1、 ISO 2012 Thermoplastics pipes for the conveyance of fluids Determination of the slow cracking resistance of pipes and fittings using the Notched Ring Test (NRT) Tubes en matires thermoplastiques pour le transport des fluides Dtermination de la rsistance des tubes et raccords la propagation lente de
2、 la fissure au moyen dessais sur sections fendues TECHNICAL SPECIFICATION ISO/TS 16479 First edition 2012-10-01 Reference number ISO/TS 16479:2012(E) ISO/TS 16479:2012(E) ii ISO 2012 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2012 All rights reserved. Unless otherwise specified, no part of
3、 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 the requester. ISO copyright office Case postale 56 CH
4、-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 Switzerland ISO/TS 16479:2012(E) ISO 2012 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references 1 3 Terms and definitions . 1 4 Principle 2
5、5 Apparatus . 3 5.1 Loading apparatus . 3 5.2 Ring deflection measuring device 3 5.3 Temperature chamber 4 5.4 Test medium 4 5.5 Timing device . 4 5.6 Microscope . 4 5.7 Notching apparatus . 5 6 Test specimen 7 6.1 Specimen geometry and dimensions . 7 6.2 Specimen preparation 7 6.3 Specimen conditio
6、ning . 9 7 Procedure. 9 7.1 Conditioning 9 7.2 Load application 9 7.3 On-set slow cracking time detection .10 7.4 Notch depth measurement 10 7.5 Number of specimens 10 8 Test report 10 Annex A (informative) On-set slow cracking time detection 12 Annex B (informative) Stress intensity factor plot .16
7、 Annex C (informative) Flexure load estimation .20 Bibliography .21 ISO/TS 16479:2012(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
8、 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 with ISO, also take part in the work. ISO col
9、laborates 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 technical committees is to prepare International S
10、tandards. 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. In other circumstances, particularly when there is an urgent ma
11、rket requirement for such documents, a technical committee may decide to publish other types of document: an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in an ISO working group and is accepted for publication if it is approved by more than 50 % of
12、 the members of the parent committee casting a vote; an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting a vote. An ISO/PAS or ISO/TS is reviewed
13、after three years in order to decide whether it will be confirmed for a further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an Interna
14、tional Standard or be withdrawn. 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/TS 16479 was prepared by Technical Committee ISO/TC 138, Plastic
15、s pipes, fittings and valves for the transport of fluids, Subcommittee SC 5, General properties of pipes, fittings and valves of plastic materials and their accessories Test methods and basic specifications. iv ISO 2012 All rights reserved ISO/TS 16479:2012(E) Introduction At the present time ISO/TC
16、 138 provides several test methods for determining the resistance to slow cracking which are essential for assessing properties and durability of thermoplastics pipes and fittings. In fact, they constitute a basis for determining the long term performance characteristics of these parts. In line with
17、 the development of better slow crack resistant materials, new accelerated test methods for evaluating slow crack resistance of thermoplastic piping parts are frequently under investigation 1-3. In consideration of this, the Notched Ring Test (NRT) method has been developed and applied to determine
18、its applicability as the standard test method and has demonstrated its effectiveness in generating slow cracking within the time frame of interest 4-7. This Technical Specification provides details of the NRT method in terms of test implementation, its SCG performance evaluation, and the application
19、 of the method utilizing the stress intensity factor approach. ISO 2012 All rights reserved v Thermoplastics pipes for the conveyance of fluids Determination of the slow cracking resistance of pipes and fittings using the Notched Ring Test (NRT) 1 Scope T h i s T e c h n i c a l S p e c i f i c a t
20、i o n d e t e r m i n e s t h e s l o w c r a c k i n g r e s i s t a n c e o f p i p e s a n d f i t t i n g s u s i n g t h e Notched Ring Test (NRT) which is a method for determining the slow crack resistance of thermoplastics resins and compounds in pipe form and/or finished products (e.g. pipes
21、 and fittings) from which a ring specimen can be cut and notched. The test is performed under sustained constant loading in a test medium at a specified temperature and the time to the on-set of slow cracking is measured. This method applies to the rings from pipes or fittings having a wall thicknes
22、s greater than 5 mm. This Technical Specification specifies the method of testing using notched ring specimens directly obtained from pipes or fittings. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the ed
23、ition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 6108, Double equal angle cutters with plain bore and key drive ISO 13479, Polyolefin pipes for the conveyance of fluids Determination of resistance to crack propagation
24、Test method for slow crack growth on notched pipes (notch test) 3 Terms and definitions 3.1 slow crack growth SCG crack growth that occurs below the critical stress intensity factor at which the unstable rapid crack propagation takes place NOTE The crack growth is stable and hence can grow to a subs
25、tantial length before causing material to fail either by rapid fracture or ligament yielding. In some polyolefin materials, distinct fracture surface features characteristic of slow crack growth are apparent and are often used as an indicator of slow crack growth 3.2 ring deflection curve t ime depe
26、ndent def lec t ion cur ve obt ained f rom t he sust ained const ant f lex ure loading of t he r ing specimen NOTE 1 See Annex A. NOTE 2 The curve may have similar features of a creep curve, normally consisting of primary, steady state secondary and tertiary regions. Deflection is normally taken at
27、the notch position and directly above the line of load application. 3.3 on-set slow cracking time t i(h) time for first noticeable abnormal change to appear on the recorded ring deflection curve NOTE 1 See Annex A. TECHNICAL SPECIFICATION ISO/TS 16479:2012(E) ISO 2012 All rights reserved 1 ISO/TS 16
28、479:2012(E) NOTE 2 For this definition to be complete, the fracture surface must show features of slow cracking in any degree or features defined otherwise. EXAMPLE Examples of abnormal change are discontinuity, slope change etc. 3.4 applied load L (N) load applied in three point flexure mode 3.5 ap
29、plied stress intensity factor K 0(N/m 3/2 ) crack-tip stress intensity factor calculated based on the initial notch dimension 4 Principle A suitable NRT specimen is an undisturbed full ring of certain width directly removed from the pipes or fittings (see Figure 1), having features that include an i
30、nner wall notch along the sample width between the tips of two coplanar sidewall notches (see Figure 5). The inner wall and sidewall notches are all in the same plane and the notch and specimen dimensions are such that conditions for the plane- strain slow crack growth are met at the notch tip. Copl
31、anar sidewall notches are introduced to further maintain the plane strain condition as well as to act to guide the loading rod accurately along the line of the crack tip. NRT specimens are subjected to sustained and constant flexure load in a temperature controlled medium and the time to on-set crac
32、king as defined in 3.3 is determined from the measured ring deflection curve (see 3.2 and Annex A). In the NRT specimen, the slow cracking can be initiated in a relatively shorter time due to the possibility of constrained crack tip deformation induced by the sample and the loading geometry, hence a
33、llowing higher stress intensity to develop at the crack tip without gross yielding. 2 ISO 2012 All rights reserved ISO/TS 16479:2012(E) Key W width of the ring S span length W n width between sidewall notches a razor notch depth R 1 inside radius L applied load R 2 outside radius D diameter of loadi
34、ng and supporting rods t wall thickness Figure 1 The diagram and loading configuration of NRT specimen 5 Apparatus 5.1 Loading apparatus A suitable device for loading the ring specimen in a sustained and constant manner under flexure mode shall be used. The device may utilize dead weights, pneumatic
35、ally actuated loading or any other means for producing a sustained constant load with accuracy better than 1,0 % of the applied load. The loading, supporting and guiding rods (see Figure 1) are made from a 316 stainless steel having the same ground surface and they are positioned parallel to each ot
36、her. The guiding rod guides the loading rod right on top of the inner wall notch by means of adapting the sidewall notches (see Figures 1 and 5). An impression of a typical loading jig is shown in Figure 2. 5.2 Ring deflection measuring device Ring deflection of the mid-span containing the plane of
37、the crack front (see Figure 1) shall be measured by means of a suitable device that will not influence the specimen in any way. Particular caution should be practiced to ensure the stability of the measuring device with time, temperature and humidity. The device shall be capable of deflection measur
38、ement with accuracy better than 1,0 % and a resolution of 0,01 mm. Since it is important to continuously monitor the deflection, it is recommended to use an automatic deflection measuring system. An example of an electronic displacement gauge and its assembly to an overall loading-measuring device i
39、s shown in Annex A. The measurement shall not be influenced by any mechanical and/or electric disturbances that may end up in the deflection curve being obtained. ISO 2012 All rights reserved 3 ISO/TS 16479:2012(E) Figure 2 Flexure apparatus for loading notched ring specimen 5.3 Temperature chamber
40、A suitable chamber should contain the environment needed for this test and ensure complete immersion of the specimen. The construction material of this chamber shall not affect the environment or vice versa. The chamber can usually be closed with a lid to prevent medium evaporation as well as to pro
41、tect the loading-measuring apparatus. The temperature of the environment is controlled to maintain the specimens within 1,0 C of the specified test temperature. Replenishment of the lost medium due to evaporation is achieved best through the use of an auxiliary container using gravity feeding to min
42、imize temperature variation during feeding. 5.4 Test medium The tests are usually performed in water, unless stated otherwise. 5.5 Timing device A suitable timing device that can monitor time accumulation shall be used. The accuracy of the measurement is recommended to be better than 1 % of the elap
43、sed time. 5.6 Microscope A travelling microscope or an equivalent device is used to measure the initial razor notch length accurately after the slow crack test. The recommended resolution for this method is 100 m. NOTE A combination of digital camera and image processing software is considered a rea
44、dily available solution. This method can provide a razor notch depth measurement with required accuracy and convenience. 4 ISO 2012 All rights reserved ISO/TS 16479:2012(E) 5.7 Notching apparatus 5.7.1 Inner wall notching device The device shall be capable of producing a sharp notch at the inner wal
45、l of the ring specimen at a cutting speed of less than 300m per minute. NOTE Such cutting speeds are generally available in a typical universal testing machine and the load- displacement curve can be readily obtained simultaneously by installing the notching device on such machines see Figure 3b). H
46、igher notching speed is known to create abnormality at the notch tip which can affect the slow crack initiation. It is recommended that the device utilized is also able to produce load-razor blade displacement curve during notching for the purpose of checking consistency and uniformity of notching.
47、The notch tip radius produced depends on the type of razor blade (blade thickness not exceeding 0,2 mm) and shall be less than 10 m. A broaching device is also acceptable provided that the notch tip radius is also less than 10 m. Figure 3 shows an inner wall notching device. It consists of a removab
48、le arm for accommodating the razor blade holder, depth adjusting parts and the ring specimen, a base to hold the arm perpendicular to the compression load and a mechanism for firmly holding the base to the universal testing machine. 5.7.2 Sidewall notching device A suitable device capable of machini
49、ng a 90 angle “V”-notch at each sidewall of the ring specimen opposite each other and the notch tips in the same plane (see Figure 1) shall be used. The device should provide a notching rate of 0,010 0,002 (mm/rev)/tooth (see ISO 13479 for details) and the cutter subject to a pre-treatment amounting to 10 m of notching prior to its first use. It is strongly recommended to use the cutter solely for this purpose and only on this material, to be replaced after 100 m of notching. The 90-included-angle “V”-cutter e
