prEN IEC 61788-28:2025

Mechanical properties measurement - Tensile test of practical REBCO and BSCCO composite superconductors at cryogenic temperatures

Merjenje mehanskih lastnosti - Natezni preskus praktičnih kompozitnih superprevodnikov REBCO in BSCCO pri kriogenih temperaturah

General Information

• Status: Not Published
• Publication Date: 03-Mar-2027
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: CLC/SR 90 - Superconductivity
• Current Stage: 4060 - Enquiry results established and sent to TC, SR, BTTF - Enquiry
• Start Date: 31-Oct-2025
• Completion Date: 31-Oct-2025
• Ref Project: oSIST prEN IEC 61788-28:2025 - Mechanical properties measurement - Tensile test of practical REBCO and BSCCO composite superconductors at cryogenic temperatures

Overview

prEN IEC 61788-28:2025 defines a standardized tensile test method for practical REBCO and BSCCO flat, tape-shaped composite superconductors at cryogenic (liquid nitrogen) temperature. The document specifies how to measure key mechanical properties-principally the modulus of elasticity and 0.2% proof strength-under conditions relevant to high-temperature superconductor (HTS) applications such as magnets and power devices.

Key topics and technical requirements

• Scope and principle: tensile measurement of REBCO and BSCCO composite tapes at liquid nitrogen temperature (≈77 K).
• Apparatus: requirements for testing machines and low‑mass extensometers (double and single types) suitable for cryogenic tensile tests.
• Specimen preparation: guidance on specimen length, geometry and cross‑sectional area evaluation for thin, tape-shaped conductors.
• Testing conditions: specimen gripping methods, setting of extensometers, cooling procedures, and controlled testing speed to ensure reliable cryogenic tensile data.
• Data and calculations: determination of modulus of elasticity and 0.2% proof strength, stress–strain behavior, and reporting of percentage elongation after fracture.
• Measurement uncertainty: procedures and annexed uncertainty budgets (Type A/Type B) for combined standard uncertainty of elastic modulus and proof strength.
• Test report: required specimen descriptions, test conditions and explicit result reporting to support traceability and comparison.
• Informative annexes: additional guidance on extensometer selection, gripping forces, cross‑section evaluation and uncertainty evaluation from round‑robin test data.

Applications and who should use this standard

• Manufacturers of REBCO and BSCCO coated conductors for quality control and product specification.
• Test laboratories performing cryogenic mechanical characterization of HTS tapes.
• Magnet designers and engineers assessing mechanical reliability of windings under Lorentz forces.
• Materials scientists and R&D teams developing reinforced or stabilized superconducting tapes.
• Certification bodies and procurement teams requiring standardized tensile data for supplier comparison.

SEO keywords (naturally integrated)

REBCO tensile test, BSCCO tensile test, HTS mechanical properties, cryogenic tensile testing, liquid nitrogen tensile test, modulus of elasticity 77 K, 0.2% proof strength, IEC 61788-28, superconducting tape testing.

Related standards

• Other parts of the IEC 61788 series covering characterization and test methods for superconducting materials and composite conductors. (Users should consult the IEC webstore for the latest related parts and normative references.)

This standard provides a consistent, reproducible framework for measuring mechanical properties of practical HTS tapes at cryogenic temperature-critical input for design, quality assurance, and reliability assessment of superconducting systems.

Standards Content (Sample)

SLOVENSKI STANDARD
01-oktober-2025
Merjenje mehanskih lastnosti - Natezni preskus praktičnih kompozitnih
superprevodnikov REBCO in BSCCO pri kriogenih temperaturah
Mechanical properties measurement - Tensile test of practical REBCO and BSCCO
composite superconductors at cryogenic temperatures
Ta slovenski standard je istoveten z: prEN IEC 61788-28:2025
ICS:
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

90/548/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 61788-28 ED1
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2025-08-08 2025-10-31
SUPERSEDES DOCUMENTS:
90/527/CD, 90/541A/CC
IEC TC 90 : SUPERCONDUCTIVITY
SECRETARIAT: SECRETARY:
Japan Mr Hideki II
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft
for Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some
Countries” clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is
the final stage for submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Mechanical properties measurement - Tensile test of practical REBCO and BSCCO composite
superconductors at cryogenic temperatures

PROPOSED STABILITY DATE: 2037
NOTE FROM TC/SC OFFICERS:
electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.
You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without
permission in writing from IEC.
IEC CDV 61788-28 © IEC 2025
3 CONTENTS
5 FOREWORD . 4
6 INTRODUCTION . 6
7 1 Scope . 7
8 2 Normative references . 7
9 3 Terms and definitions . 8
10 4 Principle . 10
11 5 Apparatus . 10
12 5.1 General . 10
13 5.2 Testing machine . 10
14 5.3 Extensometer . 11
15 6 Specimen preparation . 11
16 6.1 General . 11
17 6.2 Length of specimen . 11
18 6.3 Determination of cross-sectional area (𝑺𝑺𝑺𝑺) . 11
19 7 Testing conditions . 12
20 7.1 Specimen gripping . 12
21 7.2 Setting of extensometers . 12
22 7.3 Cooling procedure. 12
23 7.4 Testing speed . 12
24 7.5 Test . 12
25 8 Calculation of results . 12
26 8.1 Modulus of elasticity (𝑬𝑬𝑺𝑺 and 𝑬𝑬𝐔𝐔) . 12
27 8.2 0,2% proof strength (𝑹𝑹𝐩𝐩𝑺𝑺,𝟐𝟐_𝑺𝑺 and 𝑹𝑹𝐩𝐩𝑺𝑺,𝟐𝟐_𝐔𝐔) . 13
28 9 Uncertainty of measurand . 13
29 10 Test report . 14
30 10.1 Specimen . 14
31 10.2 Results . 14
32 Annex A (informative) Additional information relating to measurement, apparatus, and
33 calculation . 15
34 A.1 Scope . 15
35 A.2 Extensometer . 15
36 A.2.1 Double extensometer . 15
37 A.2.2 Single extensometer . 16
38 A.3 Gripping force . 16
39 A.4 Percentage elongation after fracture (𝑨𝑨𝑨𝑨) . 16
40 A.5 Condition of straining to fracture . 17
41 A.6 Additional information for test report . 17
42 A.6.1 General . 17
43 A.6.2 Test result . 17
44 A.6.3 Test conditions . 17
45 A.7 Evaluation of cross-sectional area of the specimen . 17
46 Annex B (informative) Evaluation of combined standard uncertainty for HTS 𝑬𝑬𝑺𝑺 and
47 𝑹𝑹𝐩𝐩𝑺𝑺,𝟐𝟐_𝑺𝑺 measurements . 20
48 B.1 Relative standard uncertainty (RSU) . 20
IEC CDV 61788-28 © IEC 2025
49 B.2 Type-B uncertainty evaluation . 22
50 B.3 Comparison between Types A and B uncertainties . 25
51 Bibliography . 26
53 a) general view . 9
54 Figure 1 – Typical stress-strain curve and definition of modulus of elasticity and 0,2%
55 proof strengths at 77 K. . 9
56 Figure A.1 – Low-mass Siam twin type extensometer. Dimensions in millimeters. . 15
57 Figure A.2 – Low-mass double extensometer. Dimensions in millimeters. . 15
58 Figure A.3 – An example of the extensometer provided with balance weight and
59 vertical specimen axis. . 16
60 Figure A.4 – Typical cross-sectional area of a 2G HTS REBCO tape . 17
61 Figure A.5 – Schematical illustration of the HTS specimen with points where the
62 thickness of the specimen shall be measured. . 18
63 a) side view           b) front view . 18
64 Figure A.6 – Blade anvil. . 18
65 Figure B.1 – Force-permanent strain curve for the sample C2-05 G . 23
67 Table B.1 – Specimens distributed in the international RRT . 20
68 Table B.2 – 𝑬𝑬𝑺𝑺 and relative standard uncertainty for all specimens . 21
69 Table B.3 – 𝑹𝑹𝐩𝐩𝑺𝑺,𝟐𝟐_𝑺𝑺 and relative standard uncertainty for all specimens . 21
70 Table B.4 – 𝑬𝑬𝐔𝐔 and relative standard uncertainty for all specimens . 21
71 Table B.5 –  𝑹𝑹𝐩𝐩𝑺𝑺,𝟐𝟐_𝐔𝐔 and relative standard uncertainty for all specimens . 22
72 Table B.6 – Uncertainty budget for 𝑬𝑬𝑺𝑺 for sample C2-05 G . 22
73 Table B.7 – Uncertainty budget for 𝑹𝑹𝑹𝑹𝑺𝑺,𝟐𝟐_𝑺𝑺 for sample C2-05 G . 24
IEC CDV 61788-28 © IEC 2025
76 INTERNATIONAL ELECTROTECHNICAL COMMISSION
77 ____________
79 SUPERCONDUCTIVITY
81 Part 28: Mechanical properties measurement – Tensile test of practical
82 REBCO and BSCCO flat tape composite superconductors at liquid
83 nitrogen temperature
85 FOREWORD
86 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
87 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
88 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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94 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
95 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
96 consensus of opinion on the relevant subjects since each technical committee has representation from all
97 interested IEC National Committees.
98 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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100 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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110 members of its technical committees and IEC National Committees for any personal injury, property damage or
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112 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
113 Publications.
114 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
115 indispensable for the correct application of this publication.
116 9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
117 patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
118 respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
119 may be required to implement this document. However, implementers are cautioned that this may not represent
120 the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
121 shall not be held responsible for identifying any or all such patent rights.
122 IEC 661788-28 has been prepared by IEC technical committee 90: SUPERCONDUCTIVITY. It
123 is an International Standard.
124 The text of this International Standard is based on the following documents:
Draft Report on voting
XX/XX/FDIS XX/XX/RVD
126 Full information on the voting for its approval can be found in the report on voting indicated in
127 the above table.
128 The language used for the development of this International Standard is English.
IEC CDV 61788-28 © IEC 2025
129 This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
130 accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
131 at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
132 described in greater detail at www.iec.ch/publications.
133 The committee has decided that the contents of this document will remain unchanged until the
134 stability date indicated on the IEC website under webstore.iec.ch in the data related to the
135 specific document. At this date, the document will be
136 • reconfirmed,
137 • withdrawn,
138 • replaced by a revised edition, or
139 • amended.
IEC CDV 61788-28 © IEC 2025
141 INTRODUCTION
142 Several types of high-temperature composite superconductors have now been commercialized.
143 The rare-earth-based oxide superconductor (SC) with chemical formula RE Ba Cu O is used
1 2 3 7-x
144 as practical SC tapes, where the rare-earth element RE is Y, Dy, Gd, Eu, Nd, Ho and Sm or a
145 mixture of them. This type of practical SC tapes is usually called REBCO coated conductors. A
146 typical architecture consists of a substrate made of Hastelloy, Ni-W alloy, or stainless steel; a
147 buffer layer composed of multiple oxides; a superconducting layer; and a protective Ag layer,
148 resulting in a flat, tape-shaped conductor. To resist the large electromagnetic forces, the tapes
149 are often externally reinforced by laminating thin foils of stainless steel, copper, or copper alloys.
150 For electrical and chemical stabilization, the silver layer is deposited on the superconducting
151 layer. Often the additional copper layer is electroplated on the silver layer. Two types of
152 bismuth-based oxide superconductors with chemical formula (Bi, Pb) Sr Ca Cu O where
2 2 n-1 n 2n+4
153 n = 2 or 3, have been developed as practical SC tapes. In either case, superconducting
154 filaments are embedded in a pure silver matrix. In the Bi-2223 tapes, a silver alloy outer sheath
155 surrounds the matrix for increasing mechanical strength. Bi-2223 tapes are exclusively made
156 in flat tape-shaped form. Commercially available tapes consist of thin metallic sheets—such as
157 copper alloys, stainless steel, or nickel alloys—soldered onto both sides of the SC tapes to
158 improve the strain dependence of the critical current and enhance mechanical properties.
159 Practical composite superconductors have a high current density and a small cross-sectional
160 area. The major application of composite superconductors is to build electrical power devices
161 and superconducting magnets. For example, during magnet fabrication, complex stresses and
162 strains are applied to its windings. Additionally, when the magnet is energized at cryogenic
163 temperatures, the superconducting tapes experience significant Lorentz forces due to their high
164 current density. Knowledge of mechanical properties at room-temperature is insufficient for
165 predicting the operational behaviour of an HTS magnet. It is therefore important to measure the
166 mechanical properties of practical SC tapes at both room temperature and liquid nitrogen
167 temperature.
IEC CDV 61788-28 © IEC 2025
169 SUPERCONDUCTIVITY
171 Part 28: Mechanical properties measurement – Tensile test of practical
172 REBCO and BSCCO flat, tape-shaped composite superconductors at
173 liquid nitrogen temperature
176 1 Scope
177 This part of IEC 61788 covers a test method detailing the tensile test procedures to be carried
178 out on practical REBCO and BSCCO flat, tape-shaped composite superconductors at liquid
179 nitrogen temperature. This test is used to measure the modulus of elasticity and 0,2% proof
180 strength. The values for elastic limit, fracture strength and percentage elongation after fracture
181 shall serve only as a reference. The sample covered by this test procedure for REBCO tapes
2 2
182 should have a rectangular cross-section with an area of 0,06 mm to 4,0 mm (corresponding
183 to the tapes with width of 2,0 mm to 20,0 mm and thickness of 0,03 mm to 0,2 mm). The sample
184 covered by this test procedure for BSCCO tapes should have rectangular cross-section with an
2 2
185 area of 0,3 mm to 2,5 mm (corresponding to the tape-shaped tapes with width of 2,0 mm to
186 5,0 mm and thickness of 0,15 mm to 0,5 mm).
187 2 Normative references
188 The following documents are referred to in the text in such a way that some or all of their content
189 constitutes requirements of this document. For dated references, only the edition cited applies.
190 For undated references, the latest edition of the referenced document (including any
191 amendments) applies.
192 IEC 60050-815:2024, International Electrotechnical Vocabulary (IEV) – Part 815:
193 Superconductivity
195 IEC 61788-21 Ed. 1: Superconductivity - Part 21: Superconducting tapes – Test Methods for
196 Practical Superconducting Tapes, General Characteristics and Guidance
198 IEC 61788-6, Ed.3: Superconductivity – Part 6: Mechanical properties measurement – Room
199 temperature tensile test of Cu/Nb-Ti composite superconductors
201 IEC 61788-18, Ed. 1: Superconductivity – Part 18: Mechanical properties measurement – Room
202 temperature tensile test of BSCCO composite superconductors
204 IEC 61788-19, Ed. 1: Superconductivity – Part 19: Mechanical properties measurement – Room
205 temperature tensile test of Nb3Sn composite superconductors
207 IEC 61788-25, Ed. 1: Superconductivity – Part 25: Mechanical properties measurement – Room
208 temperature tensile test of REBCO composite superconductors
210 ISO 376:2011 Metallic materials — Calibration of force-proving instruments used for the
211 verification of uniaxial testing machines
213 ISO/AWI 6892-6, Metallic materials — Tensile testing Part 6: Tensile test on foils and strips of
214 metals with a nominal thickness less than 0,200 mm by using computer-controlled testing
215 machines
216 ISO 7500-1:2018 Metallic materials — Calibration and verification of static uniaxial testing
217 machines Part 1: Tension/compression testing machines — Calibration and verification of the
218 force-measuring system
IEC CDV 61788-28 © IEC 2025
219 ISO 9513:2012 Metallic materials — Calibration of extensometer systems used in uniaxial
220 testing
221 3 Terms and definitions
222 For the purposes of this part of IEC 61788, the definitions given in IEC 60050-815 and ISO
223 6892, as well as the following, apply.
224 ISO and IEC maintain terminology databases for use in standardization at the following
225 addresses:
226 • IEC Electropedia: available at https://www.electropedia.org/
227 • ISO Online browsing platform: available at https://www.iso.org/obp
228 3.1
229 tensile stress
230 𝑅𝑅
231 tensile force divided by the original cross-sectional area at any moment during the test
232 3.2
233 tensile strain
234 𝐴𝐴
235 displacement increment divided by initial gauge length of extensometers at any moment during
236 the tensile test
237 3.3
238 extensometer gauge length
239 𝐿𝐿
G
240 length of the parallel portion of the specimen used for the measurement of elongation by means
241 of an extensometer
242 3.4
243 distance between grips
244 𝐿𝐿
245 length between grips that hold the test specimen in position before the test is started
246 3.5
247 modulus of elasticity
248 𝐸𝐸
249 slope of the linear portion of the stress-strain curve in the elastic deformation region (see Figure
250 1)
251 Note 1 to entry: It is basically defined as gradient of the straight portion of the stress-strain curve in the elastic deformation
252 region. In the case of composite superconductor, however, it can be determined differently depending upon the adopted
253 procedures; one from the initial loading curve by the zero offset line expressed as 𝐸𝐸 , the other one given by the slope of line
254 during unloading, expressed as 𝐸𝐸 .
U
256 However, it should be noted that the straight portion of the initial stress-strain curve is quite narrow as indicated in Figure 1. To
257 measure this quantity with a small standard uncertainty, the use of double extensometer systems will be an appropriate
258 technique. In this context, the quantity 𝐸𝐸 should be a representative result of the present test, while 𝐸𝐸 should be reported only
U 0
259 when the measurement is performed by means of double extensometer system.
IEC CDV 61788-28 © IEC 2025
261 a) general view
263 b) enlarged view
264 The blue and red curves are the observed data for REBCO and BSCCO tapes, respectively, and the black continuous and black
265 dotted straight lines are additional lines to indicate how to determine the moduli of elasticity and 0,2% proof strengths. ( 𝑅𝑅 , 𝐴𝐴 )
U U
266 is the point where the unloading begins, ( 𝑅𝑅 , 𝐴𝐴 ) is the point where reloading starts. P indicates the point of limitation of linear
L L
267 portion of the curve for determination 𝐸𝐸 .
268 Figure 1 – Typical stress-strain curve and definition of modulus of elasticity and 0,2%
269 proof strengths at 77 K.
IEC CDV 61788-28 © IEC 2025
270 3.6
271 0,2% proof strength
272 𝑅𝑅 (ee Figure 1)
p0,2
273 stress value where the test specimen yields by 0,2%
274 The designated stress,𝑅𝑅 or 𝑅𝑅 corresponds to that obtained from the initial loading or
p0,2_0 p0,2_U
275 unloading curves in Figure 1, respectively.
276 3.7
277 fracture strength
278 𝑅𝑅
f
279 tensile stress at the fracture
280 3.8
281 tensile stress at elastic limit
282 𝑅𝑅
el
283 tensile force divided by the original cross-sectional area to tensile stress at elastic limit
284 corresponding to transition instant from elastic to plastic deformation, which is indicated by
285 point P in Figure 1.
286 3.9
287 tensile strain at elastic limit
288 𝐴𝐴
el
289 strain at elastic limit
290 4 Principle
291 The test involves straining a specimen within a cryostat system using a tensile force, generally
292 until fracture, to determine the mechanical properties defined in Clause 3 in liquid nitrogen bath.
293 However, depending on the strain measurement method used, the quantities determined by this
294 test may be limited. When using the conventional single extensometer system, 𝐸𝐸 and 𝑅𝑅
U p0,2_U
295 shall be determined. On the other hand, all quantities described here can be determined using
296 a double extensometer system, due to its ability to compensate for bending effects in the
297 specimen and ensure accurate determination of the modulus of elasticity.
298 Additional information relating to Clauses 1 to 10 is given in Annex A.
299 5 Apparatus
300 5.1 General
301 The test machine and the extensometer shall conform to ISO 7500-1 and ISO 9513, respectively.
302 The calibration shall obey ISO 376. The special requirements of this standard are presented in
303 5.2 and 5.3.
304 5.2 Testing machine
305 The testing machine to measure the mechanical properties consists of a tensile machine control system
306 that provides a constant cross head velocity, and a cryostat system that ensures a constant and
307 homogenous temperature of the specimen and extensometers during the test. The grips shall have a
308 structure and strength appropriate for the test specimen and shall be constructed to provide a firm
309 connection with the tensile machine. Additionally, the specimen gripping should be designed to allow
310 axial deformation of the test specimen during cooling down. The gripping surfaces shall be filed, knurled,
IEC CDV 61788-28 © IEC 2025
311 or otherwise roughened to prevent the test specimen from slipping during testing. During the mounting
312 of the specimen, bending or deformation due to twisting shall be prevented; for this, the loading frame
313 should be able to lock the grips.
314 Hazards exist in measurements at cryogenic conditions. Direct contact of skin with cold liquid of gas
315 transfer lines, storage Dewars or other components can cause skin damages. Safety precautions for
316 the handling of cryogenic devices shall be established. Many structural materials are brittle at liquid
317 nitrogen temperatures. To prevent service failure, grips and other load-transferring components should
318 be fabricated from strong, tough, and ductile alloys suitable for liquid nitrogen temperatures. Materials
319 with low thermal conductivity shall be used to minimize heat flow into the cryostat system.
320 5.3 Extensometer
321 The extensometers shall be suitable for testing at liquid nitrogen temperature. The mass of the
322 extensometer shall be 30 g or less to avoid affecting the mechanical properties of
323 superconductive composite tapes. The mass of the extensometers shall be balanced
324 symmetrically around the tape to avoid any non-alignment force. Care shall also be taken to
325 prevent bending moments from being applied to the test specimen (see Clause A.2).
326 To prevent the influence of heating of the strain gauges on strain signal due to bubbles on the
327 gauge grid, the bridge voltage of the strain gauge system shall be lowered to ensure the lowest
328 power consumption. Additionally, the casing of a commercial extensometer may be removed to
329 reduce its weight and allow liquid nitrogen to freely access the active elements, enhancing
330 cooling efficiency. Since the extensometer calibration factor may vary with temperature, the
331 extensometer shall be cal
...