ASTM F2516-22

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Designation: F2516 − 18 F2516 − 22
Standard Test Method for
Tension Testing of Nickel-Titanium Superelastic Materials
This standard is issued under the fixed designation F2516; 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 the tension testing of superelastic nickel-titanium (nitinol) materials, specifically the methods for
determination of upper plateau strength, lower plateau strength, residual elongation, tensile strength, and elongation.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 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:
E6 Terminology Relating to Methods of Mechanical Testing
E8/E8M Test Methods for Tension Testing of Metallic Materials
E83 Practice for Verification and Classification of Extensometer Systems
E111 Test Method for Young’s Modulus, Tangent Modulus, and Chord Modulus
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
E1876 Test Method for Dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio by Impulse Excitation of Vibration
E3098 Test Method for Mechanical Uniaxial Pre-strain and Thermal Free Recovery of Shape Memory Alloys
F2004 Test Method for Transformation Temperature of Nickel-Titanium Alloys by Thermal Analysis
F2005 Terminology for Nickel-Titanium Shape Memory Alloys
F2082/F2082M Test Method for Determination of Transformation Temperature of Nickel-Titanium Shape Memory Alloys by
Bend and Free Recovery
3. Terminology
3.1 The definitions of terms relating to tension testing appearing in Terminology E6 and the terms relating to nickel-titanium shape
This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.15 on Material Test Methods.
Current edition approved Oct. 1, 2018June 1, 2022. Published October 2018June 2022. Originally approved in 2005. Last previous edition approved in 20142018 as
F2516 – 14.F2516 – 18. DOI: 10.1520/F2516-18.10.1520/F2516-22.
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
F2516 − 22
memory alloys appearing in Terminology F2005 shall be considered as applying to the terms used in this test method. Engineering
stress and strain are assumed unless otherwise noted. Additional terms being defined are as follows (see Fig. 1):
3.2 Definitions:
3.2.1 alignment stress, n—stress (not to exceed 7 MPa) applied to the specimen after it is installed in the grips to ensure that the
specimen is straight and aligned to the grips.
3.2.2 elongation at fracture (El ), n—elongation measured just prior to the sudden decrease in force associated with fracture. See
Ffr
Fig. 1 and X1.2. E6
3.2.2.1 Discussion—
Elongation at fracture results may be very sensitive to test variables such as test speed, specimen geometry, heat dissipation, surface
finish, and alignment. See Test Methods E8/E8M.
3.2.2.2 Discussion—
Corrections for non-uniformnonuniform strains between the extensometer attachments, including in the necked region, are beyond
the scope of this standard. See Test Methods E8/E8M.
3.2.3 fracture ductility (ɛ ), n—true plastic strain at fracture. See X1.2. E6
ffr
3.2.3.1 Discussion—
For prismatic specimens, the fracture ductility is calculated as follows:
A 1
O
ε 5 ln 5 ln (1)
S D S D
f
A 12 RA%⁄100
f
A 1
O
ε 5 ln 5 ln (1)
S D S D
fr
A 12 RA%⁄100
fr
FIG. 1 Terms Illustrated on Typical Stress-Strain Diagram of Superelastic Nitinol
F2516 − 22
where:
A = original cross-sectional area,
O
A = area at fracture of its smallest cross section after testing, and
f
A = area at fracture of its smallest cross section after testing, and
fr
RA% = reduction of area, %. See Terminology E6.
3.2.4 lower plateau strength (LPS), n—stress at 2.5 % strain during unloading of the sample, after loading to 6 % strain. See Fig.
1. E6
3.2.5 reduction of area percent (RA%), n—percent difference between the original cross-sectional area of a tension test specimen
and the area of its smallest cross section after fracture.
3.2.5.1 Discussion—
When the specimen necks prior to fracture, reduction in area provides a measure of the material ductility. The reduction of area
of a prismatic specimen is calculated using the difference in the original cross-sectional area, A , of a specimen and the area at
O
fracture of its smallest cross section, A , after testing as follows:
ffr
A 2 A
O f
RA%5 100% (2)
A
O
A 2 A
O fr
RA%5 100% (2)
A
O
3.2.5.2 Discussion—
For measuring a specimen’s A with an original circular or rectangular cross sections, see Test Methods E8/E8M, Sectionsubection
ffr
7.12.
3.2.6 residual elongation, El , %—difference between the strain at a set stress at or between the alignment stress and a maximum
f
of 7 MPa during unloading and the strain at that same set stress during the initial loading. See Fig. 1 and X1.4.
3.2.7 uniform elongation, El , %—elongation determined at the maximum force sustained by the test piece just prior to necking,
u
or fracture, or both. See Fig. 1.
3.2.7.1 Discussion—
Uniform elongation is not an accurate measure of ductility. See X1.2.
3.2.8 upper plateau strength (UPS)—stress at 3 % strain during loading of the sample. See Fig. 1. E6
4. Summary of Test Method
4.1 Using conventional tensile testing apparatus, the material is pulled to 6 % strain, then unloaded to less than 7 MPa, then pulled
to failure.
5. Significance and Use
5.1 Tension tests provide information on the strength and the elastic and plastic properties of materials under uniaxial tensile
stresses.
5.2 Tension tests, as described in this test method, also provide information on the superelasticity, as defined in Terminology
F2005, of the material at the test temperature.
6. Apparatus
6.1 Apparatus is as described in Test Methods E8/E8M.
7. Test Specimen
7.1 Test specimens are as described in Test Methods E8/E8M.
F2516 − 22
8. Procedure
8.1 Procedure shall be per Test Methods E8/E8M with the following additions:
8.1.1 The material should be tested at a temperature that is a minimum of 5°C5 °C above the austenitic finish transformation
temperature (A ) in order to prevent testing of a partially transformed material. The temperature of the test should be 22.0 6
f
2.0°C2.0 °C or 37 6 2.0°C,2.0 °C, unless otherwise specified. See Terminology F2005 for the definition of A . See Test Methods
f
F2004, F2082/F2082M, and E3098 to determine A .
f
8.1.2 The free-running crosshead speed shall be limited per Table 1. See X1.3.
8.1.3 The test shall consist of zeroing the test machine per Test MethodMethods E8/E8M, gripping the specimen, loading the
specimen to the alignment stress, pulling the specimen to 6 % strain, reversing the motion to unload the specimen to the alignment
stress, and then pulling the specimen to failure. See X1.4.
8.1.4 For materials with diameter greater than 0.2 mm, strain shall be determined by use of a calibrated extensometer of classClass
C or better (see Practice E83). For materials with diameter less than or equal to 0.2 mm, strain may be determined by use of an
extensometer or by crosshead motion. When using crosshead motion to calculate strain, the length between the grips shall be a
minimum of 150 mm. See X1.5.
NOTE 1—Strain should be measured using extensometer versus crosshead displacement, as this will result in a more accurate measurement of strain.
8.1.4.1 When using a clip-on extensometer with small-diameter wire, care shall be taken not to bend or distort the wire when
attaching the extensometer.
8.1.5 Upper plateau strength shall be determined as the value of the stress at a strain of 3.0 % during the initial loading of the
specimen.
8.1.6 Lower plateau strength shall be determined as the value of the stress at a strain of 2.5 % during the unloading of the
specimen.
8.1.7 Residual elongation shall be determined by the difference between the strain at a set stress at or between the alignment stress
and a maximum of 7 MPa during unloading and the strain at that same set stress during the initial loading.
NOTE 2—Slippage of the blades of a mechanical contact extensometer can cause variations in the measurement of residual elongation. These errors may
be prevented by using O-ring blades or other modifications that increase the contact friction between the mechanical contact extensometer and the test
specimen.
NOTE 3—If using a mechanical contact extensometer on a tensile test machine, systematic deviations in the measurement of residual el
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