Page 338 - Mechanical Engineer's Data Handbook

326 MECHANICAL ENGINEER’S DATA HANDBOOK
statics The branch of applied mathematics dealing stroboscope A flashing lamp of precisely variable
with the combination of forces so as to produce periodicity which can be synchronized with a moving
equilibrium. object to give a stationary appearance.
steady flow energy equation For a flow process this sudden contraction A sudden decrease in the cross-
statesthath, +(C:/2)+Q=h2+(C:/2)+ W, whereh,, sectional area of a conduit, involving a loss of energy.
h, =inlet and outlet enthalpies, C,, C, =inlet and sudden enlargement A sudden increase in the cross-
outlet velocities, Q= heat supplied, W= work out. sectional area of a conduit, involving an energy loss.
steam plant A power plant operating on a steam superheated steam Steam heated at constant press-
cycle, e.g. steam power station. ure out of contact with the water from which it was
steam turbine A turbine using steam as a working formed, Le. at a temperature above saturation tem-
substance. See: ‘turbines’. perature.
std Iron based alloy containing manganese, carbon surface finish The condition of a surface after final
and other alloying elements. treatment.
stianesS The ability of a metal, etc., to resist elastic surface grinder A grinding machine which produces
deformation. It is proportional to the appropriate a flat surface on the workpiece which is mounted on a
modulus of elasticity. reciprocating table.
stoichiometric &/fuel ratio The mixture of air and surface hardening Heat treatment such as nitriding,
fuel for engines and boiler furnaces which contains just cyaniding, etc., which increases the surface hardness of
sufficient oxygen for complete combustion. a metal.
strain The change in shape or size of a stressed body surface tension Interfacial tension between two
divided by its original shape or size, e.g. ‘linear strain’, phases, one of which is a gas.
‘shear strain’, ‘volumetric strain’. swaging Forming a reduction in a metal part by
strain energy The work done in deforming a body forging, squeezing or hammering, sometimes when
elastically. rotating.
strain gauge A metal grid or semiconductor rod on a swarf Chips removed from a workpiece during cut-
backing sheet which is cemented to a strained body. ting operations.
The increase in length alters the electrical resistance of
the grid or rod from which the strain may be deduced. tachogenerator An electric generator producing a
strain-gauge bridge A form of Wheatstone bridge in voltage proportional to the speed of a shaft to which it
which strain gauges are connected to give a sensitive is connected. Connected to a voltmeter calibrated in
reading of resistance change. speed of rotation.
strain-gauge rosette A combination of three strain tachometer An electrical or mechanical instrument
gauges which give the principal strains in two-dimen- which measures the rotational speed of a shaft, etc.
sional stress situations. tap A cylindrical cutter used to produce an internal
strain bardening The increase in hardness caused by screw thread.
plastic deformation. temperature The degree of hotness or coldness with
strain rate The time rate of stress application used in reference to an arbitrary zero, e.g. the melting point of
testing. ice, absolute zero.
stress Force per unit area in a solid. The area is temperature coefficient of resistance A coefficient
perpendicular to the force for tensile stress and parallel giving the change in resistance of a piece of material
to it for shear stress. Unit: newtons per square metre per degree change in temperature.
(Nm-2). tempering The reheating of hardened steel or cast
stress concentration factor The ratio of the greatest iron to a temperature below the eutectoid value to
stress at a ‘stress raiser’ to the nominal stress in a decrease hardness and increase toughness.
component. tensile strength Ratio of maximum load to original
stress raiser A local change in contour in a part, e.g. a cross-sectional area of a component. Also called
hole, notch, change of section, etc., which gives rise to ‘ultimate strength’.
an increase in stress. tensile stress Tensile load divided by cross-sectional
stress diving Heating a material to a suitable area.
temperature and holding it long enough to remove tension The state of stress in a part which tends to
residual stresses, then slowly cooling. increase its length in the direction of the load.