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1、 Reference number ISO 15850:2002(E) ISO 2002 INTERNATIONAL STANDARD ISO 15850 First edition 2002-06-15 Plastics Determination of tension-tension fatigue crack propagation Linear elastic fracture mechanics (LEFM) approach Plastiques Dtermination de la propagation de fissure par fatigue en traction Ap
2、proche de la mcanique linaire lastique de la rupture (LEFM) Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without license fr
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6、the address given below. ISO 2002 All rights 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
7、 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.ch Web www.iso.ch Printed in Switzerland ii ISO 2002 All rights reserved Copyright International Organization for Standardizat
8、ion Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15850:2002(E) ISO 2002 All rights reserved iii Contents Page Foreword.iv 1 Scope1 2 Normative re
9、ferences1 3 Terms and definitions .1 4 Principle4 5 Significance and use.4 6 Test specimens5 7 Apparatus.9 8 Test procedure.14 9 Calculation and interpretation of results 14 10 Test report16 Bibliography17 Copyright International Organization for Standardization Provided by IHS under license with IS
10、O Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15850:2002(E) iv ISO 2002 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation
11、 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.
12、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 accordance wit
13、h the rules given in the ISO/IEC Directives, Part 3. 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 approv
14、al by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 15850 was prepared by Tech
15、nical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical properties. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted
16、 without license from IHS -,-,- INTERNATIONAL STANDARD ISO 15850:2002(E) ISO 2002 All rights reserved 1 Plastics Determination of tension-tension fatigue crack propagation Linear elastic fracture mechanics (LEFM) approach 1 Scope This International Standard specifies a method for measuring the propa
17、gation of a crack in a notched specimen subjected to a cyclic tensile load varying between a constant positive minimum and a constant positive maximum value. The test results include the crack length as a function of the number of load cycles and the crack length increase rate as a function of the s
18、tress intensity factor and energy release rate at the crack tip. The possible occurrence of discontinuities in crack propagation is detected and reported. The method is suitable for use with the following range of materials: rigid and semi-rigid thermoplastic moulding and extrusion materials (includ
19、ing filled and short-fibre-reinforced compounds) plus rigid and semi-rigid thermoplastic sheets; rigid and semi-rigid thermosetting materials (including filled and short-fibre-reinforced compounds) plus rigid and semi-rigid thermosetting sheets. 2 Normative references The following normative documen
20、ts contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encourag
21、ed to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 291,
22、Plastics Standard atmospheres for conditioning and testing ISO 527 (all parts), Plastics Determination of tensile properties ISO 2818, Plastics Preparation of test specimens by machining ISO 13586, Plastics Determination of fracture toughness (GIC and KIC ) Linear elastic fracture mechanics (LEFM) a
23、pproach 3 Terms and definitions For the purposes of this International Standard, the following terms and definitions apply. 3.1 cycle smallest segment of a load-time or stress-time function which is repeated periodically NOTE The terms fatigue cycle, load cycle and stress cycle are also commonly use
24、d. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15850:2002(E) 2 ISO 2002 All rights rese
25、rved 3.2 number of cycles completed N number of load cycles since the beginning of a test 3.3 waveform shape of the load-time curve within a single cycle 3.4 maximum load Pmax highest value of the load during a cycle NOTE 1 It is expressed in newtons. NOTE 2 Only positive, i.e. tensile, loads are us
26、ed in this test method. 3.5 minimum load Pmin lowest value of the load during a cycle NOTE 1 It is expressed in newtons. NOTE 2 Only positive, i.e. tensile, loads are used in this test method. 3.6 load range P difference between the maximum and the minimum loads in one cycle, given by: P = Pmax Pmin
27、 3.7 load ratio stress ratio R ratio of the minimum to the maximum load in one cycle, i.e.: R = Pmin/Pmax 3.8 stress intensity factor K limiting value of the product of the stress (r) perpendicular to the crack area at a distance r from the crack tip and of the square root of 2r, as r tends to zero:
28、 0 = lim( ) 2 r Krr NOTE 1 It is expressed in pascal root metres (Pam1/2). NOTE 2 The term factor is used here because it is in common usage, even though the quantity has dimensions. ISO 13586 3.9 maximum stress intensity factor Kmax highest value of the stress intensity factor in one cycle Copyrigh
29、t International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15850:2002(E) ISO 2002 All rights reserved 3 3.10 m
30、inimum stress intensity factor Kmin lowest value of the stress intensity factor in one cycle 3.11 stress intensity factor range K difference between the maximum and minimum stress intensity factors in one cycle, given by: K = Kmax Kmin 3.12 energy release rate G difference between the external work
31、Uext done on a body to enlarge a cracked area by an amount A and the corresponding change in strain energy US: extS = UU G AA NOTE 1 It is expressed in joules per square metre. NOTE 2 Assuming linear elastic behaviour, the following relationship between the stress intensity factor K and the energy r
32、elease rate G holds: 2 = K G E where E = E for plane stress, and 2 = 1 E E for plane strain conditions; E and are the tensile modulus and Poissons ratio respectively. 3.13 maximum energy release rate Gmax highest value of the energy release rate in one cycle 3.14 minimum energy release rate Gmin low
33、est value of the energy release rate in one cycle 3.15 energy release rate range G difference between the maximum and minimum energy release rates in one cycle, given by: G = Gmax Gmin 3.16 notch sharp indentation made in the specimen, generally using a razor blade or a similar sharp tool, before a
34、test and intended as the starting point of a fatigue-induced crack Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without lic
35、ense from IHS -,-,- ISO 15850:2002(E) 4 ISO 2002 All rights reserved 3.17 initial crack length a0 length of the notch (3.16) NOTE 1 It is expressed in metres. NOTE 2 For compact tensile (CT) specimens, it is measured from the line joining the load-application points (i.e. the line through the centre
36、s of the loading-pin holes) to the notch tip (see Figure 2). For single-edge-notched tensile (SENT) specimens, it is measured from the edge of the specimen to the notch tip. Details of the measurement procedure are given in 7.3. 3.18 crack length a total crack length at any time during a test, given
37、 by the initial crack length a0 plus the crack length increment due to fatigue loading NOTE It is expressed in metres. 3.19 fatigue crack growth rate da/dN rate of crack extension caused by fatigue loading and expressed in terms of average crack extension per cycle NOTE It is expressed in metres per
38、 cycle. 3.20 stress intensity calibration mathematical expression, based on empirical or analytical results, that relates the stress intensity factor to load and crack length for a specific specimen geometry 3.21 gauge length L0 single-edge-notched tensile (SENT) specimen free distance between the u
39、pper and lower grips after the specimen has been mounted in the test machine NOTE It is expressed in metres. 4 Principle A constant-amplitude cyclic tensile load is imposed on a specimen under suitable test conditions (specimen shape and size, notching, maximum and minimum loads, load cycle frequenc
40、y, etc.), causing a crack to start from the notch and propagate. The crack length a is monitored during the test and recorded as a function of the number N of load cycles completed. Numerical differentiation of the experimental function a(N) provides the fatigue crack growth rate da/dN which is repo
41、rted as a function of stress intensity factor and energy release rate at the crack tip. 5 Significance and use Fatigue crack propagation, particularly when expressed as the fatigue crack growth rate da/dN as a function of crack-tip stress intensity factor range K or energy release rate range G chara
42、cterizes a materials resistance to stable crack extension under cyclic loading. Background information on the fatigue behaviour of plastics and on the fracture mechanics approach to fatigue for these materials is given in 1 and 2 (see the Bibliography). Copyright International Organization for Stand
43、ardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/19/2007 03:28:35 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 15850:2002(E) ISO 2002 All rights reserved 5 Expressing da/dN as a function of K or G pro
44、vides results that are independent of specimen geometry, thus enabling exchange and comparison of data obtained with a variety of specimen configurations and loading conditions. Moreover, this feature enables da/dN versus K or G data to be utilized in the design and evaluation of engineering structu
45、res. The concept of similitude is assumed, which implies that cracks of differing lengths subjected to the same nominal K or G will advance by equal increments of crack extension per cycle. Fatigue crack propagation data are not geometry-independent in the strict sense since thickness effects genera
46、lly occur. The potential effects of specimen thickness have to be considered when generating data for research or design. Anisotropy in the molecular orientation or in the structure of the material, and the presence of residual stresses, can have an influence on fatigue crack propagation behaviour.
47、The effect can be significant when test specimens are removed from semi-finished products (e.g. extruded sheets) or finished products. Irregular crack propagation, namely excessive crack front curvature or out-of-plane crack growth, generally indicates that anisotropy or residual stresses are affect
48、ing the test results. This test method can serve the following purposes: a) to estabilish the influence of fatigue crack propagation on the lifetime of components subjected to cyclic loading, provided data are generated under representative conditions and combined with appropriate fracture toughness data (see ISO 13586) and stress analysis information; b) to establish material-selection criteria and inspection re