Tamil Nadu HSE Second Year Basic Mechanical Engineering key terms

A ferrous alloy containing more than about two per cent carbon, plus silicon. It is brittle in tension but strong in compression, absorbs vibration well, and is used for machine bases, beds and pipe fittings.

A low-carbon steel with roughly 0.05 to 0.25 per cent carbon. It is ductile, tough, easily welded and machined, and is widely used for structural sections, shafts, bolts and general workshop fabrication.

The resistance of a material to local indentation, scratching or abrasion. It is measured by tests such as Brinell or Rockwell and usually increases as carbon content and heat treatment raise strength.

The ability of a material to undergo large plastic deformation in tension before fracture, allowing it to be drawn into wires. Mild steel is ductile; cast iron is not.

A method of representing a three-dimensional object by separate two-dimensional views projected onto planes that are at right angles to one another, usually front, top and side views.

A projection convention in which the object is imagined between the observer and the plane, so the view is placed on the far side. In India, the front view appears above the top view.

A pictorial drawing in which the three principal axes are inclined at 120 degrees to each other and lengths along them are drawn to the same scale, giving a single three-dimensional-looking view.

A drawing view that imagines part of the object cut away to reveal internal features. The cut surface is shown with hatching lines, and hidden details become visible solid outlines.

The internal resisting force developed per unit cross-sectional area of a material when it is subjected to an external load. It is normally expressed in newtons per square millimetre or megapascals.

The change in dimension of a material divided by its original dimension when a load is applied. It is a dimensionless ratio and may be tensile, compressive or shear.

The ratio of direct tensile or compressive stress to the corresponding strain within the elastic limit. A higher value means the material is stiffer and deforms less under the same stress.

The ratio of the ultimate or yield strength of a material to the working stress allowed in a component. It accounts for uncertain loads, material defects and consequences of failure.

The algebraic sum of the moments of all forces acting on one side of a section of a beam, taken about that section. It produces bending stress and varies along the beam.

A foundry process in which molten metal is poured into a cavity formed in a sand mould and allowed to solidify. The mould is made from sand mixed with clay or a binder.

A replica of the casting, slightly larger to allow for shrinkage, used to form the mould cavity in sand casting. Patterns may be made of wood, metal or plastic.

A fusion welding process in which an electric arc between an electrode and the workpiece generates heat to melt the edges and filler metal, forming a joint after solidification.

A metal forming process in which compressive forces, applied by hammering or pressing, shape a heated or cold workpiece into the required form. It improves grain structure and strength.

A forming process in which metal is passed between rotating rolls that reduce its thickness and change its cross-section. Hot rolling is common for plates, sections and rails.

A machine tool that rotates the workpiece about an axis while a single-point cutting tool is fed into it to produce cylindrical surfaces, threads, tapers and drilled holes.

A machining operation in which a rotating multi-tooth cutter removes material from a workpiece that is fed past it. It can produce flat surfaces, slots, gears and complex profiles.

The relative speed between the cutting tool edge and the workpiece surface, usually expressed in metres per minute. It depends on tool and workpiece material and affects tool life.

The distance the cutting tool advances along the workpiece per revolution or per stroke during machining. It influences surface finish, chip thickness and machining time.

A defined quantity of matter or region in space selected for study, separated from its surroundings by a boundary. It may be closed, open or isolated.

An energy conservation statement for a system: heat supplied equals the increase in internal energy plus the work done by the system. It rules out creating energy from nothing.

A thermodynamic property that measures the degree of disorder or energy unavailable for useful work. It increases in all real irreversible processes, giving direction to natural changes.

A closed pressure vessel in which water is heated by burning fuel or another heat source to generate steam at a required pressure and temperature for power or process use.

An internal combustion engine that completes a cycle in four piston strokes: suction, compression, power and exhaust. A crankshaft converts the reciprocating piston motion into rotation.

The ratio of the total cylinder volume when the piston is at bottom dead centre to the clearance volume when it is at top dead centre. Higher ratios generally improve efficiency.

An energy equation for steady, incompressible, frictionless flow along a streamline. It states that pressure energy, kinetic energy and potential energy per unit weight remain constant.

A dimensionless ratio of inertial forces to viscous forces in a fluid flow. It predicts whether flow is laminar or turbulent and is used in pipe and model studies.

A rotodynamic pump that uses a rotating impeller to impart kinetic energy to a liquid, which is then converted partly into pressure as the liquid leaves the casing.

A precision measuring instrument with a main scale and a sliding vernier scale, used to measure external and internal dimensions and depths. Its least count is usually 0.02 mm.

A precision instrument using a calibrated screw to measure small dimensions, commonly outside diameters and thicknesses. A typical external micrometer reads to 0.01 mm.

The smallest measurement that an instrument can read directly. For a vernier caliper it equals one main-scale division minus one vernier-scale division.

The permissible difference between the upper and lower limits of a dimension. It allows for unavoidable manufacturing variation while ensuring that parts assemble and function correctly.

Clothing and devices worn by a worker to reduce exposure to workplace hazards, such as safety goggles, helmets, gloves, ear protection and safety shoes. It is a last line of defence.

Scheduled inspection, cleaning, lubrication and replacement of parts carried out before failure occurs, intended to keep machines reliable, safe and available.

The process of identifying workplace hazards, evaluating the likelihood and severity of harm, and deciding on controls to reduce risk to an acceptable level.