1、BRITISH STANDARD BS ISO 16241:2005 Notch tensile test to measure the resistance to slow crack growth of polyethylene materials for pipe and fitting products (PENT)ICS 23.040.20; 25.040.45 BS ISO 16241:2005 This British Standard was published under the authority of the Standards Policy and Strategy C
2、ommittee on 23 August 2005 BSI 23 August 2005 ISBN 0 580 46143 2 National foreword This British Standard reproduces verbatim ISO 16241:2005 and implements it as the UK national standard. The UK participation in its preparation was entrusted by Technical Committee PRI/88, Plastic piping systems, to S
3、ubcommittee PRI/88/4, Method of tests for plastic piping systems and components, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications re
4、ferred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary pro
5、visions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretatio
6、n, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, pages 1 to 13 and a back
7、cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments Reference number ISO 16241:2005(E)INTERNATIONAL STANDARD ISO 16241 First edition 2005-02-15 Notch tensile test to measure the resistance
8、to slow crack growth of polyethylene materials for pipe and fitting products (PENT) Essai de traction dune entaille pour mesurer la rsistance la propagation lente de fissure des polythylnes pour tubes et raccords (PENT) BS ISO 16241:2005 ii BS ISO 16241:2005 iiiContents Page Foreword iv Introduction
9、 v 1 Scope 1 2 Normative references . 1 3 Terms and definitions. 1 4 Principle . 2 5 Apparatus 2 6 Test piece preparation 4 6.1 Test piece geometry . 4 6.2 Test piece preparation 5 6.3 Test piece notching 5 6.4 Number of test pieces. 6 7 Preconditioning. 6 8 Procedure 6 8.1 Calculation of test mass.
10、 6 8.2 Loading the test piece 6 8.3 Checking temperature 7 8.4 Recording time to failure 7 8.5 Examination of failed test piece 7 9 Test report . 7 Annex A (informative) Application of the test 8 Annex B (informative) Measurement of extension 9 Annex C (informative) Notch depth 10 Annex D (informati
11、ve) Recommended minimum requirements for polyethylene 11 Annex E (informative) Precision .12 Bibliography . 13 BS ISO 16241:2005 iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing Inte
12、rnational 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. International organizations, governmental and non-governmental, in liaison wi
13、th 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 accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technic
14、al 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 approval by at least 75 % of the member bodies casting a vote. Attention is drawn t
15、o 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 16241 was prepared by Technical Committee ISO/TC 138, Plastics pipes, fittings and valves for the transport of fluids
16、, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic materials and their accessories Test methods and basic specifications. BS ISO 16241:2005 vIntroduction This test method is based on ASTM F 14731 , which was originally developed at the University of Pennsylvania. It has
17、 been used for assessing and comparing the resistance to slow crack growth of a wide range of polyethylene pipe compounds used primarily for gas applications in the USA and Europe. The test had been evaluated by ten laboratories in the USA prior to acceptance as an ASTM standard. Further work was th
18、en carried out by an ad-hoc group of ISO/TC 138/SC4, Plastics pipes and fittings for the supply of gaseous fuels, to evaluate and refine the procedure, involving six laboratories in Europe and the USA. Resistance to slow crack growth is an important consideration for polyethylene materials used for
19、pipeline applications and tests to assess this property are incorporated in pressure pipe system standards. The test is also applicable to polyethylene materials used for other pipeline applications as well as to other thermoplastics materials used for other applications. Although seen primarily as
20、a materials test, it has been applied to assess the performance of test pieces cut from pipe and fitting products and butt fusion welds. BS ISO 16241:2005 BS ISO 16241:2005 blank1Notch tensile test to measure the resistance to slow crack growth of polyethylene materials for pipe and fitting products
21、 (PENT) 1 Scope This International Standard specifies a method for determining the resistance to slow crack growth of polyethylene (PE) materials for pipes and fitting products. 2 Normative references The following referenced documents are indispensable for the application of this document. For date
22、d references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 291, Plastics Standard atmospheres for conditioning and testing ISO 293, Plastics Compression moulding of test specimens of thermoplastic materi
23、als ISO 1872-2, Plastics Polyethylene (PE) moulding and extrusion materials Part 2: Preparation of test specimens and determination of properties ISO 2818, Plastics Preparation of test specimens by machining 3 Terms and definitions For the purposes of this document, the following terms and definitio
24、ns apply. 3.1 brittle failure failure with a fracture surface which exhibits no visible permanent material deformation, e.g. stretching, elongation or necking down 3.2 ductile failure failure with a fracture surface which clearly exhibits permanent material deformation with stretching, elongation an
25、d necking down 3.3 slow crack growth slow extension of a crack with time which is of a brittle appearance 3.4 remaining ligament remaining cross section after notching and crack growth BS ISO 16241:2005 BS ISO 16241:2005 2 4 Principle To assess the resistance to slow crack growth of a material, a te
26、st piece is cut from a compression-moulded sheet. The rectangular shaped test piece containing a centre notch in one face and side notches in the same plane is subjected to a constant static tensile load at a specified test temperature. The time to failure is recorded. NOTE 1 The test may be carried
27、 out on test pieces machined from pipe and fitting products or butt welds (see Annex A). The following characteristics are described in this method: the shape and dimensions of the test piece; the notch depth and the depth of the side grooves; the number of test pieces; the test temperature of the t
28、est pieces; the method of preparation of the test pieces. The following parameters shall be specified by the referring standard (a standard making reference to this International Standard in its own provisions): the test piece thickness and notch depth if different from the preferred dimensions (see
29、 6.1); the stress to be applied to the test piece for the duration of the test; the number of test pieces if differing from the number specified in 6.4; the test temperature if differing from the value specified in this method (see 5.2). NOTE 2 The applied stress chosen is such as to preclude ductil
30、e behaviour by inducing a fracture surface which is flat, exhibiting no visible permanent material deformation (i.e. stretching, elongation or necking down). Such a surface as a result of the gradual extension of the crack with time is considered to be akin to slow crack growth. Typically, a load to
31、 give a stress level of 2,4 MPa at 80 C will produce a mode of failure related to slow crack growth in polyethylene materials. Alternative stress levels may be used providing a similar mode of failure is produced. 5 Apparatus 5.1 Test rig, consisting of the following. 5.1.1 Test machine, capable of
32、applying, via grips (see 5.1.2) an axial load on the test piece controlled with an accuracy of within 0,5 % of the calculated or applied load, e.g. a lever-loading machine, with a lever arm ratio of around 5:1 to 10:1 be applied directly using dead weights or a constant load. 5.1.2 Grips, having a l
33、ow friction universal action to prevent bending and to ensure that the load is transmitted axially through the test piece. The grips shall be designed to prevent slippage of the test piece (e.g. serrated grips). NOTE Measurement of the extension of the test piece or movement of the lever arm provide
34、s useful information. The rate of extension of the test piece will increase when initiation of the crack has occurred and will increase rapidly when failure is imminent (see Annex B). 5.2 Heating chamber or oven, where the loading frame shall be located with air circulation by a fan or other means t
35、o maintain the test piece at (80 1,0) C or an alternative test temperature specified by the referring standard. BS ISO 16241:2005 35.3 Temperature measuring device, i.e. calibrated thermometer or a thermocouple, capable of checking conformity to 5.2. NOTE Temperature is a critical parameter and meas
36、urement made remote from the test piece may not be indicative of temperature of the test piece. 5.4 Clock or timing device, for recording the elapsed time, which shall automatically stop or record the point when the test piece is deemed to fail by either fracture or excessive displacement of the gri
37、ps. 5.5 Alignment jig, as shown in Figure 1 or similar, to facilitate the alignment the grips and the test piece when it is being tightened in the grips. Key 1 screw clamps 2 test piece 3 grips Figure 1 Typical arrangement for an alignment jig 5.6 Notching apparatus, for notching the test piece (see
38、 Figure 2) so that the main notch and any side notches are coplanar and the plane of the notching is perpendicular to the tensile axis of the test piece. A blade of approximate thickness of 0,15 mm to 0,25 mm shall be used for preparing the notch. The notch-machining equipment shall have a blade pen
39、etration speed of not more than 0,25 mm/min and be capable of producing a specified notch depth to within 0,1 mm. NOTE The indicated notch depth can be checked by notching and measurement of a dummy test piece. 5.7 Microscope, suitable for measuring the notch depth and examining the fracture surface
40、. 4 Key 1 test piece 2 razor blade 3 guides Figure 2 Typical arrangement for apparatus for notching test pieces 6 Test piece preparation 6.1 Test piece geometry The test piece geometry is shown in Figure 3, with a preferred nominal width, b, not less than 25 mm and not greater than the width of the
41、grips used, a thickness, h, of a nominal 10 mm, a principal notch depth (3) of 3,5 mm and with side notch depths (2) of 1 mm. Alternative thickness samples with appropriate notch depths are given in Table C.1. The depth of the principal notch for test pieces of thickness other than those given in th
42、e table may be obtained by linear interpolation. The length of the test piece, l, shall be sufficient to allow at least 10 mm between the end of each grip and the notch, see 8.2. NOTE Significant variation from the preferred width could influence the result. BS ISO 16241:2005 5Key l length b width h
43、 thickness (sheet thickness) 1 ligament area 2 side notch 3 principal notch Figure 3 Test piece geometry 6.2 Test piece preparation Test pieces shall be prepared from compression-moulded sheets made from the material to be tested. Alternatively, test pieces can be prepared from pipe and fitting prod
44、ucts or butt welds (see Annex A). For the compression moulding of the sheets from polyethylene materials, general instructions are given in ISO 1872-2 and ISO 293, but the following specific procedure shall be applied. Heat the material in granular form in the range of 140 C to 160 C and then apply
45、and remove the pressure three times. Increase the temperature in the range of 170 C to 190 C for between 10 min and 15 min without pressure. Then apply and remove the pressure three times in order to eliminate voids. Turn off the heat and apply a nominal pressure (force per unit area) of 1,7 MPa. Al
46、low cooling at a rate such that either the time to cool between 130 C and 90 C is greater than 80 min or so that the time to cool from the moulding temperature to about room temperature is greater than 5 h. During cooling the pressure shall be maintained. After allowing at least one day of storage o
47、f the sheet following moulding, the test pieces shall be machined from the sheet to the required geometry (see 6.1) in accordance with ISO 2818. NOTE 1 Higher moulding temperatures of u 200 C are advised for lower MFR materials, i.e those of MFR u 0,5 (5 kg load, Condition T, in accordance with ISO
48、1133). NOTE 2 The cooling conditions specified are crucial and any deviation from the specified conditions could influence the result of the test. The moulding and thermal processing cycle specified above might not be representative of the manufacturing process to which the material will be subjecte
49、d. 6.3 Test piece notching The principal notch shall be machined by pressing a sharp blade, e.g. a razor blade with a blade tip radius of less than 10 m, into the specimen at a speed of not more than 0,25 mm/min; the tolerance on the required BS ISO 16241:2005 6 notch depth is 0,1 mm. Each blade shall be used for one day only and for notching not more than six test pieces. The side notches (see Figure 3) shall be coplanar to th
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