Friction, Lubrication, and Wear Technology (1997) Part 15 pptx

• Note: This number is normally written as: • in which Z denotes the dynamic viscosity, N the frequency of rotation, and p the pressure (Ref 1). See also Ocvirk number , Sommerfeld number , and Stribeck curve . • Hertzian contact area • (1) The contact area (also, diameter or radius of contact) between two bodies calculated according to Hertz's equations of elastic deformation (Ref 1m). (2) The apparent area of contact between two nonconforming solid bodies pressed against each other, as calculated from Hertz's equations of elastic deformation (Ref 2). • Hertzian contact pressure • (1) The pressure at a contact between two solid bodies calculated according to Hertz's equations of elastic deformation (Ref 1). (2) The magnitude of the pressure at any specified location in a Hertzian contact area, as calculated from Hertz's equations of elastic deformation (Ref 2). • high-stress abrasion • A form of abrasion in which relatively large cutting forces are imposed on the particles or protuberances causing the abrasion, and that produces significant cutting and deformation of the wearing surface. Note: In metals, high-stress abrasion can result in significant surface strain hardening. This form of abrasion is common in mining and agricultural equipment, and in highly loaded bearings where hard particles are trapped between mating surfaces (Ref 3m). See also low-stress abrasion . • highly deformed layer • In tribology, a layer of severely plastically deformed material that results from the shear stresses imposed on that region during sliding contact. See also Beilby layer and white layer . • Hohman A-6 wear machine • A widely used type of wear and friction testing machine in which a rotating ring specimen is squeezed between two diametrically opposed rub blocks. Note: This design is said to eliminate shaft flexure such as that found in other machines whose load application from the rub block to the ring is from one side only. Block geometry can be changed from flat to conforming or V- block. This type of machine is designed for use with either lubricated or unlubricated specimens. Hohman A-6 wea r machine testing arrangement. Courtesy of Hohman Plating and Manufacturing Company • horseshoe thrust bearing • A tilting-pad thrust bearing in which the top pads are omitted, making an incomplete annulus (Ref 1). • hydraulic fluid • A fluid used for transmission of hydraulic pressure or action, not necessarily involving lubricant properties. Note: Hydraulic fluids can be based on oil, water, or synthetic (fire-resistant) liquids (Ref 1). • hydrodynamic lubrication • A system of lubrication in which the shape and relative motion of the sliding surfaces causes the formation of a fluid film that has sufficient pressure to separate the surfaces (Ref 1). See also elastohydrodynamic lubrication and gas lubrication . • hydrodynamic seal • A seal that has special geometric features on one of the mating faces. These features are designed to produce interfacial lift, which arises solely from the relative motion between the stationary and rotating portions of the seal (Ref 4). • hydrostatic bearing • A bearing in which the solid bodies are separated and supported by a hydrostatic pressure, applied by an external source, to a compressible or incompressible fluid interposed between those bodies. • hydrostatic lubrication • A system of lubrication in which the lubricant is supplied under sufficient external pressure to separate the opposing surfaces by a fluid film (Ref 1). See also pressurized gas lubrication . • hydrostatic seal • A seal incorporating features that maintain an interfacial film thickness by means of pressure. The pressure is provided either by an external source or by the pressure differential across the seal. The interfacial pressure profile of a seal face is normally speed-dependent; the interfacial pressure profile of the hydrostatic seal is not speed-dependent (Ref 4). • hypoid gear lubricant (hypoid oil) • A gear lubricant with extreme-pressure characteristics used in hypoid gears (Ref 1). • I • impact velocity • The relative velocity between the surface of a solid body and an impacting liquid or solid particle. Note: To describe this velocity completely, it is necessary to specify the direction of motion of the particle relative to the solid surface in addition to the magnitude of the velocity. The following related terms are also in use: (1) absolute impact velocity the magnitude of the impact velocity, and (2) normal impact velocity the component of the impact velocity that is perpendicular to the surface of the test solid at the point of impact (Ref 2). • impact wear • Wear of a solid surface resulting from repeated collisions between that surface and another solid body. Note: The term erosion (erosive) wear is preferred in the case of multiple impacts and when the impacting body or bodies are very small relative to the surface being impacted. • impaction ratio • See collection efficiency . • impingement • A process resulting in a continuing succession of impacts between liquid or solid particles and a solid surface. Note: In preferred usage, impingement also connotes that the impacting particles are smaller than the solid surface, and that the impacts are distributed over the surface or a portion of the surface. If all impacts are superimposed on the same point or zone, then the term repeated impact is preferred (Ref 2m). • impingement corrosion • A form of erosion-corrosion generally associated with the impingement of a high-velocity flowing liquid containing air bubbles against a solid surface (Ref 2). • impingement erosion • Loss of material from a solid surface due to impingement . • impingement umbrella • The partial screening of the surface of a solid specimen subjected to solid impingement that sometimes occurs when some of the solid particles rebound from the surface and impede the motion of other impinging particles (Ref 2). • incubation period • (1) In cavitation and impingement erosion, the initial stage of the erosion rate-time pattern during which the erosion rate is zero or negligible compared to later stages. (2) In cavitation and impingement erosion, the exposure duration associated with the initial stage of the erosion rate- time pattern during which the erosion rate is zero or negligible compared to later stages. Note: Quantitatively, incubation period is sometimes defined as the intercept on the time or exposure axis, of a straight-line extension of the maximum slope portion of the cumulative erosion-time curve (Ref 2m). See also cavitation erosion and impingement erosion . • indentation hardness • Resistance of a solid surface to the penetration of a second, usually harder, body under prescribed conditions. Note: Numerical values used to express indentation hardness are not absolute physical quantities, but depend on the hardness scale used to express hardness. See also Brinell hardness test , Knoop (microindentation) hardness number , microindentation hardness number , nanohardness test , Rockwell hardness number , and Vickers (microindentation) hardness number . • indenter • In hardness testing, a solid body of prescribed geometry, usually chosen for its high hardness, that is used to determine the resistance of a solid surface to penetration. • initial pitting • Surface fatigue occurring during the early stages of gear operation, associated with the removal of highly stressed local areas and running-in (Ref 1). • instantaneous erosion rate • The slope of a tangent to the cumulative erosion-time curve at a specified point on that curve (Ref 2). • interval erosion rate • The slope of a line connecting two specified points on the cumulative erosion-time curve (Ref 2). • IRG transition diagram • Developed by the International Research Group (IRG) on Wear of Engineering Materials of the Organization of Economic Cooperation and Development (OECD), it is a plot of normal force in newtons (ordinate) versus sliding velocity in meters per second (abscissa) wherein boundaries identify three distinct regions of varying lubricant effectiveness. • J • jewel bearing • A bearing made of diamond, sapphire, or a hard substitute metal (Ref 1). • journal • The part of a shaft or axle that rotates or oscillates relative to a radial bearing. Note: A journal is part of a larger unit, for example, a crankshaft or lineshaft, and it is preferred that the term shaft be kept for the whole unit (Ref 1). • journal bearing • A sliding-type bearing in which a journal rotates or oscillates relative to its housing. Note: A full journal bearing extends 360°, but partial bearings may extend, for example, over 180° or 120° (Ref 1). • judder • Intermittent motion. See also spragging . • K • kinematic viscosity • See viscosity . • kinetic coefficient of friction • The coefficient of friction under conditions of macroscopic relative motion between two bodies (Ref 2). • kinetic friction • Friction under conditions of macroscopic relative motion between two bodies. Note: This term is sometimes used as a synonym for kinetic coefficient of friction ; however, it can also be used merely to indicate that the type of friction being indicated is associated with macroscopic motion rather than static conditions. • kinematic wear marks • In ball bearings, a series of short curved marks on the surface of a bearing race due to the kinematic action of imbedded particles or asperities rolling and spinning at the ball or roller contact points. Note: The length and curvature of these marks depend on the degree of spinning and on the distance from the spinning axis of the rolling element (Ref 3m). • Kingsbury bearing • See tilting-pad bearing . • knock • In a spark ignition engine, uneven burning of the air/fuel charge that causes violent, explosive combustion and an audible metallic hammering noise. Note: Knock results from premature ignition of the last part of the charge to burn (Ref 8). • Knoop (microindentation) hardness number • Developed by F.C. Knoop in the late 1930s, it is the numerical value of microindentation hardness obtained using the Knoop indenter (diamond) and calculated as follows: • where HK P (units of GPa) is the ASTM symbol used to represent Knoop microindentation hardness number (with the subscript indicating applied indenter load), P is the applied load (in grams), and d is the length of the long diagonal of the impression (in micrometers). Note: To obtain HK in kg/mm 2 , replace 139.6 by 14229.0. See ASTM Standard Test Method E 384 for further details. • L • L 10 -life • See rating life . • lacquer • In lubrication, a deposit resulting from the oxidation and/or polymerization of fuels and lubricants when exposed to high temperatures. Note: Softer deposits are described as varnishes or gums (Ref 1). • lapping • (1) A surface finishing process involving motion against an abrasive embedded in a soft metal (Ref 1). (2) Rubbing two surfaces together, with or without abrasives, for the purpose of obtaining extreme dimensional accuracy or superior surface finish (Ref 11). • large-end bearing • See big-end bearing . • layer bearing • A bearing constructed in layers (Ref 1). See also bimetal bearing and trimetal bearing . • layer-lattice material • Any material having a layerlike crystal structure, but particularly solid lubricants of this type (Ref 1). • L/D ratio • In bearing technology, the ratio of the axial length of a plain bearing to its diameter (Ref 1m). • leaded bronzes • See bearing bronzes . • lemon bearing (elliptical bearing) • A two-lobed bearing (Ref 1m). • light fraction • The first liquid produced during the distillation of a crude oil (Ref 1). • limiting static friction • The resistance to the force tangential to the interface that is just sufficient to initiate relative motion between two bodies under load. Note: The term static friction, which properly describes a tangential resistance called into operation by a force less than this, should not be substituted for limiting static friction (Ref 1). • linishing • A method of finishing by grinding on a continuous abrasive belt (Ref 1). • liquid impact erosion • See erosion (erosive wear) . • liquid impingement erosion • See erosion (erosive wear) . • little-end bearing • A bearing at the smaller (piston) end of a connecting rod in an engine (Ref 1). See also big-end bearing . • load • In tribology, the force applied normal to the surface of one body by another contacting body or bodies. Note: The term normal force is more precise and therefore preferred; however, the term normal load is also in use. If applied vertically, the load can be expressed in mass units, but it is preferable to use force units such as newtons (N). • load-carrying capacity (of a lubricant) • (1) The maximum load that a sliding or rolling system can support without failure (Ref 1m). (2) The maximum load or pressure that can be sustained by a lubricant (when used in a given system under specific conditions) without failure of moving bearings or sliding contact surfaces as evidenced by seizure or welding (Ref 11). • loading • (1) The filling of an abrasive paper or other bound abrasive material by abraded material from a second body. (2) The concentration of abrasive bound in a matrix material or added to a lap wheel as a loose abrasive. • lobed bearing • A journal bearing with two or more lobes around its periphery produced by machining or by elastic distortion to increase stability or to provide adjustable clearance (Ref 1). • low-stress abrasion • A form of abrasion in which relatively low contact pressures on the abrading particles or protuberances cause only fine scratches and microscopic cutting chips to be produced (Ref 3m). See also high-stress abrasion . • lubricant • Any substance interposed between two surfaces in relative motion for the purpose of reducing the friction or wear between them (Ref 1). Note: The above definition implies intentional addition of a substance to an interface; however, species such as oxides and tarnishes on certain metals can also act as lubricants even though they were not added to the system intentionally. • lubricant compatibility • See compatibility (lubricant) . • lubrication • The reduction of frictional resistance and wear, or other forms of surface deterioration, between two load-bearing surfaces by the application of a lubricant (Ref 1). • lubrication regimes • Ranges of operating conditions for lubricated tribosystems that can be distinguished by their frictional characteristics and/or by the manner and amount of separation of the bearing surfaces. See also boundary lubrication , elastohydrodynamic lubrication , full-film lubrication , hydrodynamic lubrication , and quasi-hydrodynamic lubrication . • lubricious (lubricous) • Relating to a substance or surface condition that tends to produce relatively low friction. • lubricity • The ability of a lubricant to reduce wear and friction, other than by its purely viscous properties (Ref 1). • M • macrohardness test • A term applied to such hardness testing procedures as the Rockwell, Brinell, or macro-Vickers (high-load) hardness tests to distinguish them from microindentation hardness tests such as the Knoop or Vickers tests. See also microindentation hardness number . • macroslip • A type of sliding in which all points on one side of the interface are moving relatively to those on the other side in a direction parallel to the interface. Note: The term macroslip is sometimes used to denote macroslip velocity. This usage is not recommended (Ref 1). See also microslip . • magnetic bearing • A type of bearing in which the force that separates the relatively moving surfaces is produced by a magnetic field. • magnetic seal • A seal that uses magnetic material, instead of springs or bellows, to provide the closing force (Ref 4). • magnetohydrodynamic lubrication • Hydrodynamic lubrication in which a significant force contribution arises from electromagnetic interaction. Note: Magnetohydrodynamic bearings have been proposed for very high-temperature operation, for example, in liquid sodium (Ref 1). • magnetostrictive cavitation test device • A vibratory cavitation test device driven by a magnetostrictive transducer (Ref 2). • main bearing • A bearing supporting the main power-transmitting shaft (Ref 1). • mass concentration (in a slurry) • The mass of solid particles per unit mass of mixture, expressed in percent (Ref 13). • maximum erosion rate • The maximum instantaneous erosion rate in a test that exhibits such a maximum followed by decreasing erosion rates. Note: Occurrence of such a maximum is typical of many cavitation and liquid impingement tests. In some instances it occurs as an instantaneous maximum; in others it occurs as a steady-state maximum that persists for some time (Ref 2). • maximum rate period • In cavitation and liquid impingement erosion, a stage following the acceleration period, during which the erosion rate remains constant (or nearly so) at its maximum value (Ref 2). • mechanical activation • The acceleration or initiation of a chemical reaction by mechanical exposure of a nascent solid surface. Note: Metal cutting is an effective method of exposing large areas of fresh surface. • mechanical seal • See face seal . • mechanical stability (of a grease) • Grease shear stability tested in a standard rolling tester (Ref 1). • mechanical wear • Removal of material due to mechanical processes under conditions of sliding, rolling, or repeated impact. Note: The term mechanical wear includes adhesive wear , abrasive wear , and fatigue wear (Ref 1). Compare with corrosive wear and thermal wear . • melt lubrication • Lubrication provided by steady melting of a lubricating species. Also known as phase-change lubrication (Ref 1m). • metallic wear • Typically, wear due to rubbing or sliding contact between metallic materials that exhibits the characteristics of severe wear, for example, significant plastic deformation, material transfer, and indications that cold welding of asperities possibly has taken place as part of the wear process. See also adhesive wear and severe wear . • metallurgical burn • Modification of the microstructure near the contact surface due to frictional temperature rise (Ref 1m). • metallurgical compatibility • See compatibility (metallurgical) . • microhardness number • A commonly used term for the more technically correct term microindentation hardness number . • microindentation • (1) In hardness testing, the small residual impression left in a solid surface when an indenter, typically a pyramidal diamond stylus, is withdrawn after penetrating the surface. Notes: Typically, the dimensions of the microindentations are measured to determine microindentation hardness number, but newer methods measure the displacement of the indenter during the indentation process to use in the hardness calculation. The precise size required to qualify as a "microindentation" has not been clearly defined; however, typical measurements of the diagonals of such impressions range from approximately 10 to 200 m, depending on normal force and material. (2) The process of indenting a solid surface, using a hard stylus of prescribed geometry and under a slowly applied normal force, usually for the purpose of determining its microindentation hardness number. See also Knoop (microindentation) hardness number , microindentation hardness number , and Vickers (microindentation) hardness number . • microindentation hardness number • A numerical quantity, usually stated in units of pressure, that expresses the resistance to penetration of a solid surface by a hard indenter of prescribed geometry and under a specified, slowly applied normal force. Notes: The prefix "micro" indicates that the indentations produced are typically between 10.0 and 200 m across. See also Knoop (microindentation) hardness number , nanohardness test , and Vickers (microindentation) hardness number . • microslip • Small relative tangential displacement in a contacting area at an interface, when the remainder of the interface in the contacting area is not relatively displaced tangentially. Notes: Microslip can occur in both rolling and stationary contacts. (2) The term microslip is sometimes used to denote the microslip velocity. This usage is not recommended (Ref 1). See also macroslip and slip . • mild wear • A form of wear characterized by the removal of material in very small fragments. Notes: Mild wear is an imprecise term, frequently used in research, and contrasted with severe wear . In fact, the phenomena studied usually involve the transition from mild to severe wear and the factors that influence this transition. Mild wear may be appreciably greater than can be tolerated in practice. With metallic sliders, mild wear debris usually consists of oxide particles (Ref 1m). See also normal wear and severe wear . • Miller number • A measure of slurry abrasivity as related to the instantaneous mass-loss rate of a standard metal wear block at a specific time on the cumulative abrasion-corrosion time curve (Ref 13). See also slurry abrasion response number . • mineral oil • A refined hydrocarbon oil without animal or vegetable additives (Ref 1m). • mist lubrication • Lubrication by an oil mist produced by injecting oil into a gas stream (Ref 1). • Mitchell bearing • See tilting-pad bearing . • mixed lubrication • See quasi-hydrodynamic lubrication . • Mohs hardness • The hardness of a body according to a scale proposed by Mohs, based on ten minerals, each of which would scratch the one below it (Ref 1). These minerals, in decreasing order of hardness, are: Diamond 10 Corundum 9 Topaz 8 Quartz 7 Orthoclase (feldspar) 6 Apatite 5 Fluorite 4 Calcite 3 Gypsum 2 Talc 1 • molecular seal • A seal that is basically of the windback type, but that is used for sealing vapors or gases. Note: Because of this use, the grooves and lands are dimensioned differently from those of a windback seal (Ref 4). • multigrade oil • An oil having relatively little change in viscosity over a specified temperature range (Ref 1). • N • nanohardness test • An indentation hardness testing procedure, usually relying on indentation force versus tip displacement data, to make assessments of the resistance of surfaces to penetrations of the order of 10 to 1000 nm deep. Notes: The prefix "nano-" normally would imply hardnesses one thousand times smaller than "microhardness"; however, use of this prefix was primarily designed as a means to distinguish this technique from the more traditional microindentation hardness procedures. Most nanohardness testing procedures use three-sided pyramidal diamond indenters first described by Berkovich. • nascent surface • A completely uncontaminated surface, produced for example by cleavage fracture under ideal vacuum conditions (Ref 1). • Navier-Strokes equations • Basic equations of hydrodynamic lubrication (Ref 1). • neat oil • Hydrocarbon oil with or without additives, used undiluted. Note: This term is used particularly in metal cutting to distinguish these fluids from soluble oils (emulsions) (Ref 1m). • needle bearing • A bearing in which the relatively moving parts are separated by long, thin rollers that have a length-to-diameter ratio exceeding 5.0 (Ref 1m). • net positive suction head • The difference between total pressure and vapor pressure in a fluid flow, expressed in terms of equivalent height of fluid, or "head," by the following equation: • where P o is the static pressure, P v is the vapor pressure, V is the flow velocity, w is the specific weight of fluid, and g is the gravitational acceleration. Note: This quantity is used in pump design as a measure of the tendency for cavitation to occur at the pump inlet. It can be related to the cavitation number (Ref 2). • neutral oil • A lubricating oil obtained by distillation, not treated with acid or with alkali (Ref 1). • Newt • The former English unit of kinematic viscosity (Ref 1). • Newtonian fluid • A fluid exhibiting Newtonian viscosity wherein the shear stress is proportional to the rate of shear (Ref 1m). Compare with dilatant , rheopectic material , and thixotropy . • nip • In a bearing, the amount by which the outer circumference of a pair of bearing shells exceeds the inner circumference of the housing (Ref 1). Also known as crush . • NLGI number • Abbreviation for the National Lubricating Grease Institute number, which is the numerical classification of the consistency of greases, based on the ASTM D 217 test (Ref 1). • nominal area (of contact) • The area bounded by the periphery of the region in which macroscopic contact between two solid bodies is occurring. Note: This is often taken to mean the area enclosed by the boundaries of a wear scar, even though the real area of contact, in which the solids are touching instantaneously, is usually much smaller. See also area of contact and apparent area of contact . • nonconformal surfaces • (1) Surfaces whose centers of curvature are on the opposite sides of the interface, as in rolling- element bearings or gear teeth (Ref 1). (2) In wear testing, a geometric configuration in which a "point" or "line" of contact is initially established between specimens before the test is started. Note: Examples of nonconformal contacts are ball-on-ring and flat block-on-ring geometries (tangent to the circumferential surface). When wear occurs, the nominal area of contact tends to increase. Nonconformal. (left) and conformal (right) test geometries • noncontact bearing • A bearing in which no solid contact occurs between relatively moving surfaces. Note: Strictly speaking, a bearing in which full-film lubrication is occurring would be considered a noncontact bearing; however, this term is more typically applied to gas bearings and magnetic bearings. See also gas lubrication and magnetic bearing . • non-Newtonian viscosity • The apparent viscosity of a material in which the shear stress is not proportional to the rate of shear (Ref 1). • nonsoap grease • A grease made with a thickener other than soap, such as clay or asbestos (Ref 1). • normal force • See load . • normal load • See load . • normal wear • Loss of material within the design limits expected for the specific intended application. Note: The concept of normal wear depends on economic factors, such as the expendability of a worn part. • normalized erosion resistance • The volume loss rate of a specified reference material divided by the volume loss rate of a test material obtained under similar testing and analysis conditions. Notes: "Similar testing and analysis conditions" means that the volume loss rates of the two materials are determined at the corresponding portions of the erosion rate-time pattern, for example, the maximum erosion rate or the terminal erosion rate. A recommended complete wording has the form: "the normalized erosion resistance of (test material) relative to the (reference material) based on (criterion of data analysis) is (numerical value)" (Ref 2m). • O • Ocvirk number • A dimensionless number used to evaluate the performance of journal bearings, and defined by the following equation: [...]... is included in tribology (Ref 1) (2) Friction, lubrication, and wear science and technology tribometer • (1) An instrument or testing rig to measure normal and frictional forces of relatively moving surfaces (Ref 1) (2) Any device constructed for or capable of measuring the friction, lubrication, and wear behavior of materials or components tribophysics • That part of physics dealing with interacting... Glossary of Terms and Definitions in the Field of Friction, Wear and Lubrication (Tribology), Research Group on Wear of Engineering Materials, Organisation for Economic Cooperation and Development (OECD), Paris, 1969 2 "Standard Terminology Relating to Erosion and Wear, " G 40, Annual Book of ASTM Standards, ASTM 3 M.B Peterson and W.O Winer, Ed., Wear Control Handbook, American Society for Mechanical Engineers,... this definition, and when encountered, it is best to verify its meaning from context wear constant • A term sometimes used interchangeably with the term wear coefficient ; however, it should not be used because wear rate is often not constant under different sliding conditions, and, therefore, the term is misleading wear debris • Particles that become detached in a wear process (Ref 1m) wear factor •... must be taken from its immediate context Sometimes, the term is used to refer to the sliding wear rate in terms of mm3N · m See also specific wear rate wear rate • There is no single, standard way to express wear rate The units used depend on the type of wear and the nature of the tribosystem in which wear occurs Wear rate can be expressed, for example, as (1) volume of material removed per unit time,... in order to be considered wear Sometimes surface damage , which may not involve material removal, is differentiated from wear as defined under the first definition This Handbook treats wear and surface damage individually wear coefficient • In sliding wear, a dimensionless number that usually represents the proportionality factor k in the Archard wear law Note: The term wear coefficient has been used... of Tribologists and Lubrication Engineers, 1983 5 E.L McMurtrey, Ed., High Performance Solid and Liquid Lubricants, Noyes Data Corp., 1987, p 399-402 6 E.A Avallone and T Baumeister III, Ed., Marks Standard Handbook for Mechanical Engineers, 9th ed., 1987, p 8-133 to 8-135 7 E.E Bisson and W.J Anderson, "Advanced Bearing Technology, " Special Publication SP-38, National Aeronautics and Space Administration,... methods In other cases, standards are established for given sectors of technology (for example, mechanical face seal technology) See the sections on specific wear types in this Handbook for more information wear rate (of seals) • The amount of seal-surface wear, stated in terms of mils worn in some designated time period Note: One commonly used unit is mils per hundred hours (Ref 4m) wear resistance • The... fragments Notes: Severe wear is an imprecise term, frequently used in research, and contrasted with mild wear In fact, the phenomena studied usually involve the transition from mild to severe wear and the factors that influence that transition With metals, the fragments are usually predominantly metallic rather than oxidic Severe wear is frequently associated with heavy loads and/ or adhesive contact... resistance • The resistance of a body to removal of material by wear processes, expressed as the reciprocal of wear rate Notes: Wear resistance is a function of the conditions under which the wear process takes place These conditions should always be carefully specified Relative wear resistance is sometimes quoted, using arbitrary standards (Ref 1m) wear scar • The portion of a solid surface that exhibits... the pin is one triboelement and the disk is another • • • • • tribology • The science and technology of interacting surfaces in relative motion and of the practices related thereto Notes: This term was introduced in a report by a group set up by the British Department of Education and Science It was defined in their report "Lubrication (Tribology)" in 1966 The study of wear by erosion or cavitation . impact. Note: The term mechanical wear includes adhesive wear , abrasive wear , and fatigue wear (Ref 1). Compare with corrosive wear and thermal wear . • melt lubrication • Lubrication provided. deformation, material transfer, and indications that cold welding of asperities possibly has taken place as part of the wear process. See also adhesive wear and severe wear . • metallurgical burn. oxide particles (Ref 1m). See also normal wear and severe wear . • Miller number • A measure of slurry abrasivity as related to the instantaneous mass-loss rate of a standard metal wear block