ASTM G40-99
(Terminology)Standard Terminology Relating to Wear and Erosion
Standard Terminology Relating to Wear and Erosion
SCOPE
1.1 The terms and their definitions given herein represent terminology relating to wear and erosion of solid bodies due to mechanical interactions such as occur with cavitation, impingement by liquid jets or drops or by solid particles, or relative motion against contacting solid surfaces or fluids. This scope interfaces with but generally excludes those processes where material loss is wholly or principally due to chemical action and other related technical fields, as, for instance, lubrication.
1.2 This terminology is not exhaustive; the absence of any particular term from this collection does not necessarily imply that its use within this scope is discouraged. However, the terms given herein are the recommended terms for the concepts they represent unless otherwise noted.
1.3 Certain general terms and definitions may be restricted and interpreted, if necessary, to make them particularly applicable to the scope as defined herein.
1.4 The purpose of this terminology is to encourage uniformity and accuracy in the description of test methods and devices and in the reporting of test results in relation to wear and erosion.
Note 1—All terms are listed alphabetically. When a subsidiary term is defined in conjuntion with the definition of a more generic term, and alphabetically-listed cross-reference is provided.
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Designation: G 40 – 99
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Terminology Relating to
Wear and Erosion
This standard is issued under the fixed designation G 40; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope abrasivity, n—the ability of a material or substance to cause
abrasive wear.
1.1 The terms and their definitions given herein represent
absolute impact velocity— See impact velocity.
terminology relating to wear and erosion of solid bodies due to
acceleration period, n— in cavitation and liquid impingement
mechanical interactions such as occur with cavitation, im-
erosion, the stage following the incubation period during
pingement by liquid jets or drops or by solid particles, or
which the erosion rate increases from near zero to a
relative motion against contacting solid surfaces or fluids. This
maximum value. (See also erosion rate-time pattern.)
scope interfaces with but generally excludes those processes
accumulation period, n— in cavitation and liquid impinge-
where material loss is wholly or principally due to chemical
ment erosion, a less-preferred term for acceleration period.
action and other related technical fields as, for instance,
adhesive wear, n—wear due to localized bonding between
lubrication.
contacting solid surfaces leading to material transfer be-
1.2 This terminology is not exhaustive; the absence of any
tween the two surfaces or loss from either surface.
particular term from this collection does not necessarily imply
angle of attack, n— in impingement erosion, the angle
that its use within this scope is discouraged. However, the
between the direction of motion of an impinging liquid or
terms given herein are the recommended terms for the concepts
solid particle and the tangent to the surface at the point of
they represent unless otherwise noted.
impact.
1.3 Certain general terms and definitions may be restricted
angle of incidence, n— in impingement erosion, the angle
and interpreted, if necessary, to make them particularly appli-
between the direction of motion of an impinging liquid or
cable to the scope as defined herein.
solid particle and the normal to the surface at the point of
1.4 The purpose of this terminology is to encourage unifor-
impact.
mity and accuracy in the description of test methods and
apparent area of contact, n—in tribology, the area of contact
devices and in the reporting of test results in relation to wear
between two solid surfaces defined by the boundaries of their
and erosion.
macroscopic interface. (Contrast with real area of contact.)
NOTE 1—All terms are listed alphabetically. When a subsidiary term is
asperity, n—in tribology, a protuberance in the small-scale
defined in conjunction with the definition of a more generic term, an
topographical irregularities of a solid surface.
alphabetically-listed cross-reference is provided.
attenuation period, n— in cavitation and liquid impingement
erosion, a less-preferred term for deceleration period.
2. Referenced Documents
average erosion rate, n—a less preferred term for cumulative
2.1 ASTM Standards:
erosion rate.
C 242 Terminology of Ceramic Whitewares and Related
2 Beilby layer, n—an altered surface layer of supposedly amor-
Products
phous material formed on a crystalline solid during mechani-
3. Terminology cal polishing, whose existence was proposed in Sir George
Beilby’s writings. The existence of such a layer is not
abrasive wear, n—wear due to hard particles or hard protu-
supported by recent research, and the use of this term is
berances forced against and moving along a solid surface.
therefore considered archaic and is strongly discouraged.
abrasion-corrosion, n—a synergistic process involving both
break-in, n—See run-in.
abrasive wear and corrosion in which each of these processes
break in, v—See run in.
is affected by the simultaneous action of the other and, in
brinelling, n—damage to a solid bearing surface characterized
many cases, is thereby accelerated.
by one or more plastically formed indentations caused by
static or impulsive overloads, especially as found in rolling
This terminology is under the jurisdiction of ASTM Committee G-2 on Wear
contact bearings. (See also false brinelling.)
and Erosion and is the direct responsibility of Subcommittee G02.91 on Terminol-
brittle erosion behavior, n—erosion behavior having charac-
ogy and Definitions.
teristic properties that can be associated with brittle fracture
Current edition approved April 10, 1999. Published June 1999. Originally
published as G 40 – 73. Last previous edition G 40 – 98b.
of the exposed surface; that is, little or no plastic flow occurs,
Annual Book of ASTM Standards, Vol 15.02.
G40
depending on whether flow cavitation or vibratory cavitation is
but cracks form that eventually intersect to create erosion
generated.
fragments. (See also ductile erosion behavior.)
cavitation number, s, n—a dimensionless number that mea-
DISCUSSION—In solid impingement an easily observable aspect of
erosion helps to distinguish brittle from ductile behavior. This is the sures the tendency for cavitation to occur in a flowing stream
manner in which volume removal varies with the angle of attack. With
of liquid, and that is computed from the equation:
brittle erosion the maximum volume removal occurs at an angle near
90°, in contrast to approximately 25° for ductile erosion behavior.
s5 P 2 P !/ rV (1)
S o v o
carrier fluid, n— in impingement or slurry erosion, fluid
where:
medium that transports impinging solid or liquid particles
P 5 vapor pressure,
v
and that gives the particles their momentum relative to the
P 5 static pressure in the stream in an undisturbed state,
o
solid surface on which they are impinging.
V 5 undisturbed stream velocity, and
o
catastrophic period, n— in cavitation or liquid impingement
r5 liquid density.
erosion, a stage during which the erosion rate increases so
DISCUSSION—The cavitation number and the net positive suction head
drastically that continued exposure threatens or causes gross
(NPSH) are related by the equation:
disintegration of the exposed surface. This stage is not
inevitable; it is observed most commonly with some brittle
NPSH 5 ~s1 1!V /2g (2)
o
materials. When it does occur, it may begin during any stage where g is the acceleration due to gravity.
of the more common erosion rate-time pattern.
cavitation tunnel, n—a flow cavitation test facility in which
catastrophic wear, n—rapidly occurring or accelerating sur-
liquid is pumped through a pipe or tunnel, and cavitation is
face damage, deterioration, or change of shape caused by
induced in a test section by conducting the flow through a
wear to such a degree that the service life of a part is
constriction, or around an obstacle, or a combination of
appreciably shortened or its function is destroyed.
these.
cavitating disk device (or apparatus), n—a flow cavitation
coefficient of friction μorf, n—in tribology, the dimension-
test device in which cavitating wakes are produced by holes
less ratio of the friction force (F) between two bodies to the
in, or protuberances on, a disk rotating within a liquid-filled
normal force (N) pressing these bodies together. (See also
chamber. Erosion test specimens are attached flush with the
static coefficient of friction and kinetic coefficient of
surface of the disk, at the location where the bubbles are
friction.)
presumed to collapse.
μ 5 ~F/N! (3)
cavitating jet, n—a continuous liquid jet (sometimes sub-
collection efficiency, n— in impingement erosion and particu-
merged) in which cavitation is induced by the nozzle design,
late flows, the cross-sectional area of undisturbed fluid
or sometimes by an obstruction placed in the center of the
containing particles that will all ultimately impinge on a
flow passage.
given solid surface, divided by the projected area of the solid
cavitating wake, n— See flow cavitation.
surface, where these two areas are perpendicular to the
cavitation, n, n—the formation and subsequent collapse,
direction of relative motion between the solid surface and the
within a liquid, of cavities or bubbles that contain vapor or
particles in the undisturbed fluid.
gas or both.
DISCUSSION—“Undisturbed fluid” means fluid that is sufficiently
DISCUSSION—Cavitation originates from a local decrease in hydro-
ahead of the solid surface to be undisturbed by the flow around the solid
static pressure in the liquid, usually produced by motion of the liquid
surface. For example, the particles could be carried in a stream of fluid
(see flow cavitation) or of a solid boundary (see vibratory cavitation).
moving toward a solid surface that is stationary, or the solid surface
It is distinguished in this way from boiling, which originates from an
could be moving through a suspension of particles. Not all of the
increase in liquid temperature.
particles that move in the direction of the solid surface or lie in its path
DISCUSSION—The term cavitation, by itself, should not be used to
will impinge upon it, since some will be carried away in the fluid as it
denote the damage or erosion of a solid surface that can be caused by
flows around the surface.
it; this effect of cavitation is termed cavitation damage or cavitation
DISCUSSION—A variety of terms having the same meaning can be
erosion. To erode a solid surface, bubbles or cavities must collapse on
found in the literature. These include “collision efficiency,” “capture
or near that surface.
efficiency,” “catchment efficiency,” “impaction ratio,” and others. The
cavitation cloud, n—a collection of a large number of cavita-
term “collection efficiency,” being perhaps the most widely used, is
tion bubbles. The bubbles in a cloud are small, typically less preferred.
than 1 mm (0.04 in.) in cross section. A surface that is being
continuous jet, n— See liquid jet.
eroded by cavitation is usually obscured by a cavitation
corrosive wear, n—wear in which chemical or electrochemical
cloud.
reaction with the environment is significant.
cavitation damage, n— See damage.
cumulative erosion, n— in cavitation and impingement ero-
cavitation erosion, n—progressive loss of original material
sion, the total amount of material lost from a solid surface
from a solid surface due to continued exposure to cavitation.
during all exposure periods since it was first exposed to
cavitation erosion test, n—a procedure whereby the surface of
cavitation or impingement as a newly-finished surface.
a solid is subjected to cavitation attack under specified, or
(More specific terms that may be used are cumulative mass
measurable, or at least repeatable conditions.
loss, cumulative volume loss,or cumulative mean depth of
DISCUSSION—Such tests can be divided into two major classes erosion. See also cumulative erosion-time curve.)
G40
DISCUSSION—Unless otherwise indicated by the context, it is implied
sprays or simulated rainfields. If the impacts are distributed uniformly
that the conditions of cavitation or impingement have remained the over the surface, the term “uniformly distributed impact test” may be
same throughout all exposure periods, with no intermediate refinishing used. (Contrast with repetitive impact erosion test.)
of the surface.
drop, liquid, n—see liquid drop.
cumulative erosion rate, n—the cumulative erosion at a
drop size, n—the diameter of a liquid drop if it is approxi-
specified point in an erosion test divided by the correspond-
mately spherical; otherwise, the approximate shape and
ing cumulative exposure duration; that is, the slope of a line
appropriate dimensions must be described.
from the origin to the specified point on the cumulative
DISCUSSION—In a spray or rainfall, there will normally be a spectrum
erosion-time curve. ( Synonym: average erosion rate)
of drop sizes, which can be presented by distribution curves or
cumulative erosion-time curve, n—in cavitation and im-
histograms, showing either number of drops or combined volume of
pingement erosion, a plot of cumulative erosion versus
drops as a function of drop size. A representative drop size for a
cumulative exposure duration, usually determined by peri-
distribution is afforded by the sauter mean diameter, or else by the size
odic interruption of the test and weighing of the specimen. interval containing the largest total volume.
This is the primary record of an erosion test. Most other
ductile erosion behavior, n—erosion behavior having charac-
characteristics, such as the incubation period, maximum
teristic properties that can be associated with ductile fracture
erosion rate, terminal erosion rate, and erosion rate-time
of the exposed solid surface; that is, considerable plastic
curve, are derived from it.
deformation precedes or accompanies material loss from the
cutting wear, n— in solid impingement erosion, the erosive
surface which can occur by gouging or tearing or by eventual
wear associated with the dissipation of kinetic energy of
embrittlement through work hardening that leads to crack
impact arising from the tangential component of the velocity
formation. (See also brittle erosion behavior.)
of the impacting particles.
DISCUSSION—In solid impingement, two easily observable aspects of
DISCUSSION—Since erosion due to oblique particle impact inevitably
erosion help to distinguish ductile erosion behavior. The first is the
involves deformation wear as well as cutting wear, the magnitude of the
manner in which volume removal varies with the angle of attack.
cutting wear can be experimentally determined by conducting a
Ductile materials show maximum volume removal for angles from
separate test at normal impact to determine the deformation wear, and
approximately 20 to 30°, in contrast to near 90° for brittle erosion
subtracting that from the total wear at any angle of impact, where both
behavior. A second indication of ductile behavior is the characteristic
tests are conducted with the same normal component of impact velocity
ripple pattern that forms on the exposed surface at low values of angle
and both results are normalized to the mass of impacting particles. See
of attack.
also related terms deformation wear, ductile erosion behavior, and
erosion, n—in tribology, progressive loss of original material
brittle erosion behavior.
from a solid surface due to mechanical interaction between
damage, n—in cavitation or impingement, any effect on a solid
that surface and a flu
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