1、BS ISO 18608:2017Fine ceramics (advancedceramics, advanced technicalceramics) Mechanicalproperties of ceramiccomposites at ambienttemperature in air atmosphericpressure Determinationof the resistance to crackpropagation by notchsensitivity testingBSI Standards PublicationWB11885_BSI_StandardCovs_201
2、3_AW.indd 1 15/05/2013 15:06BS ISO 18608:2017 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 18608:2017.The UK participation in its preparation was entrusted to TechnicalCommittee RPI/13, Advanced technical ceramics.A list of organizations represented on this
3、committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2017. Published by BSI Standards Limited 2017ISBN 978 0 580 82470 8ICS 81.0
4、60.30Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 March 2017.Amendments/corrigenda issued since publicationDate Text affectedBS ISO 18608:2017 ISO 2017Fine c
5、eramics (advanced ceramics, advanced technical ceramics) Mechanical properties of ceramic composites at ambient temperature in air atmospheric pressure Determination of the resistance to crack propagation by notch sensitivity testingCramiques techniques Proprits mcaniques des cramiques composites te
6、mprature ambiante sous pression atmosphrique Dtermination de la rsistance la propagation de fissure par un essai de sensibilit lentailleINTERNATIONAL STANDARDISO18608First edition2017-03Reference numberISO 18608:2017(E)BS ISO 18608:2017ISO 18608:2017(E)ii ISO 2017 All rights reservedCOPYRIGHT PROTEC
7、TED DOCUMENT ISO 2017, 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 the internet or an intranet, without prior
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9、2017ISO 18608:2017(E)Foreword iv1 Scope . 12 Normative references 13 Terms and definitions . 14 Principle 25 Significance and use 26 Apparatus . 46.1 Test machine . 46.2 Load train. 46.2.1 General 46.2.2 Grips 46.2.3 Load train couplers 46.3 Data recording system 56.4 Micrometers 56.5 Ligament size
10、measuring device 57 Specimens 57.1 Un-notched test specimens 57.2 Notched test specimens 57.3 Notches 68 Test specimen preparation 78.1 Machining and preparation 78.2 Number of test specimens . 79 Test procedure 79.1 Test on reference specimen . 79.2 Test on notched specimen . 79.2.1 Displacement ra
11、te . 79.2.2 Measurement of test specimen dimensions . 79.2.3 Test technique 79.2.4 Test validity 810 Calculation of results . 810.1 Test specimen origin 810.2 Tensile strength of un-notched specimen 810.3 Tensile strength of the notched specimen . 810.4 Plotting of notch sensitivity diagram . 810.5
12、Calculation of equivalent fracture toughness for the different classes of behaviour . 910.5.1 Class A behaviour 910.5.2 Class B behaviour 910.5.3 Class C behaviour .1011 Test report 10Bibliography .11 ISO 2017 All rights reserved iiiContents PageBS ISO 18608:2017ISO 18608:2017(E)ForewordISO (the Int
13、ernational 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 ha
14、s 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 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical
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19、llowing URL: www .iso .org/ iso/ foreword .html.This document was prepared by Technical Committee ISO/TC 206, Fine ceramics.iv ISO 2017 All rights reservedBS ISO 18608:2017INTERNATIONAL STANDARD ISO 18608:2017(E)Fine ceramics (advanced ceramics, advanced technical ceramics) Mechanical properties of
20、ceramic composites at ambient temperature in air atmospheric pressure Determination of the resistance to crack propagation by notch sensitivity testing1 ScopeThis document describes a method for the classification of ceramic matrix composite (CMC) materials with respect to their sensitivity to crack
21、 propagation using tensile tests on notched specimens with different notch depths. Two classes of ceramic matrix composite materials can be distinguished: materials whose strength is sensitive to the presence of notches and materials whose strength is not affected. For sensitive materials, this docu
22、ment defines a method for determining equivalent fracture toughness.The parameter, Keq, is defined as the fracture toughness of a homogeneous material which presents the same sensitivity to crack propagation as the ceramic matrix composite material which is being considered. The definition of the Ke
23、qparameter offers the possibility to compare ceramic matrix composite materials with other materials with respect to sensitivity to crack propagation.For notch insensitive materials, the concept of Keqdoes not apply.This document applies to all ceramic matrix composites with a continuous fibre reinf
24、orcement, unidirectional (1 D), bidirectional (2 D), and tridirectional (x D, where 2 x 3), loaded along one principal axis of reinforcement.2 Normative referencesThe following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this docu
25、ment. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 3611, Geometrical product specifications (GPS) Dimensional measuring equipment: Micrometers for external measurements Design and me
26、trological characteristicsISO 7500-1, Metallic materials Calibration and verification of static uniaxial testing machines Part 1: Tension/compression testing machines Calibration and verification of the force-measuring systemISO 15733:2015, Fine ceramics (advanced ceramics, advanced technical cerami
27、cs) Mechanical properties of ceramic composites at ambient temperature in air atmospheric pressure Determination of tensile properties3 Terms and definitionsFor the purposes of this document, the terms and definitions given in ISO 15733 and the following apply.ISO and IEC maintain terminological dat
28、abases for use in standardization at the following addresses: IEC Electropedia: available at h t t p :/ www .electropedia .org/ ISO Online browsing platform: available at h t t p :/ www .iso .org/ obp ISO 2017 All rights reserved 1BS ISO 18608:2017ISO 18608:2017(E)3.1ligamentpart of the double edge
29、notched specimen that is located between the notchesNote 1 to entry: The width of the ligament is denoted b; the cross-section of the ligament is denoted A.3.2notch depthadistance between the side of the specimen and the tip of the notch3.3notched specimen widthbnwidth of the notched specimen outsid
30、e the notched cross-section3.4maximum tensile forceFmhighest recorded tensile force on the test specimen when tested to failure3.5un-notched specimen tensile strengtht,mtensile strength determined by measurement according to ISO 15733Note 1 to entry: The value of this parameter is designated r.3.6no
31、tched specimen tensile strengtht,m,nratio of the maximum tensile force to the ligament cross-section areaNote 1 to entry: The value of this parameter is designated n.3.7equivalent fracture toughnessKeqfracture toughness of a homogeneous and isotropic material which presents the same dependence of th
32、e stress ratio n/ron the notch depth as the investigated composite4 PrincipleTensile tests are carried out on double edge notched test specimens with notches of different depths. The results of these tests are compared with the results of tensile tests on specimens without notches. The cross-section
33、al dimensions of the notched specimens between the notches are equal to those of the un-notched specimens.The strength values observed on both types of specimens as a function of notch depth allow the determination of the range of notch size for which the tested composite is sensitive to the presenc
34、e of notches.5 Significance and useThe fracture toughness is a material property which characterizes the initiation of fracture from a sharp crack (usually obtained by fatigue cracking under plane strain conditions). The fracture toughness of 2 ISO 2017 All rights reservedBS ISO 18608:2017ISO 18608:
35、2017(E)materials at the onset of crack extension from a pre-existing fatigue crack is characterized by the value of one of the following parameters:a) Kc,a critical value of K(the stress intensity factor of the elastic stress field in the vicinity of the crack front) at the point of instability of t
36、he crack extension;b) Gc, a critical value of G(the strain-energy release rate with crack extension per unit area of newly created crack surface) at the point of instability of the crack extension;c) Jc, a critical value of J(a line or surface integral used to characterize the local stress-strain fi
37、eld around the crack front) at the onset of stable crack extension.The J integral plays an important role in nonlinear fracture mechanics. It applies to nonlinear elastic bodies, whereas linear elastic fracture mechanics (Kcand Gc) consider linear elastic bodies.Several problems arise in determining
38、 and even in defining Kc, Gcand Jcin fibre reinforced ceramic matrix composites, as a result of the following features:a) CMC are generally highly heterogeneous, consisting of different constituents (fibres and matrix), and containing pores and cracks;b) in some CMC, a damage zone of multiple matrix
39、 cracks forms ahead of a notch prior to ultimate failure;c) the associated deformations are nonlinear.The load versus load line displacement curve from a fracture test on a notched specimen involves a nonlinear domain induced by diffuse micro-cracking within the matrix at the notch tip. The damage z
40、one is in the millimetre to centimetre scale (from one to several tow diameters). At maximum load, a macroscopic crack is created from the random failure of fibres within those tows located in the damage zone. Crack extension in CMC, hence, does not result from the mechanism of extension of a single
41、 macroscopic crack as observed in monolithic materials.Because of the presence of the damage zone and of heterogeneous microstructure, the stress distribution in the damage zone differs from the one induced ahead of the crack tip in linear elastic bodies. The Kparameter does not describe the stress
42、field in the region ahead of the crack tip. A critical value Kccannot be defined.The main difficulty in the determination of the strain energy release rate G, as well as the J integral, results from the presence of the micro-cracked zone at the notch tip (which is not small compared with the specime
43、n dimensions) and the jagged surface of the macroscopic crack. As a consequence, an increase in crack length can neither be easily defined nor measured.Tensile tests performed on specimens containing holes or notches have demonstrated that many CMC are relatively notch-insensitive over a range of no
44、tch sizes. The net-section stress at fracture is typically (80 to 100) % of the un-notched strength. Notch insensitivity results from a stress relaxation at the notch tip due to the development of the damage zone. As a consequence, the fibres in the damage zone are subjected to stresses that are com
45、parable in magnitude to the remote stresses.A measure of the notch sensitivity at a given notch depth is provided by the ratio of the failure stress of a notched tensile specimen (n) to the failure stress of a corresponding un-notched tensile specimen (r):a) when n r, the composite is notch sensitiv
46、e;b) when n r, the composite is notch insensitive.The stress ratio n/ris a useful parameter for component design purposes. It allows the selection of the composites that are able to tolerate notches, holes, etc.For material comparison purposes, an equivalent fracture toughness Keqis defined over the
47、 notch depth range where the stress ratio is less than 1. ISO 2017 All rights reserved 3BS ISO 18608:2017ISO 18608:2017(E)Keqrepresents the fracture toughness of the equivalent homogeneous monolithic material which exhibits the same notch sensitivity as the actual composite. Keqis calculated from th
48、e dependence of the n/rstress ratio on notch depth, using linear elastic fracture mechanics equations.Over the range of notch depths where the CMC is notch sensitive, the calculation of the equivalent fracture toughness for the different notch depths does not usually result in a single value for Keq
49、. For reasons of conservatism, the minimum value is used.For some CMC, a transition from notch insensitive to notch sensitive has been observed with increasing notch depth. The determination of equivalent fracture toughness is not recommended when the notch insensitive range extends beyond a minimum value of notch depth (1 mm).Additional testing at different notch depths may be performed to provide a more complete understanding of the notch depth range where the CMC is notch inse
