1、BSI Standards Publication BS ISO 6914:2013 Rubber, vulcanized or thermoplastic Determination of ageing characteristics by measurement of stress relaxation in tensionBS ISO 6914:2013 BRITISH STANDARD National foreword This British Standard is the UK implementation of ISO 6914:2013. It supersedes BS I
2、SO 6914:2008 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee PRI/22, Physical testing of rubber. 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 ne
3、cessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2013. Published by BSI Standards Limited 2013 ISBN 978 0 580 78733 1 ICS 83.060 Compliance with a British Standard cannot confer immunity from legal obligations. This British Standa
4、rd was published under the authority of the Standards Policy and Strategy Committee on 31 December 2013. Amendments issued since publication Date Text affectedBS ISO 6914:2013 ISO 2013 Rubber, vulcanized or thermoplastic Determination of ageing characteristics by measurement of stress relaxation in
5、tension Caoutchouc vulcanis ou thermoplastique Dtermination des caractristiques de vieillissement par mesurage de la contrainte de relaxation en traction INTERNATIONAL STANDARD ISO 6914 Fourth edition 2013-12-01 Reference number ISO 6914:2013(E)BS ISO 6914:2013ISO 6914:2013(E)ii ISO 2013 All rights
6、reserved COPYRIGHT PROTECTED DOCUMENT ISO 2013 All rights reserved. Unless otherwise specified, no part of this publication 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
7、written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerla
8、ndBS ISO 6914:2013ISO 6914:2013(E) ISO 2013 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references 1 3 Apparatus . 2 4 Test pieces . 2 4.1 Dimensions . 2 4.2 Number 2 5 Storage and conditioning . 2 6 Test conditions . 3 6.1 Duration of test . 3 6.2 Temper
9、ature of exposure . 3 7 Procedure. 3 7.1 Method A 3 7.2 Method B 4 7.3 Method C 4 8 Expression of results 5 9 Test report . 5 Annex A (normative) Calibration . 7 Bibliography 9BS ISO 6914:2013ISO 6914:2013(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation
10、 of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee.
11、International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and thos
12、e intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the 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 (s
13、ee 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. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the doc
14、ument 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 document is information given for the convenience of users and does not constitute an endorsement. For an explanation on the meaning of ISO specific terms a
15、nd expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information The committee responsible for this document is ISO/TC 45, Rubber and rubber products
16、, Subcommittee SC 2, Testing and analysis. This fourth edition cancels and replaces the third edition (ISO 6914:2008), which has been aligned with ISO 23529 and completed with details regarding dimensions, test equipment and methods.iv ISO 2013 All rights reservedBS ISO 6914:2013ISO 6914:2013(E) Int
17、roduction The stress in a rubber test piece at a given elongation changes with time as a result of a combination of simultaneous physical and chemical processes. Chemical processes predominate in the case of thin test pieces exposed to an atmosphere containing oxygen at an elevated temperature for r
18、elatively long periods of time. Thus, the ageing characteristics of the rubber can be determined by measurement of the change of stress in a thin test piece deformed in tension after periods of exposure under such conditions. There are two variants of the technique. Measurements of stress can be mad
19、e under either a) continuous strain conditions, or b) intermittent strain conditions. In the case of a), continuous strain conditions, the test piece is held in extension throughout the ageing period in the oven. In the case of b), intermittent strain conditions, the test piece is aged in the oven i
20、n the unstressed state, but, at periodic intervals, it is stretched to a fixed extended length for a short time in order to determine the stress. Hence, this latter method is a measure of the change in modulus as a function of time. NOTE 1 The terms “continuous stress relaxation” and “intermittent s
21、tress relaxation” are commonly used to describe the two principal variants of the technique. The latter term, “intermittent stress relaxation”, is a misnomer since no true relaxation of stress occurs and indeed the measured stress can increase with time. For this reason, the use of this term has bee
22、n avoided in this International Standard although it is fairly well established in the literature. In a second version of the intermittent test, the test piece is periodically removed from the accelerated ageing atmosphere and the stress is measured under normal laboratory conditions. The advantage
23、of this method is that it does not require the use of special apparatus since a conventional tensile-testing machine can be used for the measurement of stress. Measurements made in accordance with the methods described in this International Standard provide information about the structural changes t
24、hat occur in the rubber during ageing. Under continuous strain conditions, provided physical relaxation processes are not dominant, the decay of stress provides a measure of the degradative scission reactions in the network. Any new networks formed as a result of crosslinking reactions are considere
25、d to be in equilibrium at the test strain with the main network and therefore do not impose any new stresses. NOTE 2 Even under conditions conducive to chemical processes, some physical relaxation can occur. The extent to which it does so will depend on the viscoelastic characteristics of the rubber
26、 and on the test conditions and care should be exercised in the interpretation of the results. Physical relaxation is increased by fillers and will be more evident at short times and at lower temperatures. It is often found to be proportional to logarithmic time and is less temperature sensitive tha
27、n chemical relaxation. Under intermittent strain conditions, the decay of stress provides a measure of the net effect of both degradative scission and crosslinking reactions. The validity of the methods described in this International Standard depends on the uniformity of degradation in the rubber.
28、For this reason, the thickness of the test pieces used is 1,0 mm to minimize the effect of oxygen diffusion on ageing. The change in stress might be of direct interest, but the relative resistance of rubbers to ageing will depend on the properties being measured or required by the application. This
29、International Standard should therefore be regarded as complementary to ISO 188. In addition, a distinction should be made between this test and the stress relaxation in compression tests as specified in ISO 3384-1, which is primarily intended for the testing of rubbers in applications, for example
30、as seals, where resistance to stress relaxation is a functional property. ISO 2013 All rights reserved vBS ISO 6914:2013ISO 6914:2013(E) The lifetime of the material, if this is to be investigated, can be determined using the procedures described in ISO 11346. The most important factor in achieving
31、good repeatability and reproducibility when making these tests is to keep the temperature and the elongation constant during all measurements.vi ISO 2013 All rights reservedBS ISO 6914:2013INTERNATIONAL ST ANDARD ISO 6914:2013(E) Rubber, vulcanized or thermoplastic Determination of ageing characteri
32、stics by measurement of stress relaxation in tension WARNING Persons using this International Standard should be familiar with normal laboratory practice. This International Standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of
33、the user to establish appropriate safety and health practices and to ensure compliance with any national regulatory conditions. CAUTION Certain procedures specified in this International Standard might involve the use or generation of substances, or the generation of waste, that could constitute a l
34、ocal environmental hazard. Reference should be made to appropriate documentation on safe handling and disposal after use. 1 Scope This International Standard describes three methods for the measurement of the change of stress in a test piece at a given elongation for the purpose of determining the a
35、geing characteristics of a rubber. Method A is intended for measurement under continuous strain conditions. Method B is the preferred method for measurement under intermittent strain conditions. In the case of both methods A and B, a stress relaxometer is used to record the stress at the temperature
36、 of ageing. Method C is an alternative to method B for measurement under intermittent strain conditions in which the test piece is removed from the ageing environment for measurement of the stress at standard laboratory temperature. The necessary calibration schedule for this type of measurement is
37、given in Annex A. Measurements at a single elevated ageing temperature can be used for quality control purposes as a measure of heat-ageing resistance. Measurements at a number of temperatures can be used for research and development purposes to estimate long-term ageing characteristics in accordanc
38、e with the procedures described in ISO 11346. No agreement between the three methods should be inferred. The method used will depend on the purpose of the test. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for
39、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 188:2011, Rubber, vulcanized or thermoplastic Accelerated ageing and heat resistance tests ISO 5893:2002, Rubber and pl
40、astics test equipment Tensile, flexural and compression types (constant rate of traverse) Specification ISO 18899:2013, Rubber Guide to the calibration of test equipment ISO 23529, Rubber General procedures for preparing and conditioning test pieces for physical test methods ISO 2013 All rights rese
41、rved 1BS ISO 6914:2013ISO 6914:2013(E) 3 Apparatus 3.1 Stress relaxometer, (for method A or B) consisting of two grips which hold the test piece without slipping at a fixed extended length (to within 1 %) together with a means of measuring and recording the force on the test piece. The grips shall b
42、e arranged such that the test piece can be positioned in an oven. The force-measuring system mayn be, for example, a calibrated spring or electronic load cell, but it shall be accurate and stable to within 1 % of the force reading throughout the duration of the test. For method B, the stress relaxom
43、eter shall, in addition, be equipped with a device such that the test piece can be extended and relaxed at intervals. Repeated extension of the test piece shall be constant to within 1 % of the elongation. 3.2 T ensile-testing machine, (for method C) using a constant rate of traverse, operating at 5
44、0 mm/min and complying with the requirements specified in ISO 5893:2002, force class 1 (measuring force to within 1 % of the measured value). The machine shall be capable of cycling between fixed strain limits which are accurate to within 1 % of the maximum strain. The grips of the tensile-testing m
45、achine shall hold the test piece without slippage. 3.3 Oven, complying with the requirements specified for ISO 188:2011, method A (low air speed) or method B (high air speed), for ageing the test piece. 4 Test pieces 4.1 Dimensions Test pieces shall be parallel-sided strips cut from a sheet. For the
46、 tests described in this International Standard, it is vital to ensure uniform degradation in the rubber. For this reason, the thickness of the test pieces shall be (1,0 0,05) mm in order to minimize the effect of oxygen diffusion on ageing. Samples of uniform thickness of less than 1,0 mm or more t
47、han 1,0 mm can be used, but these can give different results. NOTE For temperatures above 125 C, reducing the test piece thickness to 0,5 mm will be advantageous because of the increased effect of oxygen diffusion at higher temperatures. Alternatively, product parts or complete products can be used
48、as test pieces taking into account the requirement for thickness. The other dimensions of the test pieces, i.e. width and length, shall be chosen to suit the sensitivity of the load-measuring device and the precision of the mechanism used for adjusting the strain, in order that the requirements of 3
49、.1 and 3.2 relating to the accuracy of the force and the strain are satisfied. 4.2 Number The preferred number of test pieces is three for each test temperature, but for routine and screening tests, one or two test pieces are acceptable. 5 Storage and conditioning The time interval between vulcanization and testing shall be in accordance with ISO 23529. Material and test pieces shall be protected from light as much as possible during the interval between vulcanization and testing. They shall not be allowed to come into con
