Page 339 - Mechanical Engineer's Data Handbook

GLOSSARY OF TERMS 327

thermal shock The development of a steep tempera- and four-stroke engines.
ture gradient in a component and accompanying high tolerance The specified permissible deviation from a
stress. dimension or permissible variation in the size of a
thermal stress Stress in a body due to a temperature component.
gradient. toroid (torus) A solid generated by rotating a circle
thermiitor A semiconductor mixture of cobalt, about an external point in its plane.
nickel and manganese oxides and finely divided copper torque The algebraic sum of couples, or moments of
in the form of a bead with leads. The device has a high external forces, about the axis of twist. Also called
temperature coefficient of resistance and is used for ‘torsional moment’.
temperature measurement. torsion A twisting action resulting in shear stress.
therrnoeollgle A device consisting of a junction of torsional Oseillntion Oscillations, e.g. in a shaft in
dissimilar metals which produce an e.m.f. approxi- which it is twisted periodically in opposite directions.
mately proportional to the temperature difference total bead pressure The sum of dynamic pressure and
between the hot and cold junctions at the ends. static pressure in fluid flow.
thermodynamic process A gas process involving toughwss The ability of a metal to absorb energy and
changes in pressure, volume, temperature or state. deform plastically before fracturing. Determined by
tlsermaleetrrer ‘ty The interchange of heat and elec- impact tests.
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tric energy, e.g. as in a thermocouple. traducer A device which converts a physical mag-
thermometer An instrument for measuring tempera- nitude of one form ofenergy to another form according
ture. to a specified formula, e.g. mechanical to electrical
thermoplastic Any plastic which can be melted by energy as in a microphone.
heat and resolidified, the process being repeatable any transformer An electrical device without moving
number of times. parts which transfers alternating current energy,
thermosetting resin Compositions in which a chemi- usually with a change in voltage.
cal reaction takes place while being moulded under transistor A three-electrode semiconductor device
heat and pressure. The properties are changed and the used to give a voltage, current or power gain.
product is resistant to further change. triaxial stress A state of stress where none of the three
thick cylinder A cylinder in which the thickness of principal stresses is zero. Three-dimensional stress.
wall is large compared with the bore. Stress analysis is turbine A prime mover running on steam, gas or
more complicated than for a ‘thin’ cylinder subject to water, in which energy is imparted to rows of moving
internal pressure. blades on a rotor.
thin cylier A cylinder with a wall thickness rela- turbulent flow Fluid flow in which particle motion
tively small compared with the bore. Under internal varies rapidly in velocity and direction; characterized
pressure a uniform hoop stress may be assumed with by a high Reynold’s number.
no radial stress. turning Removing material from a rotating work-
three phase An electric supply system in which the piece using a single-point tool as in a lathe.
alternating potentials on the three wires differ in phase twisting moment See: ‘torque’.
by 120”. two4imensioaal streas A stress situation where two
throttling process The process involving the flow of a stresses act at right angles.
fluid through a small tortuous passage destroying all two-sboke cycle An engine cycle of two piston
kinetic energy; there is no change in enthalpy. strokes, i.e. one revolution.
thrust bearing A shaft bearing designed to take axial
load through a collar on the shaft. It may be a flat
surface or have balls or rollers. ultimate strength (ultimate tensile strength,
thyristor A semiconductor device used for switching UTS) The maximum tensile stress a material will
heavy currents. withstand before failure.
tie rod A rod or bar which takes a tensile load. ultrasonics Relating to sound with a frequency above
timing belt A drive belt between two pulleys having the audible range, i.e. above about 15 kHz.
teeth which engage with grooves in the pulleys. universal gas constant This is equal to the gas con-
timing diagram A circular diagram showing the stant for any gas multiplied by its molecular weight, i.e.
angular positions of valve opening and closing in two- R,= MR.