IEC 61788-6:2008

IEC 61788-6
Edition 2.0 2008-01
INTERNATIONAL
STANDARD
Superconductivity –
Part 6: Mechanical properties measurement – Room temperature tensile test of
Cu/Nb-Ti composite superconductors

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IEC 61788-6
Edition 2.0 2008-01
INTERNATIONAL
STANDARD
Superconductivity –
Part 6: Mechanical properties measurement – Room temperature tensile test of
Cu/Nb-Ti composite superconductors

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
S
ICS 29.050; 77.040.10 ISBN 2-8318-9529-4

– 2 – 61788-6 © IEC:2008(E)
CONTENTS
FOREWORD.3
INTRODUCTION.5

1 Scope.6
2 Normative references .6
3 Terms and definitions .6
4 Principle .7
5 Apparatus.7
5.1 Conformity.7
5.2 Testing machine .7
5.3 Extensometer .8
6 Specimen preparation.8
6.1 Straightening the specimen .8
6.2 Length of specimen .8
6.3 Removing insulation .8
6.4 Determination of cross-sectional area (S ) .8
o
7 Testing conditions .8
7.1 Specimen gripping.8
7.2 Pre-loading and setting of extensometer .8
7.3 Testing speed.8
7.4 Test.9
8 Calculation of results .9
8.1 Tensile strength (R ) .9
m
8.2 0,2 % proof strength (R and R ) .9
p0,2A p0,2B
8.3 Modulus of elasticity (E and E ) .9
o a
9 Uncertainty.10
10 Test report.10
10.1 Specimen .10
10.2 Results.10
10.3 Test conditions.11

Annex A (informative) Additional information relating to Clauses 1 to 10 .13
Annex B (informative) Uncertainty considerations .18

Bibliography.21

Figure 1 – Stress-strain curve and definition of modulus of elasticity and 0,2 % proof
strengths .12
Figure A.1 – An example of the light extensometer, where R1 and R3 indicate the
corner radius .16
Figure A.2 – An example of the extensometer provided with balance weight and
vertical specimen axis.17

61788-6 © IEC:2008(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
SUPERCONDUCTIVITY –
Part 6: Mechanical properties measurement –
Room temperature tensile test of Cu/Nb-Ti
composite superconductors
FOREWORD
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all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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 61788-6 has been prepared by IEC technical committee 90:
Superconductivity.
This second edition cancels and replaces the first edition published in 2000. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– the minimum distance between grips was changed from 100 mm to 60 mm;
– accuracy and precision statement were converted to uncertainty statements.

– 4 – 61788-6 © IEC:2008(E)
The text of this standard is based on the following documents:
FDIS Report on voting
90/207/FDIS 90/209/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.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
A bilingual version of this standard may be issued at a later date.

61788-6 © IEC:2008(E) – 5 –
INTRODUCTION
The Cu/Nb-Ti superconductive composite wires currently in use are multifilamentary
composite material with a matrix that functions as a stabilizer and supporter, in which ultrafine
superconductor filaments are embedded. A Nb-40~55 mass % Ti alloy is used as the
superconductive material, while oxygen-free copper and aluminium of high purity are
employed as the matrix material. Commercial composite superconductors have a high current
density and a small cross-sectional area. The major application of the composite
superconductors is to build superconducting magnets. While the magnet is being
manufactured, complicated stresses 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, of which the windings are made.

– 6 – 61788-6 © IEC:2008(E)
SUPERCONDUCTIVITY –
Part 6: Mechanical properties measurement –
Room temperature tensile test of Cu/Nb-Ti
composite superconductors
1 Scope
This part of IEC 61788 covers a test method detailing the tensile test procedures to be carried
out on Cu/Nb-Ti superconductive composite wires at room temperature.
This test is used to measure modulus of elasticity, 0,2 % proof strength of the composite due
to yielding of the copper component, and tensile strength.
The value for percentage elongation after fracture and the second type of 0,2 % proof
strength due to yielding of the Nb-Ti component serves only as a reference (see Clauses A.1
and A.2).
The sample covered by this test procedure has a round or rectangular cross-section with an
2 2
area of 0,15 mm to 2 mm and a copper to superconductor volume ratio of 1,0 to 8,0 and
without the insulating coating.
2 Normative references
The following referenced documents are indispensable for the application 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.
IEC 60050-815, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity
ISO 376, Metallic materials – Calibration of force-proving instruments used for the verification
of uniaxial testing machines
ISO 6892, Metallic materials – Tensile testing at ambient 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 extensometers used in uniaxial testing
3 Terms and definitions
For the purposes of this document, the definitions given in IEC 60050-815 and ISO 6892, as
well as the following, apply.
3.1
tensile stress
tensile force divided by the original cross-sectional area at any moment during the test

61788-6 © IEC:2008(E) – 7 –
3.2
tensile strength
R
m
tensile stress corresponding to the maximum testing force
NOTE The symbol σ is commonly used instead of R .
UTS m
3.3
extensometer gauge length
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
g
length between grips that hold a test specimen in position before the test is started
3.5
0,2 % proof strength
R (see Figure 1)
p0,2
stress value where the copper component yields by 0,2 %
NOTE 1 The designated stress, R or R corresponds to point A or B in Figure 1, respectively. This
p0,2A p0,2B
strength is regarded as a representative 0,2 % proof strength of the composite. The second type of 0,2 % proof
strength is defined as a 0,2 % proof strength of the composite where the Nb-Ti component yields by 0,2 %, of
which value corresponds to the point C in Figure 1 as described complementarily in Annex A (see Clause A.2).
NOTE 2 The symbol σ is commonly used instead of R .
0.2 p0.2
3.6
modulus of elasticity
E
gradient of the straight portion of the stress-strain curve in the elastic deformation region
4 Principle
The test consists of straining a test piece by tensile force, generally to fracture, for the
purpose of determining the mechanical properties defined in Clause 3.
5 Apparatus
5.1 Conformity
The test machine and the extensometer 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 strain rate shall be used. Grips
shall have a structure and strength appropriate for the test specimen and shall be constructed
to provide an effective 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 on them during
testing. Gripping may be a screw type, or pneumatically or hydraulically actuated.

– 8 – 61788-6 © IEC:2008(E)
5.3 Extensometer
The weight of the extensometer shall be 30 g or less, so as not to affect the mechanical
properties of the superconductive wire. Care shall also be taken to prevent bending moments
from being applied to the test specimen (see Clause A.3).
6 Specimen preparation
6.1 Straightening the specimen
When a test specimen sampled from a bobbin needs to be straightened, a method shall be
used that affects the material as little as possible.
6.2 Length of specimen
The total length of the test specimen shall be the inward distance between grips plus 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, that coating shall be
removed. Either a chemical or mechanical method shall be used, with care taken not to
damage the specimen surface (see Clause A.4).
6.4 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 a round wire shall be calculated using the arithmetic mean of the two
orthogonal diameters. The cross-sectional area of a rectangular wire 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.5).
7 Testing conditions
7.1 Specimen gripping
The test specimen shall be mounted on the grips of the tensile machine. At this time, the test
specimen and tensile loading axis must be on a single 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.6).
7.2 Pre-loading and setting of extensometer
If there is any slack in the specimen when it is mounted, a force between one-tenth and one-
third of the 0,2 % proof strength of the composite shall be applied to take up the slack before
the extensometer is mounted. When mounting the extensometer, care shall be taken to
prevent the test specimen from being deformed. The extensometer shall be mounted at the
centre between the grips, aligning the measurement direction with the specimen axis
direction. After installation, loading shall be zeroed.
7.3 Testing speed
–4 –3
The strain rate shall be 10 /s to 10 /s during the test using the extensometer. After
–3
removing the extensometer, the strain rate may be increased to a maximum of 10 /s.

61788-6 © IEC:2008(E) – 9 –
7.4 Test
The tensile machine shall be started after the testing speed has been set to the specified
level. The signals from the extensometer and load cell shall be plotted on the abscissa and
ordinate, respectively, as shown in Figure 1. When the total strain has reached approximately
2 %, reduce the force by approximately 10 % and then remove the extensometer. The step of
removing the extensometer can be omitted in the case where the extensometer is robust
enough not to be damaged by the total strain and the fracture shock of this test. At this time,
care shall be taken to prevent unnecessary force from being applied to the test specimen.
Then, increase loading again to the previous level and continue testing until the test specimen
fractures. Measurement shall be made again if a slip or fracture occurs on the gripped
surfaces of the test specimen.
8 Calculation of results
8.1 Tensile strength (R )
m
Tensile strength R shall be the maximum force divided by the original cross-sectional area of
m
the wire before loading.
8.2 0,2 % proof strength (R and R )
p0,2A p0,2B
The 0,2 % proof strength of the composite due to yielding of the copper component is
determined in two ways from the loading and unloading stress-strain curves as shown in
Figure 1. The 0,2 % proof strength under loading R shall be determined as follows: the
p0,2A
initial linear portion under loading of the stress-strain curve is moved 0,2 % in the strain axis
(0,2 % offset line under loading) and the point A at which this linear line intersects the stress-
strain curve (point A) shall be defined as the 0,2 % proof strength under loading. The 0,2 %
proof strength of the composite under unloading R shall be determined as follows: the
p0,2B
linear portion under unloading is to be 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. This measurement shall be discarded if the 0,2 % proof
strength of the composite is less than three times the pre-load specified in 7.2.
Each 0,2 % proof strength shall be calculated using formula (1) given below:
R = F / S (1)
p0,2i i o
where
R is the 0,2 % proof strength (MPa) at each point;
p0,2i
F is the force (N) at each point;
i
S is the original cross-sectional area (in square millimetres) of the test specimen;
...