IEC 61788-18:2013
(Main)Superconductivity - Part 18: Mechanical properties measurement - Room temperature tensile test of Ag- and/or Ag alloy-sheathed Bi-2223 and Bi-2212 composite superconductors
Superconductivity - Part 18: Mechanical properties measurement - Room temperature tensile test of Ag- and/or Ag alloy-sheathed Bi-2223 and Bi-2212 composite superconductors
IEC 61788-18:2013 specifies a test method detailing the tensile test procedures to be carried out on Ag/Bi-2223 and Ag/Bi-2212 superconductive composite wires at room temperature. This test is used to measure the modulus of elasticity and to determine the 0,2 % proof strength. When the 0,2 % proof strength could not be determined due to earlier failure, the stress level at apparent strains of 0,05 %, 0,1 %, 0,15 %, 0,2 %, 0,25 % with increment of 0,05 % is measured. The values for elastic limit, fracture strength, percentage elongation after fracture and the fitted type of 0,2 % proof strength serve only as a reference. The sample covered by this test procedure should have a round or rectangular cross-section with an area of 0,3 mm2 to 2,0 mm2 (corresponding to the tape-shaped wires with width of 2,0 mm to 5,0 mm and thickness of 0,16 mm to 0,4 mm). Key words: superconductivity, mechanical properties measurement
Supraconductivité - Partie 18: Mesure des propriétés mécaniques - Essai de traction à température ambiante des supraconducteurs composites Bi-2223 et Bi-2212 avec gaine Ag et/ou en alliage d'Ag
La CEI 61788-18:2013 spécifie une méthode d'essai détaillant les modes opératoires d'essai de traction à exécuter sur des fils composites supraconducteurs d'Ag/Bi-2223 et d'Ag/Bi-2212 à température ambiante. Cet essai est utilisé pour mesurer le module d'élasticité et pour déterminer la charge d'épreuve à 0,2 %. Lorsqu'on ne peut pas déterminer la charge d'épreuve à 0,2 % en raison d'une défaillance antérieure, on mesure le niveau de contrainte pour des déformations apparentes de 0,05 %, 0,1 %, 0,15 %, 0,2 %, 0,25 % avec un incrément de 0,05 %. Les valeurs de la limite élastique, de la résistance à la rupture, du pourcentage d'allongement après fracture et du type ajusté de charge d'épreuve à 0,2 % ne servent que de référence. Il convient que l'échantillon couvert par ce mode opératoire d'essai ait une section circulaire ou rectangulaire d'une surface de 0,3 mm2 à 2,0 mm2 (correspondant aux fils en forme de bande d'une largeur de 2,0 mm à 5,0 mm et d'une épaisseur de 0,16 mm à 0,4 mm). Mots clé: supraconductivité, propriétés mécaniques
General Information
Standards Content (Sample)
IEC 61788-18 ®
Edition 1.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Superconductivity –
Part 18: Mechanical properties measurement – Room temperature tensile test of
Ag- and/or Ag alloy-sheathed Bi-2223 and Bi-2212 composite superconductors
Supraconductivité –
Partie 18: Mesure des propriétés mécaniques – Essai de traction à température
ambiante des supraconducteurs composites Bi-2223 et Bi-2212 avec gaine Ag
et/ou en alliage d'Ag
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IEC 61788-18 ®
Edition 1.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Superconductivity –
Part 18: Mechanical properties measurement – Room temperature tensile test of
Ag- and/or Ag alloy-sheathed Bi-2223 and Bi-2212 composite superconductors
Supraconductivité –
Partie 18: Mesure des propriétés mécaniques – Essai de traction à température
ambiante des supraconducteurs composites Bi-2223 et Bi-2212 avec gaine Ag
et/ou en alliage d'Ag
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 29.050 ISBN 978-2-8322-1051-2
– 2 – 61788-18 © IEC:2013
CONTENTS
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Principle . 9
5 Apparatus . 9
5.1 General . 9
5.2 Testing machine . 9
5.3 Extensometer . 9
6 Specimen preparation . 9
6.1 General . 9
6.2 Length of specimen . 10
6.3 Removing insulation . 10
6.4 Determination of cross-sectional area (S ) . 10
7 Testing conditions . 10
7.1 Specimen gripping . 10
7.2 Setting of extensometer . 10
7.3 Testing speed . 10
7.4 Test . 10
8 Calculation of results . 12
8.1 Modulus of elasticity (E) . 12
8.2 0,2 % proof strength (R ) . 13
p 0,2
8.3 Tensile stress at specified strains (R ) . 13
A
8.4 Fracture strength (R ) . 14
f
9 Uncertainty of measurement . 14
10 Test report . 14
10.1 Specimen . 14
10.2 Results . 15
10.3 Test conditions . 15
Annex A (informative) Additional information relating to Clauses 1 to 14 . 16
Annex B (informative) Uncertainty considerations . 26
Annex C (informative) Specific examples related to evaluation of uncertainties for
Ag/Bi-2223 and Ag/Bi-2212 wires . 30
Figure 1 – Typical stress-strain curve and definition of modulus of elasticity and 0,2 %
proof strengths of an externally laminated Ag/Bi-2223 wire by brass foil . 11
Figure 2 – Typical stress-strain curve of an Ag/Bi-2223 wire where the 0,2 % proof
strengths could not be determined and definition of tensile stresses at specified strains . 12
Figure A.1 – Low mass Siam twin type extensometer with a gauge length of ~ 12,3 mm
(total mass ~ 0,5 g) . 16
Figure A.2 – Low mass double extensometer with a gauge length of ~ 25,6 mm (total
mass ~ 3 g) . 17
Figure A.3 – An example of the extensometer provided with balance weight and vertical
specimen axis . 18
Figure A.4 – Original raw data of an Ag/Bi-2223 wire measurement in form of load and
displacement graph . 19
61788-18 © IEC:2013 – 3 –
Figure A.5 – Typical stress versus strain of an Ag/Bi-2223 wire up to the elastic limit
corresponding to the transition region from elastic to plastic deformation (point G) . 20
Figure C.1 – Measured stress versus strain curve for Bi-2223 wire . 31
Table A.1 – Results of relative standard uncertainty values achieved on different
Ag/Bi-2223 wires during the international round robin tests . 23
Table A.2 – Selected data for F test for E of Sample E bare wire . 24
Table A.3 – Results of F-test for the variations of E of four kinds of Bi-2223 wires . 24
Table B.1 – Output signals from two nominally identical extensometers . 27
Table B.2 – Mean values of two output signals . 27
Table B.3 – Experimental standard deviations of two output signals . 27
Table B.4 – Standard uncertainties of two output signals . 27
Table B.5 – Coefficient of variations of two output signals . 28
Table C.1. – Load cell specifications according to manufacturer’s data sheet. 32
Table C.2 – Uncertainties from various factors for stress measurement . 33
Table C.3 – Uncertainties with respect to measurement of strain measurement . 35
Table C.4 – Summary of evaluated uncertainties caused by various factors . 35
Table C.5 – Results of uncertainty evaluation for the modulus of elasticity (E = 86,1
GPa) as a function of initial cross head rate . 36
Table C.6 – Uncertainties from various factors for stress measurement . 37
Table C.7 – Results of uncertainty evaluation for the stress (R = 42,5 MPa) as a function
of initial strain rate . 37
– 4 – 61788-18 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 18: Mechanical properties measurement –
Room temperature tensile test of Ag- and/or Ag alloy-sheathed
Bi-2223 and Bi-2212 composite superconductors
FOREWORD
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indispensable for the correct application of this publication.
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-18 has been prepared by IEC technical committee 90:
Superconductivity.
The text of this standard is based on the following documents:
FDIS Report on voting
90/326/FDIS 90/327/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61788 series, published under the general title Superconductivity,
can be found on the IEC website.
61788-18 © IEC:2013 – 5 –
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 61788-18 © IEC:2013
INTRODUCTION
Several types of composite superconductors have now been commercialised. Especially, high
temperature superconductors such as Ag- and/or Ag alloy-sheathed Bi-2223 (Ag/Bi-2223) and
Ag- and/or Ag alloy-sheathed Bi-2212 (Ag/Bi-2212) wires are now manufactured in industrial
scale. Commercial composite superconductors have a high current density and a small
cross-sectional area. The major applications of composite superconductors are to build
electrical power devices and superconducting magnets. While the magnet is being
manufactured, complicated stresses/strains are applied to its windings and, while it is being
energized, a large electromagnetic force is applied to the superconducting wires because of its
high current density. It is therefore indispensable to determine the mechanical properties of the
superconductive wires from which the windings are made.
The Ag/Bi-2223 and Ag/Bi-2212 superconductive composite wires fabricated by the powder-in
-tube method are composed of a number of oxide filaments with silver and silver alloy as a
stabilizer and supporter. In the case that the external reinforcement of Ag/Bi-2223 and
Ag/Bi-2212 wires by using thin stainless or Cu alloy foils has been adopted in order to resist the
large electromagnet force, this standard shall be also applied.
61788-18 © IEC:2013 – 7 –
SUPERCONDUCTIVITY –
Part 18: Mechanical properties measurement –
Room temperature tensile test of Ag- and/or Ag alloy-sheathed
Bi-2223 and Bi-2212 composite superconductors
1 Scope
This International Standard specifies a test method detailing the tensile test procedures to be
carried out on Ag/Bi-2223 and Ag/Bi-2212 superconductive composite wires at room
temperature.
This test is used to measure the modulus of elasticity and to determine the 0,2 % proof strength.
When the 0,2 % proof strength could not be determined due to earlier failure, the stress level at
apparent strains of 0,05 %, 0,1 %, 0,15 %, 0,2 %, 0,25 % with increment of 0,05 % is measured.
The values for elastic limit, fracture strength, percentage elongation after fracture and the fitted
type of 0,2 % proof strength serve only as a reference (see Clauses A.4, A.5, A.6 and A.10).
The sample covered by this test procedure should have a round or rectangular cross-section
2 2
with an area of 0,3 mm to 2,0 mm (corresponding to the tape-shaped wires with width of 2,0
mm to 5,0 mm and thickness of 0,16 mm to 0,4 mm).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
)
ISO 376, Metallic materials – Calibration of force-proving instruments used for the verification of
uniaxial testing machines
ISO 6892-1, Metallic materials – Tensile testing – Part 1: Method of test at room temperature
ISO 7500-1, Metallic materials – Verification of static uniaxial testing machines – Part 1:
Tension/compression testing machines – Verification and calibration 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, terms and definitions given in IEC 60050-815 and
ISO 6892-1, as well as the following terms and definitions apply.
– 8 – 61788-18 © IEC:2013
3.1
tensile stress
R
tensile force divided by the original cross-sectional area 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 test
3.3
extensometer gauge length
L
G
length of the parallel portion of the test piece used for the measurement of displacement by
means of an extensometer
3.4
distance between grips
L
o
length between grips that hold a test specimen in position before the test is started
3.5
modulus of elasticity
E
gradient of the straight portion of the stress-strain curve in the elastic deformation region
SEE: Figure 1.
Note 1 to entry: It can be determined differently depending upon the adopted procedures:
a) one from the initial loading curve by zero offset line expressed as E ,
b) the other one given by the slope of line during the elastic unloading, expressed as E .
U
3.6
0,2 % proof strength
R
p0,2
stress value when the superconductive composite wire yields by 0,2 %
SEE: Figure 1.
Note 1 to entry: The designated stress, R or R corresponds to point A or B obtained from the initial loading
p0,2-0 p0,2-U
or unloading curves in Figure 1, respectively. This strength is regarded as a representative 0,2 % proof strength of the
composite.
3.7
tensile stress at specified strains
R
A
tensile stress corresponding to different specified strain (A)
3.8
fracture strength
R
f
tensile stress at the fracture
Note 1 to entry: In most cases, the fracture strength is defined as tensile stress corresponding to the maximum
testing force
61788-18 © IEC:2013 – 9 –
3.9
tensile stress at elastic limit
R
el
tensile stress at elastic limit corresponding to transition instant from elastic to plastic
deformation
3.10
tensile strain at elastic limit
A
el
strain at elastic limit
Note 1 to entry: The stress R and the corresponding strain A refer to point G in Figure A.5, respectively and are
el el
regarded as the transition point from elastic to plastic deformation.
4 Principle
The test consists of straining a test piece by a tensile force, generally to fracture, in principle for
the purpose of determining the mechanical properties defined in Clause 3.
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 quantities described
U p0,2-U
here can be determined by using double extensometer system, because of its capability to
compensate the bending effects of the specimen thereby guaranteeing a proper determination
of the modulus of elasticity.
5 Apparatus
5.1 General
The test machine and the extensometers shall conform to ISO 7500-1 and ISO 9513,
respectively. The calibration shall obey ISO 376. The special requirements of this standard are
presented here.
5.2 Testing machine
A tensile machine control system that provides a constant crosshead 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 the test. 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
symmetrically around the wire to avoid any non-alignment force. Care shall be taken to prevent
bending moments from being applied to the test specimen (see Clauses A.2 and A.3).
6 Specimen preparation
6.1 General
When a test specimen sampled from a bobbin needs to be straightened, a method that affects
the material as little as possible shall be used. Care shall be taken to prevent bending or
pre-loading when the specimen is handled manually.
– 10 – 61788-18 © IEC:2013
6.2 Length of specimen
The length of the test specimen shall be the sum of the inward distance between grips and both
grip lengths. The inward distance between the grips shall be 60 mm or more, as requested for
the installation of the extensometer.
6.3 Removing insulation
If the test specimen surface is coated with an insulating material, the coatings shall be removed.
Either a chemical or mechanical method shall be used with care taken in removing the coating so
as not to damage the specimen surface (see Clause A.7).
6.4 Determination of cross-sectional area (S )
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. Corrections to be made for the corners of the cross-sectional area shall be determined
through consultation among the parties concerned (see Clause A.8). In addition, in the cases of
lens-shaped wires, measurement of width and thickness by photograph may also be done. Mean
value of middle and edge thickness shall be used for wires with varying thickness along its width
to minimize mismatch effect on its cross-sectional area. The cross-sectional area of a round wire
shall be calculated using the arithmetic mean of the two orthogonal diameters.
7 Testing conditions
7.1 Specimen gripping
When the test specimen is going to be mounted on the grips of the tensile machine, the test
specimen and tensile loading axis shall be aligned to be in a straight line. Sand paper may be
inserted as a cushioning material to prevent the gripped surfaces of the specimen from slipping
and fracturing (see Clause A.9). During mounting of the sample, bending or deformation shall be
prevented.
7.2 Setting of extensometer
When mounting the extensometer, care shall be taken to prevent the test specimen from being
deformed like in the case of indentation due to extensometers’ sharp edges which might cause
an earlier 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 care should be taken not to pre-load the specimen. After installation, loading
shall be physically set to zero.
In the case where a double extensometer system is used, it shall be mounted symmetrically
around the cross-section to allow averaging of the strain to compensate the bending effects.
7.3 Testing speed
The tensile tests shall be performed with displacement control. The machine crosshead speed is
recommended to be set between 0,1 mm/min and 0,5 mm/min.
7.4 Test
Following this procedure, the tensile machine shall be started after the crosshead speed has
been set to the specified level. The strain and stress calculated from the output signals of the
extensometer and the load cell respectively shall be plotted on the abscissa and ordinate of the
diagram as shown in Figure 1 and Figure 2. When the total strain has reached a value of
approximately 0,1 % (point A ), the tensile stress shall be reduced by 30 % to 40 %. Then, the
u
61788-18 © IEC:2013 – 11 –
load shall be increased again to the previous level and the test shall be continued to the point
where the specimen is fractured.
Prior to the start of any material test program it is advisable to check the complete test
equipment using similar size wires of known elastic properties (see Clause A.13).
1 2 3 4
A
Slope during unloading
B
at ∼0,1 % strain
0 0,1 0,2 0,3 0,4 0,5 0,6
A
u
Tensile strain (%)
IEC 2164/13
1 Straight line drawn from the initial loading curve (zero offset line)
2 Straight line drawn from the unloading curve
3 0,2 % offset line drawn from the initial loading curve by parallel shifting
4 0,2 % offset line drawn from the unloading curve by parallel shifting
A 0,2% proof strength obtained by the offset line 3
B 0,2% proof strength obtained by the offset line 4
NOTE The slope of the initial loading curve decreases usually with increasing strain. Then, two straight lines can be
drawn from the 0,2 % offset point on the abscissa to obtain 0,2 % proof strength of the composite. Point A is obtained
from the initial loading curve, and Point B is obtained from the unloading curve.
Figure 1 – Typical stress-strain curve and definition of modulus of elasticity and
0,2 % proof strengths of an Ag/Bi-2223 wire externally laminated by brass foil
Tensile stress (MPa)
– 12 – 61788-18 © IEC:2013
R could not be
p0,2
determined due to
R
f
earlier failure
R
A=0,20
R
A=0,15
R
A=0,10
R
A=0,05
R
el
0,0 A 0,1 0,2 A 0,3 0,4
el f
Tensile strain (%)
IEC 2165/13
NOTE In cases where the 0,2 % offset proof strength could not be determined due to earlier failure of the wires, the
tensile stresses at specified strains such as 0,05 %, 0,10 %, 0,15 %, and 0,20 % with an increment of 0,05 % are
measured. In addition, the fracture strength, R and the percentage elongation to fracture A were derived from the
f f
stress-strain curve.
Figure 2 – Typical stress-strain curve of an Ag/Bi-2223 wire where the 0,2 % proof
strengths could not be determined and definition of tensile stresses at specified strains
8 Calculation of results
8.1 Modulus of elasticity (E)
Modulus of elasticity shall be calculated in general using the following equation and the straight
portion of the initial loading curve and of the unloading one. Appropriate software for data
evaluation, with the function of enlargement of the stress strain graph especially around the
region where the deviation from linearity is expected, should be used for post analyses of the
plotted data (see Clause A.12).
E = ∆F/(S ∆A) (1)
where
E is the modulus of elasticity;
∆F is the increment of the corresponding force;
∆A is the increment of strain corresponding to ∆F;
S is the original cross – sectional area of the test specimen.
in Figure 1, the
Since the unloading process is carried out at the strain indicated by the point A
U
same equation (1) is used for both the unloading modulus (E ) and the initial loading one (E ).
U 0
Tensile stress (MPa)
61788-18 © IEC:2013 – 13 –
It is recommended to measure the unloading curve at the starting point A , where A is
U U
recommended to be approximately 0,1 %.
After the test, the results shall be examined using the ratio E /E . The ratio shall satisfy the
0 U
condition as given in condition (2) in which Δ = 0,3 (see Clause A.11).
E
(2)
1−∆< < 1+∆
E
U
If it does not satisfy the condition (2), 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.
It is recommended to achieve the unloading – reloading procedure as follows: When the loading
curve reaches the strain of A = 0,10 %, the stress is reduced by 30 % to 40 % and then the wire
U
is reloaded.
The slope of the unloading curves shall be obtained in the linear portion between the stress
where the unloading started and the stress which is generally 90 % referring to the onset of the
unloading stress.
8.2 0,2 % proof strength (R )
p 0,2
The 0,2 % proof strength of the composite shall be 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 parallel to 0,2 % along the strain
axis (0,2 % offset line under loading) and the point A at which this linear line intersects the
stress-strain curve shall be defined as the 0,2 % proof strength under initial loading.
The 0,2 % proof strength under unloading R shall be determined as follows: the linear
p0,2-U
portion of the unloading line is moved parallel to the 0,2 % offset strain point. The intersection of
this line with the stress-strain curve determines the point B that shall be defined as the 0,2 %
proof strength under unloading. Depending on the unloading line (4 in Figure 1) 0,2 % proof
strength (R ) is determined.
p0,2-U
Each 0,2 % proof strength shall be calculated using equation (3) given below:
R = F / S (3)
p0,2-i i 0
where
R is the 0,2 % proof strength (MPa) at each point;
p0,2-i
F is the force (N) at each point;
i
S is the original cross-sectional area (in square millimetres) of the test specimen;
further, i = 0 at 0 % and i = U at 0,1 %.
8.3 Tensile stress at specified strains (R )
A
On the other hand, when the 0,2 % proof strength could not be determined due to earlier failure,
then the stress level at strains of 0,05 %, 0,1 %, 0,15 %, 0,2 %, 0,25 % with increment of 0,05 %
strength is measured (see Figure 2).
– 14 – 61788-18 © IEC:2013
8.4 Fracture strength (R )
f
Tensile strength R shall be the maximum force divided by the original cross-sectional area of
f
the wire before loading (see Clause A.6).
9 Uncertainty of measurement
Unless otherwise specified, measurements shall be carried out in a temperature that can range
from 280 K to 310 K. A force measuring cell with relative standard uncertainty less than 0,1 %,
valid between zero and the maximum force capacity of load cell, shall be used. The
extensometers should have relative standard uncertainty of strain less than 0,05 %. The
displacement measuring transducer (e.g. LVDT [linear variable differential transformer]) used
for the calibration should have relative standard uncertainty less than 0,01 %.
The relative standard uncertainty values of measured moduli of elasticity E and E , tensile
0 U
stresses at specified strains R and the proof strengths R currently achieved with respect to
A p0,2
the International Round Robin Test of 8 representative research laboratories are given in
Table A.1 (see Clause A.11).
The relative standard uncertainty corresponding to the number of samples tested shall be
calculated using equation (4) given below:
U (N)= COV / N (4)
RSU
where
U (N) is the relative standard uncertainty,
RSU
N is the number of samples tested,
COV is the averaged coefficient of variation for all data tested.
According to the international round robin test (see [4] and [5] of Clause A.14), the relative
standard uncertainty corresponding to the number of sample tested can be calculated by using
equation (4). For example, the uncertainty was 1,8 % for E for the test data of N = 18 in the
case of sample E bare after the qualification check. Similarly, the uncertainty was 1,5 % for E
U
(N = 18). For two bare BSSCO wires, R was not possible to assess. But for metallic foils
p0,2
laminated 3 ply Ag/Bi-2223 wires, 1,4 % for R (N = 9) were reported. Further uncertainties in
p0,2
the range of 1,0 % to 2,7 % were reported for the stresses at specified strains R (N = 16).
A
10 Test report
10.1 Specimen
a) Name of the manufacturer of the specimen
b) Classification and/or symbol
c) Lot number
The following information shall be reported if possible.
d) Raw materials and their chemical composition
e) Cross-sectional shape and dimension of the tape-shaped wire
f) Number of filaments
g) Non-superconductor to superconductor ratio
61788-18 © IEC:2013 – 15 –
10.2 Results
Results of the following mechanical properties shall be reported.
a) Modulus of elasticity (E and E with A )
0 U U
b) 0,2 % proof strengths (R and R )
p0,2-0 p0,2-U
c) Tensile stress (R ) at strains of 0,1 %, 0,15 %, 0,2 %, 0,25 % with increment of 0,05 %
A
The following information shall be reported as an option upon requirement.
d) Percentage elongation to fracture (A ) derived from the stress-strain curves and the location
f
of the fracture (i. e. within the extensometer or at the grips)
e) Tensile strength (R )
f
The following information shall be reported if possible.
f) Coefficient of curve fit function obtained with an exponential function (see Clause A.5)
g) Tensile stress at elastic limit (R )
el
h) Tensile strain at elastic limit (A )
el
10.3 Test conditions
The following information shall be reported as necessary.
a) Crosshead speed
b) Distance between grips
c) Temperature
d) Manufacturer and model of testing machine
e) Manufacturer and model of extensometer
f) Gripping method
– 16 – 61788-18 © IEC:2013
Annex A
(informative)
Additional information relating to Clauses 1 to 14
A.1 General
This annex gives reference information on the variable factors that can seriously affect the
tensile test methods, together with some precautions to be observed when using the standard.
A.2 Extensometer
A.2.1 Double extensometer
In the international RRT for Ag/Bi-2223 wires, a double extensometer system consisting of two
single extensometers were generally used to record two signals to be averaged by software or
one signal already averaged by the extensometer system itself. The mass of the low-mass
double extensometers shall be 5 g or less [1] .
In Figure A.1 and Figure A.2, a typical advanced low-mass double extensometer is shown.
∼0,5 g
IEC 2166/13
Dimensions in millimetres
NOTE The two extensometers are wired together into a single type extensometer, thus averaging the two
displacement records electrically.
Figure A.1 – Low mass Siam twin type extensometer
with a gauge length of ~ 12,3 mm (total mass ~ 0,5 g)
___________
Numbers in square brackets refer to the reference documents in Clause A.14 of this annex.
12,3
61788-18 © IEC:2013 – 17 –
∼3 g
IEC 2167/13
Dimensions in millimetres
Each of the two extensometers is a single type extensometer, the averaging should be carried out by software.
Figure A.2 – Low mass double extensometer with
a gauge length of ~ 25,6 mm (total mass ~ 3 g)
A.2.2 Single extensometer
Figure A.3 shows a single extensometer with a total weight of 31 g together with a balance
weight, which was used to establish International Standard IEC 61788-6.
25,6
– 18 – 61788-18 © IEC:2013
Bar spring
a) Top view
Stopper
Strain gauge
Specimen
Balance weight
Frame
22 35
Cross spring plate
Frame
Gauge length setting hole
b) Side view
IEC 2168/13
Dimensions in millimetres
Figure A.3 – An example of the extensometer provided
with balance weight and vertical specimen axis
A.3 Requirements of high resolution extensometers
From Figure A.4 the requirements for such extensometers can be derived. In order to meet the
target that the recorded values obtained from the raw data should have a low relative standard
uncertainty in particular between 0 % strain and 0,01 % strain, the total displacement in this
range shall be 2,5 µm for the case of 25 mm gauge length or 1,2 µm for 12 mm gauge length. In
fact, the signals should be acquired with a signal to noise ratio around 100 times better to ensure
stable records within the required strain range. The calibration factor for a 12 mm gauge length
extensometer is usually 10 V per 1 mm displacement. The peak-to-peak voltage of the signal
should be around 1 mV to ensure this low relative standard uncertainty. Using state-of-the-art
signal conditioners, shielded and twisted cables, and high resolution data acquisition systems of
greater than 16 bit resolution, it is thus possible to ensure this demand [1]. Figure A.4 shows the
G.L. 25
61788-18 © IEC:2013 – 19 –
original raw data of an Ag/Bi-2223 wire measurement in the form of load and displacement graph.
To achieve a low scatter of data as shown below, it is necessary to have a high signal to noise
ratio enabling to resolve the curve well below the 1 µm range [2,3].
To obtain a zero offset gradient with a sufficient low relative standard uncertainty, which allows
an assessment for the modulus of elasticity, it is prerequisite to use high resolution
extensometers with extremely high signal to noise ratio.
Load = 2 716,6
Displacement + 0,1069
R = 0,999 5
0,000 0,015 0,030
Displacement (mm)
IEC 2169/13
Figure A.4 – Original raw data of an Ag/Bi-2223 wire
measurement in form of load and displacement graph
A.4 Elastic limit
A.4.1 Tensile stress at elastic limit (R )
el
The tensile stress at elastic limit corresponding to the transition of elastic to plastic deformation
shall be calculated in general using the following equation (see Figure A.5).
R = F /S (A.1)
el el 0
where
R is the tensile stress (MPa) at the transition from elastic to plastic deformation;
el
F is the force (N) at the transition from elastic to plastic deformation.
el
A.4.2 Tensile strain at elastic limit (A )
el
The strain at elastic limit (see Figure A.5) referred to the stress R is defined as follows:
el
∆A = A − A (A.2)
total max 0
where
∆A is the total strain increment referring to zero offset strain which corresponds to strain
total
where the transition from elastic to plastic deformation occurs;
A the observed value of strain referred to the stress R ;
max el
A : the zero offset strain.
Load (N)
– 20 – 61788-18 © IEC:2013
R = 762,61A + 0,021
R = 0,099 5
G
R
el
A
el
0,00 0,02 0,04 0,06
Strain (%)
IEC 2170/13
st
The plots (large circles) show the region of the initial straight portion of the record. The linear 1 order regression
analysis gives the modulus of elasticity E (E = 76 GPa) and the measure of linearity as square of regression
coefficient. The value of computed 76 GPa is the result of the regression line analysis, where the origin has been
determined to have an offset in the ordinate owing to the plot scatter. In addition, the square of regression coefficient
should be greater than 0,99 to ensure the linearity. The stress R and the corresponding strain A correspond to the
el el
transition region of elastic plastic deformation. In particular, th
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