IEC 61788-25:2018

IEC 61788-25 ®
Edition 1.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 25: Mechanical properties measurement – Room temperature tensile test on
REBCO wires
Supraconductivité –
Partie 25: Mesure des propriétés mécaniques – Essai de traction à température
ambiante des fils REBCO
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IEC 61788-25 ®
Edition 1.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 25: Mechanical properties measurement – Room temperature tensile test on

REBCO wires
Supraconductivité –
Partie 25: Mesure des propriétés mécaniques – Essai de traction à température

ambiante des fils REBCO
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.050; 77.040.10 ISBN 978-2-8322-5988-7

– 2 – IEC 61788-25:2018 © IEC 2018
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Principle . 10
5 Apparatus . 10
5.1 General . 10
5.2 Testing machine . 10
5.3 Extensometer . 10
6 Specimen preparation . 10
6.1 General . 10
6.2 Length of specimen . 10
6.3 Determination of cross-sectional area (S ) . 11
o
7 Testing conditions . 11
7.1 Specimen gripping . 11
7.2 Setting of extensometer . 11
7.3 Testing speed . 11
7.4 Test . 11
8 Calculation of results . 11
8.1 Modulus of elasticity (E) . 11
8.2 0,2 % proof strength (R and R ) . 12
p0,2-0 p0,2-U
9 Uncertainty of measurement . 12
10 Test report . 13
10.1 Specimen . 13
10.2 Results . 13
Annex A (informative) Additional information relating to Clauses 1 to 10 . 14
A.1 General . 14
A.2 Extensometer . 14
A.2.1 Double extensometer . 14
A.2.2 Single extensometer . 16
A.3 Elastic limit . 16
A.4 Gripping force . 17
A.5 Percentage elongation after fracture (A ) . 17
f
A.6 Condition of straining to fracture . 17
A.7 Relative standard uncertainty (RSU) . 17
A.8 Discretion applying this document . 19
A.9 Assessment on the reliability of the test equipment . 19
A.10 Additional information for test report . 19
A.10.1 General . 19
A.10.2 Test result . 19
A.10.3 Test conditions . 19
Annex B (informative) Evaluation of combined standard uncertainty for the modulus of
elasticity . 20
B.1 Model equation . 20
B.2 Estimation of standard uncertainty . 21

B.2.1 Precondition . 21
B.2.2 Stress measurement . 21
B.2.3 Size measurement . 22
B.2.4 Strain measurement . 23
B.2.5 Uncertainties on measurement of gauge length . 24
B.3 Significant experimental factor . 25
B.3.1 Initial strain rate [Osamura et al., 2014] . 25
B.3.2 Thickness measurement [Osamura et al., 2014] . 26
Bibliography . 27

Figure 1 – Typical stress–strain curve and definition of moduli of elasticity and 0,2 %
proof strengths. 9
Figure A.1 – Low-mass Siam twin type extensometer . 14
Figure A.2 – Low-mass double extensometer . 15
Figure A.3 – An example of the extensometer provided with balance weight and vertical
specimen axis . 16
Figure B.1 – Strain rate dependence of the relative standard uncertainty given by

Formula (B.6) . 25
Figure B.2 – Relative standard uncertainty for the thickness measurement as a function
of tape thickness . 26

Table A.1 – Relative standard uncertainty (X ) and coefficient of variance (X )
RSU
for experimental data of E and E . 17
0 U
Table A.2 – Relative standard uncertainty and coefficient of variance for experimental
data of R and R . 18
p0,2-0 p0,2-U
Table A.3 – Value of X for the data of the modulus of elasticity and the 0,2 %

proof strength tested according to this document . 19
Table B.1 – Uncertainties for experimental variables in Formula (B.6) . 24
Table B.2 – Summary of standard uncertainty evaluation, where the initial strain rate and
−4
the thickness were used as 3 × 10 /s and 0,1 mm, respectively . 25

– 4 – IEC 61788-25:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 25: Mechanical properties measurement –
Room temperature tensile test on REBCO wires

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in
addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-25 has been prepared by IEC technical committee 90:
Superconductivity.
The text of this International Standard is based on the following documents:
FDIS Report on voting
90/404/FDIS 90/411/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61788 series, published under the general title Superconductivity,
can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 6 – IEC 61788-25:2018 © IEC 2018
INTRODUCTION
Several types of composite superconductors have now been commercialized. The
rare-earth-based oxide superconductor (SC) with chemical formula REBa Cu O is used for
2 3 7
practical SC wires, where the rare-earth element RE is typically Y, Dy, Gd, Nd, Ho or Sm, or a
combination of two or more among them. This type of practical SC wire is usually called
REBCO coated conductors. A typical architecture consists of a substrate of Ni-Cr-Mo based
alloy, Ni-W alloy or stainless steel, a buffer layer consisting of a plurality of oxides, a SC layer
and a protection layer of Ag. The substrate and buffer layer act as template to facilitate the
well-oriented SC layer. In order to resist the large electromagnetic force, the wires are often
externally reinforced by laminating thin stainless steel or Cu alloy foils. Commercial composite
superconductors have a high current density and a small cross-sectional area. The major
application of composite superconductors is to build electrical power devices and
superconducting magnets. Complex stresses and strains are applied to the composite
superconducting wires when devices are manufactured and energized. In the case of
superconducting magnets, large electromagnetic forces are experienced by the windings due to
the combination of high magnetic fields and high current density. It is therefore indispensable to
determine the mechanical properties of the practical REBCO wires.

SUPERCONDUCTIVITY –
Part 25: Mechanical properties measurement –
Room temperature tensile test on REBCO wires

1 Scope
This part of IEC 61788 specifies the test method and procedures for testing tensile mechanical
properties of REBCO superconductive composite tapes at room temperature. This test is used
to measure the modulus of elasticity and 0,2 % proof strength. The values for elastic limit,
fracture strength and percentage elongation after fracture serve only as a reference. This
document applies to samples having a rectangular cross-section with an area of 0,12 mm to
6,0 mm (corresponding to the tapes with width of 2,0 mm to 12,0 mm and thickness of 0,06
mm to 0,5 mm).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
ISO 376, Metallic materials – Calibration of force-proving instruments used for the verification of
uniaxial testing machines
ISO 7500-1, Metallic materials – Calibration and verification of static uniaxial testing machines –
Part 1: Tension/compression testing machines – Calibration and verification of the
force-measuring system
ISO 9513, Metallic materials – Calibration of extensometer systems used in uniaxial testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
tensile stress
R
tensile force divided by the original cross-sectional area of the test piece at any moment during
the test
3.2
tensile strain
A
displacement increment divided by initial gauge length of extensometers at any moment during
the tensile test
– 8 – IEC 61788-25:2018 © IEC 2018
3.3
extensometer gauge length
L
G
length of the parallel portion of the test piece used for the measurement of elongation by means
of an extensometer
3.4
distance between grips
L
inward distance between grips that hold a test specimen in position before the test is started
3.5
modulus of elasticity
E
slope of the straight portion of the stress–strain curve in the elastic deformation region
SEE: Figure 1
Note 1 to entry: The straight portion of the initial stress–strain curve is very narrow as indicated in Figure 1. To
measure this quantity with a small standard uncertainty, the use of double extensometer systems will be an
appropriate technique. In this sense, the quantity of E should be a representative data for the present text, while E
U 0
should be reported only when the measure is performed by means of double extensometer system.
Note 2 to entry: In the case of composite superconductor, however, it can be determined differently depending upon
the adopted procedures; one from the initial loading curve by the zero offset line expressed as E , the other one
given by the slope of line during unloading, expressed as E . The dotted straight lines drawn along the initial loading
U
curve and the unloading one in Figure 1 b) are only a guide to the eye for determining the slope.
IEC
a)
IEC
b)
The red curves are the observed data and the black continuous and black dotted straight lines are additional lines to
indicate how to determine the moduli of elasticity and 0,2 % proof strengths.
Figure 1 – Typical stress–strain curve and definition of moduli of elasticity
and 0,2 % proof strengths
3.6
0,2 % proof strength
R
p0,2
stress value where the superconductive composite wire yields by 0,2 %
SEE: Figure 1
3.7
fracture strength
R
f
tensile stress at the fracture
3.8
tensile stress at elastic limit
R
el
tensile force divided by the original cross-sectional area at the elastic limit corresponding to the
transition from elastic to plastic deformation indicated by point P in Figure 1 b)
3.9
tensile strain at elastic limit
A
el
strain at the elastic limit corresponding to the transition from elastic to plastic deformation
indicated by point P in Figure 1 b)

– 10 – IEC 61788-25:2018 © IEC 2018
4 Principle
The test consists of straining a test piece by a tensile force, generally to fracture, for the
purpose of determining the modulus of elasticity and 0,2 % proof strength described in
Clause 1.
Depending on the employed strain measuring method, however, the quantities determined by
the present test should be limited. When using the conventional single extensometer system,
the determination of E and R is recommended. On the other hand, all E , E , R and
U p0,2-U 0 U p0,2-0
R can be determined by using double extensometer system, because of its capability to
p0,2-U
compensate the bending effects of the specimen and to guarantee a proper determination of
the modulus of elasticity.
Additional information relating to Clauses 1 to 10 is given in Annex A.
5 Apparatus
5.1 General
The test machine and the extensometer shall conform to ISO 7500-1 and ISO 9513,
respectively. The calibration shall obey ISO 376. The special requirement for this document is
presented in 5.2 and 5.3.
5.2 Testing machine
A tensile machine control system that provides a constant cross head speed shall be used.
Grips shall have a structure and strength appropriate for the test specimen and shall be
constructed to provide a firm connection with the tensile machine. The faces of the grips shall
be filed or knurled, or otherwise roughened, so that the test specimen will not slip during testing.
Gripping may be a screw type, or pneumatically or hydraulically actuated.
5.3 Extensometer
The mass of the extensometer shall be 30 g or less, so as not to affect the mechanical
properties of superconductive composite wires. The mass of the extensometers shall be balanced
around the wire to avoid any non-alignment force. The generation of bending moments due to the
non-alignment force shall be prevented (see Clause A.2).
6 Specimen preparation
6.1 General
Bending and/or pre-loading shall be prevented when the specimen is handled manually.
6.2 Length of specimen
The length of the test specimen shall be the sum of the inward distance between grips and the
grip lengths. The minimum specimen length (L ) shall be calculated as,
sm
L = 2× L + L + 2× L (1)
sm g G x
where L is the grip length, L is the gauge length of extensometer. L is the free gap distance
g G x
between grip and extensometer and shall meet the condition,
L ≥ 0,7× L (2)
x G
6.3 Determination of cross-sectional area (S )
o
A micrometer or other dimension-measuring apparatus shall be used to obtain the
cross-sectional area of the specimen after the insulation coating has been removed. The
cross-sectional area of tape-shaped wires shall be obtained from the product of its thickness
and width.
7 Testing conditions
7.1 Specimen gripping
When the test specimen is mounted on the grips of the tensile machine, the test specimen and
tensile loading axis shall be aligned to a straight line. Sand paper may be inserted as a
cushioning material to prevent the gripped surfaces of the specimen from slipping and
fracturing. During mounting of the sample, bending or deformation shall be prevented.
7.2 Setting of extensometer
When mounting the extensometer, deformation of the test specimen shall be prevented like the
indentation due to extensometer’s sharp edges which might cause an early fracture of the
specimen. The extensometer shall be mounted at the centre between the grips, aligning the
measurement direction with the specimen axis direction. During mounting, pre-loading the
specimen shall be prevented. After installation, loading shall be physically zeroed.
7.3 Testing speed
−4 −1
The initial strain rate shall be slower than 10 s during the test using the extensometer
(see B.3.1).
7.4 Test
The tensile machine shall be started after the testing speed has been set to the specified level.
The stress and strain calculated from the output signals of load cell and extensometer,
respectively, shall be plotted on the ordinate and abscissa of the diagram as shown in
Figure 1 a) and b). When the strain has reached a value between 0,1 % and 0,2 % as indicated
A , the stress shall be reduced by approximately 30 % to 40 % of R to R . Then, the stress
U U L
shall be increased again and the test should be continued to the point where the specimen is
fractured.
Prior to the start of any material test programme, the test equipment shall be checked
completely using similar size wires of known elastic properties (see Clause A.9).
8 Calculation of results
8.1 Modulus of elasticity (E)
Modulus of elasticity shall be calculated in general using the following formula and the straight
portion of the initial loading curve and of the unloading one as shown in Figure 1 b).
Appropriate software for data evaluation, with the function of enlargement of the stress–strain
diagram especially around the region where the deviation from linearity is expected, should be
used for post analyses of the plotted data.
E = ∆F/(S ∆A) (3)
o
– 12 – IEC 61788-25:2018 © IEC 2018
where
E is the modulus of elasticity (GPa);
∆F is the increment of the force (N);
∆A is the increment of strain corresponding to ∆F;
S is the original cross-sectional area of the test specimen (mm ).
o
Since the unloading process is carried out at the strain indicated by the point A in Figure 1, the
U
same Formula (3) is used for both the unloading modulus (E ) and the initial loading one (E ). It
U 0
is recommended to measure the unloading curve at the starting point A , where A is
U U
recommended to be approximately 0,1 % to 0,2 %.
After the test, the results shall be examined using the ratio E /E . The ratio shall satisfy the
0 U
∆ = 0,2 [Osamura et al., 2008 and 2014].
condition as given in Formula (4) in which
E
1−∆< < 1+∆ (4)
E
U
When it does not satisfy the condition, the test is judged not to be valid. Then the test shall be
repeated after checking the experimental procedure according to the present test method.
8.2 0,2 % proof strength (R and R )
p0,2-0 p0,2-U
The 0,2 % proof strength of the composite is determined in two ways from the initial loading
part and the unloading/reloading part of the stress–strain curve as shown in Figure 1.
The 0,2 % proof strength under loading R shall be determined as follows: the initial linear
p0,2-0
portion of the loading line of the stress–strain curve is moved to 0,2 % along the strain axis
(0,2 % offset line under loading) and the point at which this linear line intersects the
stress–strain curve shall be defined as the 0,2 % proof strength under loading.
The 0,2 % proof strength under unloading R shall be determined as follows: the initial
p0,2-U
linear portion under unloading is moved parallel to the 0,2 % offset strain point. The
intersection of this line with the stress–strain curve determines the point that shall be defined
as the 0,2 % proof strength under unloading.
Each 0,2 % proof strength shall be calculated using Formula (5):
R = F / S (5)
p0,2-i i o
where
R is the 0,2 % proof strength at each point (MPa);
p0,2-i
F is the force at each point (N);
i
S is the original cross-sectional area of the test specimen (mm );
o
i indicates 0 or U.
9 Uncertainty of measurement
Unless otherwise specified, measurements shall be carried out in a temperature that can range
from 285 K to 305 K. A force measuring cell with the relative standard uncertainty less than
0,1 %, valid between zero and the maximum force value shall be used. The extensometers
should have the relative standard uncertainty of strain less than 0,5 %. The displacement
measuring transducer (e.g. LVDT [linear variable differential transformer]) used for the
calibration should have the relative standard uncertainty less than 0,1 %.

The value of relative standard uncertainty corresponding to the number of specimens tested of
measured moduli of elasticity E and E , proof strength R and R shall be calculated
0 U p0,2-0 p0,2-U
using Formula (6):
X (N)= X N (6)
RSU
where
X (N) is the value of relative standard uncertainty;
RSU
N is the number of specimens tested;
X is the value of averaged coefficient of variation for all data tested.

According to the international round robin test (RRT, see Clause A.7), the parameter X

has been evaluated as follows: 7,0 %, 4,6 %, 4,3 % and 4,1 % for E , E , R and R ,
0 U p0,2-0 p0,2-U
respectively.
Evaluation of combined standard uncertainty for the modulus of elasticity is given in Annex B.
10 Test report
10.1 Specimen
a) Name of the manufacturer of the specimen
b) Classification and/or symbol
c) Lot number
d) Cross-sectional shape and dimension of the wire
e) Materials comprising the substrate and stabilizer
10.2 Results
Results of the following mechanical properties shall be reported:
a) Modulus of elasticity (E and E )
0 U
b) 0,2 % proof strengths (R and R )
p0,2-0 p0,2-U
– 14 – IEC 61788-25:2018 © IEC 2018
Annex A
(informative)
Additional information relating to Clauses 1 to 10
A.1 General
This document is based on the axial stress–strain measurements at room temperature.
Mechanical properties in the perpendicular orientation (c-axis) are also of importance in the
manufacture of superconducting devices; they are not treated in this document. For wider strips,
bi-axial stress–strain measurements done with bi-axial strain gauges are not uncommon but
these measurements too are outside the scope of this document.
Annex A gives reference information on the variable factors that can seriously affect the tensile
test method, together with some precautions to be observed when using this document.
A.2 Extensometer
A.2.1 Double extensometer
In the international RRT for REBCO tapes, a double extensometer system consisting of two
single extensometers was generally used to record two signals to be averaged by software or
one signal already averaged by the extensometer system itself.
Typical advanced low-mass double extensometers are shown in Figures A.1 and A.2.
Dimensions in millimetres
IEC
Figure A.1 – Low-mass Siam twin type extensometer
Figure A.1 shows a low-mass Siam twin type extensometer with a gauge length of 12,3 mm
(total mass 0,5 g). The two extensometers are wired together into a single type extensometer,
thus averaging the two displacement records electrically.
12,3
Dimensions in millimetres
IEC
Figure A.2 – Low-mass double extensometer
Figure A.2 shows a low-mass double extensometer with a gauge length of 25,6 mm (total mass
3,0 g). Each of the two extensometers is a single type extensometer; the averaging should be
carried out by software.
25,6
– 16 – IEC 61788-25:2018 © IEC 2018
A.2.2 Single extensometer
Figure A.3 shows a single extensometer with total mass of 30 g together with a balance weight.
Dimensions in millimetres
Bar spring
IEC
a) top view
Stopper
Specimen
Strain gauge
Frame
Balance weight
22 35
Cross spring plate
Frame
Gauge length setting hole
IEC
L gauge length
G
b) side view
Figure A.3 – An example of the extensometer provided with balance weight
and vertical specimen axis
A.3 Elastic limit
Figure 1 shows the result of tensile test at room temperature for a REBCO coated conductor.
Mechanical properties are usually divided into two regions of elastic and plastic deformation.
The macroscopic yielding took place at R = 682 MPa. When the stress–strain curve is
p0,2
precisely analysed, a small change of slope started just after elastic limit (el) as point P shown
in Figure 1 b). The tensile stress and strain at elastic limit are defined in principle as
corresponding to the transition of elastic to plastic deformation as shown in Figure 1 b). The
elastic strain limit is lying near A = 0,05 %. However their quantitative determination is difficult
el
because the slope changes very gradually.
L 25
G
A.4 Gripping force
A weak gripping force results in slippage but a strong gripping force can break the gripped
surface. Care should therefore be taken when adjusting the gripping force. A cushioning
material such as sand paper may be inserted to prevent the gripped surfaces of the specimen
from slipping and fracturing.
A.5 Percentage elongation after fracture (A )
f
The measurement of elongation after fracture is necessary to serve only as a reference. The
movement of the cross-head may be used to find the approximate value for elongation after
fracture, instead of using the butt method. To use this method, it is necessary to record the
cross-head position at fracture. The following formula is used to obtain the elongation after
fracture, given as a percentage.
A = 100 (L − L ) / L (A.1)
f f o o
where
A is the percentage elongation after fracture;
f
L is the initial inward distance between grips;
o
L is the distance between grips after fracture.
f
A.6 Condition of straining to fracture
Clause 4 describes that the test consists of straining a test piece by a tensile force, generally to
fracture. In practice, however, it is difficult to strain properly the specimen to fracture, because
the present specimen with equi-parallel tape shape often causes a grip fracture. The test
straining to fracture is not the mandatory test condition.
A.7 Relative standard uncertainty (RSU)
To assess the quality of the measured data, the concept of uncertainty serves as a sound basis
for an independent judgment [ISO/IEC Guide 98-3]. In the case of REBCO tapes, substantial
information was gathered from the international RRT carried out recently by seven research
groups [Osamura et al., 2014]. Four kinds of commercial REBCO superconductive tapes were
used for test specimens as designated by A to D in Table A.1. Their general structural feature is
characterized as follows. A thin superconductive layer with thickness of 1 μm to 2,5 μm is
grown on the substrate via the intermediate oxide layers. The surface of superconductive layer
is covered by a thin Ag layer. Metallic sheets with thickness of 40 μm to 100 μm are laminated
on both sides. The data obtained by five repeated tests for each sample were reported by
individual group.
Table A.1 – Relative standard uncertainty (X ) and coefficient of variance (X )
RSU
for experimental data of E and E
0 U
E E
0 U
a
Sample N X X X X
RSU RSU
(%) (%) (%) (%)
A 32 1,27 7,2 0,70 3,7
B 32 1,96 11,1 0,92 5,3
C 35 0,72 4,2 0,83 4,9
D 35 0,91 5,4 0,78 4,6
a
N is the total number of experiments accepted after the qualification test.

– 18 – IEC 61788-25:2018 © IEC 2018
As mentioned in 8.1, the data were entrusted to the qualification test, where Δ = 0,2 was
employed. The number of experimental data available for the successive analysis was listed in
Table A.1. For instance, all data (N = 35) were qualified for tapes C and D, but three of them
were unqualified for tapes A and B.
The average of the modulus was calculated by using Formula (A.2),
N
E = E (i) (A.2)
j ∑ j
N
i=1
where j indicates 0 or U. Then the value of relative standard uncertainty (X ) was evaluated
RSU
from Formula (A.3),
N
(E (i)− E )
j j
∑
i=1
X = (A.3)
RSU
j
N(N−1)
E
j
The evaluated results are listed in Table A.1. Further, the RSU value relates to the coefficient of
variance value (X ) as given in Formula (A.4),

X

j
X = (A.4)
RSU
j
N
When knowing X and N, the X could be obtained as given in Table A.1.
RSU
j
In the same manner, the statistical information on the 0,2 % proof strength was evaluated as
listed in Table A.2.
Table A.2 – Relative standard uncertainty and coefficient of variance
for experimental data of R and R
p0,2-0 p0,2-U
R R
p0,2-0 p0,2-U
Sample N
X X X X
RSU RSU
(%) (%) (%) (%)
A 28 0,83 4,7 0,86 4,9
B 32 0,58 3,3 0,66 3,7
C 35 0,83 4,9 0,71 4,2
D 35 0,70 4,1 0,58 3,4
As listed in Tables A.1 and A.2, the values of X and X differ for different specimens,
RSU
because mechanical properties like rigidity are different depending on the cross section and
constituent materials, as analysed in detail in the literature [Osamura et al., 2014]. In order to
establish the International Standard on the tensile test method for the practical REBCO tapes,
it is reasonable to take a grand average of data for four tapes as listed in Table A.3. In
conclusion, the standard uncertainty can be predicted from Formula (A.4), when the tensile test
is carried out and the modulus and the proof strength are determined according to this
document, where the constant X value is given in Table A.3.

Table A.3 – Value of X for the data of the modulus of elasticity and

the 0,2 % proof strength tested according to this document
E E R R
0 U p0,2-0 p0,2-U
X 7,0 4,6 4,3 4,1

A.8 Discretion applying this document
In order to guarantee the accuracy of this test method, it is necessary to confirm the testing
conditions specified in Clause 7. However, when the supplier establishes the measurement
technique, by which a sufficiently small RSU is realized for the measurement result, unless
otherwise agreed upon between the customer and the supplier, the supplier may measure and
report either E or E by means of the customer's own technique.
0 U
A.9 Assessment on the reliability of the test equipment
The reliability of the test equipment, which comprises the tensile testing unit, load cell and
extensom
...