension meter. |
| Tension joint |
A joint which is primarily subjected to loads acting more or less parallel to the axes of the bolts. |
| Tension testing |
A method of determining the behavior of materials subjected to uniaxial loading, which tends to stretch the metal. A longitudinal specimen of known length and diameter is gripped at both ends and stretched at a slow, controlled rate until rupture occurs. Also known as tensile testing. |
| Tension, bolt |
Tension (tensile stress) created in the bolt by assembly preloads and=or such things as thermal expansion, service loads, etc. |
| Tensioner |
A hydraulic tool used to tighten a fastener by stretching it rather than by applying a substantial torque to the nut. After the tension has stretched the bolt or stud, the nut is run down against the joint with a modest torque, and the tensioner is disengaged from the fastener. The nut holds the stretch produced by the tensioner. |
| Tensometer |
A bench-top device, used to perform tension and compression tests. |
| Tera (T) |
An SI unit prefix indicating a multiplier of 1012; thus terawatt (TW) is a unit of power equal to one trillion watts. |
| Terminal temperature difference (Unit K) |
The temperature difference between the two fluid streams at either inlet or outlet of a heat exchanger. |
| Terminal velocity (Unit m/s) |
The velocity reached by an object in free fall through a fluid when the upward drag and buoyancy forces just balance the object’s weight. For an object with a density lower than that of the fluid, the terminal velocity is vertically upwards. |
| Testing machine |
A machine used to apply either a steady or oscillatory or impact load to a testpiece. The load may be tensile, compressive, shear, bending, or torsional. |
| Testing machine (load-measuring type) |
A mechanical device for applying a load (force) to a specimen. |
| 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 compressor |
1. (thermocompressor) A jet compressor used to boost the pressure of low-pressure waste or exhaust steam. 2. A device consisting of an absorber, a generator, a pump, and a throttling device, used instead of a mechanical vapour compressor in an absorption-cooling refrigeration system. |
| Thermal efficiency |
The ratio, for a heat engine or thermodynamic cycle, of the net work output to the net heat input into the system. |
| Thermal electromotive force |
The electromotive force generated in a circuit containing two dissimilar metals when one junction is at a temperature different from that of the other. |
| Thermal energy (heat energy) (Unit J) |
The sensible and latent forms of internal energy. |
| Thermal fatigue |
Fatigue resulting from the presence of temperature gradients that vary with time in such a manner as to produce cyclic stresses in a structure. |
| Thermal fatigue |
Fracture resulting from the presence of temperature gradients that vary with time in such a manner as to produce cyclic stresses in a structure. |
| Thermal insulation (insulation) |
A material that may be a low-conductivity solid, or a porous solid or fabric in which there are voids containing air or another gas, resulting in overall low thermal conductivity. When applied to the surface of a hot or cold object, surface heat transfer is generally reduced. |
| Thermal reactor |
An enlarged exhaust manifold bolted directly to the cylinder head of a piston engine, in which the oxidation of carbon monoxide and unburned hydrocarbons in the exhaust gas is enhanced. |
| Thermal shock |
The development of a steep temperature gradient and accompanying high stresses within a structure. |
| Thermal stresses |
Stresses in metal resulting from nonuniform temperature distribution. |
| Thermochemical treatment |
Heat treatment carried out in a medium suitably chosen to produce a change in the chemical composition of the object by exchange with the medium. |
| Thermocouple |
A device for measuring temperature, consisting of lengths of two dissimilar metals or alloys that are electrically joined at one end and connected to a voltage-measuring instrument at the other end. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions. |
| Thermodynamic pressure (Unit Pa) |
The pressure within a fluid given by an equation of state such as p(ρ,T) where ρ is the fluid density and T is the absolute temperature of the fluid. |
| Thermodynamic process |
A change in equilibrium state undergone by a quantity of matter or a system. |
| Thermodynamic properties |
Temperature, pressure, and the intensive properties that define the state of a working fluid: specific internal energy, specific enthalpy and specific entropy. |
| Thermodynamic state |
The condition of a system or working fluid according to its properties. |
| Thermodynamics laws |
The zeroth, first, second, and third laws of thermodynamics. |
| Thermoelastic effect |
The change in temperature of material under adiabatic elastic deformation, e.g. when loading is so rapid that the material is not in thermal equilibrium with its surroundings. For most materials, elastic tension lowers the temperature and compression raises it. The reverse occurs in elastomers such as rubber that exhibit entropic elasticity because stretching reduces the number of possible molecular configurations and so reduces the entropy. The thermoelastic effect gives rise to a stress–strain hysteresis loop in cyclic elastic loading and is one mechanism by which vibrational energy is dissipated internally in materials. |
| Thermoelectric converter |
(thermoelectric generator) A device consisting of series-connected alternate n- and p-type semiconductor elements sandwiched between two ceramic plates. Due to the Seebeck effect, electrical power is generated when a temperature difference is maintained across the plates. Due to the Peltier effect, a thermoelectric converter can act as either a thermoelectric heater or a thermoelectric cooler (thermoelectric refrigerator) by passing an electrical current through it. The thermoelectric figure of merit (Z), with unit 1/K, is a dimensional parameter on which the efficiency of a thermoelectric device is primarily dependent, defined by Z = σα2/k where α is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity. The product of Z and a temperature is non-dimensional. |
| Thermoelectric junction |
A welded, soldered, or twisted connection between the ends of two wires of dissimilar metals, as in a thermocouple. |
| Thermoelectric material |
A material in which any of the thermoelectric phenomena, such as the Peltier, Seebeck, and Thomson effects, are especially strong. |
| Thermomechanical working |
A general term covering a variety of processes combining controlled thermal and deformation treatments to obtain specific properties. Same as thermal-mechanical treatment. |
| Thread form |
The cross-sectional shape of the threads, defining thread angle, root, and crest profiles, etc. Thread length Length of that portion of the fastener which contains threads cut or rolled to full depth. |
| Thread grinding |
A method for producing or finishing very precise screw threads using a profiled grinding wheel. |
| Thread insert |
(threaded bushing) Either a thin cylinder with an internal thread (and sometimes also an external thread) or a helical coil of wire, pressed or screwed into a hole to accept a bolt or screw. Used in material too soft or a component too thin to be threaded, to change one form of thread to another or to repair a damaged thread. |
| Thread milling |
Thread milling is a method of cutting screw threads with a milling cutter in a thread mill. Thread milling cutters are either single form or multiple form and are used in either conventional or planetary thread mills. |
| Thread rolling |
Thread rolling (also known as roll threading) is a cold forming process for producing threads or other helical or annular forms by rolling the impression of hardened steel dies into the surface of a cylindrical or conical blank. Polygonal blanks are also thread rolled for the purpose of fabricating thread-forming and self-locking screws. The preferred polygonal shape is trilobular and is produced in flat die machines. |
| Thread run-out |
That portion of the threads which are not cut or rolled full depth, but which provide the transition between full-depth threads and the body or head. Officially called thread washout or vanish, although the term run-out is more popular. (Run-out is officially reserved for rotational eccentricity, as defined by total indicator readings or the like.) |
| Threaded fastener |
Studs, bolts, and screws of all sorts, with associated nuts. One of the most interesting, complex, useful—and frustrating—components yet devised. |
| Threading machine |
A machine used to cut an external thread on a rod, tube, bolt blank, etc. or an internal thread in a hole, tube, nut blank, etc. |
| Three-quarters hard |
A temper of nonferrous alloys and some ferrous alloys characterized by tensile strength and hardness about midway between those of half hard and full hard tempers. |
| Threshold stress for stress-corrosion cracking (σth) |
An experimentally determined critical gross-section stress below which stress-corrosion cracking will not occur under specified test conditions. |
| Thumb screw |
A type of screw having a winged or knurled head for turning by hand when a quick and light clamping effect is desired. |
| Tightness |
A measure of the mass leak rate from a gasketed joint. |
| Tightness parameter |
A dimensionless parameter which defines the mass leakage of a gasket as a functionof contained pressure and a contained fluid constant. |
| Tightness, acceptable |
Wholly leak-free joints are impossible, at least if the contained fluid is a gas, so it has been proposed that the design of a gasketed joint should start with the selection of an ‘‘acceptable’’ leak rate. The designer would dimension bolts and joint members so that the actual leak rate would never exceed this. Three standard levels of tightness have been proposed as well. |
| Time quenching |
A term used to describe a quench in which the cooling rate of the part being quenched must be changed abruptly at some time during the cooling cycle. |
| Toggle (toggle clamp) |
A device consisting of two pinned levers that are almost in line between two end points in the same plane. Bringing the levers into line generates large forces between the ends. Used to obtain a large mechanical advantage or as a locking mechanism. |
| Tolerance |
A fractional allowance for variation from the specifications. |
| Tolerance limits |
The extreme values (upper and lower) that define the range of permissible variation in size or other quality characteristic of a part. |
| Tolerances |
In mass production, using automatic machines, parts are intended to be completely or partially interchangeable, and in batch production parts should ideally fit without the need for selection. In practice it is impossible for mass-produced parts to have exactly the same size, owing to tool wear, variations in raw materials, thermal effects, etc. In consequence, variations from exactness, termed tolerances, are assigned to what is permissible on the basic size. |
| Tooth lock washers |
These washers serve to lock fasteners, such as bolts and nuts, to the component parts of an assembly, or increase the friction between the fasteners and the assembly. They are designated in a manner similar to helical spring lock washers, and are available in carbon steel. |
| Toothed belt |
A flat belt, typically of a reinforced-rubber material, with transverse teeth that engage with teeth on a wheel or pulley. |
| Toothed gearing |
In principle, friction between circular discs in tangential contact could be used to transmit rotation and power between shafts, but the power level would be very limited and the velocity ratio affected by slip. To make the drive positive, gear wheels are used instead in which teeth extend above and below the diameters (the pitch-circle diameters) of discs in ideal rolling contact. The diagram shows the nomenclature for spur gears, the simplest type of gearing between parallel shafts, which are cylindrical in shape with straight teeth parallel to the axis of rotation. |
| Torque |
The twisting moment, product of force and wrench length, applied to a nut or bolt (for example). |
| Torque (T) (Unit N.m) |
The twisting moment of a force or couple about an axis which results in torsion. |
| Torque arm |
A bar fixed at one end used to resist torque applied at the other, for example by an electric drill. |
| Torque coefficient |
1. (KT) For a propeller of diameter D, a non-dimensional parameter defined by KT = T/ρΩ2D5 where Ω is the rotational speed (in rad/s) and ρ is the fluid density. 2. (CT) An alternative to (1) for a wind turbine, defined by CT = 2T/ρV2AR where V is the wind speed, A is the swept area of the blades, and R is the blade radius. 3. (K) An empirical coefficient used to calculate the torque T required to achieve an axial load F in a bolt according to T = KFd where d is the nominal bolt diameter. |
| Torque control |
A system of optimizing rotor speed for a variable-speed wind turbine by controlling the torque demands of the generator. |
| Torque converter |
A turbomachine used for torque amplification consisting of an impeller, a turbine, and a reaction member. Applications include motor-vehicle transmissions. |
| Torque meter |
An instrument for measuring torque using spring-loaded, piezoelectric, or strain-gauged devices. |
| Torque monitor |
A torque tool control system which monitors the amount of torque being developed by the tool during use, but does not control the tool or the torque produced. |
| Torque motor |
A type of induction motor that can apply a steady torque even when prevented from rotating. |
| Torque multiplier |
A gearbox used to multiply the torque produced by a small hand wrench (usually a Torque wrench). The output of the multiplier drives the nut or bolt with a torque that is higher, and a speed that is lower, than input torque and speed. There is no torque gage or readout on the multiplier. |
| Torque pack |
A geared wrench which multiplies input torque and provides a read-out of output torque. In effect, a combination of a Torque wrench and a Torque multiplier. |
| Torque reaction (Unit N.m) |
The torque needed to counteract an applied torque. For example, in a helicopter with a single main rotor, the tendency of the fuselage to rotate in the opposite direction to the rotor. |
| Torque wrench |
A manual wrench which incorporates a gage or measuring apparatus of some sort to measure and display the amount of torque being delivered to the nut or bolt. All wrenches produce torque. Only a torque wrench tells how much torque. |
| Torque wrench |
A socket wrench or ring spanner that can be set to allow a specific torque to be applied to a nut or bolt head. |
| Torr |
A non-SI unit of pressure commonly used in vacuum systems; defined by 760 torr = 1 atm so that 1 torr = 133.322 368 4 Pa, and approximately equivalent to the pressure corresponding to 1 mm of mercury. |
| Torricellean barometer |
A vertical glass tube with its upper end sealed and the lower end submerged in a pool of mercury. The space above the mercury is under vacuum. The height to which the mercury rises up the tube is a measure of the barometric pressure. |
| Torsion |
A twisting deformation of a solid body about an axis in which lines that were initially parallel to the axis become helices. |
| Torsion |
The twisting of an object about an axis due to an applied couple (torque). |
| Torsion bar |
A metal bar designed to act as an elastic spring when torque is applied. |
| Torsion spring |
1. A spring in the form of a torsion bar. 2. A helical spring to which torque can be applied at the ends. |
| Torsion test |
A test designed to provide data for the calculation of the shear modulus, modulus of rupture in torsion, and yield strength in shear. |
| Torsional angle (ϕ) |
(Unit ° or rad) The angular deflexion between two locations on a straight bar subjected to a torque. |
| Torsional shaft vibration |
The rapid back-and-forth angular twisting along a rotating unbalanced shaft which reaches maxima at critical rotation speeds. Shaft eccentricity, unbalanced mass distribution, oscillatory torque, misalignment, etc. all influence torsional vibration. |
| Torsional stress |
The shear stress on a transverse cross section resulting from a twisting action. |
| Torsion-bar suspension |
A type of motor-vehicle suspension in which one end of a torsion bar is rigidly fixed to the chassis while the other carries a lever to which are attached the components that carry a wheel. In a torsion-beam suspension, a beam connects the wheels on either side of the vehicle. |
| Total carbon |
The sum of the free and combined carbon (including carbon in solution) in a ferrous alloy. |
| Total combustion air (Unit kg/s) |
1. The combination of the stoichiometric flow of air required for combustion together with any excess air. 2. The flow of fresh air into a boiler plus any flue gas recirculated. |
| Total elongation |
A total amount of permanent extension of a test piece broken in a tensile test. |
| Total energy (Unit J) |
The sum of all forms of energy associated with a system, including kinetic, potential, internal, magnetic, chemical, and electrical energy. |
| Total head (hT) (Unit m) |
Total pressure pT expressed in terms of the vertical height of a column of liquid, typically water or mercury, i.e. hT = pT/ρg where g is the acceleration due to gravity and ρ is the liquid density. |
| Total heat (Unit kJ) |
An alternative term for enthalpy. It is inappropriate as it suggests that it includes kinetic energy in the same way as total enthalpy, but it does not. Also, heat and enthalpy are quite different quantities, as their definitions show. |
| Total-loss lubrication |
A system in which the lubricating oil for an internal-combustion engine is burned together with the fuel. |
| Toughening mechanisms |
Various methods of increasing the resistance to crack initiation and propagation in materials. They include transformation toughening, in which the microstructure around the crack tip alters so as to slow down or arrest cracks; deflexion of cracks; various ways of de-sharpening crack tips; fibre bridging of cracks; and fibre pull-out. |
| Toughness |
The ability of a metal to absorb energy and deform plastically before fracturing. |
| Toughness (Unit J/m2) |
1. The ability of a material to resist crack initiation and propagation. 2. The ability of a material to absorb strain energy without fracturing. |
| Tow |
1. To cause a vehicle to move by pulling with a rope, chain, bar, etc. 2. A bundle of fibres employed in reinforcement. |
| Track rod |
A bar connecting the ends of the steering arms in an automotive vehicle. |
| Tracking problem |
A control problem where the set point changes with time and thus the plant output must follow the changing set point. The opposite of a regulator problem. |
| Transducer |
A device which converts one form of energy into another. An ultrasonic transducer, for example, converts electrical energy into acoustic energy (at ultrasonic frequencies) and vice versa. |
| Transfer machines |
These specialized machine tools are used to perform various machining operations on parts or parts in fixtures as the parts are moved along on an automatic conveyor which is part of the machine tool set-up. In a set-up, the parts can move in a straight line from their entry point to their exit point, or the setup may be constructed in a U-shape so that the parts are expelled near where they start. |
| Transfer moulding |
(resin-transfer moulding, RTM) A method of compression moulding polymers in which the dies are closed before the operation starts. |
| Transfer ratio |
(transfer constant) A complex variable representing the ratio between the output of a transducer and the input causing that output. |
| Transformation temperature |
The temperature at which a change in phase occurs. The term is sometimes used to denote the limiting temperature of a transformation range. The following symbols are used for iron and steels. |
| Transformation toughening |
The improvement of fracture toughness of a material by stress-induced transformation of the microstructure. |
| Transgranular |
Through or across crystals or grains. Also known as intracrystalline or transcrystalline. |
| Transgranular fracture |
Fracture in crystalline materials where the path of cracking is predominantly across grains. |
| Transition metals |
Metallic elements from groups (columns) 3 to 12 of the periodic table. They include important metals such as titanium, vanadium, chromium, manganese, iron, cobalt, zirconium, niobium, molybdenum, tantalum, tungsten, and the noble metals. They have either body-centred cubic, face-centred cubic, or hexagonal close-packed crystal structure at room temperature and have a wide range of mechanical and physical properties. |
| Transition temperature |
(1) An arbitrarily defined temperature that lies within the temperature range in which metal fracture characteristics (as usually determined by tests of notched specimens) change rapidly, such as from primarily fibrous (shear)to primarily crystalline (cleavage) fracture. (2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature. |
| Transition temperature |
(1) An arbitrarily defined temperature that lies within the temperature range in which metal fracture characteristics (as usually determined by tests of notched specimens) change rapidly, such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture. Commonly used definitions are “transition temperature for 50% cleavage fracture,” “10 ft · lbf transition temperature,” and “transition temperature for half maximum energy.” (2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature. |
| Transition temperature (Unit K) |
(transition point) 1. The temperature at which the mechanism of fracture in metal alloys having a face-centred cubic crystal structure changes from ductile void growth to brittle cleavage. 2. The temperature at which a material changes from one crystal state to another. |
| Translational joint |
A robot joint where the controlled variable is straight line movement. |
| Transmissibility |
The ratio of the transmitted force to the disturbing force for a system subjected to a vibratory disturbance. The ratio may also be defined in terms of displacements, velocities, or accelerations. |
| Transmission |
The system that transmits power and torque from a power source; for example a shaft, belts and pulleys, or a gear train. In the case of a motor vehicle, it includes the gearbox, clutch, propeller shaft, differential and final drive shafts. |
| Transmission dynamometer |
A dynamometer in which the power transmitted by a shaft is obtained from the product of its rotation speed and the torque determined from measured shear strains along the shaft. |
| Transverse direction |
Literally, the “across” direction, usually signifying a direction or plane perpendicular to the direction of working. In rolled plate or sheet, the direction across the width is often called long transverse, and the direction through the thickness, short transverse. |
| Transverse strain |
Linear strain in a plane perpendicular to the loading axis of a specimen. |
| Trepanning |
Trepanning is a machining process for producing a circular hole or groove in solid stock, or for producing a disk, cylinder, or tube from solid stock, by the action of a tool containing one or more cutters (usually single-point) revolving around a center. |
| Tribology |
The science and technology concerned with interacting surfaces in relative motion. |
| True strain |
(1) The ratio of the change in dimension, resulting from a given load increment, to the magnitude of the dimension immediately prior to applying the load increment. (2) In a body subjected to axial force, the natural logarithm of the ratio of the gage length at the moment of observation to the original gage length. Also known as natural strain. Compare with engineering strain. |
| True stress |
The value obtained by dividing the load applied to a member at a given instant by the cross-sectional area over which it acts. Compare with engineering stress. |
| True stress (σ) (Unit Pa) |
The applied load on a test specimen divided by the current cross-section area over which it acts. σ = s expε where s is the engineering stress given by the applied load divided by the original cross-section area over which it acts, and ε is the true strain. |
| T-slot |
A recessed or undercut slot made with a special T shaped cutter in the tables of machine tools to receive the square head of a T bolt for clamping workpiece. |
| Turbine |
A turbomachine in which a rotor (turbine wheel) or impeller is caused to rotate and convert flow energy into shaft power or thrust. |
| Turbine blades (turbine buckets) |
1. The aerofoil-shaped vanes that form the rotor and stator of a gas, steam or hydraulic turbine. 2. The cup-shaped vanes of a Pelton wheel. |
| Turbine flow meter |
(axial flow meter, propeller meter) An in-line flow meter in which the rotation speed N of a propeller or rotor is a measure of the mass flowrate ṁ. Calibration is always necessary but with appropriate design ṁ is closely proportional to N over a wide range. |
| Turbine pump (turbopump) |
An axial or centrifugal pump driven by a turbine. Typically used to supply fuel to the combustion chamber of a rocket engine such as on the space shuttle. |
| Turbo generator |
(turboset) The combination of a steam or gas turbine and an electrical generator with a single shaft or connected coaxial shafts. |
| Turboblower |
A centrifugal or axial compressor or fan. |
| Turbocharging |
A method of supercharging in which the hot exhaust gas from a piston engine is used to drive a turbine which powers the supercharging compressor. A turbocharger is the turbine/compressor combination. The compressor is usually of radial outflow design while radial, axial, and mixed-flow turbines are all in use. The wastegate is a valve that reduces the flow of exhaust gas into the turbine to limit the boost produced or overspeeding. Not shown in the diagram are bearings, oil passages, etc. |
| Turbomachine |
(rotodynamic machine) A machine in which there is a transfer of energy between a continuous stream of fluid and a component, called a rotor, rotating about a fixed axis. Fans and turbines (gas, hydraulic, steam, or wind) are turbomachines in which energy is transferred to the rotor, causing it to rotate. Pumps and compressors are turbomachines in which energy is transferred from the externally driven rotor to the fluid. |
| Turbomolecular pump |
A high-vacuum (pressure down to about 10−8 Pa) pump in which momentum is transferred to the gas molecules by a rapidly rotating bladed disc. |
| Turbulent flow (turbulence) |
Fluid motion characterized by disorderly, rotational (i.e. vortical) three-dimensional velocity fluctuations covering a wide range of frequency and length scales. The pressure, temperature, and other fluid properties also fluctuate and the diffusion of heat, mass, and momentum is greatly enhanced. As are laminar and transitional flow, turbulent flow of a Newtonian fluid is governed by the Navier–Stokes equations which can in principle be solved by direct numerical simulation (DNS) in which all time and length scales of the fluctuating motion are resolved. |
| Turning |
Turning is a machining process for generating external surfaces of revolution by the action of a cutting tool on a rotating workpiece, usually in a lathe. |
| Turning |
The rotation of a workpiece held against a cutting tool in a lathe to produce components with a circular cross section. |
| Turning angle (θ) |
The change in direction experienced by a gas flow passing through an oblique shock wave or Prandtl–Meyer expansion fan. |
| Turn-of-nut |
Sometimes used to describe the general rotation of the nut (or bolt head) as the fastener is tightened. More often used to define a particular tightening procedure in which a fastener is first tightened with a preselected torque, and is then tightened further by giving the nut an additional, measured, turn such as ‘‘three flats’’ (180°). |
| Turn-of-nut method |
It applies preload by turning a nut through an angle that corresponds to a given elongation. |
| Turret lathe |
A capstan lathe in which the capstan is driven mechanically or hydraulically to provide assigned tool paths to perform a specified sequence of operations in the repetitive production of parts. |
| Twist |
The helix produced in a cylindrical component, such as a shaft, wire, tensioned cable, or rope, when one end is rotated relative to the other. Measured either as the number of turns per unit length, or by the helix angle (twist angle). |
| Twist drill |
A hardened-steel drill bit having one or more helical flutes running from a conical tip to the smooth part of the shank. |
| Two-dimensional flow |
A fluid flow in which the velocity at any time depends upon two spatial coordinates, such as the radial and axial locations in developing pipe flow. |
| Two-phase flow |
A flow in which two phases are present, for example gas bubbles in a liquid, liquid bubbles in another liquid with which it is immiscible, solid particles in a liquid or gas. |
| Two-stage compressor |
A machine in which gas is compressed from low pressure toan intermediate pressure in a low-pressure cylinder, and then to final pressure in a highpressure cylinder. Efficiency is improved if the two cylinders are separated by an intercooler. |
| Two-stroke engine |
(two-cycle engine) A petrol or diesel engine in which an air/fuel charge is introduced through an induction port, compressed and burned, expanded and then exhausted through an exhaust port. The two ports in the cylinder wall are opened and closed by the piston. There are two strokes in each revolution of the crankshaft. In total-loss lubrication petrol engines, the lubricating oil is mixed with the fuel. |
| Typical basis |
The typical property value is an average value. No statistical assurance is associated with this basis. |
| Tyre |
A flexible ring-shaped cover mounted on a wheel rim that supports the weight of a vehicle, such as a motor vehicle, aircraft, or bicycle, and transmits power and torque to a road surface. Some pneumatic tyres are inflated directly, others have a separate inner tube that is inflated. For certain applications, solid tyres are used. |
