1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58composites at ambient temperature Evaluation of the resistance to crack propagation by notch sensit
2、ivity testingThe European Standard EN 13234:2006 has the status of a British StandardICS 81.060.30Advanced technical ceramics Mechanical properties of ceramic BRITISH STANDARDBS EN 13234:2006BS EN 13234:2006This British Standard was published under the authority of the Standards Policy and Strategy
3、Committee on 29 December 2006 BSI 2006ISBN 0 580 49864 6Amendments issued since publicationAmd. No. Date Commentscontract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.National forewordThis British Standard was pub
4、lished by BSI. It is the UK implementation of EN 13234:2006. It supersedes DD ENV 13234:2000 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee RPI/13, Advanced technical ceramics.A list of organizations represented on RPI/13 can be obtained on request t
5、o its secretary.This publication does not purport to include all the necessary provisions of a EUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN 13234October 2006ICS 81.060.30 Supersedes ENV 13234:1998 English VersionAdvanced technical ceramics - Mechanical properties of ceramiccomposites at ambient
6、 temperature - Evaluation of theresistance to crack propagation by notch sensitivity testingCramiques techniques avances - Proprits mcaniquesdes cramiques composites temprature ambiante -Evaluation de la rsistance la propagation de fissure parun essai de sensibilit lentailleHochleistungskeramik - Me
7、chanische Eigenschaften vonkeramischen Verbundwerkstoffen beiUmgebungstemperatur - Beurteilung derRissausbreitungsbestndigkeit durch dieKerbempfindlichkeitsprfungThis European Standard was approved by CEN on 11 September 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations
8、which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Sta
9、ndard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standa
10、rds bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN
11、 COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2006 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13234:2006: EEN 13234:2006 (E) 2 Co
12、ntents Page Foreword. 3 1 Scope 4 2 Normative references . 4 3 Principle . 4 4 Significance and use 5 5 Terms, definitions and symbols 6 6 Apparatus. 7 6.1 Test machine . 7 6.2 Load train. 7 6.3 Data recording system . 7 6.4 Micrometers. 8 6.5 Ligament size measuring device. 8 7 Specimens . 8 7.1 Un
13、-notched test specimens . 8 7.2 Notched test specimens. 8 7.3 Notches 10 8 Test specimen preparation 10 8.1 Machining and preparation 10 8.2 Number of test specimens . 10 9 Test procedure 10 9.1 Test on reference specimen 10 9.2 Test on notched specimen. 10 10 Calculation of results 11 10.1 Test spe
14、cimen origin 11 10.2 Tensile strength of un-notched specimen 11 10.3 Tensile strength of the notched specimen. 12 10.4 Plotting of notch sensitivity diagram 12 10.5 Calculation of equivalent fracture toughness for the different classes of behaviour . 13 11 Test report . 13 Bibliography . 15 EN 13234
15、:2006 (E) 3 Foreword This document (EN 13234:2006) has been prepared by Technical Committee CEN/TC 184 “Advanced technical ceramics”, the secretariat of which is held by BSI. This European Standard shall be given the status of a national standard, either by publication of an identical text or by end
16、orsement, at the latest by April 2007, and conflicting national standards shall be withdrawn at the latest by April 2007. This document supersedes ENV 13234:1998. ENV 13234 was approved by CEN/TC 184 for development into a full European Standard. The principal changes to the ENV are in the normative
17、 references, as follows: - in 6.1, reference to EN 10002-2 has been replaced by reference to EN ISO 7500-1; - in 6.2.1, reference to WI 136 has been removed. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this
18、 European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
19、 EN 13234:2006 (E) 4 1 Scope This European Standard describes a method for the classification of ceramic matrix composite (CMC) materials with respect to their sensitivity to crack propagation using tensile tests on notched specimens with different notch depths. Two classes of ceramic matrix composi
20、te 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 European Standard defines a method for determining equivalent fracture toughness. The parameter, Keq, is defined as the frac
21、ture 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 Keqparameter offers the possibility to compare ceramic matrix composite materials with other materials with resp
22、ect to sensitivity to crack propagation. For notch insensitive materials, the concept of Keqdoes not apply. This European Standard applies to all ceramic matrix composites with a continuous fibre reinforcement, unidirectional (1 D), bidirectional (2 D), and tridirectional (x D, where 2 x 3), loaded
23、along one principal axis of reinforcement. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amen
24、dments) applies. EN 658-1:1998, Advanced technical ceramics Mechanical properties of ceramic composites at room temperature Part 1: Determination of tensile properties EN ISO 7500-1, Metallic materials Verification of static uniaxial testing machines Part 1: Tension/compression testing machines Veri
25、fication and calibration of the force-measuring system (ISO 7500-1:2004) ISO 3611, Micrometer callipers for external measurement 3 Principle Tensile 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
26、of tensile tests on specimens without notches. The cross sectional 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 notc
27、h size for which the tested composite is sensitive to the presence of notches. EN 13234:2006 (E) 5 4 Significance and use The fracture toughness is a material property which characterises the initiation of fracture from a sharp crack (usually obtained by fatigue cracking under plane strain condition
28、s). The fracture toughness of materials at the onset of crack extension from a pre-existing fatigue crack is characterised by the value of one of the following parameters: i) Kc,a critical value of K(the stress intensity factor of the elastic stress field in the vicinity of the crack front), at the
29、point of instability of the crack extension; ii) 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; iii) Jc, a critical value of J(a line or surface integral used to character
30、ise the local stress-strain field around the crack front) at the onset of stable crack extension. The J integral plays an important role in non-linear fracture mechanics. It applies to non-linear elastic bodies, whereas linear elastic fracture mechanics (Kcand Gc) consider linear elastic bodies. Sev
31、eral problems arise in determining and even in defining Kc, Gcand Jcin fibre reinforced ceramic matrix composites, as a result of the following features: 1) CMC are generally highly heterogeneous, consisting of different constituents (fibres and matrix), and containing pores and cracks; 2) in some C
32、MC a damage zone of multiple matrix cracks forms ahead of a notch prior to ultimate failure; 3) the associated deformations are non-linear. The load versus load line displacement curve from a fracture test on a notched specimen involves a non-linear domain induced by diffuse micro-cracking within th
33、e matrix at the notch tip. The damage zone 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
34、 the mechanism of extension of a single 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
35、Kparameter does not describe the stress 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 (whi
36、ch is not small compared with the specimen 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 relati
37、vely notch-insensitive over a range of notch 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 zo
38、ne are subjected to stresses that are comparable 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): E
39、N 13234:2006 (E) 6 a) when n r, the composite is notch sensitive; 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
40、purposes, an equivalent fracture toughness Keqis defined over the notch depth range where the stress ratio is less than 1. Keq represents the fracture toughness of the equivalent homogeneous monolithic material which exhibits the same notch sensitivity as the actual composite. Keqis calculated from
41、the 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
42、Keq. 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 min
43、imum value of notch depth (1 mm). NOTE 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 insensitive. 5 Terms, definitions and symbols For the purposes of this document, the terms, definitions and sy
44、mbols given in EN 658-1:1998 and the following apply. 5.1 ligament part of the double edge notched specimen that is located between the notches. The width of the ligament is denoted b; the cross-section of the ligament is denoted A 5.2 notch depth, a distance between the side of specimen and the tip
45、 of the notch 5.3 notched specimen width, bnwidth of the notched specimen outside the notched cross-section 5.4 maximum tensile force, Fmhighest recorded tensile force on the test specimen when tested to failure 5.5 un-notched specimen tensile strength, t,mtensile strength determined by measurement
46、according to EN 658-1. The value of this parameter is designated r5.6 notched specimen tensile strength, t,m,nratio of the maximum tensile force to the ligament cross section area. The value of this parameter is designated nEN 13234:2006 (E) 7 5.7 equivalent fracture toughness Keqfracture toughness
47、of a homogeneous and isotropic material which presents the same dependence of the stress ratio n/ron the notch depth as the investigated composite 6 Apparatus 6.1 Test machine The machine shall be equipped with a system for measuring the force applied to the test specimen, which, when tested in acco
48、rdance with EN ISO 7500-1, shall meet the requirements of grade 1 or better of that standard. 6.2 Load train 6.2.1 General The load train is composed of the moveable and fixed crosshead, the loading rods, and the grips. Load train couplers may additionally be used to connect the grips to the loading
49、 rods. The load train shall align the specimen axis with the direction of load application without introducing bending or torsion in the specimen. The alignment shall be verified and documented. The maximum percent bending shall not exceed 5 at an axial strain of 50010-6. 6.2.2 Grips The grips transmit the axial load applied by the testing machine to the specimen. They shall prevent slipping of the specimen in the gripping section. The selection of a particular type of
