ASTM F3143-20

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: F3143 − 20
Standard Test Method for
Determination of Frictional Torque and Friction Factor for
Hip Replacement Bearings under Standard Conditions
Using a Reciprocal Friction Simulator
This standard is issued under the fixed designation F3143; 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 E122 Practice for Calculating Sample Size to Estimate,With
Specified Precision, the Average for a Characteristic of a
1.1 This test procedure provides a method of determining
Lot or Process
the frictional torque and friction factor of artificial hip joint
F86 Practice for Surface Preparation and Marking of Metal-
bearings used in total hip replacement (THR) systems under
lic Surgical Implants
laboratoryconditionsusingareciprocalfrictionsimulator.This
test method specifies the angular movement between the
2.2 Other Standards:
articulating components, the pattern of applied force, and the
ISO 14242-1 Implants for Surgery—Wear of total hip-joint
way data can be measured and analyzed.
prostheses, Part 1: Loading and displacement parameters
forwear-testingmachinesandcorrespondingenvironmen-
1.2 Many variables can be investigated using this test
tal conditions for test
method including, but not limited to, the effect of head size,
ISO 14242-2 Implants for Surgery—Wear of total hip-joint
different inclination/version angles, different deformation lev-
prostheses, Part 2: Methods of measurement
els of the acetabular cup, bearing clearances, lubrication,
ISO 14242-3 Implants for Surgery—Wear of total hip-joint
scratched heads, and artificial ageing.
prostheses, Part 3: Loading and displacement parameters
1.3 The values stated in SI units are to be regarded as
for orbital bearing type wear testing machines and corre-
standard. No other units of measurement are included in this
sponding environmental conditions for test
standard.
1.4 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
3.1.1 friction, n—the resisting force tangential to the com-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use. mon boundary between two bodies when, under the action of
1.5 This international standard was developed in accor- an external force, one body moves or tends to move relative to
dance with internationally recognized principles on standard- the surface of the other.
ization established in the Decision on Principles for the
3.1.2 friction factor, n—in the spherical portions of articu-
Development of International Standards, Guides and Recom-
lar surfaces, friction factor is defined as an effective (nominal)
mendations issued by the World Trade Organization Technical
frictional coefficient, equal to the overall total tangential
Barriers to Trade (TBT) Committee.
frictional forces on the hip divided by the overall compressive
force on the hip.
2. Referenced Documents
3.1.3 frictional torque, n—in the case of spherical portions
2.1 ASTM Standards:
of articular surfaces such as those of a THR, the actual
E4 Practices for Force Verification of Testing Machines
frictionalforceatanyinstantvariesatdifferentlocationsonthe
surfaces.Theoverallfrictioncanbeconvenientlycharacterized
This test method is under the jurisdiction ofASTM Committee F04 on Medical
as a frictional torque, which represents the overall tangential
and Surgical Materials and Devices and is the direct responsibility of Subcommittee
forces on the bearing surface multiplied by a nominal radius of
F04.22 on Arthroplasty.
the spherical articulating surfaces.
Current edition approved Oct. 1, 2020. Published November 2020. DOI:
10.1520/F3143-20.
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 Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
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F3143 − 20
3.1.4 overall tangential force, n—total of all tangential or “adverse” conditions; or provide specific methods to deform
forces on the hip surface equal to the overall frictional torque the acetabular cup, simulate Mode 3 wear conditions (for
divided by the nominal radius of the articular surfaces of the example, third-body particles, scratched heads), or artificially
THR system. aged materials. As these methods are not included in the
standard and if they are to become the subject of the investi-
4. Summary of Test Method
gation then it is up to the user to justify the couple(s) selected
4.1 The total frictional torque under dynamic simulated and method(s) used in the test and, if necessary, provide a
loading and angular motion regime is determined by using a rationale for how the “worst-case” couple(s) and method(s)
force transducer and a friction simulator with a low friction were selected to represent clinically relevant “normal” and
bearing with a coefficient of friction less than 0.001 such as a “adverse” conditions as part of the report.
hydrostatic or pneumatic bearing.
6. Confounding Variables
4.2 The input profile is a simplified loading cycle and
6.1 The natural deterioration of the machine can affect the
angular motion of the head with respect to the cup.
results. Therefore accurate calibration and verification of the
4.3 Calf serum is used as the base lubricant.
equipment used shall be carried out on regular basis to ensure
4.4 The frictional torque is determined at the highest force thatthemeasuredandtheappliedforcesarecorrect,repeatable,
and reliable.
and highest velocity part of the testing cycle.
4.5 The friction factor, f, is calculated using the following 6.2 Deterioration of the low-friction bearing or oil within
T
the hydrostatic bearing, if used, can lead to generation of
equation: f5 where T is the total frictional torque
rL
friction that can affect the frictional torque of the hip bearing
determined, r is the radius of the femoral head, and L is the
being measured.
applied force.
6.3 Incorrect fixturing and alignment of the test samples
such as the center of the acetabular cup not being concentric
5. Significance and Use
with the center of angular rotations of the test machine may
5.1 This test procedure provides a method of evaluating the
result in incorrect friction values and errors in calculating the
frictional torque and friction factor of hip replacement bear-
frictional torque and friction factor.
ings.
5.2 The procedure may be used as a standardized method of 7. Apparatus
measuring friction to investigate the effects of specific test
7.1 Testing machine (Fig. 1) capable of producing an
parameters such as hip materials, sizes, designs, radial or
angular displacement of 625° (Fig. 2) and applying a dynamic
diametral clearance, different lubricants, different deformation
axial force of a range of 300 N to 2000 N (Fig. 3) while
levels of the acetabular cup, clamping (non-uniform
operating at a frequency of 1 Hz.
sphericity), damaged/scratched bearings, artificial ageing, mis-
7.2 Means of aligning and positioning the femoral head so
alignments during installation, etc.
that its center is situated at the center of the axes of rotation of
5.3 Friction torque, and in particular the maximum value, is
the test machine and so that the same position and orientation
useful to assess the applicable torques that may compromise
may be reproduced following removal for measurement or
fixation, or even risk disassociation of modular components in
cleaning if required.
the acetabular cup or liner/shell assemblies through a lever-out
7.3 Means of aligning and positioning the acetabular cup so
or torsion-out mechanism.
that its center is situated at the center of the axes of rotation of
5.4 Friction factor is a useful parameter for comparison of
the test machine and so that the same position and orientation
materials and designs, and provides insights into the lubrica-
may be reproduced following removal for measurement or
tion regime operating in the implant system. Friction factor
cleaning if required.
measurement may also be able to detect acetabular liner
7.4 Motioncontrolsystemcapableofgeneratingtheangular
deformation (clamping referred to earlier).
movement of the femoral component given in Fig. 2 with an
5.5 The loading and motion of a hip replacement in vivo
accuracy of 63° at the maxima and minima of the motion and
differ from the loading and the motion defined in this standard.
61 % of the cycle time for phasing.
The amount of frictional forces in vivo will, in general, differ
7.5 Force control system capable of generating a dynamic
from the frictional forces evaluated by this standard test
force and maintaining the magnitude of the maxima of this
method. The results obtained from this test method cannot be
force cycle to a tolerance of 65 % of the force value for the
used to directly predict in vivo performance. However, this
cycle and 65 % of the cycle time for phasing.
standard is designed to allow for in-vitro comparisons for
different hip designs, when tested under similar conditions. 7.6 The loading frame should be free to move in the vertical
axisallowingtheverticalforcetobetransmittedfreelythrough
5.6 Although this test method can be used to investigate the
the center of the femoral head.
many variables listed in 1.2 and 5.2, it does not either provide
a method to determine beforehand the combination of these 7.7 Low friction bearings (machine bearings) capable of
variables that will produce the worst-case couple(s) among a providing a low-friction environment under the testing condi-
range of sizes; the worst-case testing condition(s) for “normal” tions.
F3143 − 20
FIG. 1 Conceptual Drawing of a Friction Simulator
7.8 Ahigh sensitivity force sensor connected to the front of 8.2 Test Specimen, Femoral Head, and Acetabular
friction carriage that can detect the torques within the system Components—The test specimens should be fixed in the test
by measuring the forces transferred between the fixed frame cell without causing any unintentional deformation of the
and the carriage. The force sensor should not constrain the cup bearing surfaces. The test specimens may be partially finished
translationthatallowsself-centering.Thehighsensitivityforce providedthattheinternalmaterials,finish,lockingmechanism,
sensor should have a range of 200 N (if positioned 100 mm and geometry are identical to the actual specimens.
away from center of the machine) with a standard combined
8.3 Control Specimen—It is recommended that two similar
error not larger than 1 %.
control-bearingcouplesbekeptwiththetestrigandthefriction
7.9 Low-friction self-aligning feature for unrestrained mo- factor determined on both the control samples (avoid using
tion of the cup in the horizontal plane.
metal-on-metal bearings). Thereafter, only one of the control
samples should be used on a regular basis to make sure that the
8. Reagents and Materials
measuring equipment is producing consistent results and any
8.1 The Fluid Test Medium—Fluid test medium shall be as deviationinthefrictionfactorduetomachinedeteriorationcan
per ISO 14242-1 or ISO 14242-3. Other test fluids may be be detected. Note that the long-term use of control samples can
selected if justified. To minimize microbial contamination, the cause wear and roughening or smoothing of the surface,
biological fluid test medium should be stored frozen until producing higher or lower friction factors than were obtained
required for the test. when they were new.The second control specimen should then
F3143 − 20
FIG. 2 Angular Rotation Input on the Friction Simulator
FIG. 3 Force Profile Input on the Friction Simulator
F3143 − 20
beusedforcomparisonwhenanewcontrolsampleisrequired. 11.5 The position of the center of the cup versus the force
Thenewcontrolsamplethenreplacesthecontrolspecimenthat sensor (see 7.8) shall be known within 60.2 mm. The position
has only been used once. This removes the drift in machine of the femoral head in respect to the machine axis is not as
performancethatcouldbeseenbetweentheproductionandtest critical; however, larger offsets shall be avoided as they result
of the control samples. in greater motion of the cup in the horizontal plane.
11.6 It is advisable to have alignment marks on the test
9. Hazards
specimens in case it is necessary to repeat the test.
9.1 Appropriate personal protective equipment should be
used at all times during the operation of the machine. 12. Calibration and Standardization
12.1 Accurate calibration an
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