1、BSI Standards Publication BS ISO 6892-4:2015 Metallic materials Tensile testing Part 4: Method of test in liquid heliumBS ISO 6892-4:2015 BRITISH STANDARD National foreword This British Standard is the UK implementation of ISO 6892-4:2015. It supersedes BS ISO 19819:2004 which is withdrawn. The UK p
2、articipation in its preparation was entrusted to Technical Committee ISE/101/1, Uniaxial testing. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are resp
3、onsible for its correct application. The British Standards Institution 2015. Published by BSI Standards Limited 2015 ISBN 978 0 580 84558 1 ICS 77.040.10 Compliance with a British Standard cannot confer immunity from legal obligations. This British Standard was published under the authority of the S
4、tandards Policy and Strategy Committee on 31 October 2015. Amendments issued since publication Date T e x t a f f e c t e dBS ISO 6892-4:2015 ISO 2015 Metallic materials Tensile testing Part 4: Method of test in liquid helium Matriaux mtalliques Essai de traction Partie 4: Mthode dessai dans lhlium
5、liquide INTERNATIONAL STANDARD ISO 6892-4 First edition 2015-10-01 Reference number ISO 6892-4:2015(E)BS ISO 6892-4:2015ISO 6892-4:2015(E)ii ISO 2015 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2015, Published in Switzerland All rights reserved. Unless otherwise specified, no part of this p
6、ublication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the c
7、ountry of the requester. ISO copyright office Ch. de Blandonnet 8 CP 401 CH-1214 Vernier, Geneva, Switzerland Tel. +41 22 749 01 11 Fax +41 22 749 09 47 copyrightiso.org www.iso.orgBS ISO 6892-4:2015ISO 6892-4:2015(E)Foreword iv Introduction v 1 Scope . 1 2 Normative references 1 3 T erms and defini
8、tions . 1 4 Symbols and designations 4 5 Principle 4 6 Apparatus . 4 7 Test piece 7 7.1 General . 7 7.2 Standard round bar test piece . 7 7.3 Alternatives 7 7.4 Sub-size test pieces . 7 7.5 Sampling . 7 8 Testing conditions . 8 8.1 Test piece installation . 8 8.2 Cooling procedure 8 8.3 Rate of test
9、ing 8 8.3.1 Rate limit. 8 8.3.2 Rate selection 8 9 Procedure. 9 9.1 Determination of original cross-sectional area (S o ) . 9 9.2 Marking of the original gauge length (L o ) . 9 9.3 Determination of percentage elongation after fracture (A) . 9 9.4 Determination of the 0,2 % proof-strength, plastic e
10、xtension (R p0,2 ) 9 9.5 Discontinuous yielding strength (R i ) 10 9.6 Tensile strength (R m ) 10 9.7 Reduction of area (Z) 10 10 Test report 10 11 Measurement uncertainty .10 Annex A (informative) Examples of test pieces for tensile testing in liquid helium 11 Bibliography .13 ISO 2015 All rights r
11、eserved iii Contents PageBS ISO 6892-4:2015ISO 6892-4:2015(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical comm
12、ittees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
13、International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for th
14、e different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives). Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. I
15、SO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents). Any trade name used in this doc
16、ument is information given for the convenience of users and does not constitute an endorsement. For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Tra
17、de (TBT) see the following URL: Foreword - Supplementary information The committee responsible for this document is ISO/TC 164, Mechanical testing of metals, Subcommittee SC 1, Uniaxial testing. This first edition of ISO 6892-4 cancels and replaces ISO 19819:2004, which has been technical revised. I
18、SO 6892 consists of the following parts, under the general title Metallic materials Tensile testing: Part 1: Method of test at room temperature Part 2: Method of test at elevated temperature Part 3: Method of test at low temperature Part 4: Method of test in liquid heliumiv ISO 2015 All rights reser
19、vedBS ISO 6892-4:2015ISO 6892-4:2015(E) Introduction The force-time and force-extension records for alloys tested in liquid helium using displacement control are serrated. Serrations are formed by repeated bursts of unstable plastic flow and arrests. The unstable plastic flow (discontinuous yielding
20、) is a free-running process occurring in localized regions of the parallel length at higher rates than nominal strain rates with internal test piece heating. Examples of serrated stress-strain curves for a typical austenitic stainless steel with discontinuous yielding are shown in Figure 1. Key 1 st
21、ress, N/mm 2 2 strain 3 temperature, K Figure 1 Example of typical stress-strain curves and test piece temperature histories at four different nominal strain rates, for AISI 304L stainless steel tested in liquid helium A constant test piece temperature cannot be maintained at all times during testin
22、g in liquid helium. Due to adiabatic heating, the test piece temperature at local regions in the parallel length rises temporarily above 4 K during each discontinuous yielding event (see Figure 1). The number of events and the magnitude of the associated force drops are a function of the material co
23、mposition and other factors such as test piece size and test speed. Typically, altering the mechanical test variables can change the type of serration but not eliminate the discontinuous yielding. Therefore, tensile property measurements of alloys in liquid helium (especially tensile strength, elong
24、ation, and reduction of area) may lack the usual significance of property measurements at room temperature where deformation is more nearly isothermal and discontinuous yielding typically does not occur. Strain control is the preferred control mode (Method A, 6892-1) and displacement control is the
25、secondary method, according to Method B 6892-1. ISO 2015 All rights reserved vBS ISO 6892-4:2015BS ISO 6892-4:2015Metallic materials Tensile testing Part 4: Method of test in liquid helium 1 Scope This part of ISO 6892 specifi es th e m eth od o f te nsil e testing o f m etalli c mate rials in li qu
26、i d h eli um (the boiling point is 269 C or 4,2 K, designated as 4 K) and defines the mechanical properties that can be determined. This part of ISO 6892 may apply also to tensile testing at cryogenic temperatures (less than 196 C or 77 K), which requires special apparatus, smaller test pieces, and
27、concern for serrated yielding, adiabatic heating, and strain-rate effects. To conduct a tensile test according to this part of ISO 6892 at 4 K, the test piece installed in a cryostat is fully submerged in liquid helium (He) and tested using displacement control at a nominal strain rate of 10 3s 1or
28、less. NOTE The boiling point of the rare 3 He isotope is 3,2 K. Usually, the tests are performed in 4 He or a mixture of 3 He and 4 He with a high concentration of 4 He. Therefore, the temperature is, as designated before, 4 K. 2 Normative references The following documents, in whole or in part, are
29、 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. ISO 6892-1: 1) , Metallic materials Tensile testing Part
30、 1: Method of test at room temperature ISO 6892-3, Metallic materials Tensile testing Part 3: Method of test at low temperature ISO 7500-1 1 , Metallic materials Calibration and verification of static uniaxial testing machines Part 1: Tension/compression testing machines Calibration and verification
31、 of the force-measuring system ISO 9513, Metallic materials Calibration of extensometer systems used in uniaxial testing 3 T erms a nd definiti ons For the purpose of this document, the terms and definitions given in ISO 6892-1 and in ISO 6892-3 apply. 3.1 adiabatic heating internal heating of a tes
32、t piece resulting from deformation under conditions such that the heat generated by plastic work cannot be quickly dissipated to the surrounding cryogen 1) To be published. INTERNATIONAL ST ANDARD ISO 6892-4:2015(E) ISO 2015 All rights reserved 1BS ISO 6892-4:2015ISO 6892-4:2015(E) 3.2 axial strain
33、longitudinal strains measured at opposite or equally spaced surface locations on the sides of the longitudinal axis of symmetry of the test piece Note 1 to entry: The longitudinal strains are measured using two or more strain-sensing transducers located at the mid-length of the parallel length. 3.3
34、bending strain difference between the strain at the surface of the test piece and the axial strain Note 1 to entry: The bending strain varies around the circumference and along the parallel length of the test piece. 3.4 dewar vacuum-insulated container for cryogenic fluids 3.5 discontinuous yielding
35、 strength R i peak stress at the initiation of the first measurable serration on the stress-strain curves 3.6 tensile cryostat test apparatus for applying tensile forces to test pieces in cryogenic environments Note 1 to entry: See Figure 2.2 ISO 2015 All rights reservedBS ISO 6892-4:2015ISO 6892-4:
36、2015(E) 1 12 11 10 9 8 7 2 3 4 5 6 Key 1 force 7 extensometer 2 room temperature load frame 8 vacuum-insulated dewar 3 vent 9 dewar seal 4 vacuum-insulated transfer tube 10 electrical feed-through 5 cryogenic load frame 11 load cell 6 test piece 12 pull rod Figure 2 Schematic illustration of typical
37、 cryostat for tensile testing at 4 K ISO 2015 All rights reserved 3BS ISO 6892-4:2015ISO 6892-4:2015(E) 4 Symbols and designations Symbols and corresponding designations are given in Table 1. Table 1 Symbols and designations Symbol Unit Designation d o mm diameter of the parallel length of a cylindr
38、ical test piece or diameter of a circular wire L o mm original gauge length L u mm final gauge length after fracture L c mm parallel length L e mm extensometer gauge length S o mm 2 original cross-sectional area of the parallel length S u mm 2 minimum cross-sectional area after fracture (final cross
39、-sectional area) Z % percentage reduction of area: A % percentage elongation after fracture: F m N maximum force R m N/mm 2 tensile strength R p0,2 N/mm 2 0,2 % proof strength, plastic extension R i N/mm 2 discontinuous yielding strength 5 Principle The test consists of straining a test piece in liq
40、uid helium by a tensile force, generally to fracture, for the purpose of determining one or more of the mechanical properties defined in Clause 4. 6 Apparatus 6.1 Testing machine The testing machine shall be verified and calibrated in accordance with ISO 7500-1 and shall be of at least class 1, unle
41、ss otherwise specified in the product standard. 6.1.1 Testing machine compliance Compliance (displacement per unit of applied force of the apparatus itself) of the test facility (tensile machine and the cryogenic load frame) should be known. Measure the compliance by coupling the load train with a r
42、igid test piece or by using a special calibration test piece. Then, measure the compliance at a low force and at the highest force used to qualify the machine, as indicated in 6.1.4. A practical procedure for the determination of the compliance respective of the stiffness is described in ISO 6892-1:
43、, Annex F. NOTE Different system compliances may result in different stress-extension curves and material properties (e.g. elongation after fracture, tensile strength) of the material because a larger discontinuous deformation occurs in a lower compliance test facility.4 ISO 2015 All rights reserved
44、BS ISO 6892-4:2015ISO 6892-4:2015(E) 6.1.2 System design Typically, alloys in liquid helium exhibit double or triple their ambient strengths at ambient temperature. For the same test piece geometry, higher forces shall be applied to the cryostat, test piece, load train members, and grips at cryogeni
45、c temperatures. Since many conventional test machines have a maximum force of 100 kN or less, it is recommended that the apparatus be designed to accommodate one of the small test pieces cited in 7.2. 6.1.3 Construction materials Many construction materials, including the vast majority of ferritic s
46、teels, are brittle at 4 K. To prevent service failures, fabricate the grips and other load train members using strong, tough, cryogenic alloys. Materials that have low thermal conductivity are desirable to reduce heat flow. Austenitic stainless steels (AISI 304LN), maraging steels (200, 250, or 300
47、grades, with nickel plating to prevent rust), wrought nickel-base superalloys, and titanium alloys (Ti-6Al-4V and Ti-5Al-2,5Sn) have been used with proper design, for grips, pull rods, and cryostat frames. Non-metallic materials (for example, glass- epoxy composites) are excellent insulators and are
48、 sometimes used for compression members. 6.1.4 Alignment Proper system alignment is essential to minimize bending strains in the tensile tests. The machine and grips should be capable of applying force to a precisely machined calibration test piece so that the maximum bending strain should be accord
49、ing to ISO 23788 class 10. Reduce bending strain to an acceptable level by making proportional adjustments to a cryostat with alignment capability, or by using spacing shims to compensate an unadjustable fixture. Calculate the strain based on readings taken while the calibration test piece is subjected to a low force, as well as at the highest force for which the machine and load train are being qualified. Qualify the apparatus by making axiality meas
