ASTM F2118-01
(Test Method)Test Method for Constant Amplitude of Force Controlled Fatigue Testing of Acrylic Bone Cement Materials
Test Method for Constant Amplitude of Force Controlled Fatigue Testing of Acrylic Bone Cement Materials
SCOPE
1.1 This standard describes test procedures for evaluating the constant amplitude, uniaxial, tension-compression uniform fatigue performance of acrylic bone cement materials.
1.2 This standard is relevant to orthopaedic bone cements based on acrylic resins, as specified in Specification F451. The procedures in this guide may or may not apply to other surgical cement materials.
1.3 It is not the intention of this standard to define levels of performance of these materials. Furthermore, it is not the intention of this standard to directly simulate the clinical use of these materials.
1.4 A rationale is given in Appendix X1.
1.5 The values stated in SI units are to be regarded as the standard.
1.6 This standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to consult and establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: F 2118 – 01
Test Method for
Constant Amplitude of Force Controlled Fatigue Testing of
Acrylic Bone Cement Materials
This standard is issued under the fixed designation F 2118; 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 3. Terminology
Unless otherwise given, the definitions for fatigue
1.1 This standard describes test procedures for evaluating
terminology given in Terminology E 1823 will be used.
the constant amplitude, uniaxial, tension-compression uniform
fatigue performance of acrylic bone cement materials. 3.1 Median Fatigue Strength at N Cycles—The maximum
1.2 This standard is relevant to orthopaedic bone cements stress at which 50 % of the specimens of a given sample would
based on acrylic resins, as specified in Specification F 451. The be expected to survive N loading cycles. For the purposes of
procedures in this guide may or may not apply to other surgical this test method, the fatigue strength will be determined at 5
cement materials. million load cycles. A rationale for this is provided in the
1.3 It is not the intention of this standard to define levels of Appendix X1.4.
performance of these materials. Furthermore, it is not the 3.2 Runout—A predetermined number of cycles at which
intention of this standard to directly simulate the clinical use of the testing on a particular specimen will be stopped, and no
these materials. further testing on that specimen will be performed. For the
1.4 A rationale is given in Appendix X1. purposes of this test method, the runout will be 5 million load
1.5 The values stated in SI units are to be regarded as the cycles.
standard. 3.3 Stress Level—The value of stress at which a series of
1.6 This standard does not purport to address all of the duplicate tests are performed. For the purposes of this method,
safety concerns associated with its use. It is the responsibility the stress level is reported as the maximum stress applied to the
of the user of this standard to consult and establish appropriate specimen.
safety and health practices and determine the applicability of 3.4 Specimen Failure—The condition at which the speci-
regulatory limitations prior to use. men completely breaks or is damaged to such an extent that the
load frame is no longer able to apply the intended stress within
2. Referenced Documents
the required limits.
2.1 ASTM Standards:
4. Summary of Test Method
E 466 Practice for Conducting Force Controlled Constant
Amplitude Axial Fatigue Tests of Metallic Materials 4.1 Uniform cylindrical reduced gage section test specimens
E 467 Practice for Verification of Constant Amplitude Dy- are manufactured from acrylic bone cement and mounted in a
namic Forces in an Axial Fatigue Testing System uniaxial fatigue frame. The specimen is subjected to fully
E 1823 Terminology Relating to Fatigue and Fracture Test- reversed tensile and compressive loading in a sinusoidal cyclic
ing manner at a specified frequency in phosphate buffered saline
F 451 Standard Specification for Acrylic Bone Cement (PBS). The fatigue loading is continued until the specimen fails
2.2 ISO Standard: or a predetermined number of cycles (runout limit) is reached.
ISO 7206-8 Implants for Surgery, Partial and Total Hip Joint
5. Significance and Use
Prostheses, Part 8—Endurance Performance of Stemmed
5.1 This test method describes a uniaxial, constant ampli-
Femoral Components with Application of Torsion
tude, fully reversed fatigue test to characterize the fatigue
performance of a uniform cylindrical waisted specimen manu-
factured from acrylic bone cement.
This test method is under the jurisdiction of ASTM Committee F04 on Medical
5.2 This method considers two approaches to evaluating the
and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.15 on Material Test Methods. fatigue performance of bone cement:
Current edition approved June 10, 2001. Published October 2001.
5.2.1 Testing is conducted at three stress levels to charac-
Annual Book of ASTM Standards, Vol 03.01.
terize the general fatigue behavior of a cement over a range of
Annual Book of ASTM Standards, Vol 13.01.
stresses. The stress level and resultant cycles to failure of the
Available from American National Standards Institute, 25 W. 43rd St, 4th Floor,
New York, NY 10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
F2118
specimens are plotted on an S-N diagram. 6.3 Load Cell—A load cell capable of measuring dynamic
5.2.2 Another approach is to determine the fatigue strength tensile and compressive loads in accordance with Practice
of a particular cement. The fatigue strength for orthopaedic E 467.
bone cement is to be determined at 5 million (5 3 10 ) cycles. 6.4 Limit—A device capable of detecting when a test
The “two-point method” is the specified procedure for con- parameter (for example, load magnitude, actuator displace-
ducting fatigue testing to determine fatigue strength [1]. ment, DC error, and so forth) reaches a limiting value, at which
5.3 This standard does not define or suggest required levels time the test is stopped and the current cycle count recorded.
of performance of bone cement. This fatigue test method is not 6.5 Environmental Chamber—A chamber designed to im-
intended to represent the clinical use of orthopaedic bone merse the fatigue specimen completely in a solution. The
cement, but rather to characterize the material using standard chamber should have provisions for maintaining a constant
and well-established methods. The user is cautioned to con- temperature to an accuracy of 62°C.
sider the appropriateness of this test method in view of the
7. Test Specimen
material being tested and its potential application.
5.4 It is widely reported that multiple clinical factors affect 7.1 Test specimens shall be fabricated from cement that is
representative of the final product with regard to materials,
the fatigue performance of orthopaedic bone cement; however,
the actual mechanisms involved are not well understood. manufacturing processes, sterilization, and packaging. Steril-
ization methods have been shown to have an effect on fatigue
Clinical factors which may affect the performance of bone
cement include: temperature and humidity, mixing method, performance. Any deviations of the test cement from the
clinically used product must be reported.
time of application, surgical technique, bone preparation,
7.2 Cylindrical reduced gage section test specimens with a
implant design, and patient factors, among others. This test
method does not specifically address these clinical factors. The straight 5-mm diameter by 10-mm-long gage section shall be
used. The diameter of the specimen ends shall be substantially
test method can be used to compare different acrylic bone
cement formulations and products and different mixing meth- greater than the gage diameter to ensure that fracture occurs in
the gage section. A smooth radius or taper between the
ods and environments (that is, mixing temperature, vacuum,
centrifugation, and so forth). specimen ends and gage section is suggested to ensure the gage
section is subjected to a uniform stress field. Suggested
6. Apparatus
specimen dimensions are provided in Fig. 1.
6.1 Uniaxial Load Frame—A testing machine capable of
8. Specimen Preparation
applying cyclic sinusoidal tensile and compressive loads.
6.1.1 The crossheads of the load frame shall be aligned such 8.1 Cement Mixing
that the alignment meets the requirements of 8.2 of Practice 8.1.1 Store the liquid and powder portions of the cement
E 466. The alignment should be checked at both the maximum according to the manufacturer’s instructions before mixing.
tensile and minimum compressive load to be applied during the 8.1.2 Allow the mixing equipment to equilibrate to room
course of a test program. temperature before mixing. Record the room temperature at the
6.2 Cycle Counter—A device capable of counting the num- onset of mixing.
ber of loading cycles applied to a specimen during the course 8.1.3 Mix the powder and liquid components according to
of a fatigue test. the manufacturer’s instructions and begin recording the time
FIG. 1 Specimen Dimensions
F2118
from this point using a stopwatch. Report any deviations from 8.6 Specimen Conditioning:
the manufacturer’s storage and mixing recommendations. 8.6.1 Place the test specimens in PBS which is maintained at
8.1.4 Report the mixing method and any equipment used. a temperature of 37 6 2°C.
8.6.2 Maintain the specimens in the PBS solution for a
The method used for mixing the cement may affect its fatigue
behavior. See X1.13 for further information. minimum of 7 days. The cement specimens shall be maintained
in the PBS solution for 7 to 60 days. The specimens shall be
8.2 Specimen Fabrication—The cylindrical reduced gage
continually immersed in the test solution so that they do not dry
section test specimens are fabricated using one of two methods:
out. Distilled water shall be added to the soaking chamber
8.2.1 Direct Molding:
during the soaking period to make up for evaporation loss.
8.2.1.1 Insert the mixed cement into a specimen mold
Each specimen should be soaked up to the time immediately
(manufactured from silicone, aluminum, Teflon, or other suit-
before its being mounted on the load frame. See X1.5 for
able material) with an internal cavity which has the same
further information.
dimensions as the final cement test specimen. Close the mold.
Record the method of cement insertion into the mold (that is,
9. Fatigue Test Procedures
pour or inject) and method used to close the mold.
9.1 Mount the specimens in a test frame test such that a
8.2.1.2 Place the mold in a container of phosphate buffered
uniaxial load is applied. Collets, Jacob’s chucks, or pressurized
saline (PBS). The PBS solution should be maintained at 37 6
grips should be used to firmly grip the specimen at each end.
2°C. After the specimens have polymerized for at least 1 h, the
Ensure the longitudinal centerline of the test specimens are
specimens may be removed from the mold. Appendix X2
aligned with test machine loading axis such that no bending
describes a suggested procedure for molding cement speci-
moment may be applied to the specimens.
mens.
9.2 Mount an environmental chamber on the load frame and
8.2.2 Machining:
fill with fresh test solution immediately after the specimen is
8.2.2.1 Insert the mixed cement into cylindrical mold
mounted to keep the specimen from drying out. The chamber
(manufactured from aluminum, glass, or Teflon tube). The
should be filled to a level such that the entire specimen is
inside diameter of the molding tube should be a few millime-
immersed. Distilled water shall be added to the test chamber
tres greater than the final specimen grip diameter.
during the course of a test to make up for evaporation loss. The
8.2.2.2 Maintain the temperature of the mold at at 376 2°C.
temperature controller should be programmed and activated to
After the specimens have polymerized for at least 1 h, the
heat the test solution to 37°C, and then maintain that tempera-
specimens may be removed from the mold.
ture within 62°C. Fatigue testing should not begin until at least
8.2.2.3 Machining should not be performed until at least 24
⁄2 h after the solution temperature has reached 37°C to ensure
h after initial mixing to ensure that the cement is completely
equilibration.
polymerized.
9.3 Program the test frame controller to apply a fully
8.3 Specimen Examination:
reversed sinusoidal cyclic waveform at a constant frequency.
8.3.1 Radiographically examine the fabricated specimens
When testing at frequencies above 1 Hz, the user should verify
for internal defects. Visually examine specimens for surface
that for the formulation being tested the chosen frequency has
defects. Defects in the gage or transition sections (radii) shall
a negligible effect on the test results. See X1.6 for further
be rejected from testing and discarded. A surface defect is
information.
defined as a surface discontinuity greater than 250 μm in major
9.4 Program the test frame controller to apply the desired
diameter. In addition, the specimens shall be examined radio-
maximum stress level and a stress ratio of R = –1, indicating
graphically in two orthogonal planes. Specimens with internal
fully reversed loading. A rationale for using fully reversed
defects greater than 1 mm in major diameter in the gage section
loading is provided in Appendix X1.10. The load shall be
shall be rejected from testing and discarded. The total number
calculated by multiplying the desired stress by the specimen’s
of specimens rejected divided by the total number of specimens
cross-section area, based on each specimen’s gage diameter
manufactured (rejection rate) shall be reported. A rationale for
determined in 8.5.
these rejection criteria is provided in X1.11.
9.4.1 Report the stress level to the nearest 0.5 MPa.
NOTE 1—The development of fabrication defects may be related to the 9.4.2 When developing an S-N curve, it is recommended
tendency of a material to develop porosity during polymerization. The
that testing be conducted at the following maximum stress
amount of porosity or fabrication defects in the test specimens may be a
levels: 15, 12.5, and 10 MPa. Other stress levels may also be
characteristic of the cement being evaluated. The rejection rate may give
appropriate. See X1.7 for a rationale regarding the selection of
a general indication of a material’s tendency toward porosity formation.
the recommended stress levels.
8.4 Specimen Finishing—If necessary, lightly polish the
9.4.3 When determining a fatigue strength, the stress levels
gage length of the specimens with 600-grit abrasive paper in shall be chosen in accordance with the “two-point method” [1].
the longitudinal direction until the surface is free of machining
9.5 Number of Specimens—When developing an S-N curve,
and/or mold marks. a minimum of eight specimens shall be tested at each stress
8.5 Specimen Measurement—Measure the diameter of the level. The desired statistical power of the comparison and the
specimens at a minimum of three places along the gage length variability to be expected from the cement formulation(s) being
of each specimen. The average of these measurements shall be investigated should be considered when determining the ap-
used as the specimen’s gage diameter for calculation of the propriate sample size. See X1.12
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