ASTM G181-11(2017)
(Test Method)Standard Test Method for Conducting Friction Tests of Piston Ring and Cylinder Liner Materials Under Lubricated Conditions
Standard Test Method for Conducting Friction Tests of Piston Ring and Cylinder Liner Materials Under Lubricated Conditions
SIGNIFICANCE AND USE
5.1 The efficiency and fuel economy of spark ignition and diesel engines is affected in part to the friction between moving parts. Although no reliable, in situ friction measurements exist for fired internal combustion engines, it has been estimated that at least half of the friction losses in such engines are due to those at the ring and liner interface. This test method involves the use of a reciprocating sliding arrangement to simulate the type of oscillating contact that occurs between a piston ring and its mating cylinder bore surface near the top-dead-center position in the cylinder where most severe surface contact conditions occur. There are many types of engines and engine operating environments; therefore, to allow the user the flexibility to tailor this test to conditions representative of various engines, this standard test method allows flexibility in selecting test loads, speeds, lubricants, and durations of testing. Variables that can be adjusted in this procedure include: normal force, speed of oscillation, stroke length, duration of testing, temperature of testing, method of specimen surface preparation, and the materials and lubricants to be evaluated. Guidance is provided here on the set-up of the test, the manner of specimen fixturing and alignment, the selection of a lubricant to simulate conditioned oil characteristics (for a diesel engine), and the means to run-in the ring specimens to minimize variability in test results.
5.2 Engine oil spends the majority of its operating lifetime in a state that is representative of use-conditioned oil. That is, fresh oil is changed by exposure to the heat, chemical environment, and confinement in lubricated contact. It ages, changing viscosity, atomic weight, solids content, acidity, and chemistry. Conducting piston ring and cylinder liner material evaluations in fresh, non-conditioned oil is therefore unrealistic for material screening. But additive-depleted, used oil can result in high wear and corros...
SCOPE
1.1 This test method covers procedures for conducting laboratory bench-scale friction tests of materials, coatings, and surface treatments intended for use in piston rings and cylinder liners in diesel or spark-ignition engines. The goal of this procedure is to provide a means for preliminary, cost-effective screening or evaluation of candidate ring and liner materials. A reciprocating sliding arrangement is used to simulate the contact that occurs between a piston ring and its mating liner near the top-dead-center position in the cylinder where liquid lubrication is least effective, and most wear is known to occur. Special attention is paid to specimen alignment, running-in, and lubricant condition.
1.2 This test method does not purport to simulate all aspects of a fired engine’s operating environment, but is intended to serve as a means for preliminary screening for assessing the frictional characteristics of candidate piston ring and liner material combinations in the presence of fluids that behave as use-conditioned engine oils. Therefore, it is beyond the scope of this test method to describe how one might establish correlations between the described test results and the frictional characteristics of rings and cylinder bore materials for specific engine designs or operating conditions.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
1.5 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, Guide...
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Designation:G181 −11 (Reapproved 2017)
Standard Test Method for
Conducting Friction Tests of Piston Ring and Cylinder Liner
Materials Under Lubricated Conditions
This standard is issued under the fixed designation G181; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method covers procedures for conducting
laboratory bench-scale friction tests of materials, coatings, and
2. Referenced Documents
surface treatments intended for use in piston rings and cylinder
liners in diesel or spark-ignition engines. The goal of this
2.1 ASTM Standards:
procedure is to provide a means for preliminary, cost-effective
D6838 Test Method for Cummins M11 High Soot Test
screening or evaluation of candidate ring and liner materials.A
E177 Practice for Use of the Terms Precision and Bias in
reciprocating sliding arrangement is used to simulate the
ASTM Test Methods
contact that occurs between a piston ring and its mating liner
E691 Practice for Conducting an Interlaboratory Study to
near the top-dead-center position in the cylinder where liquid
Determine the Precision of a Test Method
lubrication is least effective, and most wear is known to occur.
G40 Terminology Relating to Wear and Erosion
Special attention is paid to specimen alignment, running-in,
and lubricant condition.
3. Terminology
1.2 This test method does not purport to simulate all aspects
3.1 For definitions, see Terminology G40.
of a fired engine’s operating environment, but is intended to
3.2 Definitions of Terms Specific to This Standard:
serve as a means for preliminary screening for assessing the
3.2.1 conditioned oil—a lubricating oil whose viscosity,
frictional characteristics of candidate piston ring and liner
composition, and other function-related characteristics have
material combinations in the presence of fluids that behave as
been altered by use in an operating engine, such that the oil’s
use-conditioned engine oils. Therefore, it is beyond the scope
effects on friction and wear reflect those characteristic of the
of this test method to describe how one might establish
long-term, steady-state engine operation.
correlationsbetweenthedescribedtestresultsandthefrictional
characteristics of rings and cylinder bore materials for specific 3.2.2 conformal contact—in friction and wear testing, any
macro-geometric specimen configuration in which the curva-
engine designs or operating conditions.
ture of one contact surface matches that of the countersurface.
1.3 The values stated in SI units are to be regarded as
3.2.2.1 Discussion—Examples of conformal contact include
standard. No other units of measurement are included in this
a flat surface sliding on a flat surface and a ball rotating in a
standard.
socket that conforms to the shape of the ball.Apair of surfaces
1.4 This standard does not purport to address all of the
may begin a wear or friction test in a non-conforming contact
safety concerns, if any, associated with its use. It is the
configuration, but develop a conformal contact as a result of
responsibility of the user of this standard to establish appro-
wear.
priate safety and health practices and determine the applica-
3.2.3 lubrication regime—in liquid-lubricated sliding
bility of regulatory limitations prior to use.
contact, a certain range of friction coefficients that results from
1.5 This international standard was developed in accor-
a combination of contact geometry, lubricant viscosity
dance with internationally recognized principles on standard-
characteristics, surface roughness, normal pressure, and the
ization established in the Decision on Principles for the
relative speed of the bearing surfaces.
Development of International Standards, Guides and Recom-
3.2.3.1 Discussion—Common designations for lubrication
This test method is under the jurisdiction of ASTM Committee G02 on Wear
and Erosion and is the direct responsibility of Subcommittee G02.50 on Friction. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved June 1, 2017. Published June 2017. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2004. Last previous edition approved in 2011 as G181 – 11. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0181-11R17. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G181−11 (2017)
FIG. 1Schematic Drawing of the Test Configuration Showing Conformal and Non-conformal Contact
regimes are boundary lubrication, mixed film lubrication, engine), and the means to run-in the ring specimens to
elasto-hydrodynamic lubrication and hydrodynamic lubrica- minimize variability in test results.
tion.
5.2 Engine oil spends the majority of its operating lifetime
in a state that is representative of use-conditioned oil. That is,
4. Summary of Test Method
fresh oil is changed by exposure to the heat, chemical
4.1 A reciprocating friction test apparatus is used to simu-
environment, and confinement in lubricated contact. It ages,
late the back-and-forth motion of a piston ring within a
changing viscosity, atomic weight, solids content, acidity, and
cylinder bore in the presence of a heated lubricant. Other types
chemistry. Conducting piston ring and cylinder liner material
of motions, like ring rotation, ring-groove fretting motion, and
evaluationsinfresh,non-conditionedoilisthereforeunrealistic
ringrocking,arenotsimulatedwiththisprocedure.Thecontact
for material screening. But additive-depleted, used oil can
geometry, selection of testing parameters, and the methods of
result in high wear and corrosive attack of engine parts. The
specimen surface finishing and characterization are described.
current test is intended for use with lubricants that simulate
The lubricating fluid is selected to simulate the effects of used
tribological behavior after in-service oil conditioning, but
oil.Arunning-in procedure is used to increase the repeatability
preceding the point of severe engine damage.
of results.
6. Reagents
5. Significance and Use
6.1 Cleaning Solvents—Suitable solvents may be used to
degreaseandcleanspecimenspriortoconductingthedescribed
5.1 The efficiency and fuel economy of spark ignition and
procedure. No specific solvents are recommended here, except
dieselenginesisaffectedinparttothefrictionbetweenmoving
that they should not chemically attack the test surfaces, nor
parts.Although no reliable, in situ friction measurements exist
leave a residual film or stain after cleaning.
forfiredinternalcombustionengines,ithasbeenestimatedthat
at least half of the friction losses in such engines are due to
6.2 Lubricants—Lubricants shall be handled appropriately
those at the ring and liner interface. This test method involves
with awareness of, and precautions taken against, any hazards
the use of a reciprocating sliding arrangement to simulate the
indicated in the Material Safety Data Sheets for those lubri-
typeofoscillatingcontactthatoccursbetweenapistonringand
cants. A further description of simulated used engine oil is
its mating cylinder bore surface near the top-dead-center
further described in an appendix to this standard.
position in the cylinder where most severe surface contact
7. Apparatus and Specimen Preparation
conditions occur. There are many types of engines and engine
operating environments; therefore, to allow the user the flex- 7.1 Description of the Test Apparatus—A schematic repre-
ibility to tailor this test to conditions representative of various sentation of the reciprocating contact geometry is shown in
engines,thisstandardtestmethodallowsflexibilityinselecting Fig. 1. Two versions of this test are shown. In the first case
test loads, speeds, lubricants, and durations of testing. Vari- (Fig. 1, bottom left), the lower specimen conforms to the shape
ables that can be adjusted in this procedure include: normal of the ring segment. In the second case (Fig. 1, bottom right),
force, speed of oscillation, stroke length, duration of testing, the ring segment slides on a flat lower specimen. Specimens
temperature of testing, method of specimen surface areplacedinaheated,temperature-controlledbathoflubricant.
preparation, and the materials and lubricants to be evaluated. Alternate means of supplying the lubricant, such as drip feed,
Guidance is provided here on the set-up of the test, the manner may be used.
of specimen fixturing and alignment, the selection of a lubri- 7.1.1 Motion—The test apparatus shall be capable of im-
cant to simulate conditioned oil characteristics (for a diesel parting a back-and-forth (herein called reciprocating) motion
G181−11 (2017)
achieve with conformal starting geometry. When testing ring and cylinder
of constant stroke length and repeatable velocity profile to the
materials from the same type of engine, the ring curvature in the actual
simulated piston ring specimen which slides against the simu-
engine is produced by elastically confining the ring in its groove. The
lated cylinder bore under a controlled normal force. The motor
same ring, out of the engine, will tend to have a larger curvature, and
shall be sufficiently powered so that the velocity profile and
hence rest on the edges of the corresponding cylinder bore specimen
constancy of operation shall be unaffected by the friction force
unless the ring can be pre-stressed or in some other way forced into a
radius of curvature that precisely matches that of the opposing specimen
developed between the test specimens. The velocity versus
cut from the cylinder. A non-conformal, ring-on-flat geometry with a
time response of crank-driven devices tends to be approxi-
suitable running-in procedure, has been shown to produce a more
mately sinusoidal, and this type of motion is appropriate to
repeatable worn-in condition for friction testing.
simulate a piston driven by a crankshaft. The frequency of
7.1.5 Normal Force Application—The apparatus shall have
reciprocation, given in cycles per second, shall be selected to
the ability to apply a controlled normal force to the ring and
induce the appropriate lubrication regime experienced by the
cylinder specimens. The loading mechanism can be a dead-
pistonringduringitsslowdownandreversalofdirectioninthe
weight system, a levered type of device, or a hydraulic or
engine of interest. Typical frequencies for slider-crank testing
electromagnetic actuator. The loading system shall have suffi-
equipment of this type range between 5 and 40 cycles per
cient rigidity and damping capacity to avoid excessive deflec-
second. The average sliding speed for each stroke, s, in metres
tions or vibrations during testing, and to maintain the desired
per second, is calculated as follows:
normal force within 2 % of the intended value.
s 5 2fL (1)
7.2 Specimen Preparation—Test specimens are herein re-
where:
ferred to as the ring specimen and the cylinder bore specimen.
f = frequency of reciprocation in cycles per second, and Theprecisemannerofpreparingtestspecimensdependsinpart
L = stroke length in meters. on the kinds of materials, coatings, or surface treatments to be
evaluated.
7.1.2 Stroke Length Selection—It is unnecessary to set the
7.2.1 Ring Specimen—The ring specimen shall be prepared
stroke length equal to the full stroke of the piston in the engine
by cutting a segment from a production piston ring, or
because the greatest frictional influence of the materials is
machining a test piece of equal dimensions and finish to a
experiencedattheendsoftheringtravelwhereoperationinthe
production piston ring. The ring specimen may be used in its
boundary lubrication regime increases the likelihood that
original, factory-finished condition or it may be altered by
contactwilloccurbetweenthesurfacesoftheringandcylinder
applying a coating or surface treatment. The surface shall be
materials. The stroke length should typically range between 5
prepared to simulate that for a particular engine or class of
and10timesthewidthoftheworn-incontactfaceofthepiston
engines. The surface roughness of the ring specimen, in the
ring specimen.
area of the contact, shall be measured by a suitable method and
NOTE 1—The design of certain testing machines and motor drive
included in the test record. All pertinent descriptors (type of
systems limits the maximum frequency achievable for a given stroke
profiling method, surface finish parameters, and measuring
length. Therefore, a compromise may be necessary between the highest
conditions) shall be reported.
desired stroke length and the desired reciprocating frequency.
7.2.2 Cylinder Bore Specimen—The specimen intended to
7.1.3 Specimen Fixturing—A means shall be provided to
simulate the cylinder bore surface shall constitute either a cut
clamp the ring specimen to the reciprocating portion of the
section of a production-finished cylinder or a flat specimen
machine in such a way as to ensure correct alignment during
whose form and finish is similar to that of the cylinders used in
sliding.Likewise,thecylinderborespecimenshallbemounted
the engine of interest. Methods have been developed to
in a suitable, heated lubricant container such that no loosening
simulate the roughness and lay of production cylinder liners on
orothermisalignmentoccursduringthetest.Forringsegments
flat cast iron test coupons. Alternatively, a polished surface
with a rectangular cross-section, a suitable flat-faced ring-
may be used to simulate the worn condition of a cylinder bore
segment grip may be used. For non parallel-sided piston rings
near at the top-dead-center position. In certain cases, the
(for example, those with keystone-like cross-sections), it may
cylinder bore specimen may be fabricated from experimental
benecessarytoprepareaholderfromanactualpistonordesign
materials, coated, or surface-treated. The surface roughness of
a holder that clamps the inclined sides of the ring firmly.
the cylinder bore specimen shall be measured by a suitable
7.1.4 Specimen Alignment—Proper alignment and centering
method and included in the test record. With stylus-type
between sliding surfaces is a critical factor for ensuring
instruments, it is traditional to measure and report the surface
repeatable friction test results. Alignment affects the distribu-
roughnessprofileparalleltothedirectionofmotionofthering,
tion of normal forces on
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G181 − 11 G181 − 11 (Reapproved 2017)
Standard Test Method for
Conducting Friction Tests of Piston Ring and Cylinder Liner
Materials Under Lubricated Conditions
This standard is issued under the fixed designation G181; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers procedures for conducting laboratory bench-scale friction tests of materials, coatings, and surface
treatments intended for use in piston rings and cylinder liners in diesel or spark-ignition engines. The goal of this procedure is to
provide a means for preliminary, cost-effective screening or evaluation of candidate ring and liner materials. A reciprocating sliding
arrangement is used to simulate the contact that occurs between a piston ring and its mating liner near the top-dead-center position
in the cylinder where liquid lubrication is least effective, and most wear is known to occur. Special attention is paid to specimen
alignment, running-in, and lubricant condition.
1.2 This test method does not purport to simulate all aspects of a fired engine’s operating environment, but is intended to serve
as a means for preliminary screening for assessing the frictional characteristics of candidate piston ring and liner material
combinations in the presence of fluids that behave as use-conditioned engine oils. Therefore, it is beyond the scope of this test
method to describe how one might establish correlations between the described test results and the frictional characteristics of rings
and cylinder bore materials for specific engine designs or operating conditions.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D6838 Test Method for Cummins M11 High Soot Test
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
G40 Terminology Relating to Wear and Erosion
3. Terminology
3.1 For definitions, see Terminology G40.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 conditioned oil—a lubricating oil whose viscosity, composition, and other function-related characteristics have been
altered by use in an operating engine, such that the oil’s effects on friction and wear reflect those characteristic of the long-term,
steady-state engine operation.
3.2.2 conformal contact—in friction and wear testing, any macro-geometric specimen configuration in which the curvature of
one contact surface matches that of the countersurface.
This test method is under the jurisdiction of ASTM Committee G02 on Wear and Erosion and is the direct responsibility of Subcommittee G02.50 on Friction.
Current edition approved May 1, 2011June 1, 2017. Published May 2011June 2017. Originally approved in 2004. Last previous edition approved in 20092011 as
G181–04(2009).G181 – 11. DOI: 10.1520/G0181-11.10.1520/G0181-11R17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G181 − 11 (2017)
3.2.2.1 Discussion—
Examples of conformal contact include a flat surface sliding on a flat surface and a ball rotating in a socket that conforms to the
shape of the ball. A pair of surfaces may begin a wear or friction test in a non-conforming contact configuration, but develop a
conformal contact as a result of wear.
3.2.3 lubrication regime—in liquid-lubricated sliding contact, a certain range of friction coefficients that results from a
combination of contact geometry, lubricant viscosity characteristics, surface roughness, normal pressure, and the relative speed of
the bearing surfaces.
3.2.3.1 Discussion—
Common designations for lubrication regimes are boundary lubrication, mixed film lubrication, elasto-hydrodynamic lubrication
and hydrodynamic lubrication.
4. Summary of Test Method
4.1 A reciprocating friction test apparatus is used to simulate the back-and-forth motion of a piston ring within a cylinder bore
in the presence of a heated lubricant. Other types of motions, like ring rotation, ring-groove fretting motion, and ring rocking, are
not simulated with this procedure. The contact geometry, selection of testing parameters, and the methods of specimen surface
finishing and characterization are described. The lubricating fluid is selected to simulate the effects of used oil. A running-in
procedure is used to increase the repeatability of results.
5. Significance and Use
5.1 The efficiency and fuel economy of spark ignition and diesel engines is affected in part to the friction between moving parts.
Although no reliable, in situ friction measurements exist for fired internal combustion engines, it has been estimated that at least
half of the friction losses in such engines are due to those at the ring and liner interface. This test method involves the use of a
reciprocating sliding arrangement to simulate the type of oscillating contact that occurs between a piston ring and its mating
cylinder bore surface near the top-dead-center position in the cylinder where most severe surface contact conditions occur. There
are many types of engines and engine operating environments; therefore, to allow the user the flexibility to tailor this test to
conditions representative of various engines, this standard test method allows flexibility in selecting test loads, speeds, lubricants,
and durations of testing. Variables that can be adjusted in this procedure include: normal force, speed of oscillation, stroke length,
duration of testing, temperature of testing, method of specimen surface preparation, and the materials and lubricants to be
evaluated. Guidance is provided here on the set-up of the test, the manner of specimen fixturing and alignment, the selection of
a lubricant to simulate conditioned oil characteristics (for a diesel engine), and the means to run-in the ring specimens to minimize
variability in test results.
5.2 Engine oil spends the majority of its operating lifetime in a state that is representative of use-conditioned oil. That is, fresh
oil is changed by exposure to the heat, chemical environment, and confinement in lubricated contact. It ages, changing viscosity,
atomic weight, solids content, acidity, and chemistry. Conducting piston ring and cylinder liner material evaluations in fresh,
non-conditioned oil is therefore unrealistic for material screening. But additive-depleted, used oil can result in high wear and
corrosive attack of engine parts. The current test is intended for use with lubricants that simulate tribological behavior after
in-service oil conditioning, but preceding the point of severe engine damage.
6. Reagents
6.1 Cleaning Solvents—Suitable solvents may be used to degrease and clean specimens prior to conducting the described
procedure. No specific solvents are recommended here, except that they should not chemically attack the test surfaces, nor leave
a residual film or stain after cleaning.
6.2 Lubricants—Lubricants shall be handled appropriately with awareness of, and precautions taken against, any hazards
indicated in the Material Safety Data Sheets for those lubricants. A further description of simulated used engine oil is further
described in an appendix to this standard.
7. Apparatus and Specimen Preparation
7.1 Description of the Test Apparatus—A schematic representation of the reciprocating contact geometry is shown in Fig. 1.
Two versions of this test are shown. In the first case (Fig. 1, bottom left), the lower specimen conforms to the shape of the ring
segment. In the second case (Fig. 1, bottom right), the ring segment slides on a flat lower specimen. Specimens are placed in a
heated, temperature-controlled bath of lubricant. Alternate means of supplying the lubricant, such as drip feed, may be used.
7.1.1 Motion—The test apparatus shall be capable of imparting a back-and-forth (herein called reciprocating) motion of constant
stroke length and repeatable velocity profile to the simulated piston ring specimen which slides against the simulated cylinder bore
under a controlled normal force. The motor shall be sufficiently powered so that the velocity profile and constancy of operation
G181 − 11 (2017)
FIG. 1 Schematic Drawing of the Test Configuration Showing Conformal and Non-conformal Contact
shall be unaffected by the friction force developed between the test specimens. The velocity versus time response of crank-driven
devices tends to be approximately sinusoidal, and this type of motion is appropriate to simulate a piston driven by a crankshaft.
The frequency of reciprocation, given in cycles per second, shall be selected to induce the appropriate lubrication regime
experienced by the piston ring during its slow down and reversal of direction in the engine of interest. Typical frequencies for
slider-crank testing equipment of this type range between 5 and 40 cycles per second. The average sliding speed for each stroke,
s, in metres per second, is calculated as follows:
s 5 2 f L (1)
where:
f = frequency of reciprocation in cycles per second, and
L = stroke length in meters.
7.1.2 Stroke Length Selection—It is unnecessary to set the stroke length equal to the full stroke of the piston in the engine
because the greatest frictional influence of the materials is experienced at the ends of the ring travel where operation in the
boundary lubrication regime increases the likelihood that contact will occur between the surfaces of the ring and cylinder materials.
The stroke length should typically range between 5 and 10 times the width of the worn-in contact face of the piston ring specimen.
NOTE 1—The design of certain testing machines and motor drive systems limits the maximum frequency achievable for a given stroke length.
Therefore, a compromise may be necessary between the highest desired stroke length and the desired reciprocating frequency.
7.1.3 Specimen Fixturing—A means shall be provided to clamp the ring specimen to the reciprocating portion of the machine
in such a way as to ensure correct alignment during sliding. Likewise, the cylinder bore specimen shall be mounted in a suitable,
heated lubricant container such that no loosening or other misalignment occurs during the test. For ring segments with a rectangular
cross-section, a suitable flat-faced ring-segment grip may be used. For non parallel-sided piston rings (for example, those with
keystone-like cross-sections), it may be necessary to prepare a holder from an actual piston or design a holder that clamps the
inclined sides of the ring firmly.
7.1.4 Specimen Alignment—Proper alignment and centering between sliding surfaces is a critical factor for ensuring repeatable
friction test results. Alignment affects the distribution of normal forces on the contact surface as well as the lubrication regimes
that change as the ring specimen moves back and forth. Two approaches are used together to ensure proper alignment: (1)
mechanical alignment of the test fixtures during the initial test set-up, and (2) running-in of the ring specimen against the
counterface surface. The former approach addresses macro-contact aspects of alignment and the latter micro-scale aspects of
alignment. A method for running in specimens is given in Appendix X1.
NOTE 2—Mechanical specimen alignment tends to be difficult to achieve with conformal starting geometry. When testing ring and cylinder materials
from the same type of engine, the ring curvature in the actual engine is produced by elastically confining the ring in its groove. The same ring, out of
the engine, will tend to have a larger curvature, and hence rest on the edges of the corresponding cylinder bore specimen unless the ring can be pre-stressed
or in some other way forced into a radius of curvature that precisely matches that of the opposing specimen cut from the cylinder. A non-conformal,
ring-on-flat geometry with a suitable running-in procedure, has been shown to produce a more repeatable worn-in condition for friction testing.
7.1.5 Normal Force Application—The apparatus shall have the ability to apply a controlled normal force to the ring and cylinder
specimens. The loading mechanism can be a dead-weight system, a levered type of device, or a hydraulic or electromagnetic
actuator. The loading system shall have sufficient rigidity and damping capacity to avoid excessive deflections or vibrations during
testing, and to maintain the desired normal force within 2 % of the intended value.
G181 − 11 (2017)
7.2 Specimen Preparation—Test specimens are herein referred to as the ring specimen and the cylinder bore specimen. The
precise manner of preparing test specimens depends in part on the kinds of materials, coatings, or surface treatments to be
evaluated.
7.2.1 Ring Specimen—The ring specimen shall be prepared by cutting a segment from a production piston ring, or machining
a test piece of equal dimensions and finish to a production piston ring. The ring specimen may be used in its original,
factory-finished condition or it may be altered by applying a coating or surface treatment. The surface shall be prepared to simulate
that for a particular engine or class of engines. The surface roughness of the ring specimen, in the area of the con
...
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