1、BS ISO 27306:2016Metallic materials Methodof constraint loss correction ofCTOD fracture toughness forfracture assessment of steelcomponentsBSI Standards PublicationWB11885_BSI_StandardCovs_2013_AW.indd 1 15/05/2013 15:06BS ISO 27306:2016 BRITISH STANDARDNational forewordThis British Standard is the
2、UK implementation of ISO 27306:2016. It supersedes BS ISO 27306:2009 which is withdrawn.This International Standard describes methods for adjusting for differences in crack-tip constraint: between fracture toughness values, generated from standard, deeply-notched, single-edge notched bend (SENB), an
3、d tension (CT) fracture toughness specimens where fracture is by cleavage and other structural geometries loaded in tension. The effect is referred to as a constraint loss, which elevates the fracture toughness value for use in Engineering Critical Assessments (ECAs). However, no recommendations are
4、 given on which ECA procedure to use. Currently there is no International Standard that describes ECA methods. However, it is the opinion of the UK Committee that BS 7910 describes ECA methods in a comprehensive manner which includes a procedure for constraint correction, discussed below. Although I
5、SO 27306 defines fracture toughness primarily in terms of Crack-tip opening displacement (CTOD), K and J parameters can be used as well. However, some of the procedures (for example, choice of the Weibull parameter for a Level 2 assessment) would be difficult to implement if CTOD data were not avail
6、able.In steels, fracture toughness values are usually subject to significant scatter, especially when fracture is by cleavage (brittle fracture). However, no guidance is given in ISO 27306 on the statistical analysis that should be carried out to choose the fracture toughness value to which the cons
7、traint correction is applied. In the opinion of the UK Committee, BS 7910 provides a complete and comprehensive assessment procedure which includes guidance on the choice of fracture toughness value, the assessment procedure and, in Annex N, an alternative constraint correction procedure. This is di
8、fferent from that described in ISO 27306 and, in addition, Annex N can be applied to materials in which crack extension is by ductile crack growth (tearing) as well as brittle fracture. Therefore, there is the potential danger that an ECA based on BS 7910 but using the ISO 27306 correction procedure
9、 could give different results to an ECA completely based on BS 7910 and the constraint procedure in AnnexN. This could lead to differences in the risk assessment, with respect to failure by fracture, of a structural component. In structurally critical components this could have significant economic
10、and safety consequences.The title and scope of ISO 27306 suggest that the method can be used to assess constraint loss in structural steel components. However, it is the opinion of the UK Committee that the geometries allowed are four types of cracks in tension-loaded flat panels (or wide plate spec
11、imens), which do not directly relate to common engineering structures. The range of crack sizes and geometries permitted is limited. Furthermore, the method can only be applied to structural loading conditions where tension is the primary loading mode; bending stresses, stress concentrations and non
12、-uniform residual stresses cannot be accounted for. This is important as the benefits of constraint loss are mitigated by bending stresses. Therefore the method may have limited application to the assessment of actual structural components. BS 7910, on the other hand provides a general assessment pr
13、ocedure that can be applied to a wide range of crack geometries representative of structural components and loading conditions. ISO 27306 is restricted to assessment of cracks in steel plate, but BS 7910 can be applied toassess cracks in a wide range of product forms, metallic materials (not just st
14、eel) and also welded structures.BS ISO 27306:2016 BRITISH STANDARDThe UK participation in its preparation was entrusted to TechnicalCommittee ISE/101/4, Toughness testing.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purpor
15、t to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2016. Published by BSI StandardsLimited 2016ISBN 978 0 580 88918 9ICS 77.040.10Compliance with a British Standard cannot confer immunity fromlegal obligations.T
16、his British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 November 2016.Amendments issued since publicationDate Text affectedBS ISO 27306:2016 ISO 2016Metallic materials Method of constraint loss correction of CTOD fracture toughness for fracture asse
17、ssment of steel componentsMatriaux mtalliques Mthode de correction de perte de contrainte du CTOD de la tnacit la rupture pour lvaluation de la rupture des composants en acierINTERNATIONAL STANDARDISO27306Second edition2016-09-15Reference numberISO 27306:2016(E)BS ISO 27306:2016ISO 27306:2016(E)ii I
18、SO 2016 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2016, Published in SwitzerlandAll 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
19、the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 22 749 09
20、 47copyrightiso.orgwww.iso.orgBS ISO 27306:2016ISO 27306:2016(E)Foreword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Symbols and units . 35 Principle 36 Structural components of concern 47 Conditions for use . 58 Assessment levels I, II, and III . 68.1 General . 68.2 Level I: S
21、implified assessment . 68.3 Level II: Normal assessment . 78.4 Level III: Material specific assessment . 79 Equivalent CTOD ratio, . 79.1 General . 79.2 Factors influencing the equivalent CTOD ratio, .79.3 Procedure for calculating the equivalent CTOD ratio, , at assessment levels I to III . 89.3.1
22、General 89.3.2 Surface crack cases (CSCP and ESCP) 89.3.3 Through-thickness crack cases (CTCP and ETCP) 9Annex A (informative) Procedure for the selection of Weibull parameter, m, at level II assessment .17Annex B (informative) Analytical method for the determination of Weibull parameter, m, at leve
23、l III assessment .19Annex C (informative) Guidelines for the equivalent CTOD ratio, .24Annex D (informative) Examples of fracture assessment using the equivalent CTOD ratio, 31Bibliography .47 ISO 2016 All rights reserved iiiContents PageBS ISO 27306:2016ISO 27306:2016(E)ForewordISO (the Internation
24、al Organization for Standardization) is a worldwide federation 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 e
25、stablished 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 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standard
26、ization.The procedures used to develop this document and those intended for its 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
27、with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).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 an
28、y patent rights identified during the development of the document will be in the 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
29、.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.The co
30、mmittee responsible for this document is ISO/TC 164 Mechanical Testing of Metals, Subcommittee SC 4, Toughness testing Fracture (F), Pendulum (P), Tear (T).This second edition cancels and replaces the first edition (ISO 27306:2009), which has been technically revised.iv ISO 2016 All rights reservedB
31、S ISO 27306:2016INTERNATIONAL STANDARD ISO 27306:2016(E)Metallic materials Method of constraint loss correction of CTOD fracture toughness for fracture assessment of steel components1 ScopeIn fracture assessments of steel structures containing cracks, it has generally been assumed that the fracture
32、resistance of fracture toughness specimens is equal to the fracture resistance of structural components. However, such an assumption often leads to excessively conservative fracture assessments. This is due to a loss of plastic constraint in structural components, which are subjected mainly to tensi
33、le loading. By contrast, fracture toughness specimens hold a constrained stress state near the crack-tip due to bending mode. The loss of constraint is significant for high strength steels with high yield-to-tensile ratios (= yield stress/tensile strength) which have been extensively developed and w
34、idely applied to structures in recent years.This International Standard specifies a method for converting the CTOD (crack-tip opening displacement) fracture toughness obtained from laboratory specimens to an equivalent CTOD for structural components, taking constraint loss into account. This method
35、can also apply to fracture assessment using the stress intensity factor or the J-integral concept (see Clause 9).This International Standard deals with the unstable fracture that occurs from a crack-like defect or fatigue crack in ferritic structural steels. Unstable fracture accompanied by a signif
36、icant amount of ductile crack extension and ductile fractures are not included in the scope hereof.The CTOD fracture toughness of structural steels is measured in accordance with the established test methods, ISO 121351)or BS 7448-1. The fracture assessment of a cracked component is done using an es
37、tablished method such as FAD (Failure Assessment Diagram) in the organization concerned, and reference is not made to the details thereof in this International Standard.This International Standard can be used for eliminating the excessive conservatism frequently associated with the conventional frac
38、ture mechanics methods and accurately assessing the unstable fracture initiation limit of structural components from the fracture toughness of the structural steel. This is also used for rationally determining the fracture toughness of materials to meet the design requirements of performance of stru
39、ctural components.2 Normative referencesThe following referenced documents are indispensable for the application of this International Standard. For dated references, only the edition cited applies. For updated references, the latest edition of the referenced document (including any amendments) appl
40、ies.ISO 12135, Metallic materials Unified method of test for the determination of quasistatic fracture toughnessBS 7448-1, Fracture mechanics toughness tests Part 1: Method for determination of KIc, critical CTOD and critical J values of metallic materials3 Terms and definitionsFor the purposes of t
41、his document, the terms and definitions given in ISO 12135 and the following apply.1) To be published. ISO 2016 All rights reserved 1BS ISO 27306:2016ISO 27306:2016(E)3.1CTOD of standard fracture toughness specimencrack-tip opening displacement of standard fracture toughness specimenCTOD, as the fra
42、cture driving force, for the standard fracture toughness specimen (three-point bend or compact specimen) with 0,45 a0/W 0,55, where a0and W are the initial crack length and specimen width, respectively3.2CTOD fracture toughnesscrack-tip opening displacement fracture toughnesscrcritical CTOD at the o
43、nset of brittle fracture in the standard fracture toughness specimen c(B) as defined in ISO 12135 with 0,45 a0/W 0,553.3CTOD of structural componentcrack-tip opening displacement of structural componentWPCTOD, as the fracture driving force, for a through-thickness crack or a surface crack existing i
44、n a structural component regarded as a wide plateNote 1 to entry: The CTOD of a surface crack is defined at the maximum crack depth.3.4critical CTOD of structural componentcritical crack-tip opening displacement of structural componentW P,crcritical CTOD at the onset of brittle fracture in structura
45、l components3.5equivalent CTOD ratioequivalent crack-tip opening displacement ratioCTOD ratio defined by / WP, where and WPare CTODs of the standard fracture toughness specimen and the structural component, respectively, at the same level of the Weibull stress WNote 1 to entry: See Figure 1.Note 2 t
46、o entry: See Reference 1.3.6Weibull stressWfracture driving force defined with the consideration of statistical instability of microcracks in the fracture process zone against brittle fractureNote 1 to entry: See Reference 2.3.7critical Weibull stressW,crWeibull stress at the onset of unstable fract
47、ure3.8Weibull shape parametermmaterial parameter used in the definition of the Weibull stress; one of two parameters describing the statistical distribution of the critical Weibull stress, W, cr2 ISO 2016 All rights reservedBS ISO 27306:2016ISO 27306:2016(E)3.9yield-to-tensile ratioRYratio of yield
48、strength, Y, (lower yield point, ReL, or 0,2% proof strength, Rp0,2) to tensile strength, Rm4 Symbols and unitsFor the purposes of this document, the following symbols, units, and designations are applied in addition to those in ISO 12135.Symbol Unit Designationa mm Depth of surface crack or half-le
49、ngth of through-thickness crack in structural componentc mm Half-length of surface crack in structural componentm Weibull shape parametert mm Plate thicknessV0mm3Reference volume defined for Weibull stressVfmm3Volume of fracture process zoneRY Yield-to-tensile ratio (= Y/Rm) Equivalent CTOD ratio0Equivalent CTOD ratio for reference crack length(In cases of surface crack panel, 0is defined for plate thickness t = 25 mm.)2c, tEquivalent CTOD ratio for target length of centre surface crack or doubl
