1、BSI Standards PublicationBS ISO 15850:2014Plastics Determination oftension-tension fatigue crackpropagation Linear elasticfracture mechanics (LEFM)approachBS ISO 15850:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 15850:2014. Itsupersedes BS ISO 15850:20
2、02 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee PRI/21, Testing of plastics.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a
3、 contract. Users are responsible for its correctapplication. The British Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 83299 4ICS 83.080.01Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the
4、authority of theStandards Policy and Strategy Committee on 28 February 2014.Amendments issued since publicationDate Text affectedBS ISO 15850:2014 ISO 2014Plastics Determination of tension-tension fatigue crack propagation Linear elastic fracture mechanics (LEFM) approachPlastiques Dtermination de l
5、a propagation de fissure par fatigue en traction Approche de la mcanique linaire lastique de la rupture (LEFM)INTERNATIONAL STANDARDISO15850Second edition2014-02-15Reference numberISO 15850:2014(E)BS ISO 15850:2014ISO 15850:2014(E)ii ISO 2014 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2014A
6、ll 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 written permission. Permission can be requested
7、from either ISO at the address below or ISOs member body in the country of the 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 SwitzerlandBS ISO 15850:2014ISO 15850:2014(E) ISO 2014 All right
8、s reserved iiiContents PageForeword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Principle 55 Significance and use 56 Test specimens 66.1 Shape and size . 66.2 Preparation 96.3 Notching 96.4 Side grooves 106.5 Conditioning . 107 Apparatus 107.1 Test machine 107.2 Grips 117.3 Cra
9、ck length measurement . 117.4 Test atmosphere . 158 Test procedure .158.1 Measurement of specimen dimensions 158.2 Specimen mounting . 158.3 Loading . 158.4 Out-of-plane crack propagation 158.5 Discontinuous crack propagation 158.6 Number of tests . 159 Calculation and interpretation of results 169.
10、1 Crack length versus number of cycles 169.2 Crack curvature correction 169.3 Crack growth rate da/dN .169.4 Stress intensity factor range K .169.5 Energy release rate range G . 1710 Test report 1710.1 General 1710.2 For fatigue crack propagation test 1710.3 For fatigue crack propagation to failure
11、test 18Annex A (informative) Abnormality in the use of cyclic fatigue crack propagation test for ranking long-term static fatigue behaviour .19Bibliography .23BS ISO 15850:2014ISO 15850:2014(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national stan
12、dards 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. International org
13、anizations, 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 those intended for its
14、 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 (see www.iso.org/dir
15、ectives).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 document will be in th
16、e 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 and expressions relate
17、d 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 61, Plastics, Subcommittee SC 2, Mechanical propert
18、ies.This second edition cancels and replaces the first edition (ISO 15850:2002) of which it constitutes a minor revision.iv ISO 2014 All rights reservedBS ISO 15850:2014INTERNATIONAL STANDARD ISO 15850:2014(E)Plastics Determination of tension-tension fatigue crack propagation Linear elastic fracture
19、 mechanics (LEFM) approach1 ScopeThis International Standard specifies a method for measuring the propagation 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 leng
20、th as a function of the number of load cycles and the crack length increase rate as a function of the stress intensity factor and energy release rate at the crack tip. The possible occurrence of discontinuities in crack propagation is detected and reported.The test can be also used for the purpose o
21、f determining the resistance to crack propagation failure. In this case, the results can be presented in the form of number of cycles to failure or total time taken to cause crack propagation failure versus the stress intensity factor (see Annex A).The method is suitable for use with the following r
22、ange of materials: rigid and semi-rigid thermoplastic moulding and extrusion materials (including 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 rig
23、id and semi-rigid thermosetting sheets.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the re
24、ferenced document (including any amendments) applies.ISO 291, Plastics Standard atmospheres for conditioning and testingISO 527 (all parts), Plastics Determination of tensile propertiesISO 2818, Plastics Preparation of test specimens by machining3 Terms and definitionsFor the purposes of this docume
25、nt, the following terms and definitions apply.3.1cyclesmallest segment of a load-time or stress-time function which is repeated periodicallyNote 1 to entry: The terms fatigue cycle, load cycle, and stress cycle are also commonly used.3.2number of cycles completedNnumber of load cycles since the begi
26、nning of a test ISO 2014 All rights reserved 1BS ISO 15850:2014ISO 15850:2014(E)3.3waveformshape of the load-time curve within a single cycle3.4maximum loadPmaxhighest value of the load during a cycleNote 1 to entry: It is expressed in newtons.Note 2 to entry: Only positive, i.e. tensile, loads are
27、used in this test method.3.5minimum loadPminlowest value of the load during a cycleNote 1 to entry: It is expressed in newtons.Note 2 to entry: Only positive, i.e. tensile, loads are used in this test method.3.6load rangePdifference between the maximum and the minimum loads in one cycle, given by:P
28、= Pmax Pmin3.7load ratiostress ratioRratio of the minimum to the maximum load in one cycle, i.e.:RPPminmax3.8stress intensity factorKlimiting 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:Krr
29、r=lim ()20 pi SOURCE: ISO 13586:2000, 3.3Note 1 to entry: It is expressed in pascal root metres (Pam1/2).Note 2 to entry: The term factor is used here because it is in common usage, even though the quantity has dimensions.3.9maximum stress intensity factorKmaxhighest value of the stress intensity fa
30、ctor in one cycle2 ISO 2014 All rights reservedBS ISO 15850:2014ISO 15850:2014(E)3.10minimum stress intensity factorKminlowest value of the stress intensity factor in one cycle3.11stress intensity factor rangeKdifference between the maximum and minimum stress intensity factors in one cycle, given by
31、:K = Kmax Kmin3.12energy release rateGdifference between the external work Uextdone on a body to enlarge a cracked area by an amount A and the corresponding change in strain energy US:GUAUA=extS Note 1 to entry: It is expressed in joules per square metre.Note 2 to entry: Assuming linear elastic beha
32、viour, the following relationship between the stress intensity factor K and the energy release rate G holds:GKE=2whereE = E for plane stress;EE=12for plane strain conditions;E and are the tensile modulus and Poissons ratio, respectively.3.13maximum energy release rateGmaxhighest value of the energy
33、release rate in one cycle3.14minimum energy release rateGminlowest value of the energy release rate in one cycle3.15energy release rate rangeGdifference between the maximum and minimum energy release rates in one cycle, given by:G = Gmax Gmin ISO 2014 All rights reserved 3BS ISO 15850:2014ISO 15850:
34、2014(E)3.16notchsharp indentation made in the specimen, generally using a razor blade or a similar sharp tool, before a test and intended as the starting point of a fatigue-induced crack3.17initial crack lengtha0length of the notch (3.16)Note 1 to entry: It is expressed in metres.Note 2 to entry: Fo
35、r compact tensile (CT) specimens, it is measured from the line joining the load-application points (i.e. the line through the centres 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
36、 tip. Details of the measurement procedure are given in 7.3.3.18crack lengthatotal crack length at any time during a test, given by the initial crack length a0plus the crack length increment due to fatigue loadingNote 1 to entry: It is expressed in metres.3.19fatigue crack growth rateda/dNrate of cr
37、ack extension caused by fatigue loading and expressed in terms of average crack extension per cycleNote 1 to entry: It is expressed in metres per cycle.3.20stress intensity calibrationmathematical expression, based on empirical or analytical results, that relates the stress intensity factor to load
38、and crack length for a specific specimen geometry3.21gauge lengthL0free distance between the upper and lower grips after the specimen has been mounted in the test machineNote 1 to entry: It is expressed in metres.3.22number of cycles to failureNftotal number of load cycles from the beginning of the
39、test to fatigue crack propagation to sample failure3.23tftime to failuretotal number of load cycles from the beginning of the test to fatigue crack propagation to sample failure, expressed in timeNote 1 to entry: It is expressed in hours.4 ISO 2014 All rights reservedBS ISO 15850:2014ISO 15850:2014(
40、E)4 PrincipleA 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 frequency, etc.), causing a crack to start from the notch and propagate.The crack length a is monitored during the t
41、est 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 reported as a function of stress intensity factor and energy release rate at the crack tip.For the case where tota
42、l number of cycles to failure or time to failure is to be determined, the crack length need not be monitored.5 Significance and useFatigue 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 releas
43、e rate range G, characterizes 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 References 1 and 2.Expressing da/dN as a function of K or
44、 G provides 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 s
45、tructures. 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 g
46、enerally 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 behavio
47、ur. 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 af
48、fecting the test results.This test method can serve the following purposes:a) to establish 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 toughnes
49、s data (see ISO 13586) and stress analysis information;b) to establish material-selection criteria and inspection requirements for damage-tolerant applications;c) to establish, in quantitative terms, the individual and combined effects of the materials structure, the processing conditions, and the loading variables on fatigue crack propagation;d) used as an accelerated test for the evaluation of service life performance of components subjected to static fatigue loading conditions (thi
