Bayer R.G. Mechanical Wear Fundamentals and Testing, Revised and Expanded

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by macroscopic, usually localized roughening and creation of protrusions

above the original surface, often includes plastic ﬂow or material transfer or

both or a severe form of adhesive wear.

Gouging abrasion: A form of high-stress abrasion in which easily observable

grooves or gouges are created on the surface.

Heat checkin g: A process in which ﬁne cracks are formed on the surface of a body

in sliding contact due to the buildup of excessive frictional heat.

High-stress abrasion: A form of abrasion in which relatively large cutting force

is imposed on the particles or protuberance causing the abrasion, and that

produces signiﬁcant cutting and deformation in the wearing surface.

Hydrodynamic lubrication: A form of ﬂuid lubrication in which the fricti on and ﬁlm

thickness is a function of the viscous properties of the ﬂuid lubricant.

Impact wear: Wear of a solid surface resulting from repeated collisions between

that surface and another solid body.

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.

Incubation perio d: An initial amount of wearing action that is needed for the occur-

rence of some wear mechanisms or for these mechanisms to become detectable.

IRG Transition Diagram: See transition diagram.

Kinetic friction: Friction associated with sustained motion.

Lapping: A surface ﬁnishing process involving motion against an abrasive

embedded in a soft metal or rubbing two surfaces together with or without

abrasives, for the purpose of obtaining extreme dimensional accuracy or super-

ior surface ﬁnish.

Limiting PV: The value of the PV Factor above which severe wear results.

Typically use to characterize the wear behavior of plastics and other bearing

materials.

Liquid impact erosion: See erosion.

Liquid impingement erosion: See erosion.

Low-stress abrasion: A form of abrasion in which relatively low contact pressure on

the abrading particles or protuberances cause only ﬁne scratches and micro-

scopic cutting chips to be produced.

Lubricant: Any substance interposed between two surfaces in relative motion for

the purpose of reducing the friction or wear between them.

Lubrication: The reduction of wear or friction by the use of a lubricant.

Lubricated impact wear: Impact wear with lubrication.

Lubricated rolling wear: Rolling wear with lubrication.

Lubricated sliding wear: Sliding wear with lubrication.

Measurable-wear: In the context of the Zero and Measurable Wear Models for slid-

ing and impact, it describes a state of wear in which the wear exceeds the mag-

nitude of the surface roughness.

Mechanical wear: Removal of material due to mechanical processes under condi-

tions of sliding, rolling, or repeated impacts; includes adhesive wear, abrasive

wear, and fatigue wear but not corrosive wear and thermal wear.

Metallic wear: Typically, wear due to rubbing or sliding contact between metallic

materials that exhibits the characteristics of severe wear, such as, signiﬁcant

plastic deformation, material transfer, and indications that cold welding of

asperities possibly has taken place as part of the wear process.

Mild wear: A form of wear characterized by the removal of material in very small

fragments.

Mixed lubrication: A condition of lubrication in which the friction and wear beha-

vior are determined by the properties of the surfaces and by the viscous and

non-viscous properties of ﬂuid lubricants.

Oxidative wear: A corrosive wear process in which chemical reaction with oxygen

or oxidizing environments predominates.

Peening wear: Removal of material from a solid surface caused by repeated impacts

on very small areas.

Pitting: A form of wear involving the separation of particles from a surface in the

form of ﬂakes, resulting from repeated stress cycling, generally less extensive

than spalling.

Plowing: The formation of grooves by plastic deformation of the softer of two sur-

faces in relative motion.

Polishing wear: An extremely mild form of wear, which may involve extremely ﬁne-

scale abrasion, plastics smearing of micro-asperities, and/or tribochemical

material removal.

PV Factor: Product of pressure and velocity. (See Limiting PV.)

Quasi-hydrodynamic lubrication: See mixed lubrication.

Ratcheting: A sliding wear process involving progressive deformation, ultimately

leading to the formation of loose fragments.

Rehbinder Effect: Modiﬁcation of the mechanical properties at or near the surface

of a solid, attributed to interaction with a surface-active substance or

surfactant.

Repeated-cycle deformation wear: Mechanical wear mechanisms requiring repeated

cycles of mechanical deformation or engagement.

Ridging (wear): A deep form of scratching in parallel ridges usually caused by

plastic ﬂow.

Rolling-contact fatigue: Wear to a solid surface that results from the repeated stres-

sing of a solid surface due to rolling contact between that surface and another

solid surface or surfaces, generally resulting in the formation of sub-surface

cracks, material pitting, and spallation. (Note: Often used as a synonym for

rolling-contact wear.) See rolling-contact wear.

Rolling-contact wear: Wear due to the relative motion between non-conforming

solid bodies whose surface velocities in the nominal contact location are iden-

tical in magnitude, direction, and sense; most common form is rolling-contact

fatigue.

Run-in: An initial transition process occurring in newly established wearing con-

tacts. (As a verb, run in, refers to an initial operation designed to improve wear

and friction performance of a device.)

Scoring: The formation of severe scratches in the direction of sliding or a severe

form of wear characterized by the formation of extensive grooves and scratches

in the direction of sliding. (Note: Sometimes also called scufﬁng in USA.)

See scufﬁng and scratching.

Scouring abrasion: See abrasion.

Scratch: A groove produced in a solid surface by the cutting and plowing action of

a sharp particle or protuberance moving along that surface.

Scratching: The formation of ﬁne scratches in the direction of sliding; a mild form

of scoring.

Scufﬁng: Localized damage caused by the occurrence of solid-phase welding

between sliding surfaces, without local surface melting or a mild degree of

galling that results from the welding of asperities due to frictional heat or

a form of wear occurring in inadequately lubricated tribosystems which is

characterized by macroscopically observable changes in surface texture,

with features related to the direction of relative motion. (Note: Sometimes

also called scoring in USA.) See scoring.

Selective transfer: A wear process involving the transfer and attachment of a spe-

ciﬁc species from one surface to the mating surface during sliding.

Self-lubricating material: Any solid material that shows low friction without appli-

cation of a lubricant.

Severe wear: A form of wear characterized by removal of material in relatively

large fragments.

Shelling: A term used in railway engineering to describe an advanced phase of spalling.

Single-cycle deformation wear: Mechanical wear mech anisms requiring only a

single cycle of contact or engagement.

Sliding wear: Wear due to relative sliding between two bodies in contact.

Slurry abrasion: Three-body abrasive wear involving a slurry.

Slurry erosion: Erosion produced by the movement of a slurry past a solid surface.

Smearing: Mechanical removal of material from a surface, usually involving plastic

shear deformation, and redeposition of the material as a thin layer on one or

both surfaces.

Solid impingement erosion: Progressive loss of original material from a solid surfa ce

due to continued exposure to impacts by solid particles.

Solid lubricant: Any solid used as a powder or thin ﬁlm on a surface to reduce

friction and wear.

Solid particle erosion: See solid impingement erosion.

Sommerfeld Number: A dimensionless number that is used to characterize the state

of lubrication of a bearing. (See Stribeck curve.)

Spalling: A form of wear involving the separation of particles from a surface in the

form of ﬂakes as a result of repeated stressing, generally more extensive than

pitting or a form of wear involving the separation of macroscopic particles

from a surface in the form of ﬂakes or ch ips, usually associated with rolling

but may also result from impact.

Speciﬁc wear rate: Wear volume divided by load and distance of sliding. (See wear

factor.)

Static friction: Friction associated with the initiation of motion.

Stick-slip: A relaxation oscillation in friction, which is generally characterized by a

sharp decrease, followed by a more gradual increase in the force of friction.

It generally causes jerky-type motion and squeaking.

Stiction: Term used to signify the condition in which the frictional resistance is

sufﬁcient to prevent macroscopic sliding.

Stress fracture: See brittle fracture.

Stribeck curve: A graph showing the relationship between the coefﬁcient of friction

for a jou rnal bearing and the dimensionless Sommerfeld Number. There is a

general correlation between this number and the different forms of lubrication

with a liquid, boundary, mixed, and ﬂuid. (See.)

Surface distress: In bearings and gears damage to the contacting surfaces that

occurs through intermittent solid contact involving some degree of sliding

and surface fatigue.

Traction: The transmission of tangential stress across an interface.

Traction coefﬁcient: Ratio of the traction force to the normal force pressing the

surfaces together.

Traction Force: The tangential force transmitted across an inter face.

Transfer ﬁlm: A triboﬁlm composed wear debris from the counterface.

Tribochemistry: Chemistry dealing with interacting surfaces in relative motion.

Triboﬁlm wear: Wear processes that are controlled by the formation of triboﬁlms,

such as transfer and third-body ﬁlms.

Tribosystem: All those elements that affect friction and wear behavior.

Thermal wear: Removal of material due to softening, melting, or evaporation

during sliding, rolling, or impact.

Thermoelastic instability: Sharp variation of local surface temperatures with pas-

sing of asperities leading to stationary or slowly moving hot spots of signiﬁcant

magnitude, resulting in local expansion and elevation of the surface.

Third body: A solid interposed between two contacting surfaces.

Third-body ﬁlm: A triboﬁlm containing wear debris from the surface, generally a

mixture of wear debris from both surfaces.

Three-body abrasion: Abrasive wear when the abrasive particles are free to move.

Two-body abrasion: Abrasive wear from protuberances or attached abrasive

particles.

Transfer: The process by which material from one sliding surface becomes attached

to another surface, possibly as the result of interfacial adhesion.

Transition diagram: A form of wear map, involving to or more experimental or

operating parameters, which is used to indicate boundaries between different

regimes of wear or surface damage or effectiveness of lubrication, such as

the IRG Transition Diagrams.

Vibratory cavitation: Cavitation caused by the pressure ﬂuctuations within a liquid,

induced by the vibrations of a solid surface immersed in the liquid.

Wear: Damage to a solid surface, generally involving or leading to progressive loss

of material, that is due to the relative motion between that surface and a

contacting substance or substances.

Wear coefﬁcient: Normally deﬁned as the non-dimensional coefﬁcient, k, in the fol-

lowing equation, V ¼ KPS=3 p , where V is the volume of wear, P is the load, S

is the distance of sliding, and p is hardness . Less speciﬁc, it is the dimensionless

form of a wear factor obtained dividing it by the hardness of the wearing

material.

Wear curve: Plot of wear as a function of usage, e.g., wear depth vs. sliding distance

and wear volume vs. time.

Wear factor: Constant in a linea r wear equation, V ¼ KPS, where V is the volume

of wear, P is the load, and S is the sliding distance. Wear volume divided by

load and sliding distance. (Note: An alternative deﬁnition is based on the dif-

ferential form of this equation, DV ¼ KPDS, wher e DV is the incremental

increase in wear volume over an incremental amount of sliding, DS.)

Wear-in: (See run-in.)

Wear map: A graphical characterization of wear behavior in terms of independent

operational parameters of the tribosystem, such as speed and load. Various

forms of wear maps are used to identify ranges and combinations of opera-

tional parameters for different wear mechanisms, same wear rates, and accep-

table operating conditions. (See transition diagram.)

Wedge formation: In sliding metals, the form ation of a wedge or wedges of

plastically sheared metal in local regions of interaction between sliding

surfaces.

Zero-wear: In the context of the Zero and Measurable Wear Models for sliding

and impact, it describes a state of wear in which the wear or damage is less

than the magnitude of the surface roughness.