1、Rubber, vulcanized Determination of stress in tension upon heatingCaoutchouc vulcanis Dtermination de la contrainte en traction lors du chauffage ISO 2011Reference numberISO 12493:2011(E)First edition2011-07-15ISO12493INTERNATIONAL STANDARDISO 12493:2011(E)COPYRIGHT PROTECTED DOCUMENT ISO 2011All ri
2、ghts reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of t
3、he requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in Switzerlandii ISO 2011 All rights reservedISO 12493:2011(E)Contents PageForeword ivIntroduction v1 Scope 12 Normative references .13 Terms a
4、nd definitions .14 Principle .25 Apparatus 25.1 Thermal-stress testing machine 25.2 Temperature-controlled chamber 35.3 Thickness- and width-measuring devices 36 Calibration .37 Test piece .37.1 Dimensions .37.2 Number of test pieces 47.3 Time lapse between moulding and testing .47.4 Conditioning .4
5、8 Test conditions .48.1 Temperature 48.2 Pre-strain .49 Procedure 510 Expression of results .511 Precision 712 Test report .7Annex A (normative) Calibration schedule 9Bibliography .11 ISO 2011 All rights reserved iiiForewordISO (the International Organization for Standardization) is a worldwide fede
6、ration 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 commi
7、ttee. 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.International Standards are drafted in accordanc
8、e with the rules given in the ISO/IEC Directives, Part 2.The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires ap
9、proval by at least 75 % of the member bodies casting a vote.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.ISO 12493 was prepared by Technical Commit
10、tee ISO/TC 45, Rubber and rubber products, Subcommittee SC 2, Testing and analysis.ISO 12493:2011(E)iv ISO 2011 All rights reservedIntroductionVulcanized rubber held under a constant stress will contract as the test temperature is raised, while a test piece held under a constant strain will develop
11、an increased stress. These are features of the Gough-Joule effect in rubber and, unless they are taken into account at the design stage, any resulting changes in forces and dimensions can affect the performance of some products, such as rotary seals, used at high temperatures and high strains (see R
12、eference 1 in the Bibliography).This International Standard describes a test method for the determination of the change in tensile stress that results from an increase in test temperature.ISO 12493:2011(E) ISO 2011 All rights reserved vINTERNATIONAL STANDARD ISO 12493:2011(E)Rubber, vulcanized Deter
13、mination of stress in tension upon heating1 ScopeThis International Standard specifies a method for measuring the stress in tension which is developed in vulcanized rubber when it is heated (thermal stress). The thermal stress is measured for various pre-strain and temperature conditions as a functi
14、on of time.2 Normative referencesThe 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.ISO 5893, Rubber
15、and plastics test equipment Tensile, flexural and compression types (constant rate of traverse) SpecificationISO 18899:2004, Rubber Guide to the calibration of test equipmentISO 23529, Rubber General procedures for preparing and conditioning test pieces for physical test methods3 Terms and definitio
16、nsFor the purposes of this document, the following terms and definitions apply.3.1thermal stressTforce per initial unit area which is developed in the test piece upon heatingNOTE It is expressed in N/m2or Pa.3.2maximum thermal stressmax. Tpeak value of the thermal stress recorded during the test3.3t
17、hermal stress after a specified timeT, tstress induced in the test piece upon heating for a specified time t3.4pre-strainelongation to which the test piece is subjected at the beginning of the testNOTE It is expressed as pre-strain = l llf iiwhereliis the initial length;lfis the length after elongat
18、ion. ISO 2011 All rights reserved 13.5pre-stressforce per initial unit area which results from the pre-strainNOTE It is expressed in N/m2or Pa.4 PrincipleA test piece is held at a constant pre-strain in a tensile mode at standard laboratory temperature. When the pre-stress resulting from the given p
19、re-strain has reached an apparent equilibrium value, the temperature of the test piece is increased. The thermal stress developed at the elevated temperature is measured for various pre-strain conditions as a function of time.5 Apparatus5.1 Thermal-stress testing machineAn example of a test machine
20、for measuring the thermal stress developed in rubbery materials when heated is shown in Figure 1. Two clamps hold the test piece in a temperature-controlled chamber, with the upper clamp connected to a load cell and the bottom clamp connected to a crosshead. The crosshead is moved using a screw driv
21、en by a motor to impose a pre-strain on the test piece. The thermal stress developed when the temperature is raised is transmitted to the load cell and the output is recorded to give the variation in stress as a function of time.The test machine shall comply with ISO 5893 with force measurement to c
22、lass 1 and the machine shall be capable of setting the pre-strain to within 0,1 at a speed of (20 2,5) mm/min.ISO 12493:2011(E)2 ISO 2011 All rights reserved12345678Key1 temperature-controlled chamber2 clamps3 load cell4 rod5 linear variable differential transformer6 screw7 crosshead8 motorFigure 1
23、Example of thermal-stress testing machine5.2 Temperature-controlled chamberThe temperature-controlled chamber shall be capable of raising the temperature at a rate of at least 30 C/min and maintaining the test piece at the required temperature as specified in ISO 23529. A suitable volume for the cha
24、mber is 3 litres to 5 litres. A temperature-sensing device shall be located within the chamber near the test piece.5.3 Thickness- and width-measuring devicesInstruments for measuring the thickness and width of the test piece shall be in accordance with ISO 23529.6 CalibrationThe test apparatus shall
25、 be calibrated in accordance with the schedule given in Annex A.7 Test piece7.1 DimensionsThe test piece shall be prepared by cutting from moulded flat sheet and shall have the shape and dimensions shown in Figure 2. In addition, the thickness shall be (2 0,2) mm. The test piece shall have a smooth
26、surface and be free from irregularities.ISO 12493:2011(E) ISO 2011 All rights reserved 3Dimensions in millimetresFigure 2 Test piece for thermal-stress measurements7.2 Number of test piecesAt least three test pieces shall be used for each set of test conditions.7.3 Time lapse between moulding and te
27、stingUnless otherwise specified, the following requirements shall be observed (see ISO 23529): For all test purposes, the minimum time between moulding and testing shall be 16 h. For non-product tests, the maximum time between vulcanization and testing shall be four weeks and, for evaluations intend
28、ed to be comparable, the tests, as far as possible, shall be carried out after the same time interval. For product tests, whenever possible, the time between vulcanization and testing shall not exceed three months. In other cases, tests shall be made within two months of the date of receipt of the p
29、roduct by the customer.7.4 ConditioningTest pieces shall be protected from light as completely as possible during the interval between vulcanization and testing.Test pieces shall be conditioned at a standard laboratory temperature for at least 3 h immediately before being measured and tested.If the
30、test is to be carried out at a starting temperature other than a standard laboratory temperature, the test pieces shall be conditioned at the test temperature immediately prior to testing for a period sufficient to ensure that they have reached the test temperature (see ISO 23529).8 Test conditions8
31、.1 TemperatureThe elevated temperatures to be used shall be selected from those specified in ISO 23529 unless otherwise necessary for technical reasons. Recommended test temperatures are 60 C, 100 C and 140 C.8.2 Pre-strainA minimum of three pre-strains at each temperature shall be selected. Recomme
32、nded pre-strains are 0,2, 0,4 and 0,6.ISO 12493:2011(E)4 ISO 2011 All rights reserved9 ProcedureMount a test piece in the clamps at a standard laboratory temperature and elongate it to the required pre-strain by movement of the crosshead at a speed of (20 2,5) mm/min, as shown in Figure 3. Hold the
33、test piece at the constant pre-strain until the pre-stress resulting from the pre-strain reaches an apparent equilibrium value. This will be after about 30 min. Then, reset the load cell to zero and increase the temperature to the required test temperature. Start recording the thermal stress immedia
34、tely after the heating begins (designated as zero time). Monitor the development and decay of the thermal stress as a function of time. The minimum duration of the test shall be 30 min.Unless otherwise specified, carry out the test to obtain results at a minimum of three temperatures, with three pre
35、-strains at each temperature.Figure 3 Schematic diagram of a test piece with clamps at a constant pre-strain10 Expression of resultsPlot the thermal stress in the test piece as a function of time. From the graph, obtain the maximum thermal stress, the time to reach the maximum thermal stress, and th
36、e thermal stress at a specified time, which shall be taken as 20 min unless otherwise specified.An example of the thermal stress of an unfilled natural rubber (NR) vulcanizate at a pre-strain of 0,4 is shown in Figure 4 as a function of time at three different temperatures.ISO 12493:2011(E) ISO 2011
37、 All rights reserved 5t, min0 5 10 15 20 25 30T,MPa-0,10-0,050,000,050,10100 C60 C140 CFigure 4 Thermal stress at various temperatures of an unfilled NR vulcanizate at a pre-strain of 0,4Another example of the thermal stress of an unfilled NR vulcanizate at a test temperature of 100 C is shown in Fi
38、gure 5 as a function of time at three different pre-strains.ISO 12493:2011(E)6 ISO 2011 All rights reservedt, min0 5 10 15 20 25 30-0,10-0,050,000,050,10321T,MPaKey1 pre-strain 0,22 pre-strain 0,43 pre-strain 0,6Figure 5 Thermal stress at various pre-strains of an unfilled NR vulcanizate at a test t
39、emperature of 100 C11 PrecisionNo precision data are currently available for this method.12 Test reportThe test report shall include the following information:a) a full description of the sample and its origin;b) a full reference to the test method used, i.e. the number of this International Standar
40、d;c) test details:1) the standard laboratory temperature used,2) the time and temperature of conditioning prior to the test,3) the test temperatures used,4) the pre-strains used,ISO 12493:2011(E) ISO 2011 All rights reserved 75) details of any procedures not specified in this International Standard;
41、d) test results:1) the number of test pieces used,2) the graph(s) plotted of thermal stress against time,3) the mean values of the individual results from the graph(s) maximum thermal stress (max. T), time to maximum thermal stress, and thermal stress after a specified time (T, t);e) the date of the
42、 test.ISO 12493:2011(E)8 ISO 2011 All rights reservedAnnex A (normative) Calibration scheduleA.1 InspectionBefore any calibration is undertaken, the condition of the items to be calibrated shall be ascertained by inspection and recorded in any calibration report or certificate. It shall be reported
43、whether calibration is carried out in the “as-received” condition or after rectification of any abnormality or fault.It shall be ascertained that the apparatus is generally fit for the intended purpose, including any parameters specified as approximate and for which the apparatus does not therefore
44、need to be formally calibrated. If such parameters are liable to change, then the need for periodic checks shall be written into the detailed calibration procedures.A.2 ScheduleVerification/calibration of the test apparatus is a mandatory part of this International Standard. However, the frequency o
45、f calibration and the procedures used are, unless otherwise stated, at the discretion of the individual laboratory, using ISO 18899 for guidance.The calibration schedule given in Table A.1 has been compiled by listing all of the parameters specified in the test method, together with the specified re
46、quirement. A parameter and requirement can relate to the main test apparatus, to part of that apparatus or to an ancillary apparatus necessary for the test.For each parameter, a calibration procedure is indicated by reference to ISO 18899, to another publication or to a procedure particular to the t
47、est method which is detailed (whenever a calibration procedure which is more specific or detailed than that in ISO 18899 is available, it shall be used in preference).The code-letter S used in the calibration schedule indicates the standard interval as given in ISO 18899.Table A.1 Calibration freque
48、ncy scheduleParameter Requirement Subclause in ISO 18899:2004Verification frequency guideNotesTest machine Complying with ISO 5893 SForce measurement Class 1 of ISO 5893 21.1 SPre-strain 0,1 15.2 SCrosshead speed (20 2,5) mm/min 23.4 SRate of increase of temperature in temperature-controlled cabinet
49、30 C/min minimum 23.6 SIn addition to the items listed in the table, use of the following is implied, all of which need calibrating in accordance with ISO 18899: timer; thermometers for monitoring the conditioning and test temperatures;ISO 12493:2011(E) ISO 2011 All rights reserved 9 instruments for determining the dimensions of the test piece.ISO 12493:2011(E)10 ISO 2011 All rights reservedBibliography1 Hong, C.K., Park, S., and Kaang, S., A test method for measuring th
