SIST EN 61788-6:2011
(Main)Superconductivity - Part 6: Mechanical properties measurment - Room temperature tensile test of Cu/Nb-Ti composite superconductors
Superconductivity - Part 6: Mechanical properties measurment - Room temperature tensile test of Cu/Nb-Ti composite superconductors
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 area of 0,15 mm2 to 2 mm2 and a copper to superconductor volum
Supraleitfähigkeit - Teil 6: Messung der mechanischen Eigenschaften - Messung der Zugfestigkeit von Cu/NbTi-Verbundsupraleitern bei Raumtemperatur
Supraconductivité - Partie 6: Mesures des propriétés mécaniques - Essai de traction à température ambiante des supraconducteurs composites de Cu/Nb-Ti
La CEI 61788-6:2011 spécifie une méthode d'essai détaillant les modes opératoires d'essai de traction à exécuter sur des fils composites supraconducteurs de Cu/Nb-Ti à température ambiante. Cet essai est utilisé pour mesurer le module d'élasticité, la charge d'épreuve à 0,2 % du composite due à la déformation du composant de cuivre et à la résistance à la traction. La valeur du pourcentage d'allongement après fracture et le second type de charge d'épreuve à 0,2 % due à la déformation du composant en Nb-Ti ne servent que de référence. L'échantillon spécifié par le présent mode opératoire d'essai a une section transversale circulaire ou rectangulaire avec une surface de 0,15 mm2 à 2 mm2 et un rapport volumique entre le cuivre et le supraconducteur de 1,0 à 8,0 et sans revêtement isolant. Cette troisième édition annule et remplace la deuxième édition parue en 2008. Elle constitue une révision technique avec l'ajout d'une Annexe C décrivant un exemple spécifique d'estimation d'incertitude concernant les essais mécaniques.
Superprevodnost - 6. del: Meritve mehanskih lastnosti - Natezni preskus za superprevodnike iz kompozita Cu/Nb-Ti pri sobni temperaturi
Ta del IEC 61788 zajema preskusno metodo, ki podrobneje določa postopke nateznega preskusa, ki se izvaja na superprevodniških žicah iz kompozita Cu/Nb-Ti pri sobni temperaturi. Ta preskus se uporablja za merjenje modula elastičnosti, meje tečenja kompozita pri 0,2 % zaradi prožnosti bakrene komponente in natezne trdnosti. Vrednost odstotnega podaljšanja po lomu in druga vrsta meje tečenja pri 0,2 % zaradi prožnosti komponente Nb-Ti se uporabljata le kot referenca (glej točko A.1 in A.2). Vzorec, ki ga zajema ta preskusni postopek, ima okrogel ali pravokoten prečni prerez s površino med 0,15 mm2 in 2 mm2 ter prostorninsko razmerje superprevodnika med 1,0 in 8,0 ter brez izolacijske prevleke.
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Superprevodnost - 6. del: Meritve mehanskih lastnosti - Natezni preskus za superprevodnike iz kompozita Cu/Nb-Ti pri sobni temperaturiSupraleitfähigkeit - Teil 6: Messung der mechanischen Eigenschaften - Messung der Zugfestigkeit von Cu/NbTi-Verbundsupraleitern bei RaumtemperaturSupraconductivité - Partie 6: Mesures des propriétés mécaniques - Essai de traction à température ambiante des supraconducteurs composites de Cu/Nb-TiSuperconductivity - Part 6: Mechanical properties measurment - Room temperature tensile test of Cu/Nb-Ti composite superconductors77.040.10Mehansko preskušanje kovinMechanical testing of metals29.050Superprevodnost in prevodni materialiSuperconductivity and conducting materialsICS:Ta slovenski standard je istoveten z:EN 61788-6:2011SIST EN 61788-6:2011en01-oktober-2011SIST EN 61788-6:2011SLOVENSKI
STANDARD
SIST EN 61788-6:2011
EUROPEAN STANDARD EN 61788-6 NORME EUROPÉENNE
EUROPÄISCHE NORM August 2011
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2011 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61788-6:2011 E
ICS 29.050; 77.040.10 Supersedes EN 61788-6:2008
English version
Superconductivity -
Part 6: Mechanical properties measurement -
Room temperature tensile test of Cu/Nb-Ti composite superconductors (IEC 61788-6:2011)
Supraconductivité -
Partie 6: Mesure des propriétés mécaniques -
Essai de traction à température ambiante des supraconducteurs composites de Cu/Nb-Ti (CEI 61788-6:2011)
Supraleitfähigkeit -
Teil 6: Messung der mechanischen Eigenschaften -
Messung der Zugfestigkeit von Cu/Nb-Ti-Verbundsupraleitern bei Raumtemperatur(IEC 61788-6:2011)
This European Standard was approved by CENELEC on 2011-08-15. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.
SIST EN 61788-6:2011
EN 61788-6:2011 - 2 -
Foreword The text of document 90/267/FDIS, future edition 3 of IEC 61788-6, prepared by IEC TC 90, Superconductivity was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN 61788-6:2011. The following dates are fixed: • latest date by which the document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2012-05-15 • latest date by which the national standards conflicting with the document have to be withdrawn (dow) 2014-08-15
This document supersedes EN 61788-6:2008. EN 61788-6:2011 includes the following significant technical changes with respect to EN 61788-6:2008:
– specific example of uncertainty estimation related to mechanical tests was supplemented as Annex C.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.
Endorsement notice The text of the International Standard IEC 61788-6:2011 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated: IEC 61788-5 NOTE
Harmonized as EN 61788-5. ISO 3611:2010 NOTE
Harmonized as EN ISO 3611:2010 (not modified).
SIST EN 61788-6:2011
- 3 - EN 61788-6:2011 Annex ZA (normative)
Normative references to international publications with their corresponding European publications
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.
NOTE
When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
Publication Year Title EN/HD Year
IEC 60050-815 - International Electrotechnical Vocabulary -
Part 815: Superconductivity - -
ISO 376 - Metallic materials - Calibration of force-proving instruments used for the verification of uniaxial testing machines EN ISO 376 -
ISO 6892-1 - Metallic materials - Tensile testing -
Part 1: Method of test at room temperature
EN ISO 6892-1 -
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 EN ISO 7500-1 -
ISO 9513 - Metallic materials - Calibration of extensometers used in uniaxial testing EN ISO 9513 -
SIST EN 61788-6:2011
SIST EN 61788-6:2011
IEC 61788-6 Edition 3.0 2011-07 INTERNATIONAL STANDARD NORME INTERNATIONALE Superconductivity –
Part 6: Mechanical properties measurement – Room temperature tensile test
of Cu/Nb-Ti composite superconductors
Supraconductivité –
Partie 6: Mesure des propriétés mécaniques – Essai de traction à température ambiante des supraconducteurs composites de Cu/Nb-Ti
INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE V ICS 29.050; 77.040.10 PRICE CODE CODE PRIX ISBN 978-2-88912-580-7
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale ®
SIST EN 61788-6:2011 colourinside
– 2 – 61788-6 IEC:2011 CONTENTS FOREWORD . 4 INTRODUCTION . 6 1 Scope . 7 2 Normative references . 7 3 Terms and definitions . 7 4 Principle . 8 5 Apparatus . 8 5.1 Conformity . 8 5.2 Testing machine . 8 5.3 Extensometer . 9 6 Specimen preparation. 9 6.1 Straightening the specimen . 9 6.2 Length of specimen . 9 6.3 Removing insulation . 9 6.4 Determination of cross-sectional area (So) . 9 7 Testing conditions . 9 7.1 Specimen gripping . 9 7.2 Pre-loading and setting of extensometer . 9 7.3 Testing speed. 9 7.4 Test . 10 8 Calculation of results . 12 8.1 Tensile strength (Rm) . 12 8.2 0,2 % proof strength (Rp0,2A and
Rp0,2B) . 12 8.3 Modulus of elasticity (Eo and Ea) . 12 9 Uncertainty . 12 10 Test report. 13 10.1 Specimen . 13 10.2 Results . 13 10.3 Test conditions . 13 Annex A (informative)
Additional information relating to Clauses 1 to 10 . 14 Annex B (informative)
Uncertainty considerations . 19 Annex C (informative)
Specific examples related to mechanical tests . 23 Bibliography . 32
Figure 1 – Stress-strain curve and definition
of modulus of elasticity and 0,2 % proof strengths . 11 Figure A.1 – An example of the light extensometer, where R1 and R3 indicate the corner radius . 15 Figure A.2 – An example of the extensometer provided with balance weight and vertical specimen axis . 16 Figure C.1 – Measured stress versus strain curve of the rectangular cross section NbTi wire and the initial part of the curve . 23 Figure C.2 – 0,2 % offset shifted regression line, the raw stress versus
strain curve and the original raw data of stress versus strain . 29
SIST EN 61788-6:2011
61788-6 IEC:2011 – 3 – Table B.1 – Output signals from two nominally identical extensometers . 20 Table B.2 – Mean values of two output signals . 20 Table B.3 – Experimental standard deviations of two output signals. 20 Table B.4 – Standard uncertainties of two output signals . 21 Table B.5 – Coefficient of variations of two output signals. 21 Table C.1 – Load cell specifications according to manufacturer’s data sheet . 26 Table C.2 – Uncertainties of displacement measurement . 26 Table C.3 – Uncertainties of wire width measurement . 27 Table C.4 – Uncertainties of wire thickness measurement . 27 Table C.5 – Uncertainties of gauge length measurement . 27 Table C.6 – Calculation of stress at 0 % and at 0,1 % strain using the zero offset regression line as determined in Figure C.1b). . 28 Table C.7 – Linear regression equations computed for the three shifted lines and for the stress versus strain curve in the region where the lines intersect . 29 Table C.8 – Calculation of strain and stress at the intersections of the three shifted lines with the stress strain curve . 30 Table C.9 – Measured stress versus strain data and the computed
stress based on a linear fit to the data in the region of interest . 31
SIST EN 61788-6:2011
– 4 – 61788-6 IEC:2011 INTERNATIONAL ELECTROTECHNICAL COMMISSION _____________
SUPERCONDUCTIVITY –
Part 6: Mechanical properties measurement –
Room temperature tensile test of Cu/Nb-Ti
composite superconductors
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, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
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 61788-6 has been prepared by IEC technical committee 90: Superconductivity. This third edition cancels and replaces the second edition published in 2008. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: – specific example of uncertainty estimation related to mechanical tests was supplemented as Annex C. SIST EN 61788-6:2011
61788-6 IEC:2011 – 5 – The text of this standard is based on the following documents: FDIS Report on voting 90/267/FDIS 90/278/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 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.
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.
SIST EN 61788-6:2011
– 6 – 61788-6 IEC:2011 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. SIST EN 61788-6:2011
61788-6 IEC:2011 – 7 – 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 area of 0,15 mm2 to 2 mm2 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 – Part 815: Superconductivity 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 extensometers used in uniaxial testing 3 Terms and definitions For the purposes of this document, the definitions given in IEC 60050-815 and ISO 6892-1, 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 SIST EN 61788-6:2011
– 8 – 61788-6 IEC:2011 3.2
tensile strength
Rm tensile stress corresponding to the maximum testing force NOTE The symbol σUTS is commonly used instead of Rm. 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
Lg length between grips that hold a test specimen in position before the test is started 3.5
0,2 % proof strength
Rp0,2 (see Figure 1) stress value where the copper component yields by 0,2 %
NOTE 1 The designated stress, Rp0,2A or Rp0,2B corresponds to point A or B in Figure 1, respectively. This 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 %, the value of which corresponds to the point C in Figure 1 as described complementarily in Annex A (see Clause A.2). NOTE 2 The symbol σ0,2 is commonly used instead of Rp0,2. 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 cross-head speed 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. SIST EN 61788-6:2011
61788-6 IEC:2011 – 9 – 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 (So) 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 not greater than one-tenth 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
The strain rate shall be 10–4/s to 10–3/s during the test using the extensometer. After removing the extensometer, the strain rate may be increased to a maximum of 10–3/s. SIST EN 61788-6:2011
– 10 – 61788-6 IEC:2011 7.4 Test The tensile machine shall be started after the cross-head 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. SIST EN 61788-6:2011
61788-6 IEC:2011 – 11 –
0 100 200 300 400 500 600 700 0 0,5 1,0 1,5 2,0 Stress
(MPa) Strain
(%) 0,2 A B C D E 1 2 3 4 5 6 εa IEC
1597/11
Key Initial loading line Line shifted by an offset of 0,2% parallel to the initial loading line Unloading line Line shifted by an offset of 0,2% parallel to the unloading line Second linear part of loading line Line shifted by an offset of 0,2% parallel to the second linear loading line NOTE 1 When the total strain has reached ~2 % (point E), the load is reduced by 10 % and the extensometer is removed, if necessary. Then, the load is increased again. NOTE 2 The slope of the initial loading line is usually smaller than that of the unloading line. Then, two lines can be drawn from the 0,2 % offset point on the abscissa to obtain 0,2 % proof strength of the composite due to yielding of the copper component. Point A is obtained from the initial loading line, and Point B is obtained from the unloading line. Point C is the second type of 0,2 % proof strength of the composite where the Nb-Ti component yields. Figure 1 – Stress-strain curve and definition
of modulus of elasticity and 0,2 % proof strengths SIST EN 61788-6:2011
– 12 – 61788-6 IEC:2011 8 Calculation of results 8.1 Tensile strength (Rm) Tensile strength Rm shall be the maximum force divided by the original cross-sectional area of the wire before loading. 8.2 0,2 % proof strength (Rp0,2A and
Rp0,2B) 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 Rp0,2A shall be determined as follows: the 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 shall be defined as the 0,2 % proof strength under loading. The 0,2 % proof strength of the composite under unloading Rp0,2B shall be determined as follows: the 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:
Rp0,2i = Fi / So (1) where
Rp0,2i
is the 0,2 % proof strength (MPa) at each point;
Fi
is the force (N) at each point;
So
is the original cross-sectional area (in square millimetres) of the test specimen; Further, i = A and B. 8.3 Modulu
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