1、BRITISH STANDARDBS EN ISO 18756:2005Fine ceramics (advanced ceramics, advanced technical ceramics) Determination of fracture toughness of monolithic ceramics at room temperature by the surface crack in flexure (SCF) methodThe European Standard EN ISO 18756:2005 has the status of a British StandardIC
2、S 81.060.30g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN ISO 18756:2005This British Standard was published under the authority of the Standa
3、rds Policy and Strategy Committee on 29 December 2006 BSI 2006ISBN 0 580 49897 2National forewordThis British Standard was published by BSI. It is the UK implementation of EN ISO 18756:2005. It is identical with ISO 18756:2003.The UK participation in its preparation was entrusted to Technical Commit
4、tee RPI/13, Advanced technical ceramics.A list of organizations represented on RPI/13 can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Stand
5、ard cannot confer immunity from legal obligations.Amendments issued since publicationAmd. No. Date CommentsEUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN ISO 18756July 2005ICS 81.060.30English VersionFine ceramics (advanced ceramics, advanced technicalceramics) - Determination of fracture toughne
6、ss of monolithicceramics at room temperature by the surface crack in flexure(SCF) method (ISO 18756:2003)Cramiques techniques - Dtermination de la tnacit larupture des cramiques monolithiques tempratureambiante par fissuration superficielle en flexion (ISO18756:2003)Hochleistungskeramik - Bestimmung
7、 der Bruchzhigkeitmonolithischer Keramik bei Raumtemperatur frBiegeproben mit Oberflchenriss (Knoop-Riss) (SCF-Verfahren) (ISO 18756:2003)This European Standard was approved by CEN on 2 June 2005.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions
8、 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 Standard exists in three official
9、 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 standards bodies of Austria, Belgium
10、, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUR
11、OPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2005 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN ISO 18756:2005: EForeword The text of ISO 18756:2003 has been prepared by
12、Technical Committee ISO/TC 206 “Fine ceramics“ of the International Organization for Standardization (ISO) and has been taken over as EN ISO 18756:2005 by Technical Committee CEN/TC 184 “Advanced technical ceramics“, the secretariat of which is held by BSI. This European Standard shall be given the
13、status of a national standard, either by publication of an identical text or by endorsement, at the latest by January 2006, and conflicting national standards shall be withdrawn at the latest by January 2006. This document is part of a series: CEN/TS 14425-1 Advanced technical ceramics Test methods
14、for determination of fracture toughness of monolithic ceramics Part 1: Guide to test method selection CEN/TS 14425-3 Advanced technical ceramics Test methods for determination of fracture toughness of monolithic ceramics Part 3: Chevron notched beam (CNB) method CEN/TS 14425-5 Advanced technical cer
15、amics Test methods for determination of fracture toughness of monolithic ceramics Part 5: Single-edge V-notch beam (SEVNB) method EN ISO 15732 Fine ceramics (advanced ceramics, advanced technical ceramics) Test method for fracture toughness of monolithic ceramics at room temperature by single edge p
16、recracked beam (SEPB) method EN ISO 18756 Fine ceramics (advanced ceramics, advanced technical ceramics) Determination of fracture toughness of monolithic ceramics at room temperature by the surface crack in flexure (SCF) method According to the CEN/CENELEC Internal Regulations, the national standar
17、ds organizations of the following countries are bound to implement this 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, Slov
18、akia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. Endorsement notice The text of ISO 18756:2003 has been approved by CEN as EN ISO 18756:2005 without any modifications. EN ISO 18756:2005Reference numberISO 18756:2003(E)INTERNATIONAL STANDARD ISO18756First edition2003-12-01Fine ceramics
19、(advanced ceramics, advanced technical ceramics) Determination of fracture toughness of monolithic ceramics at room temperature by the surface crack in flexure (SCF) method Cramiques techniques Dtermination de la tnacit la rupture des cramiques monolithiques temprature ambiante par fissuration super
20、ficielle en flexion EN ISO 18756:2005ii iiiContents Page Foreword iv 1 Scope 1 2 Normative references . 1 3 Terms and definitions. 1 4 Symbols . 3 5 Principle . 4 6 Apparatus. 5 7 Test specimens . 6 7.1 Specimen size, preparation and edge chamfering 6 7.2 Number of specimens. 6 8 Procedure. 7 8.1 In
21、troduction of the precrack by Knoop indentation 7 8.2 Specimen fracture. 11 8.3 Crack size measurement 12 8.4 Environmental effects. 13 8.5 Optional: Estimate of R-curve behaviour .14 8.6 Optional: Reference materials . 14 9 Calculation. 14 10 Test report 15 Annex A (informative) Environmental effec
22、ts 17 Annex B (normative) Precrack characterization . 18 Annex C (informative) R-curve estimation by the SCF method. 25 Annex D (normative) Chamfer correction factors. 27 Bibliography . 29 EN ISO 18756:2005iv Foreword ISO (the International Organization for Standardization) is a worldwide federation
23、 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.
24、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
25、h the rules given in the ISO/IEC Directives, Part 2. 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
26、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 document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 18756 was prepared by Technical Committe
27、e ISO/TC 206, Fine ceramics. EN ISO 18756:20051Fine ceramics (advanced ceramics, advanced technical ceramics) Determination of fracture toughness of monolithic ceramics at room temperature by the surface crack in flexure (SCF) method 1 Scope This International Standard describes a test method that c
28、overs the determination of fracture toughness of monolithic ceramic materials at room temperature by the surface crack in flexure (SCF) method. This International Standard is intended for use with monolithic ceramics and whisker- or particulate-reinforced ceramics that are regarded as macroscopicall
29、y homogeneous. It does not include continuous-fibre reinforced ceramic composites. The test method is applicable to materials with either flat or rising crack growth resistance curves. This method is similar to ISO 15732 except that precracks are smaller and are made by a different procedure. The me
30、thods should produce similar or identical results for materials with a flat R-curve. NOTE This test method is usually applicable to ceramic materials with a fracture toughness less than 10 MPa m1/2. It may be difficult to form precracks with a Knoop indenter for materials with greater fracture tough
31、ness or those materials which are soft (low hardness) such as some zirconias, or for porous ceramics. 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 la
32、test edition of the referenced document (including any amendments) applies. ISO 3611:1978, Micrometer callipers for external measurement ISO 7500-1:1), Metallic materials Verification of static uniaxial testing machines Part 1: Tension/ compression testing machines Verification and calibration of th
33、e force-measuring system ISO 14704:2000, Fine ceramics (advanced ceramics, advanced technical ceramics) Test method for flexural strength of monolithic ceramics at room temperature 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 1) To be publishe
34、d. (Revision of ISO 7500-1:1999) EN ISO 18756:20052 3.1 stress intensity factor KImagnitude of the elastic stress field singularity at the tip of a crack subjected to opening mode displacement NOTE It is a function of applied force and test specimen size, geometry and crack length, and has dimension
35、s of force times length to the power of three over two. 3.2 fracture toughness generic term for measures of resistance of extension of a crack 3.3 fracture toughness value KIscfracture toughness value measured by the SCF method NOTE This is the measured stress intensity factor corresponding to the c
36、rack extension resistance of a semi-elliptical small crack formed underneath a Knoop indentation. The measurement is performed to the operational procedure herein and satisfies all the validity requirements. 3.4 precrack crack introduced into the test specimen artificially prior to testing the speci
37、men to fracture 3.5 crack front line line to indicate the position of the tip of the crack 3.6 critical stress intensity factor KIccritical value of KIat which fast fracture occurs 3.7 critical crack crack at fracture at maximum load and whose stress intensity factor just reaches the critical stress
38、 intensity factor 3.8 critical crack size size of the critical crack at fracture NOTE The critical crack will be larger than the precrack if stable crack extension occurs due to environmentally-assisted slow crack growth or rising R-curve behaviour. 3.9 four-point 1/4-point flexure specific configur
39、ation of four-point flexural strength testing where the inner bearings are situated one quarter of the support span away from the two outer bearings 3.10 four-point 1/3-point flexure specific configuration of four-point flexural strength testing where the inner bearings are situated one third of the
40、 support span away from the two outer bearings 3.11 flexural strength maximum nominal stress at fracture of a specified elastic beam loaded in bending EN ISO 18756:200534 Symbols a Crack depth A Flexure fixture moment arm B Specimen width, the cross section dimension perpendicular to the direction o
41、f loading in bending c Crack half width C Chamfer size d Length of Knoop indentation long diagonal h Depth of Knoop indentation F Knoop indentation load FcChamfer correction factor H1(a/c, a/W) A polynomial in the stress intensity factor coefficient, for the point on the crack periphery where it int
42、ersects the specimen surface H2(a/c, a/W) A polynomial in the stress intensity factor coefficient, for the deepest part of the surface crack KIStress intensity factor, Mode I KIcCritical stress intensity factor, Mode I KIscFracture toughness value, surface crack in flexure method L Flexure fixture s
43、upport span LTSpecimen length M (a/c, a/W) A polynomial in the stress intensity factor coefficient P Load at fracture Q (a/c) A polynomial function of the surface crack ellipticity S (a/c, a/W) Factor in the stress intensity factor coefficient W Specimen depth, the cross section dimension parallel t
44、o the direction of loading in bending Y Stress intensity factor coefficient YdStress intensity factor coefficient at the deepest part of the surface crack YmaxThe maximum stress intensity factor coefficient along the boundary of the surface crack YsStress intensity factor coefficient at the intersec
45、tion of the surface crack with the specimen surface EN ISO 18756:20054 5 Principle This International Standard is for material development, material comparison, quality assurance, characterization, reliability, and design data generation. The method determines the fracture toughness value, KIscby fr
46、acturing a common flexure specimen which has a small surface precrack (see Figure 1). The specimen is indented with a Knoop indenter in order to make a small, semi-elliptical surface crack. The specimen is polished or ground carefully until the indentation and associated residual stress field are re
47、moved. The specimen is fractured in four-point flexure. The fracture toughness, KIsc, is calculated from the fracture load and the measured critical crack size. Fractography is required to measure the precrack size and to determine whether the crack has grown in size. Fracture toughness as a functio
48、n of crack size may be evaluated by varying the Knoop indentation load that is used to make the precrack. Background information concerning this test method may be found in References 1 and 2. An international interlaboratory comparison study (round robin) project on this method is described in Refe
49、rences 3, 4 and 5. If the ceramic is too soft (low hardness) or has too great a fracture toughness, it may be difficult to create a precrack by the SCF method. In addition, for some materials (particularly those with coarse grain or heterogeneous microstructures), it may be difficult to detect the crack on the fracture surface. If the user is not sure of the applicability of this method, then a single trial specimen may be tested with an abbreviated procedure. Indent the specimen and fracture it without removal of the i
