Karnataka SSLC Elements of Mechanical Engineering IV - JTS (KSEAB) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Young's modulus

Ratio of tensile stress to tensile strain within the elastic limit; a measure of stiffness. Steel is about 200 GPa, aluminium about 70 GPa.

Ductility

Ability of a material to undergo permanent plastic deformation before fracture, usually expressed as percentage elongation or percentage reduction in area in a tensile test.

Annealing

Heat treatment in which metal is heated above its critical temperature and cooled very slowly in the furnace, softening it and relieving internal stresses.

Brinell hardness test

Hardness test that presses a hardened steel ball of standard diameter into the surface under a known load and measures the indentation diameter to give a Brinell hardness number.

Centre punch

Hand tool with a sharp 90-degree point struck with a hammer to make a conical indentation that locates and guides a drill at the marked point.

Hacksaw blade set

Sideways offset of hacksaw teeth in a repeating pattern that makes the kerf wider than the blade, preventing binding and allowing clearance for the blade.

File cut

Arrangement of file teeth: single-cut has parallel rows for finishing, double-cut has crossing rows for fast metal removal, and a rasp has coarse individual teeth for wood.

Vernier least count

Smallest measurement a vernier caliper can read, equal to one main scale division minus one vernier division; commonly 0.02 mm on a metric caliper.

Micrometer least count

Screw gauge least count equals the screw pitch divided by the number of circular scale divisions; with a 0.5 mm pitch and 50 divisions it is 0.01 mm.

Interference fit

Fit in which the shaft is always larger than the hole, so the parts must be pressed or shrunk together and are held by friction.

Allowance

Intentional difference between the sizes of mating parts, equal to the minimum clearance; it may be negative when an interference fit is intended.

Thread pitch

Axial distance between corresponding points on adjacent thread crests, measured parallel to the thread axis; for a single-start thread it equals the lead.

Acme thread

Trapezoidal power-transmission thread with a 29-degree included angle, giving low friction and easy engagement with a split nut on lead screws.

Rivet joint efficiency

Ratio of the strength of a riveted joint to the strength of the unriveted solid plate, expressed as a percentage for tearing, shearing, or crushing.

Hydrodynamic bearing

Plain bearing in which rotation drags lubricant into a converging wedge, generating a pressure film that separates the shaft from the sleeve.

Taper roller bearing

Rolling bearing with conical rollers and races that carries combined radial and axial loads and is commonly used in vehicle wheel hubs.

Lip seal

Dynamic radial shaft seal with a flexible lip pressed against the rotating shaft by a spring, retaining lubricant and excluding dirt.

V-belt drive

Belt drive in which a trapezoidal belt wedges into a grooved pulley, giving high friction and power capacity with less slip than a flat belt.

Gear module

Standard metric gear size equal to pitch circle diameter divided by number of teeth; mating gears must have the same module and pressure angle.

Worm and worm wheel

Right-angle gear pair with a screw-like worm driving a toothed wheel, giving high speed reduction and often self-locking operation.

Velocity ratio

Ratio of the distance moved by the effort to the distance moved by the load in a machine; for a belt drive it equals driven diameter over driver diameter.

Class I lever

Lever with the fulcrum between the effort and the load, such as a crowbar, scissors, or a pair of pliers; it can give MA greater or less than one.

Screw jack velocity ratio

Velocity ratio of a screw jack equals two pi times the lever length divided by the thread pitch, giving a large mechanical advantage for lifting.

Latent heat

Heat absorbed or released during a phase change at constant temperature, such as melting ice or boiling water, without any change in temperature.

First law of thermodynamics

Energy conservation for a system: net heat supplied minus net work done equals the change in internal energy of the closed system.

Carnot efficiency

Maximum possible efficiency of a heat engine between two reservoirs, equal to one minus the cold absolute temperature divided by the hot absolute temperature.

Fusible plug

Boiler mounting with a low-melting alloy core that melts when water level falls dangerously low, releasing steam to warn and extinguish the furnace fire.

Economiser

Boiler accessory that preheats feed water using heat from the exhaust flue gases, reducing fuel consumption and improving overall boiler efficiency.

Impulse turbine

Steam turbine in which pressure drops only in fixed nozzles and remains constant across moving blades, which are driven purely by the change in steam momentum.

Compression ratio

Ratio of total cylinder volume to clearance volume in an engine; petrol engines use about 8 to 12, diesel engines about 16 to 22.

Octane number

Measure of petrol's resistance to knocking, based on a scale where iso-octane is 100 and normal heptane is 0; higher numbers suit higher compression.

Cavitation

Formation and collapse of vapour bubbles in a pump when local pressure falls below vapour pressure, causing noise, loss of head, and impeller erosion.