| Calorie |
(cal, gram calorie, small calorie) An obsolete (i.e. non-SI) unit of energy equal to 4.186 8 J. It is the amount of energy needed to raise the temperature of 1 gram of pure airfree water from 14.5°C to 15.5°C at standard atmospheric pressure. |
| Calorizing |
Imparting resistance to oxidation to an iron or steel surface by heating in aluminum powder at 800 to 1000 °C (1470 to 1830 °F). |
| Cap |
A cover, often in the form of a short cylinder, one end of which is closed. Typically used to close an orifice or pipe end, on to which it can be pushed, welded, screwed, or attached with fasteners. |
| Cap nut |
A nut with a blind threaded hole, for example a dome nut to cover the end of a bolt. |
| Cap screw |
A bolt where the thread runs right up to the head and engages in a threaded hole or captive nut in an adjoining member. |
| Cap screw |
A finished screw 5mm or larger, used for fastening two pieces together by passing the screw through a clearance hole in one part and screwing in into a tapped hole in the other. |
| Cap screw |
A finished screw, used for fastening two pieces together by passing the screw through a clearance hole in one part and screwing it into a tapped hole in the other. Heads may be hexagon, round, flat, fillister or socket type. |
| Captive nut |
A nut attached loosely or rigidly to a sheet member that is too thin to thread and which engages with a cap screw. |
| Car furnace |
A batch-type furnace using a car on rails to enter and leave the furnace area. Car furnaces are used for lower stress relieving ranges. |
| Carbon potential |
A measure of the ability of an environment containing active carbon to alter or maintain, under prescribed conditions, the carbon level of the steel. Note: In any particular environment, the carbon level attained will depend on such factors as temperature, time, and steel composition. |
| Carbon restoration |
Replacing the carbon lost in the surface layer from previous processing by carburizing this layer to substantially the original carbon level. Sometimes called recarburizing. |
| Carbon steels |
(plain carbon steels) Steels in which carbon is the principal alloying element, and the amount of manganese does not exceed 1.65% and the copper and silicon contents are less than 0.60%. There are three main types: low-carbon steels (0.08–0.35% carbon); medium-carbon steels (0.35–0.50% carbon); and high-carbon steels (0.50–2.0% carbon). |
| Carbonitriding |
A case hardening process in which a suitable ferrous material is heated above the lower transformation temperature in a gaseous atmosphere of such composition as to cause simultaneous absorption of carbon and nitrogen by the surface and, by diffusion, create a concentration gradient. The process is completed by cooling at a rate that produces the desired properties in the workpiece. |
| Carbonization |
Conversion of an organic substance into elemental carbon. |
| Carburizing |
Absorption and diffusion of carbon into solid ferrous alloys by heating, to a temperature usually above Ac3, in contact with a suitable carbonaceous material. A form of case hardening that produces a carbon gradient extending inward from the surface, enabling the surface layer to be hardened either by quenching directly from the carburizing temperature or by cooling to room temperature, then reaustenitizing and quenching. |
| Carburizing flame |
A gas flame that will introduce carbon into some heated metals, as during a gas welding operation. A carburizing flame is a reducing flame, but a reducing flame is not necessarily a carburizing flame. |
| Case |
That portion of a ferrous alloy, extending inward from the surface, whose composition has been altered so that it can be case hardened. Typically considered to be the portion of the alloy (a) whose composition has been measurably altered from the original composition, (b) that appears dark on an etched cross section, or (c) that has a hardness, after hardening, equal to or greater than a specified value. Contrast with core. |
| Case hardening |
A generic term covering several processes applicable to steel that change the chemical composition of the surface layer by absorption of carbon, nitrogen, or a mixture of the two and, by diffusion, create a concentration gradient. The processes commonly used are carburizing and quench hardening; cyaniding; nitriding; and carbonitriding. The use of the applicable specific process name is preferred. |
| Cast steel |
Steel that is cast into shapes. It has superior properties to most cast irons, but is more expensive to produce. |
| Castellated nut |
A nut having slots across the hexagonal faces, used with a bolt having a drilled hole so that a split (cotter) pin may be inserted through both nut and bolt to prevent unscrewing. |
| Catastrophic failure |
A sudden and total failure of a large engineering structure such as an aeroengine, aircraft, space vehicle, bridge, or dam. |
| Caterpillar |
(crawler vehicle) A vehicle that ‘lays its own road’ by running on endless belts, driven by toothed wheels, on each side. Used on soft ground where spreading of the load reduces contact stress. |
| Cathode |
That electrode in a battery or corrosion cell which attracts electrons. |
| Caustic cracking |
A form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromiumnickel alloys that are exposed to concentrated hydroxide solutions at temperatures of 200 to 250 °C (400 to 480 °F). Also known as caustic embrittlement. |
| Caustic quenching |
Quenching with aqueous solutions of 5 to 10% sodium hydroxide (NaOH). |
| Cavitation |
The formation of vapour- or gas-filled cavities in a liquid due to reduction of the local pressure, often due to acceleration of the fluid, such as in flow through a convergent nozzle. If there is no dissolved gas in the liquid, vaporous cavitation occurs when the pressure falls below the saturated vapour pressure. If the bubbles are formed due to high temperature, the process is termed boiling. If there is dissolved gas, gaseous cavitation occurs due to pressure reduction, temperature increase, or diffusion (degassing). At the tips of marine propellers and in hydraulic machinery, the collapse of cavitation bubbles can cause noise and vibration and lead to surface damage in the form of pitting. |
| Cavitation damage |
Erosion of a solid surface through the formation and collapse of cavities or bubbles in an adjacent liquid that contains vapor and/or gas. |
| Cavitation tunnel |
A closed-circuit recirculating water tunnel in which the static pressure can be reduced to sufficiently low levels for cavitation studies to be performed. |
| Cavitation-resistance inducer |
An axial-flow pump used upstream of a main pump in order to prevent cavitation in the latter by increasing the inlet head. |
| Cavity radiator |
A heated chamber having a small hole through which radiation, approximating blackbody radiation, passes out. |
| Cellular materials |
There are three broad classes of materials that have a sponge-like structure containing many small closed or open (interlinked) pores or cells. Natural cellular materials include bone, cork, sponge, and wood, and have numerous well-known uses. Wide ranges of cellular plastics are produced using blowing or foaming agents, such as air, ammonium carbonate, sodium bicarbonate, etc., to create pores during the processing of thermoplastic or thermosetting polymers. Rigid foams have moderate compressive strength and can be moulded and machined. |
| Celsius |
The temperature scale based on the freezing point of water (0ºC) and the boiling point of water (100ºC). The interval between these points is divided into 100 degrees. The scale was devised by Anders Celsius. |
| Celsius temperature scale |
(centigrade temperature scale) A relative, non-SI, temperature scale now defined in terms of the Kelvin absolute temperature scale as °C = K − 273.15, where °C is the symbol for degrees Celsius. The scale was previously called the centigrade scale, with two fixed points: the melting point of ice (the ice point) as 0°C, and the boiling point of water (the steam point) as 100°C. |
| Cementation |
The introduction of one or more elements into the outer portion of a metal object by means of diffusion at high temperature. |
| Cemented carbides |
Sintered mixtures of refractory metal carbides (e.g. tungsten carbide) in a metal matrix binder such as cobalt, nickel, or iron. They have high melting point, toughness, compressive strength, and wear resistance. Applications include use in grinding wheels and papers, cutting tools, drill bits, wire-drawing dies, and ball-point pen tips. Sometimes known as hard metals when the application is to machine tools. |
| Cementite |
A compound of iron and carbon, known chemically as iron carbide and having the approximate chemical formula Fe3C. It is characterized by an orthorhombic crystal structure. When it occurs as a phase in steel, the chemical composition will be altered by the presence of manganese and other carbide-forming elements. |
| Centi (c) |
An SI unit prefix indicating a multiplier of 0.01; thus centimetre is a unit of length equal to one one-hundredth of a metre or 10 mm. |
| Centigrade heat unit |
(Celsius heat unit, CHU) An obsolete (i.e. non-SI) unit equal to the energy required to increase the temperature of one pound of pure, air-free water from 14.5°C to 15.5°C at a pressure of one standard atmosphere. |
| Centre line |
1. In an engineering drawing, a line of symmetry. 2. An imaginary line along a pipe, duct, or shaft that defines an axis of symmetry. 3. An imaginary straight line parallel to the intended direction of a surface located such that the areas above and below the line and the real wavy (rough) surface cancel out. |
| Centre of pressure |
1. The location, on an aerofoil or other body that develops lift, of the resultant lift force. 2. The location, on a surface submerged in a liquid, of the resultant force due to the pressure acting on the surface. Because hydrostatic pressure increases with depth, the centre of pressure is generally below the centroid of the surface. |
| Centrifugal |
Acting or moving in a direction away from the axis of rotation of a rotating body. |
| Centrifugal clutch |
A clutch that engages and disengages at a defined speed of rotation of the driving shaft, as when expanding friction shoes act against the inside of a drum. |
| Centrifugal compressor |
A compressor in which kinetic energy is added to a fluid by radial acceleration in an impeller and then converted into a pressure increase by flow though a diffuser. |
| Centrifugal fan |
A machine with a rotor consisting of a number of blades mounted around a hub and used for moving air or other gases. The gas enters the rotor axially and is discharged radially at increased pressure. |
| Centrifugal force (Unit N) |
The inertial reaction force to the centripetal force. It is equal in magnitude but opposite in direction. |
| Centrifugal pump |
A pump into which liquid enters axially through the eye of the casing and is then accelerated through an impeller, thereby increasing both its kinetic energy and pressure before being delivered to a ring diffuser (the volute) that further increases the liquid pressure and from which it leaves. |
| Centrifuge |
A machine incorporating a rapidly spinning drum in which liquids and suspended particles of different densities are separated by centrifugal action. |
| Centripetal |
Acting or moving in a direction towards the axis of rotation. |
| Chafing fatigue |
Fatigue damage initiated in a surface damaged by rubbing against another body. |
| Chain |
A series of connected links, typically of steel. For lifting, pulling, securing, etc., each link is a closed loop, often in the form of a ring. For power transmission, the links are designed to mesh with the teeth of a sprocket wheel. In contrast to belt drives, chain drives tend to be employed in high-torque applications. |
| Chain dimensioning |
On an engineering drawing, where the end point of one dimension is the starting point for the next. Parallel dimensioning is preferred as chain dimensioning can lead to the accumulation of tolerances. |
| Charles law |
(Gay–Lussac law) The volume of a fixed mass of gas at constant pressure is proportional to its absolute temperature. |
| Charles’ law |
The volume of a gas at constant pressure is directly proportional to its absolute temperature. |
| Check valve |
(clack valve, non-return valve) A mechanical device that allows fluid flow in one direction only. The numerous designs include ball, diaphragm, disc, lift, split disc, and swing check valves. |
| Checks |
Numerous, very fine cracks in a coating or at the surface of a metal part. Checks may appear during processing or during service and are most often associated with thermal treatment or thermal cycling. |
| Cheese head |
A cylindrical head on a screw or bolt. For driving, it may be slotted, or hexagonally recessed. |
| Chilled castings |
Iron castings cooled at a rate that results in white iron (slow enough to avoid the formation of martensite, yet fast enough to prevent any silicon present from causing decomposition of cementite into iron and graphite). |
| Circlip |
(snap ring) An external or internal retaining ring that locates parts of circular cross section in an axial direction. It consists of an incomplete ring, with holes on either side of the gap, that may be expanded by a plier-like tool to pass into a groove in a shaft or contracted to pass into a groove in a bore. |
| Circular pitch |
The distance from the center of one gear tooth to the center of the next gear tooth measured on the pitch line. |
| Clamping force |
The equal and opposite forces which exist at the interface between two joint members. The clamping force is created by tightening the bolts, but is not always equal to the combined tension in the bolts. Hole interference problems, for example, can create a difference between clamping force and bolt loads. |
| Clearance |
(Unit m or μm) 1. The distance (if any) between mating components in an assembly. 2. The distance between two moving parts, or a moving part and stationary part, in a machine (e.g. the gap between a piston and a cylinder head). 3. With threads, the major clearance is the distance between the design form at the root of an internal thread and the crest of its mating external thread; the minor clearance is the corresponding dimension between the crest of an internal thread and the root of the external thread. |
| Clearance angle |
(relief angle) (Unit °) The angle between the underneath or flank of a cutting tool and the machined surface. |
| Clearance fit |
A range of clearances ranging from close sliding to loose running, i.e. a fit in which the limits for the mating parts always permit assembly. |
| Clearance hole |
A hole of specified size such that a bolt, stud, etc. of the same nominal size will always pass through. |
| Clearance volume |
(Unit m3) The ‘dead’ volume above a piston, including the recess in the cylinder head, in a reciprocating compressor or engine when the piston is at top dead centre. |
| Cleavage |
The tendency of a material to cleave or split along definite crystallographic planes. |
| Cleavage fracture |
A fracture, usually of a polycrystalline metal, in which most of the grains have failed by cleavage, resulting in bright reflecting facets. It is one type of crystalline fracture and is associated with low energy brittle fracture. Contrast with shear fracture. |
| Cleavage fracture |
A fracture created by splitting (cleavage), as between layers in materials like slate or mica. In brittle metals, and brittle microconstituents in alloys, cleavage occurs along particular crystal planes. |
| Clevis |
A U-shaped hook with holes at the ends through which a retaining bolt or pin (clevis pin) passes. |
| Clevis joint |
A joint formed by two parallel cantilever beams pressed upon a component between the beams. |
| Clip gauge |
A displacement gauge consisting of two thin strain-gauged cantilever arms attached through knife edges to a testpiece to give the load–line displacement in fracture mechanics test pieces, or used as an extensometer in tensile tests. |
| Closed system |
A closed thermodynamic system consists of a fixed amount of mass. No mass can cross its boundary although energy can, in the form of work or heat, and its volume can change. |
| Closed-die forging |
The forming of a workpiece by compression within a pair of dies having the female form of the component to be manufactured (closed dies), superfluous metal being expelled as flash where the dies meet. |
| Clutch |
A device for connecting and disconnecting rotating shafts, for example between an engine and a gearbox. |
| Coalescence |
Growth of grains at the expense of the remainder by absorption or the growth of a phase or particle at the expense of the remainder by absorption or reprecipitation. |
| Coarse threads |
Threads with relatively large separation between corresponding points on the threads. |
| Coarsening |
An increase in the grain size, usually, but not necessarily, by grain growth. |
| Coated abrasive |
An abrasive tool consisting of a flexible backing material, such as a woven cloth, paper or vulcanized fibre, a bond material, such as a glue or synthetic resin, and grit. |
| Coaxial |
A term for components having a common axis such as concentric shafts. |
| Coefficient of cubic expansion |
The fractional increase in volume per unit temperature rise. |
| Coefficient of discharge (CD) |
For flow through a nozzle or orifice plate, the ratio of the actual mass flow rate to the theoretical mass flow rate calculated assuming the flow to be isentropic. The coefficient of velocity (velocity coefficient) is the corresponding ratio of the actual average velocity to the theoretical value. For incompressible flow, the theoretical flow rate and velocity can be calculated using Bernoulli’s equation. |
| Coefficient of friction |
(coefficient of kinetic friction, coefficient of sliding friction, friction coefficient, μ) The ratio of the frictional force F to the normal force N between two surfaces in contact, i.e. μ = F/N. Static friction is when there is no relative sliding; kinetic friction when there is. |
| Coefficient of friction |
For structural components sliding on one another, the coefficient of friction is the ratio of the force causing the sliding to the force perpendicular to the sliding component surfaces. The coefficient of friction is dimensionless with values between zero and one. |
| Coefficient of friction |
The number characterising the force necessary to slide or roll one material along the€surface of another. If an object has a weight N and the coefficient of friction is μ, then the force F necessary to move it without acceleration along a level surface is F = μN. The coefficient of static friction determines the force necessary to initiate movement; the coefficient of kinetic friction determines the force necessary to maintain movement. Kinetic friction is usually smaller than static friction. |
| Coefficient of friction (μ) |
The dimensionless ratio of the force (F) between two bodies to the normal force (N) pressing these bodies together: μ (or f) = (F/N) |
| Coefficient of restitution (e) |
The ratio of the relative velocity of two colliding bodies after collision to that before. In perfectly elastic collisions e = 1; when all the impact energy is dissipated, e = 0. |
| Coefficient of rolling friction |
The ratio of force parallel to a surface, on which an object rolls, to the normal force. Unlike sliding friction, rolling friction depends on the size of the contact patch and the radius of the rolling element, and the behaviour depends on whether the contact is elastic, viscoelastic, or plastic and on hysteresis losses. |
| Coefficient of thermal expansion |
(1) Change in unit of length (or volume) accompanying a unit change of temperature, at a specified temperature. (2) The linear or volume expansion of a given material per degree rise of temperature, expressed at an arbitrary base temperature or as a more complicated equation applicable to a wide range. |
| Coextrusion |
The simultaneous extrusion through the same die of two or more materials in combination. |
| Coherent precipitate |
A crystalline precipitate that forms from solid solution with an orientation that maintains continuity between the crystal lattice of the precipitate and the lattice of the matrix, usually accompanied by some strain in both lattices. Because the lattices fit at the interface between precipitate and matrix, there is no discernible phase boundary. |
| Coherent structure |
A term given to the larger eddies of turbulent shear flow, such as boundary layers, jets, and wakes, that show distinctive correlated patterns of motion. |
| Cohesive strength |
(Unit Pa) A theoretical fracture strength for solids based on interatomic forces, approximately equal to E/10 where E is Young’s modulus. |
| Cohesive zone |
In fracture-mechanics modelling and simulation, the region at the crack tip over which an assumed traction (load-displacement) relation has to be overcome to permit initiation and propagation of a crack. |
| Coil spring |
A spiral (‘clockwork’) or helical (cylindrical) spring. |
| Coil spring |
A spring steel wire wound in a spiral pattern. |
| Coining |
A forging operation, employing a closely-fitting punch and die from which no metal is allowed to escape, in which the surface pattern on the punch and die is imprinted on the blank. |
| Cold die quenching |
A quench utilizing cold, flat, or shaped dies to extract heat from a part. Cold die quenching is slow, expensive, and is limited to smaller parts with large surface areas. |
| Cold extrusion |
In simplest terms, cold extrusion can be defined as the forcing of unheated metal to flow through a shape-forming die. It is a method of shaping metal by plastically deforming it under compression at room temperature while the metal is within a die cavity formed by the tools. The metal issues from the die in at least one direction with the desired cross-sectional contour, as permitted by the orifice created by the tools. Cold extrusion is always performed at a temperature well below the recrystallization temperature of the metal (about 1100 to 1300 degrees F. for steel) so that work-hardening always occurs. In hot extrusion, recrystallization eliminates the effects of work-hardening, unless rapid cooling of the extrusion prevents recrystallization from being completed. |
| Cold treatment |
Treatment carried out after quenching to transform retained austenite into martensite, involving cooling and holding at a temperature below ambient. |
| Cold working |
The plastic deformation of a metal, by rolling (cold rolling), drawing, forging (cold forging), etc. at a temperature well below its recrystallization temperature, which results not only in permanent shape change but also increase in strength and loss of ductility owing to work-hardening. |
| Collapse load (Unit N) |
The applied load at which a structure becomes a mechanism owing to the formation of sufficient plastic hinges for collapse to occur. |
| Collar |
A ring secured to, or integral with, a shaft to give axial location. |
| Columnar structure |
A coarse structure of parallel elongated grains formed by unidirectional growth, most often observed in castings, but sometimes in structures resulting from diffusional growth accompanied by a solid-state transformation. |
| Combined carbon |
The part of the total carbon in steel or cast iron that is present as other than free carbon. |
| Combined dimensioning |
The use of chain dimensioning and parallel dimensioning on the same engineering drawing. |
| Combined heat and power plant |
(CHP plant, COGEN, cogeneration plant, total-energy plant) A plant for the simultaneous production of more than one useful form of energy from the same energy source, such as process heat and electric power. In the arrangement shown, partially expanded steam is extracted from the steam turbine and used to produce process heat. |
| Combined stresses |
The stress state at a point in a component subjected to combination of axial, bending, torsional loadings etc., acting along all reference axes. |
| Combustible |
(inflammable) A term for substances that can be ignited and burned. |
| Combustion |
An exothermic chemical reaction in which a fuel and an oxidant, typically air, react together to release a significant quantity of thermal energy in the presence of a flame. In the case of fluid fuels, ignition may be from an electric spark or compression of the |
| Combustion chamber |
1. In a piston engine, the volume between the head of an individual cylinder and the crown of the piston in which the fuel–air mixture burns during each power stroke of the engine. 2. (combustor) In a gas-turbine engine, a ramjet, an afterburner, or a rocket motor, the component, often cylindrical or annular in shape, in which the fuel–air mixture burns in a continuous-flow process. |
| Combustion deposit |
Ash, carbon, and other incombustible solids, often due to impurities in the fuel, that build up on any surfaces exposed to products of combustion. They can lead to corrosion, reduced heat transfer and so higher flue-gas temperatures and reduced efficiency. |
| Combustion efficiency |
(source efficiency, ηCOMB) A performance measure for combustion equipment defined by ηCOMB = amount of heat released during combustion/(calorific value of the fuel burned). |
| Complete decarburization |
Decarburization with sufficient carbon loss to show only clearly defined ferrite grains under metallographic examination. |
| Composite material |
(composite structure) A general term used of two or more materials or structures acting in combination (e.g. concrete, reinforced concrete, filamentreinforced polymers, laminated materials, particulate-reinforced materials, flitched beams), resulting in values of strength, stiffness, or toughness greater than the base matrix material alone. |
| Composite property |
In thermodynamics, a property defined in terms of the properties of a closed system and its surroundings, such as the non-flow exergy function. |
| Compound pendulum |
A rigid body free to swing about an axis. |
| Compounding |
In a steam engine (compound steam engine) or impulse turbine, the progressive reduction in pressure (expansion) across two or more stages in series. |
| Compressed liquid |
A liquid subjected to a pressure greater than the saturation pressure corresponding to its temperature. |
| Compressibility (Unit 1/Pa) |
A measure of the reduction in volume or increase in density when a substance is subjected to an increase of pressure. It is defined as the reciprocal of the bulk modulus. Liquids and solids are normally considered incompressible, whereas gases are highly compressible. |
| Compressible flow |
A gas flow in which the Mach number M is sufficiently high for the gas density to change significantly. For air, this is when M > 0.3. |
| Compression |
1. Loading, the principal effect of which is to squeeze and shorten a component or testpiece. 2. The reduction in volume and increase in density of a substance as a consequence of increased pressure. |
| Compression crease |
A crease formed during the compression of composites having a high volume fraction of filaments. These composites fail in compression by forming a crease at an angle to the loading axis. |
| Compression failure |
The reduction or removal of a component’s load-bearing capacity in compression, caused by buckling, fracture, crease formation in fibre composites, etc. |
| Compression fitting |
A screwed joint for pipework made resistant to leakage by permanent deformation of a closely-fitting ring, called a ferrule or olive, on tightening. |
| Compression member |
A structural component, the major loading on which is compressive. |
| Compression pressure (Unit Pa) |
The pressure produced in a cylinder of a piston engine by compression of air in the absence of fuel. |
| Compression ratio |
For a piston engine, if the swept volume is SW and the clearance volume is CL, the compression ratio is given by ( SW + CL)/CL, i.e. it is a volume ratio rather than a pressure ratio. |
| Compression ratio |
The volume of a combustion chamber with the piston at the top of its stroke as a proportion of the total volume of the cylinder with the piston at the bottom of its stroke. |
| Compression spring |
A spring that resists compression forces, usually in the form of a helix with separated coils (giving a linear axial stiffness) or a cone with separated coils (giving a non-linear axial stiffness). |
| Compression stroke |
The stroke in a reciprocating compressor or engine during which the working fluid is compressed. |
| Compression test |
A method for assessing the ability of a material to withstand compressive loads. |
| Compression test |
The determination of the stress–strain curve of a material by axial loading of a specimen in compression. In brittle materials failure is in the elastic range; more ductile materials will yield before fracture; very ductile materials will plastically deform extensively before failure. The compression strength (compressive strength), with unit Pa, is the compressive stress that causes failure in a component or structure. |
| Compression wave |
(dilatation wave) In a fluid or a solid, a progressive wave or wavefront that compresses the medium through which it propagates. |
| Compressive strength |
Maximum compressive stress a material is capable of developing. With a brittle material that fails in compression by fracturing, the compressive strength has a definite value. For ductile, malleable, or semiviscous materials (which do not fail in compression by a shattering fracture), the value obtained for compressive strength is an arbitrary value dependent on the degree of distortion that is regarded as effective failure of the material. |
| Compressive stress |
A stress that causes an elastic body to deform (shorten) in the direction of the applied load. Contrast with tensile stress. |
| Compressive stress (Unit Pa) |
The compressive load per unit area at a point in a component. |
| Compressometer |
Instrument for measuring change in length over a given gage length caused by application or removal of a force. Commonly used in compression testing of metal specimens. |
| Compressor |
A turbomachine, of either axial or radial type, that increases the pressure of a gas or vapour. |
| Compressor blades |
The aerofoil-shaped vanes that form the rotor(s) and stator(s) of an axial-flow compressor. The aerodynamic design is more critical than is the case for turbine blades because there is an increase in pressure across each row of blades. The arrows in the diagram indicate the flow direction relative to the blades. |
| Compressor bleed |
The removal of air before the final stage of a multistage compressor operating below design speed, to prevent the final stage from choking. |
| Computational domain |
In CFD, FEM, and other numerical methods, the area or volume within which calculations are performed and on the periphery of which the boundary conditions are specified. |
| Computed path control |
In CNC or robotics, the use of a control program to determine the required path for the tool or end effector. This required path forms the set points for the motor controllers moving the machine tool or robot. |
| Computer control |
The control of an engineering device or system by pre-programmed computer or by feedback control. |
| Computer numerical control (CNC) |
A term relating to machine tools in which the movements of a tool and/or the workpiece are controlled by computer. |
| Computer vision |
The digitization and processing of optical images/patterns by computer in order to recognize parts, orientation, etc. in manufacturing. |
| Computer-aided design (CAD) |
Generally, design and calculations performed by computer; more specifically, the use of computer graphics and models to communicate design concepts. Computer-aided design and computer-aided manufacturing (CAD/CAM) is where component dimensions resulting from CAD are passed by electronic means directly to machines for manufacture. |
| Computer-aided manufacturing |
(CAM, computer-integrated manufacturing, CIM) The use of computers in all branches of manufacturing, not only to control machines and robots for manufacturing and assembly, but also for process planning, and monitoring progress of materials and components during production, etc. |
| Concentrated load |
A load on a component which is distributed over a very small area, idealized as the line load of a wedge or knife edge, and the point load of a cone. |
| Concentrated solar power plant (CSP plant) |
A power plant in which solar radiation is concentrated using mirrors or lenses, typically using parabolic trough mirrors which focus solar radiation on to receiver tubes along the trough’s focal line. In an alternative arrangement molten salt, heated by solar receivers mounted on a tower, is circulated through a steam generator. |
| Concentration ratio |
For a concentrating solar collector, the ratio of the projected area of the concentrator facing the solar beam to the actual area of the receiver. |
| Concurrent engineering |
The integration of the procedures for product design, material selection and manufacturing method to include life-cycle analysis. |
| Condensate strainer |
A filter in a steam plant used to remove particulate matter from condensate before it is added to feedwater. |
| Condensation shock |
For supersonic flow of a moist gas through a divergent nozzle, condensation occurs in the form of spontaneous nucleation at some point downstream of that at which the temperature falls to the saturation temperature. The condensation process proceeds rapidly, and results in a fairly thick discontinuity termed a condensation shock. |
| Condenser |
A heat exchanger in which a substance is changed from its vapour phase to its liquid phase by reducing its temperature to below the saturation temperature. |
| Condenser vacuum |
The sub-atmospheric pressure imposed on the condenser of a steam-power plant which leads to an appreciable increase in overall efficiency. |
| Condensing boiler |
A relatively small industrial or domestic boiler that burns sulfur-free natural gas so that the products of combustion do not contain sulfuric acid and can be allowed to condense on heat-transfer surfaces without danger of corrosion. |
| Conditioning heat treatment |
A preliminary heat treatment used to prepare a material for desired reaction to a subsequent heat treatment. For the term to be meaningful, the exact heat treatment must be specified. |
| Conduit |
A hollow object, of metal, plastic, glass, ceramic, etc., which is relatively long compared with its lateral dimensions and through which there is fluid flow. |
| Cone clutch |
A friction clutch in which an internal cone moves axially in or out of engagement with an external cone. One or both surfaces is lined with high-friction material. |
| Cone pulley |
A stepped pulley having several diameters which, when linked by a laterallymoveable transmission belt to a corresponding pulley, gives a series of speed ratios. |
| Congruent melting point (Unit K) |
congruent melting point (Unit K) The temperature at which a solid substance at a specified pressure changes phase to a liquid of identical composition. |
| Congruent transformation |
An isothermal or isobaric phase change in which both of the phases concerned have the same composition throughout the process. |
| Connecting rod |
(con rod) A link that transmits power from one system to another, often changing linear to rotary motion, as in the rod connecting the piston to the crankshaft in a reciprocating compressor or pump or to the crankshaft in an internal-combustion engine, as in the diagram. The big end (bottom end) is the larger end that connects to the bearing on one of the crankpins of the crankshaft. The little end (small end) is joined by a gudgeon pin to the piston. |
| Constant life diagram |
A plot of experimentally derived fatigue-life data; perhaps the most complex and complete of the popular charts used to represent such data. |
| Constant-force spring |
A spring that has the same restoring force regardless of displacement. The most common type takes the form of a coiled strip that, owing to tight coiling during manufacture, is pre-stressed (a steel measuring tape is an example). The uncoiling force is approximately constant as the change of curvature of the strip is approximately constant. Not to be confused with a clockwork spring from which power can be obtained. |
| Constant-mesh gearbox |
A gearbox in which the pairs of gears giving different speed ratios are constantly in mesh, different ratios being obtained by connecting or disconnecting the relevant gear to the driving shaft. |
| Constant-velocity universal joint |
(CV joint, homokinetic joint) A connexion that transmits constant angular velocity between two shafts that are neither necessarily in line nor whose axial position is necessarily fixed. |
| constitutive equation |
(constitutive relation) 1. In solid mechanics or fluid mechanics, an algebraic or numerical relation for the dependency of stress on deformation, strain, strain rate, temperature, etc. in a material. In solid mechanics such a relation is sometimes called an equation of state. Simple linear examples include Hooke’s law and Newton’s viscosity law. 2. In heat transfer, a relation, such as Fourier’s law of heat conduction, connecting heat flux with temperature gradient. |
| Contact strength (Unit N) |
The maximum allowable load between contacting bodies converted into a stress. |
| Continuous precipitation |
Precipitation from a supersaturated solid solution in which the precipitate particles grow by longrange diffusion without recrystallization of the matrix. Continuous precipitates grow from nuclei distributed more or less uniformly throughout the matrix. They usually are randomly oriented, but may form a Widmanstätten structure. |
| Continuous-type furnace |
A furnace used for heat treating materials that progress continuously through the furnace, entering one door and being discharged from another. See belt furnac, direct-fired tunnel-type furnac, rotary retort furnace, shaker-hearth furnace. |
| Controlled cooling |
Cooling from an elevated temperature in a predetermined manner, to avoid hardening, cracking, or internal damage, or to produce desired microstructure or mechanical properties. |
| Cooling coil |
A simple heat exchanger consisting of a coiled tube, typically of copper or stainless steel, through which is circulated a coolant such as a refrigerant, chilled water, or water mixed with ethylene glycol. Applications include air conditioning, process cooling, and refrigeration. |
| Cooling curve |
A curve showing the relation between time and temperature during the cooling of a material. |
| Cooling stresses |
Residual stresses resulting from nonuniform distribution of temperature during cooling. |
| Core |
In a ferrous alloy prepared for case hardening, that portion of the alloy that is not part of the case . Typically considered to be the portion that (a) appears light on an etched cross section, (b) has an essentially unaltered chemical composition, or (c) has a hardness, after hardening, less than a specified value. |
| Corrosion |
The deterioration of an exposed metal surface due to electrochemical oxidation with its surroundings. In the oxidation reaction, metal atoms give up electrons which are transferred to form another chemical species by a reduction reaction, usually with hydrogen and/or oxygen. A common example is the formation of the iron oxide rust Fe(OH)3 on iron or steel in moist air or water. Rust breaks away easily, exposing fresh iron to the atmosphere, whereas the corrosion product of some metals forms an adherent layer that prevents further oxidation reaction at fresh metal, an effect known as passivation. Examples include aluminium oxide on aluminium, chromium oxide on chromium, chromium oxide on alloys containing chromium such as stainless steels, and the patina formed on copper and zinc. Corrosion protection takes many forms. Good design to avoid crevices and stress is important. In some situations, substances known as inhibitors may be added to the environment to decrease its corrosiveness. The electrochemical nature of corrosion results in some metals having a greater tendency for oxidation than others. Zinc has a stronger tendency than iron and this is made use of in galvanizing. This is one example of cathodic protection, in which one metal is connected electrically to a more reactive metal, called a sacrificial anode, that oxidizes by giving up electrons and so protects the first metal. Coatings may be used to resist corrosion. Paints, plating, and diffusion coatings are the most common and the electrochemical process of anodizing is used to deliberately form a passive layer of oxide on aluminium alloys. Material selection plays a major role. For example, stainless steels with their high chromium content are widely used in corrosive environments. |
| Corrosion cell |
A natural ‘‘battery’’ formed when two metals having different electrical potentials (an Anode and a Cathode) are connected together in the presence of a liquid (the Electrolyte). |
| Corrosion failure |
1. The failure of a component or structure after corrosion has reduced the load-bearing area to an unsupportable level. 2. A situation in which a mechanism cannot function owing to corrosion products preventing free movement at joints. |
| Corrosion fatigue |
Cracking produced by the combined action of repeated or fluctuating stress and a corrosive environment at lower stress levels or fewer cycles than would be required in the absence of a corrosive environment. |
| Corrosive wear |
Wear in which chemical or electrochemical reaction with the environment is significant. |
| Cotter pin |
(cotter) 1. A tapered wedge or pin passing through a tapered slot or hole in one member and bearing against a second member to fix it in location. 2. A split cotter is commonly called a split pin. |
| Cotter pin |
A pin with two legs. With legs together, the pin is placed through the hole in a clevis pin. The legs are then opened outward to prevent the cotter pin from backing out of the hole. The cotter pin, in turn, prevents the load-bearing clevis pin from backing out of its retaining hole. |
| Counter sink |
To cut or shape a depression in an object so that the head of a screw may set flush or below the surface. |
| Countersinking |
The flaring out of the rim of a drilled hole to form a truncated conical depression to receive a screw having a conical head, thus giving a flush fitting. |
| Coupling |
1. Any mechanical fastening connecting two or more shafts, or parts of a mechanism, in order to transmit power. 2. A device for connecting two vehicles. |
| Coupling |
A detachable mechanism forming a joint. A connector of two components of a joint. |
| Crack |
A thin fissure-like defect in a component or structure across which material continuity is lost and which reduces the strength of the body. |
| Crack arrest |
Crack propagation that stops of its own accord when the energy release rate of the loaded component or structure falls below a critical value. If predictable, it can be incorporated into structural-integrity assessments. |
| Crack length (depth) (a) |
In fatigue and stress corrosion cracking, the physical crack size used to determine the crack growth rate and the stress-intensity factor. For the compact-type specimen, crack length is measured from the line connecting the bearing points of load application. For the center-cracked-tension specimen, crack length is measured from the perpendicular bisector of the central crack. |
| Crack size (a) |
A lineal measure of a principal planar dimension of a crack. This measure is commonly used in the calculation of quantities descriptive of the stress and displacement fields. In practice, the value of crack size is obtained from procedures for measurement of physical crack size, original crack size, or effective crack size, as appropriate to the situation under consideration. |
| Crack-extension force (G) |
The elastic energy per unit of new separation area that would be made available at the front of an ideal crack in an elastic solid during a virtual increment of forward crack extension. |
| Crack-extension resistance (KR) |
A measure of the resistance of a material to crack extension, expressed in terms of the stress-intensity factor, the crack-extension force, or values of Jderived using the J-integral concept. |
| Crack-growth rate |
Rate of propagation of a crack through a material due to statically or dynamically applied load. |
| Crank angle (Unit °) |
The angle between the crank of a slider-crank mechanism and a line from the crankshaft centreline to the piston axis. |
| Crank pin |
It is a short shaft parallel to the axis of the crankshaft but radially offset from it, to which is attached the big end of a connecting rod in a bearing. Sometimes the crank pin is supported at one end only (a wrist pin) but in built-up or one-piece forged crankshafts, the crank pin is supported by thick plates (crank arms, crank webs) at either end. |
| Crankshaft |
The main shaft, of which the cranks are a part, of a reciprocating single-or multi-cylinder machine. Crankshafts may be built up in sections or forged as a single component. In an engine, the reciprocating motion of the pistons transmits power to the crankshaft and causes it to rotate, whereas in a pump the crankshaft is driven and its rotation causes the pistons to reciprocate. |
| Creep |
Time-dependent and permanent deformation of material under constant load or stress. The strain increases with time at a rate that increases with increasing temperature. Creep can lead to large strain and eventual failure, and so limit the lifetime of components subjected to load at high temperature. Creep in metals becomes significant at homologous temperatures in excess of about 0.4, e.g. 1200°C for tungsten, 504°C for titanium, 450°C for iron, and 100°C for aluminium. |
| Creep |
The slow, plastic deformation of a body under heavy loads. Time-dependent plasticity. |
| Creep fatigue |
The effects of combined creep and fatigue at high homologous temperatures in metals, and in other materials such as polymers having time-dependent behaviour. |
| Creep limit (Unit Pa) |
The maximum allowable stress under the action of which creep deformation of a material does not exceed a specified limit. |
| Creep modulus (Unit Pa) |
The ratio of stress/strain at a chosen strain level obtained from creep tests, often plotted against time to show changes in stiffness. |
| Creep rupture strength (Unit Pa) |
The fracture stress at the end of a creep test in metals and polymers, often plotted against time to give a stress-rupture curve. |
| Creep–time relations |
Algebraic or numerical relations between creep strain and time at constant stress. |
| Crest |
The highest point of a wave or of a screw thread. |
| Crest clearance (Unit m) |
For screw threads and gearing, the radial clearance between the crest of a thread (or gear) and the root of the engaging thread (or gear). |
| Crest of screw thread |
The top surface joining the two sides of flanks of a thread. |
| Critical compression ratio |
1. The compression ratio for incipient knock of hydrocarbon fuels as determined in a variable-compression single-cylinder piston engine. 2. The compression ratio at which an air–fuel mixture will spontaneously ignite due to the temperature increase produced. |
| Critical cooling rate |
The rate of continuous cooling required to prevent undesirable transformation. For steel, it is the minimum rate at which austenite must be continuously cooled to suppress transformations above the Ms temperature. |
| Critical crack length (Unit m) |
The crack length at which a given stress applied to a body will result in crack propagation and fracture. |
| Critical diameter |
(D) Diameter of the bar that can be fully hardened with 50% martensite at its center. |
| Critical load (Unit N) |
1. The applied load that causes propagation of an existing crack of known length, and hence fracture of a component or structure. 2. The applied load that results in buckling of a column of given end fixity. |
| Critical point |
(1) The temperature or pressure at which a change in crystal structure, phase or physical properties occurs. Same as transformation temperature. (2) In an equilibrium diagram, that specific value of composition, temperature and pressure, or combinations thereof, at which the phases of a heterogeneous system are in equilibrium. |
| Critical strain |
The strain just sufficient to cause recrystallization; because the strain is small, usually only a few percent, recrystallization takes place from only a few nuclei, which produces a recrystallized structure consisting of very large grains. |
| Critical temperature |
(1) Synonymous with critical point if the pressure is constant. (2) The temperature above which the vapor phase cannot be condensed to liquid by an increase in pressure. |
| Critical temperature ranges |
Synonymous with transformation ranges, which is the preferred term. |
| Crossed threads |
When the axis of a nut offered up to a bolt is not aligned with the axis of a bolt (or a screw to a threaded member), it may be possible for the threads to engage incorrectly and even for the nut or screw to advance a turn or more, but ultimately the misaligned threads become locked together. Forcing the nut in such circumstances may irretrievably damage the threads on both. |
| Crosshead |
1. A reciprocating member, sliding between guides, to which the piston rod is firmly attached on one side and to which the connecting rod is pinned on the other for the conversion of reciprocating into rotary motion. 2. The moveable beam in early designs of mechanical testing machines. 3. A screwhead having slots in a + shape that takes a mating screwdriver. |
| Crushing strain |
The supposed single strain that results in comminution of a brittle material. The corresponding stress is termed the crushing strength. Neither quantity can be a material constant as they must obey the laws of fracture mechanics and will depend on the type of testpiece, method of loading etc. |
| Crystalline defects |
The deviations from a perfect three-dimensional atomic packing that are responsible for much of the structure-sensitive properties of the materials. Crystal defects can be point defects (dislocations) or surface defects (vacancies), line defects (dislocations), or surface defects (grain boundaries). |
| Crystalline fracture |
A pattern of brightly reflecting crystal facets on the fracture surface of a polycrystalline metal, resulting from cleavage fracture of many individual crystals. |
| Cup washer |
A dished leather or neoprene washer fitted to the rod end in some piston-style pumps. |
| Curie temperature |
The temperature of magnetic transformation below which a metal or alloy is ferromagnetic and above which it is paramagnetic. |
| Cyaniding |
A case-hardening process in which a ferrous material is heated above the lower transformation range in a molten salt containing cyanide to cause simultaneous absorption of carbon and nitrogen at the surface and, by diffusion, create a concentration gradient. Quench hardening completes the process. |
| Cycle annealing |
An annealing process employing a predetermined and closely controlled time-temperature cycle to produce specific properties or microstructures. |
| Cylinder head |
The machined casting, typically of aluminium alloy or cast iron, that fits above the cylinder block of a piston engine and closes off the cylinders. It normally includes part of the combustion chambers and holes for the valves and spark plugs. |
