ASTM G73-10(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G73 − 10 (Reapproved 2021)
Standard Test Method for
Liquid Impingement Erosion Using Rotating Apparatus
ThisstandardisissuedunderthefixeddesignationG73;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method covers tests in which solid specimens 2.1 ASTM Standards:
are eroded or otherwise damaged by repeated discrete impacts D1003Test Method for Haze and Luminous Transmittance
of liquid drops or jets. Among the collateral forms of damage of Transparent Plastics
considered are degradation of optical properties of window E92Test Methods for Vickers Hardness and Knoop Hard-
materials, and penetration, separation, or destruction of coat- ness of Metallic Materials
ings. The objective of the tests may be to determine the E140Hardness Conversion Tables for Metals Relationship
resistance to erosion or other damage of the materials or Among Brinell Hardness, Vickers Hardness, Rockwell
coatings under test, or to investigate the damage mechanisms Hardness, Superficial Hardness, Knoop Hardness, Sclero-
and the effect of test variables. Because of the specialized scope Hardness, and Leeb Hardness
natureofthesetestsandthedesireinmanycasestosimulateto E177Practice for Use of the Terms Precision and Bias in
some degree the expected service environment, the specifica- ASTM Test Methods
tionofastandardapparatusisnotdeemedpracticable.Thistest E179Guide for Selection of Geometric Conditions for
method gives guidance in setting up a test, and specifies test Measurement of Reflection and Transmission Properties
andanalysisproceduresandreportingrequirementsthatcanbe of Materials
followed even with quite widely differing materials, test G1Practice for Preparing, Cleaning, and Evaluating Corro-
facilities, and test conditions. It also provides a standardized sion Test Specimens
scale of erosion resistance numbers applicable to metals and G32Test Method for Cavitation Erosion Using Vibratory
other structural materials. It serves, to some degree, as a Apparatus
tutorial on liquid impingement erosion. G40Terminology Relating to Wear and Erosion
G134Test Method for Erosion of Solid Materials by Cavi-
1.2 The values stated in SI units are to be regarded as
tating Liquid Jet
standard. The values given in parentheses after SI units are
2.2 Military Standards:
providedforinformationonlyandarenotconsideredstandard.
MIL-C-83231Coatings, Polyurethane, Rain Erosion Resis-
1.3 This standard does not purport to address all of the
tance for Exterior Aircraft and Missile Plastic Parts
safety concerns, if any, associated with its use. It is the
MIL-P-8184Plastic Sheet, Acrylic, Modified
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3. Terminology
mine the applicability of regulatory limitations prior to use.
3.1 See Terminology G40 for definitions of terms that are
1.4 This international standard was developed in accor-
notdefinedbelowineither3.2or3.3.Definitionsappearin3.2
dance with internationally recognized principles on standard-
that are taken from Terminology G40 for important terms
ization established in the Decision on Principles for the
related to the title, Scope, or Summary of this test method.
Development of International Standards, Guides and Recom-
Definitions of Terms Specific to this Test Method are given in
mendations issued by the World Trade Organization Technical
3.3 that are not in Terminology G40.
Barriers to Trade (TBT) Committee.
1 2
This test method is under the jurisdiction of ASTM Committee G02 on Wear For referenced ASTM standards, visit the ASTM website, www.astm.org, or
and Erosion and is the direct responsibility of Subcommittee G02.10 on Erosion by contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Solids and Liquids. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Nov. 1, 2021. Published December 2021. Originally the ASTM website.
approvedin1982.Lastpreviouseditionapprovedin2017asG73–10(2017).DOI: Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,
10.1520/G0073-10R21. Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G73 − 10 (2021)
3.2 Definitions: a specified reference material similarly tested and similarly
3.2.1 AlldefinitionslistedbelowarequotedfromTerminol- analyzed. (See also normalized erosion resistance.)
ogy G40–05 (some modified).
3.3 Definitions of Terms Specific to This Standard:
3.2.2 cumulative erosion-time curve, n—in cavitation and
3.3.1 apparatus severity factor, F—an empirical factor that
impingement erosion, a plot of cumulative erosion versus
accounts for the systematic differences between rationalized
cumulative exposure duration, usually determined by periodic
erosionrates(orrationalizedincubationperiods)asdetermined
interruption of the test and weighing of the specimen. This is
forthesamematerialandimpactvelocityindifferentfacilities.
the primary record of an erosion test. Most other
It reflects variations in test conditions not accounted for by the
characteristics, such as the incubation period, maximum ero-
data reduction procedures of this test method.
sionrate,terminalerosionrate,anderosionrate-timecurve,are
derived from it.
3.3.2 erosion resistance number, NER—the normalized ero-
sion resistance of a test material relative to a standardized
3.2.3 damage, n—in cavitation or impingement, any effect
scale, calculated from test results with one or more designated
on a solid body resulting from its exposure to these phenom-
reference materials as described in this test method. See also
ena.This may include loss of material, surface deformation, or
reference erosion resistance (3.3.12).
anyotherchangesinmicrostructure,properties,orappearance.
3.2.3.1 Discussion—This term as here defined should nor-
3.3.3 exposed surface (or area)—that surface (or area) on
mally be used with the appropriate modifier, for example,
the specimen nominally subjected to liquid impingement.
“cavitation damage,” “liquid impingement damage,” “single-
(1)For“distributedimpacttests,”itisgenerallytobetaken
impact damage,” and so forth.
astheprojectedareaoftheexposedsurfaceofthespecimenon
3.2.4 incubation period, n—in cavitation and impingement
a plane perpendicular to the direction of impingement.
erosion, the initial stage of the erosion rate-time pattern during
However, if a plane specimen surface is deliberately oriented
which the erosion rate is zero or negligible compared to later
soastoobtainimpingementatanobliqueangle,thentheactual
stages.
plane area is used.
3.2.4.1 Discussion—The incubation period is usually
(2)For “repetitive impact tests,” it is to be taken as the
thought to represent the accumulation of plastic deformation
projected area of the impinging liquid bodies on the specimen,
and internal stresses under the surface that precedes significant
the projection being taken in the direction of relative motion.
material loss. There is no exact measure of the duration of the
3.3.3.1 Discussion—In practice, it is usually found that the
incubationperiod.Seerelatedterm, nominal incubation period
damaged area in repetitive impact tests is greater than the
in 3.3.9.
exposed area as defined above, but the above definition is
3.2.5 liquid impingement erosion, n—progressive loss of
adopted not only for simplicity but also for consistency
original material from a solid surface due to continued expo-
between some of the other calculations for distributed and
sure to impacts by liquid drops or jets.
repetitive tests.
−1
3.2.6 maximum erosion rate, n—in cavitation and liquid
3.3.4 impingement rate, U [LT ]—the volume of liquid
i
impingement,themaximuminstantaneouserosionrateinatest
impinging per unit time on a unit area of exposed surface; for
that exhibits such a maximum followed by decreasing erosion
a plane target surface it is given by ψ V cos θ.
rates. (See also erosion rate–time pattern.)
3.3.5 incubation impingement, H [L]—the mean cumula-
3.2.6.1 Discussion—Occurrence of such a maximum is
tive impingement corresponding to the nominal incubation
typical of many cavitation and liquid impingement tests. In
period; hence, impingement rate times nominal incubation
some instances it occurs as an instantaneous maximum, in
time.
others as a steady-state maximum which persists for some
time.
3.3.6 incubation resistance number, NOR—the normalized
incubation resistance of a test material relative to a standard-
3.2.7 normalizederosionresistance,N,n—ameasureofthe
e
ized scale, calculated from test results with one or more
erosion resistance of a test material relative to that of a
designatedreferencematerialsasdescribedinthistestmethod.
specifiedreferencematerial,calculatedbydividingthevolume
See also reference incubation resistance (3.3.13).
loss rate of the reference material by that of the test material
when both are similarly tested and similarly analyzed. By
3.3.7 incubation specific impacts, N —same as rationalized
“similarlyanalyzed,”itismeantthatthetwoerosionratesmust
incubation period.
be determined for corresponding portions of the erosion
3.3.8 mean cumulative impingement, H[L]—thecumulative
rate-timepattern;forinstance,themaximumerosionrateorthe
volume of liquid impinged per unit area of exposed surface;
terminal erosion rate.
impingement rate times exposure time.
3.2.7.1 Discussion—Arecommended complete wording has
the form, “The normalized erosion resistance of (test material)
3.3.9 nominal incubation period, t —the intercept on the
relative to (reference material) based on (criterion of data
time or exposure axis of the straight-line extension of the
analysis) is (numerical value).”
maximum-slope portion of the cumulative erosion-time curve;
3.2.8 normalized incubation resistance, N , n—in cavitation while this is not a true measure of the incubation stage, it
and liquid impingement erosion,thenominalincubationperiod serves to locate the maximum erosion rate line on the cumu-
of a test material, divided by the nominal incubation period of lative erosion versus exposure coordinates.
G73 − 10 (2021)
3.3.10 rationalized erosion rate, R —volume of material
S = normalizedincubationresistance(relativetoaspeci-
e
lostperunitvolumeofliquidimpinged,bothcalculatedforthe
fied reference material),
same area.
S = reference incubation resistance,
or
t = exposure time, s,
3.3.11 rationalized incubation period, N —the duration of
t = nominal incubation time, s,
the nominal incubation period expressed in dimensionless
U = linear erosion rate (dY/dt), m/s= Q /A,
e e
terms as the number of specific impacts; hence, the specific
U = impingement rate (dH/dt), m/s,
i
impact frequency times nominal incubation time. (Also re-
U = rainfall rate, m/s,
r
ferred to as incubation specific impacts.)
U = terminal velocity of drops in falling rainfield, m/s,
t
3.3.12 reference erosion resistance, S —a normalized ero- V = impact velocity of drop or jet relative to specimen,
er
sion resistance, based on interlaboratory test results, assigned m/s,
V = component of impact velocity normal to specimen
to a specified reference material in this test method so as to
n
surface, m/s,
constitute a benchmark in the “erosion resistance number”
Y = mean depth of erosion, m,
scale. The value of unity is assigned to 316 stainless steel of
θ = angle of incidence—the angle between the direction
hardness 155 to 170 HV.
of impacting drops and the normal to the solid
3.3.13 reference incubation resistance, S —a normalized
or
surface at point of impact,
incubation resistance, based on interlaboratory test results,
ψ = volume concentration of liquid in rainfield or in
assigned to a specific reference material in this test method so
space swept through by specimen, and
as to constitute a benchmark in the “incubation resistance
Ω = rotational speed of specimens, rev/s.
number” scale. The value of unity is assigned to 316 stainless
3.5 Except in equations where different units are expressly
steel of hardness 155 to 170 HV.
specified,theuseofSIunitslistedin3.4,oranyother coherent
3.3.14 specific impacts, N—the number of impact stress
system of units, will make equations correct without the need
cycles of damaging magnitude experienced by a typical point
of additional numerical factors.When referring to quantities in
on the exposed surface, or an approximation thereof as
text, tables, or figures, suitable multiples or submultiples of
estimated on the basis of simplified assumptions as described
these units may, of course, be used.
in this test method. (This concept has sometimes been termed
“impacts per site.”) 4. Summary of Test Method
−1
3.3.15 specific impact frequency, f [T ]—the number of
4.1 Liquid impingement tests are usually, but not always,
i
specific impacts experienced per unit time, given by (a/b) U. conducted by attaching specimens to a rotating disk or arm,
i
suchthatintheircircularpaththeyrepeatedlypassthroughand
3.3.16 volume concentration,ψ—the ratio of the volume of
impactagainstliquidspraysorjets(Sections6and7).Standard
liquid to the total volume in the path traversed or swept out by
reference materials (Section 8) should be used to calibrate the
the exposed area of the specimen.
apparatus and included in all test programs.
3.3.17 volume mean diameter [L]—in a population of drops
4.2 Data analysis begins by establishing a cumulative
of different sizes, the diameter of a sphere whose volume
erosion-time curve from measurements of mass loss (or other
equalsthetotalvolumeofalldropsdividedbythetotalnumber
damage manifestation) periodically during the tests (Section
of drops.
9). These curves are then characterized by specified attributes
3.4 Symbols:
such as the nominal incubation time and the maximum erosion
2 rate (Section 10).
A = exposed area of specimen, m ,
a = projected area of impinging drop or jet, m , 4.3 For comparative materials evaluations, the results are
b = volume of impinging drop or jet, m ,
normalized (Section 10) with respect to the standard reference
d = diameter of impinging drop or jet, m,
materials included in the test program.Astandardized scale of
F = apparatus severity factor for incubation,
“erosion resistance numbers” is provided for structural bulk
F = apparatus severity factor for erosion rate,
e
materials and coatings (10.4.3). For more in-depth analysis of
−1
f = specific impact frequency, s ,
i
the results, the incubation times or erosion rates are expressed
H = mean cumulative impingement, m,
in dimensionless “rationalized” forms that are based on more
H = incubation impingement, m,
physically meaningful exposure duration variables than clock
N = number of specific impacts for incubation, or “ratio-
time as such (Section 11).
nalized incubation period,” dimensionless,
NER = erosion resistance number, 4.4 Theinformationtobegiveninthereportdependsonthe
NOR = incubation resistance number,
objectives of the test (Section 12).
n = number of jets or drops impacting on exposed
5. Significance and Use
surface of specimen in one revolution,
Q = volumetric erosion rate, m /s,
e 5.1 Erosion Environments—This test method may be used
R = “rationalized erosion rate,” (dY/dH), dimensionless,
e
for evaluating the erosion resistance of materials for service
S = normalizederosionresistance(relativetoaspecified
e
environments where solid surfaces are subjected to repeated
reference material),
impacts by liquid drops or jets. Occasionally, liquid impact
S = reference erosion resistance,
er
tests have also been used to evaluate materials exposed to a
G73 − 10 (2021)
cavitating liquid environment. The test method is not intended tions for which the useful service life is terminated by initial
nor applicable for evaluating or predicting the resistance of surface damage even though mass loss is slight.
materials against erosion due to solid particle impingement,
5.3.3 For bulk materials, this test method provides for
dueto“impingementcorrosion”inbubblyflows,duetoliquids
determinationofthe“nominalincubationperiod”aswellasthe
or slurries “washing” over a surface, or due to continuous
“maximum erosion rate,” and material ratings based on each.
high-velocityliquidjetsaimedatasurface.Forbackgroundon
Empirical relationships are given in Annex A2 by which the
variousformsoferosionanderosiontests,seeRefs (1)through
nominal incubation period and the maximum erosion rate can
(2). Ref (3) is an excellent comprehensive treatise.
then be estimated for any liquid impingement conditions in
5.2 Discussion of Erosion Resistance—Liquid impingement
which the principal impingement variables are known. It must
erosion and cavitation erosion are, broadly speaking, similar
be emphasized, however, that because of the previously de-
processes and the relative resistance of materials to them is
scribed variation of erosion rate with exposure time, the
similar. In both, the damage is associated with repeated,
above-mentioned parameters do not suffice to predict erosion
small-scale, high-intensity pressure pulses acting on the solid
for long exposure durations. Extrapolation based on the maxi-
surface.The precise failure mechanisms in the solid have been
mumerosionratecouldoverestimatetheabsolutemagnitudeof
shown to differ depending on the material, and on the detailed
long-termcumulativeerosionbyafactorexceedinganorderof
nature, scale, and intensity of the fluid-solid interactions (Note
magnitude. In addition, it could incorrectly predict the relative
1). Thus, “erosion resistance” should not be regarded as one
difference between long-term results for different materials.
precisely-definable property of a material, but rather as a
5.3.4 Because of these considerations, some experimenters
complex of properties whose relative importance may differ
concerned with long-life components may wish to base mate-
depending on the variables just mentioned. (It has not yet been
rial ratings not on the maximum erosion rate, but on the lower
possible to successfully correlate erosion resistance with any
“terminalerosionrate”ifsuchisexhibitedinthetests.Thiscan
independently measurable material property.) For these
reasons, the consistency between relative erosion resistance as bedonewhilestillfollowingthistestmethodinmanyrespects,
measured in different facilities or under different conditions is but it should be recognized that the terminal erosion rate is
not very good. Differences between two materials of say 20%
probablymorestronglyaffectedbysecondaryvariablessuchas
or less are probably not significant: another test might well
test specimen shape, “repetitive” versus “distributed” impact
show them ranked in reverse order. For bulk materials such as
conditions, drop size distributions, and so forth, than is the
metals and structural plastics, the range of erosion resistances
maximum erosion rate. Thus, between-laboratories variability
is much greater than that of typical strength properties: On a
may be even poorer for results based on terminal erosion rate,
normalized scale on which Type 316 stainless steel is given a
and the test time required will be much greater.
value of unity, the most resistant materials (some Stellites and
5.4 This test method is applicable for impact velocities
tool steels) may have values greater than 10, and the least
ranging roughly from 60 m/s to 600 m/s; it should not be
resistant (soft aluminum, some plastics) values less than 0.1
(see Refs (2) and (4)). assumed that results obtained in that range are valid at much
higher or lower velocities. At very low impact velocities,
NOTE1—Onfailuremechanismsinparticular,seeinRef (3)under“The
corrosion effects become increasingly important.At very high
Mechanics of Liquid Impact” by W. F.Adler, “Erosion of Solid Surfaces
bytheImpactofLiquidDrops”byJ.H.BruntonandM.C.Rochester,and velocitiesthematerialremovalprocessescanchangemarkedly,
“Cavitation Erosion” by C. M. Preece.
and specimen temperature may also become a significant
5.3 Significance of the Variation of Erosion Rate with Time: factor;testingshouldthenbedoneatthevelocitiescorrespond-
5.3.1 The rate of erosion due to liquid impact or cavitation ing to the service environment.
is not constant with time, but exhibits one of several “erosion
5.5 Related Test Methods—Since the resistances of materi-
rate-time patterns” discussed more fully in 10.3.3. The most
als to liquid impingement erosion and to cavitation erosion
common pattern consists of an “incubation period” during
havebeenconsideredrelatedproperties,cavitationerosionTest
which material loss is slight or absent, followed by an
Methods G32 and G134 may be considered as alternative tests
acceleration of erosion rate to a maximum value, in turn
to this test method for some applications. For metals, the
followed by a declining erosion rate which may or may not
relative results from Test Method G32 or G134 should be
tend to a “terminal” steady-state rate. The significance of the
similar but not necessarily identical to those from a liquid
various stages in this history can differ according to the
impact test (see 5.2). EitherTest Method G32 or G134 may be
intended service applications of the materials being tested. In
less expensive than an impingement test, and provides for
almost no case, however, are significant results obtained by
standardizedspecimensandtestconditions,butmaynotmatch
simply testing all materials for the same length of time and
the characteristics of the impingement environment to be
comparing their cumulative mass loss.
simulated.Theadvantagesofaliquidimpingementtestarethat
5.3.2 The “incubation period” may be the most significant
test result for window materials, coatings, and other applica- droplet or jet sizes and impact velocities can be selected and it
can simulate more closely a specific liquid impingement
environment.Awell-designed liquid impingement test is to be
4 preferred for elastomers, coatings, and brittle materials, for
The boldface numbers in parentheses refer to a list of references at the end of
this standard. which size effects may be quite important.
G73 − 10 (2021)
6. Apparatus ation of the test chamber may be required. At the intended
operating speeds it should be possible to maintain the speed
6.1 This test method is applicable principally to those
steady within 0.5%, and to measure it within 0.1%.
erosion test devices in which one or more specimens are
attached to the periphery of a rotating disk or arm, and their
6.4 Droplet or jet diameters have ranged from around
circular path passes through one or more liquid jets or sprays,
0.1mm to about 5 mm. Droplets may be generated by spray
causing discrete impacts between the specimen and the drop-
nozzles, vibrating hollow needles, or rotating disks with water
lets or the cylindrical surface of the jets (Note 2). Fig. 1 and
fed onto their surface. The typical droplet or jet diameter, and
Fig. 2 show two representative devices of very different size
the volume of liquid actually impacting the specimen per unit
andspeedthatparticipatedintheinterlaboratorystudyreferred
time, should be determined within 10%. For jets, the diameter
toinSection13,thoughthedeviceshowninFig.2isnolonger
canusuallybeassumedtoequalthenozzlediameter.However,
in service. Considerations relating to the specimens and their
photographic verification is desirable since jets may exhibit
attachment are covered in Section 7.
instabilities under some conditions. With drops, there will
usually be a size distribution, and in most cases it will be
NOTE 2—Some representative rotating apparatus are described in Ref
necessary to determine that distribution by photography and
(5) by Ripken (pp. 3–21) and Hoff et al (pp. 42–69); in Ref. (6) by Elliott
etal(pp.127–161)andThiruvengadam(pp.249–287);andbyA.A.Fyall
analysisofthephotographs.Somedrop-generatingtechniques,
in“RadomeEngineeringHandbook,”J.D.Walton,editor,MarcelDekker,
such as vibrating needles, provide more uniform drop sizes
Inc., New York, NY, 1970, pp. 461–572.
than sprays. For a single-number characterization, the volume
6.2 Adistinctionismadebetween“distributedimpacttests”
mean diameter should be used, so as to obtain the correct
and “repetitive impact tests.” Devices using sprays or simu-
relationship between total volume and total number of drops.
lated rainfields fall into the first category, and most using jets
Ideally, the apparatus should be characterized by the drop
into the second.
population per unit volume in the path traversed by the
specimen, and the repeatability thereof, as a function of test
NOTE 3—Repetitive impact tests, as compared to distributed impact
settings. From this, the impingement rate and specific impact
tests, generally provide much higher specific impact frequencies and have
higher severity factors (see 6.5), thus producing erosion more rapidly at
frequency, needed for Section 11, can then be readily deter-
equal impact velocities. However, because the damage is localized at a
mined.
line or point on the specimen, the topography and progress of damage
differs somewhat from that in distributed impact tests or under most
6.5 Even when erosion test results are “rationalized” (see
typical service conditions.
Section 11) by taking into account the amount of liquid
6.3 Test devices of the types described above have been impacting the specimen, there will still be systematic differ-
built for peripheral velocities (and hence impact velocities) ences from one apparatus to another. These are represented by
fromabout50m/stoashighas1000m/s.Thehighervelocities the “apparatus severity factors,” which can be calculated from
pose considerable difficulties relating to power requirements, test results by equations given in 11.5, and can be estimated in
aerodynamic heating and noise, and balancing. Partial evacu- the design stage as shown in Annex A2. This can help in
FIG. 1 Example of a Small, Relatively Low-Speed, Rotating Disk-and-Jet Repetitive Impact Apparatus (Courtesy of National Engineering
Laboratory, East Kilbride, Scotland, UK)
G73 − 10 (2021)
NOTE 1—This specific apparatus is no longer in service.
FIG. 2 Example of a Large, High-Speed, Rotating Arm-and-Spray Distributed Impact Apparatus (Courtesy of Bell Aerospace TEXTRON,
Buffalo, NY)
planning an apparatus suitable for the type of materials to be 7. Test Specimens
tested and in predicting the required test times.
7.1 Specimens may present a curved (airfoil or cylindrical)
6.6 For repetitive impact tests using jets and plane
oraflatsurfacetotheimpingingliquid.Theshapechosenmay
specimens,careshouldbetakentoensurethattheerosiontrack
depend on the test objectives, such as whether a particular
is of uniform width and depth, and that undue erosion is not
prototypegeometryistobesimulated.Itshouldberecognized,
occurring at a specimen edge. This may require appropriate
however, that a curved profile will result in a variation of the
angular alignment of the specimen.
normal component of impact velocities, impact angles, and
impingement rates over the exposed surface, and a variation in
6.7 For both repetitive and distributed impact tests, care
the extent of damaged area as the test proceeds.
should be taken to ensure that the jet or spray can reconstitute
itself between successive passages of a specimen. Otherwise
7.2 Specimens may be machined from solid bar, cut from
the actual amount and shape of liquid impinging may be
sheet, or consist of a coating applied to a standardized
considerably different from that assumed.
substrate, any of which may be attached over a supporting
6.8 There are other types of liquid impact erosion-test structure.Specimensandtheirattachmentprovisionsshouldbe
devices besides those described above. Some research investi- designed to facilitate the repeated removal, cleaning, and
gations have been made with “liquid gun” devices, in which a weighing of the specimens. The specimen should fit only one
short discrete slug of liquid is projected out of a nozzle against way and be located by positive stops, or other provisions for
atargetspecimen.Bothsingle-shotandrepetitive-shotversions repeatable alignment shall be used. (Warning—Specimen
of this type exist. For tests at very high impact velocities, holdersorattachmentmethodsshouldbedesignedtominimize
specimen-carrying rocket sleds passing through an artificial localized stressing of the specimen due to centrifugal or
rain field have been used (Note 4). On the laboratory scale, clamping forces, especially when weak or brittle materials are
there are linear test devices in which a specimen carrier is to be tested.)
projectedagainstastationarysuspendeddropletorotherliquid
7.3 Ifspecimensaremachinedfrombulkorbarmaterial,the
body. Some of the provisions of this test method may be
final cuts should be light to avoid work-hardening of the
applied to these tests and their reports also.
surface, which may have a significant effect on the incubation
NOTE 4—Typical “liquid gun” apparatus are described in Ref (1) by
period. Surface roughness should be in the range from 0.4µm
deCorso and Kothmann (pp. 32–45) and Brunton (pp. 83–98); in Ref (7)
to 1.6µm (16µin. to 63µin.) rms, as obtained by fine machin-
byRochesterandBrunton(pp.128–151);andinRef (8)byFieldetal(pp.
ing or medium grinding, unless there is a specific reason for
298–319). Rocket sled tests are described by Schmitt in Ref (6) (pp.
choosing another value. In that case, it should be reported.
323–352) and in Ref (8) (pp. 376–405).
NOTE 5—It is not feasible to accelerate droplets to adequately high
7.4 If the specimen is formed from sheet material, or is a
velocitiesbyentrainmentinafast-movingstreamofgasorvapor,because
coating, it should be recognized that wave reflection from the
the droplets are likely to be broken up into such smaller sizes that their
damage potential is slight. interface with the backup or base material may affect results.
G73 − 10 (2021)
Care should be taken that sheet materials are properly sup- 8.3.2.1 Poly (methyl methacrylate)—(PMMA), conforming
ported. Deposited coatings should have the thickness to be to MIL-P-8184, Type II, Class 2 (as cast).
used in service, or the thickness must be considered a test 8.3.3 For Reinforced Plastic and Composite Materials—
variable. One of the metals specified, plus one of the following:
8.3.3.1 Glass-Epoxy Laminate (E-Glass, Style 181 fabric
7.5 Theperformanceofelastomericcoatingswilldependon
Epon 828 epoxy resin), without gel coating.
theapplicationtechniqueandonthesubstrate.Unlesstheeffect
8.3.3.2 Poly (methyl methacrylate) (PMMA), conforming to
of technique is being investigated, each coating should be
MIL-P-8184, as cast.
applied using its manufacturer’s recommended technique,
8.3.4 For Elastomers (as coatings)—One of the metals
including whatever surface preparation, curing method, and
specified, plus:
post-application conditioning are specified. Two types of
8.3.4.1 Polyurethane, sprayed, in accordance with MIL-C-
substrates are recommended: (1) a substrate identical in con-
83231.
struction to that of the end use item on which the coating is to
8.3.4.2 Uncoated Substrate (glass-epoxy laminate,
be used (this type of specimen will enable investigation of
aluminum, or other materials as above).
coating/substrate interactions under liquid impact), and (2)a
standardized substrate (such as a glass-epoxy laminate, a
9. Test Procedures
graphite-epoxy composite, or an aluminum alloy) so that
9.1 Introduction:
relative ranking and resistance of the coating may be deter-
9.1.1 Sincethetestproceduresfordifferenttypesofmaterial
mined.
differ to some extent, separate sections are provided below for
structural materials and coatings (9.2), elastomeric coatings
8. Reference Materials; Apparatus Calibration
(9.3), window materials (9.4), and transparent thin-film coat-
8.1 In any test whose objective is the determination of the
ings on window materials (9.5). A generalized cleaning and
erosion resistance properties of test materials, at least two of
drying procedure is given in 9.6 for eroded specimens where
thereferencematerialslistedin8.3shallbeincludedinthetest
retained moisture may be a problem.
program.Thisservesthedualpurposeofprovidingareference
9.1.2 Unless otherwise specified, at least three specimens
for calculating relative or normalized resistance values of the
shall be tested for each test variation (that is, for a given
test materials, and for calculating the “severity factors” of the
material at a given test condition).
facility. For the second purpose, metallic reference materials
9.1.3 A common requirement in most of these test proce-
are always used. AnnexA1 gives some of the properties of the
dures is that the test must be interrupted periodically for the
metallic reference materials and their nominal “reference
specimen to be removed for cleaning, drying, and weighing or
erosion resistance” values to be used in these calculations.The
other damage evaluation. In those cases where the time
data analysis procedures for determining normalized erosion
required for these steps is much greater than the time of actual
resistance are specified in Section 10. Optional procedures for
testing (as may be true for elastomeric coatings and other
determining “Apparatus Severity Factors” are given in Section
nonmetallic specimens), an acceptable alternative procedure is
11.
to test a series of identical specimens, each for a different
lengthofuninterruptedexposure,toobtainonesynthesizedtest
8.2 Thechoiceofthereferencematerialsshouldbebasedon
record. This option is to be taken as implied in the subsequent
theexpectederosionresistanceofthematerialstobeevaluated.
sections.
The greater the difference between test material and reference
9.1.4 When damage is determined by mass loss
material,thepooreristheconsistencyofthenormalizedresults
measurements, repeat the cleaning, drying, and weighing
among different laboratories.
operations until two successive weighings yield identical (or
8.3 Reference Materials:
acceptably similar) readings, unless prior qualification of the
8.3.1 For Metals and Other High-Resistance Materials:
cleaning procedure has proved such repetition unnecessary.
8.3.1.1 Aluminum 1100-0.
9.2 Test Procedure for Structural Bulk Materials and Coat-
8.3.1.2 Aluminum 6061-T6.
ings:
8.3.1.3 Nickel, 99.98% pure, annealed.
9.2.1 This section applies to specimens representative of
8.3.1.4 Stainless Steel TypeAISI 316, of hardness 155-170
structural materials and systems for which the loss of material
HV.
andconsequentchangeofshapeandsizeisofprimaryconcern.
8.3.1.5 (See Annex A1 for properties from interlaboratory
This includes metals, structural plastics, structural composites,
test.)
metals with metallic or ceramic coatings, and so forth. The
8.3.2 For Plastics, Ceramics, and Window Materials—One
applicable portions of this section may be followed for the
of the metals specified, plus:
other classes of materials if mass loss is also of interest.
9.2.2 The primary test result to be obtained for each
specimen is a cumulative erosion-versus-time curve, generated
Nickel 270 was used in the interlaboratory test for this test method, as well as
forthefirst(1967–68)interlaboratorytestforTestMethodG32,butitmaynolonger
be available. Nickel 200 (containing 99% Ni) was substituted for the second Plexiglas 55, conforming to MIL-P-8184, obtained from Rohm and Haas Co.,
(1990–91) interlaboratory test for Test Method G32. It proved to have an erosion was used widely as a reference material at the time this test method was first
resistance about 40% higher, and incubation resistance about 65% higher, than Ni developed,butitmaynolongerbeavailableandisnotontheQualifiedProductList
270. for MIL-P-8184.
G73 − 10 (2021)
by periodically halting the test, removing and weighing the the following equation may be used as an initial guideline; it
specimen, and recording the cumulative mass loss and the correspondstoonethirdoftheestimatedincubationtimebased
corresponding volume loss versus cumulative exposure time. on (Eq A2.1):
Allothercharacterizationsrelatingtoerosionratesanderosion
2 4.9
∆t 510~H ! K /@f ~V/100! # (1)
v m i
resistance properties are derived analytically from these
where:
curves. The following paragraphs detail the procedure. In
addition, photographs, or topographic and metallographic ob- ∆t = estimated time interval, s,
H = Vickers hardness of material, HV,
servations of the eroded surface, as well as hardness
v
V = impact velocity, m/s,
measurements,andsoforth.,maybetaken,whenmoredetailed
−1
f = specific impact frequency, s , and
information is desired on development of the damage. i
K = factorrangingfrom0.3formaterialsofpoorresistance
m
9.2.3 Begin with a specimen newly machined and prepared
in relation to hardness to 3.0 for materials of superior
in accordance with Section 7. Conduct a hardness test, prefer-
resistance in relation to hardness.
ably at a location near but not on the surface actually exposed
toerosion.Formetallicmaterials,tofacilitatecomparisons,the
9.2.9 At the conclusion of the test determine the actual area
(equivalent) Vickers hardness number should be determined.
over which significant erosion has occurred. Since this may
Test Methods E92 or Tables E140 may be applicable. Clean
require some subjective judgment, sketches or photographs
and dry the specimen carefully, and determine its mass on a
may be used to clarify and to document that determination.
balance with precision and accuracy of 1 mg or less. For the
9.3 Test Procedure for Elastomeric Coatings:
initial cleaning of metallic specimens, scrubbing with a bristle
9.3.1 The primary test result to be obtained for each
brush or nonabrasive cloth and a suitable volatile solvent is
specimenisexposuretimetofailure.Theseresultsareobtained
recommended. For nonmetallic specimens, consult the manu-
eitherbycontinuouslymonitoringtheconditionofthecoatings
facturer for preferred cleaning methods.
during the exposure by a viewing system (such as a strobo-
9.2.4 Install the specimen in the test apparatus. Bring the
scopic light and closed-circuit television or periscope arrange-
apparatus up to stable operating speed first, set any other
ment) or by periodically stopping the test and examining the
environmental conditions, then turn on the water flow and
conditionofthecoating.Failureshallbedefinedaspenetration
record the time.
of the coating to the substrate either by general erosion of the
9.2.5 After a predetermined time interval, turn off the water
coating surface until the substrate is exposed, pinpoint holes
flow, record the time, and bring the apparatus to rest. Remove
through the coating, or adhesion loss of the elastomeric layer
the specimen carefully, clean and dry it, and determine its new
fromthesubstrate.Masslossmeasurementsmaybedesiredfor
mass on a balance as before. For cleaning eroded metallic
certain bulk elastomer materials or even very thick coatings
specimens,usetheproceduresuggestedin9.2.3,unlessthereis
where rapid failure to the substrate is unlikely. Follow appli-
evidence of corrosion also being present, in which case an
cable portions of 9.2.
applicable procedure from Practice G1 is recommended. If
9.3.2 Begin with a new specimen prepared in accordance
retained water or water deposits may pose a problem, follow
with7.5.Inspectthespecimentoassurethatthecoatingsurface
9.6.
is free of defects that would accelerate its failure.
9.2.6 Calculate the cumulative exposure time, the cumula-
9.3.3 Install the specimen in the test apparatus. Bring the
tive mass loss, divide by the material density to obtain the
corresponding cumulative volume loss, tabulate these values apparatus up to stable operating speed first, set any other
environmental conditions, then turn on the water flow and
andplotthecumulativevolumelossversusexposuretimeona
test record chart. record the time.
9.2.7 Repeat steps 9.2.4 through 9.2.6 at least until the 9.3.4 After continuous exposure (desirable with elastomers,
incubationperiodandmaximumerosionratehavebeenclearly althoughnotabsolutelyessential)duringwhichthespecimenis
established and the erosion rate has begun to decline. It is observed, terminate the test when the substrate is exposed by
erosion of the coating, adhesion loss, or other damage. If
recommendedthatthetestbecontinueduntilastraightlinecan
be drawn through the origin and tangent to the cumulative observation capability is not available, the test should be run
for a predetermined time and then shut down to inspect the
erosion-time curve (see Fig. 3). Optionally, the test may be
continued longer in order to investigate long-term erosion coatingforfailure.Ineithercase,turnoffthewaterflow,record
thetime,andbringtheapparatustorest.Removethespecimen
behavior and to determine whether a terminal erosion rate is
established. (Comparative material evaluations may be based carefully, and determine whether failure to the substrate has
indeed occurred. If mass loss measurements are to be made,
on the terminal erosion rate; see 10.3.5.) Caution—Erosion
should not be allowed to progress beyond a maximum depth clean and dry it in accordance with 9.6.
exceeding the width of the actual area of damage; this applies
9.3.5 For tests of laminate and composite substrate
particularly to repetitive impact tests.
materials, it is necessary to inspect the specimens after test to
9.2.8 The time intervals between successive mass determi- determine if damage has occurred to the substrate even though
nations should be short enough so that the erosion rate-time thecoatinghasremainedintact.Examplesofsubstratedamage
pattern can be discerned, and the nominal incubation period include pulverization of the resin matrix or reinforcing fibers,
and the maximum erosion rate graphically established to an delamination between layers of cloth fabric reinforcement in
accuracy of 10%.Trial and error may be required. For metals, laminates, or crushing of thin-wall constructions.
G73 − 10 (2021)
(a) Cumulative Erosion-Time Curve
(b) Erosion Rate–Time Curve (Derivative of Cumulative Erosion–Time Curve)
FIG. 3 Typical Erosion–Time Pattern and Parameters Used to Quantify It
9.3.6 Repeat steps 9.3.3 through 9.3.5 if necessary until the length region appropriate for the end-use application, as a
failure point has been established. The time intervals between
function of exposure time. These curves are generated by
successive determinations should be short enough so that the
periodically halting the test, removing and drying the
erosion failure time can be established to an accuracy of 20%
specimen, making transmission measurements limited to the
or better. Trial and error may be required.
exposed area by an appropriate method (for example, Test
9.3.7 Attheconclusionofthetest,determinetheactualarea
Method D1003) over the wavelength region of interest, and
over which significant erosion or damage has occurred.
recordingthetransmission-versus-cumulativeexposuretime.It
9.3.8 Atleastfourandpreferablysixcoatedspecimensshall
is important that successive transmission measurements are
be tested for each test variation.
made through the same portion of the specimen. Care should
9.4 Test Procedure for Window Materials: be taken to avoid transmission measurements through areas
containing large cracks which may be associated with mount-
9.4.1 The primary test results to be obtained for each
specimen are cumulative transmission curves over the wave- ing of the specimen in the apparatus (that is, edge or corner
G73 − 10 (2021)
cracks).Concurrentmasslossmeasurementsarerecommended stable-operating speed first, set any other environmental
as a way of further characterizing the damage of the material. conditions, then turn on the water flow and record the time.
Followapplicableportionsof9.2formasslossdeterminations.
9.5.4 After a predetermined time interval, turn off the water
9.4.2 It has been found that some materials ex
...