1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS EN 14425-3:2010Advanced technical ceramics Test methods for determinationof fracture toughness ofmonolithic ceramicsPart 3: Chevron notched beam (CNB)methodBS EN 14425-3:2010
2、BRITISH STANDARDNational forewordThis British Standard is the UK implementation of EN 14425-3:2010.It supersedes DD CEN/TS 14425-3:2003 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee RPI/13, Advanced technical ceramics.A list of organizations represent
3、ed on this 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. BSI 2010ISBN 978 0 580 68820 1ICS 81.060.30Compliance with a British Standard cannot confer immuni
4、ty fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 31 July 2010Amendments issued since publicationDate Text affectedBS EN 14425-3:2010EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 14425-3 June 2010 ICS 81.060.30 Su
5、persedes CEN/TS 14425-3:2003English Version Advanced technical ceramics - Test methods for determination of fracture toughness of monolithic ceramics - Part 3: Chevron notched beam (CNB) method Cramiques techniques avances - Mthode dessai de dtermination de la tnacit la rupture des cramiques monolit
6、hiques - Partie 3: Mthode de lprouvette entaille en chevron Hochleistungskeramik - Prfverfahren zur Bestimmung der Bruchzhigkeit von monolithischer Keramik - Teil 3: Verfahren fr Biegeproben mit Chevron-Kerb (CNB-Verfahren) This European Standard was approved by CEN on 30 April 2010. CEN members are
7、 bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to t
8、he CEN Management Centre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same
9、 status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Por
10、tugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels 2010 CEN All rights of exploitation in any form and by any mean
11、s reserved worldwide for CEN national Members. Ref. No. EN 14425-3:2010: EBS EN 14425-3:2010EN 14425-3:2010 (E) 2 Contents Page Foreword 31 Scope 42 Normative references 43 Terms and definitions .44 Principle, significance and use 45 Test apparatus .56 Test pieces .56.1 Material selection .56.2 Test
12、 piece dimensions 56.3 Sawn notch .67 Procedure .68 Calculation of results 79 Interferences and errors .810 Reporting 8Bibliography . 14BS EN 14425-3:2010EN 14425-3:2010 (E) 3 Foreword This document (EN 14425-3:2010) has been prepared by Technical Committee CEN/TC 184 “Advanced technical ceramics”,
13、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 endorsement, at the latest by December 2010, and conflicting national standards shall be withdrawn at the latest by December 2010. Attent
14、ion is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. This document supersedes CEN/TS 14425-3:2003. According to the CEN/CENELEC Internal Regulati
15、ons, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
16、 Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. BS EN 14425-3:2010EN 14425-3:2010 (E) 4 1 Scope This European Standard provides a test method for fracture toughness determination based on the chevron-notch method. For the purpos
17、es of this European Standard, the term monolithic includes particle and whisker reinforced advanced technical ceramics which can be regarded as macroscopically homogeneous. It does not include long-fibre reinforced ceramics. 2 Normative references The following referenced documents are indispensable
18、 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 amendments) applies. EN 843-1:2006, Advanced technical ceramics Mechanical properties of monolithic ceramics at room tempe
19、rature Part 1: Determination of flexural strength EN 1006, Advanced technical ceramics Monolithic ceramics Guidance on the selection of test pieces for the evaluation of properties EN ISO 7500-1, Metallic materials Verification of static uniaxial testing machines Part 1: Tension/compression testing
20、machines Verification and calibration of the force-measuring system (ISO 7500-1:2004) EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories (ISO/IEC 17025:2005) ISO 3611, Micrometer callipers for external measurement 3 Terms and definitions For the purpose
21、s of this document, the following terms and definitions apply. 3.1 chevron-notch test piece test piece in which a two coplanar saw cuts are made at an angle to each other part way through a test piece to leave a remaining cross-section with a sharp tip from which a crack may be initiated in a contro
22、lled or semi-controlled manner 4 Principle, significance and use In the chevron-notched beam method, a crack is generated during the test from a sharp tip resulting when two coplanar notches are cut in a test piece (see Figure 1). This overcomes the need to generate sharp planar cracks before commen
23、cing the test. During the test, the crack front widens as the crack propagates from the tip, resulting in an increase in the force required to maintain growth. Countering this, the test piece becomes more compliant as the crack lengthens, and so the two effects result in a peak load being attained a
24、fter some distance of propagation. The toughness is determined from the peak force applied. This test method employs the chevron notch in a flexural strength test piece, loaded in four-point bending geometry. The advantage is that it can be performed on standard flexural strength test pieces. BS EN
25、14425-3:2010EN 14425-3:2010 (E) 5 The test is most appropriate for homogeneous isotropic materials, but can be used with care on anisotropic materials subject to the geometry of fracture remaining valid. In materials which are inhomogeneous on the scale of the crack dimensions, a wide scatter of res
26、ults and the development of invalid non-planar cracks may occur. In addition, the test is valid primarily for materials which do not show rising crack resistance with increasing crack length. Since the crack width progressively increases as propagation occurs, the concurrent presence of rising crack
27、 resistance means that the crack front would no longer stay straight but would become convex, producing an uncertainty in the calculated results. It should be noted that this test employs a slowly moving crack. The numerical value for the fracture toughness calculated from this method may not be the
28、 same as those from fast crack propagation tests, especially if the susceptibility to subcritical crack growth is significant. 5 Test apparatus 5.1 Flexural strength test apparatus of four-point bending type, in accordance with the requirements in EN 843-1. 5.2 Mechanical testing machine, capable of
29、 accurate recording of load/displacement data for loads in the range 0 N to 500 N. The load shall be calibrated in accordance with EN ISO 7500-1. NOTE A stiff loading system (i.e. frame, load cell and fixtures, etc.) is advantageous for this test. The compliance is ideally less than 5 10-5m/N (see 1
30、). 5.3 Micrometer in accordance with ISO 3611 but measuring to an accuracy of 0,002 mm. 5.4 Calibrated device for measuring dimensions of the cut chevron after fracture, reading to an accuracy of 0,002 mm or better. NOTE This may be achieved by use of an appropriate travelling microscope, or a conve
31、ntional microscope with a calibrated stage micrometer, or a microscope with a micrometer eyepiece. 5.5 Humidity measuring device for measuring relative humidity to an accuracy of 2 %, e.g. those according to ISO 4677. 6 Test pieces 6.1 Material selection Select the material or components from which
32、test pieces are to be machined with reference to the considerations given in EN 1006. 6.2 Test piece dimensions 6.2.1 The test pieces shall preferably be of dimensions as for determination of flexural strength and described in EN 843-1. Alternatively, if availability of material permits, the dimensi
33、ons may be scaled larger for convenience of machining of the notch. NOTE It is usually advantageous to test coarse-grained or heterogeneous materials in larger test piece sizes because it improves the chances of obtaining a valid test (see 7.9). 6.2.2 The standard size test pieces shall be (3,00 0,1
34、5) mm (4,00 0,15) mm in cross-section, and have a minimum length of 45 mm. The surfaces shall be machined to a flatness of better than 0,01 mm over the test piece length, and opposite pairs of faces shall be parallel to better than 0,01 mm over the test piece length. The section should be visibly re
35、ctangular. NOTE Chamfering in accordance with EN 843-1 is unnecessary for this test. BS EN 14425-3:2010EN 14425-3:2010 (E) 6 6.2.3 The test piece surfaces shall be ground to a good quality finish using final grinding with a peripheral wheel of grit size between 320 and 500 mesh grit, using a depth o
36、f cut of no more than 0,002 mm for the last 0,04 mm of material removed from each surface. No edge treatment is necessary. NOTE Although a large notch is placed in the test piece, the quality of grinding remains important for dimensional accuracy for registration in cutting the notch and for minimiz
37、ing residual stresses. 6.3 Sawn notch 6.3.1 The notch is produced by two saw cuts at an appropriate angle to each other as shown in Figure 1. The notch width shall be less than 0,20 mm at the surface, and the notch root radius should be less than 0,1 mm. The grit size of the saw or grinding wheel em
38、ployed shall be 320 mesh or smaller. For standard test pieces, the test piece shall be orientated such that the notch tip is opposite the 3 mm width face. The notch geometry may be selected to suit requirements. However, it is recommended that: a) the angles of the two sides of the notch to the test
39、 piece faces are equal to within 1, and the notch tip is central within the test piece to within 0,05 B where B is the test piece width; b) the position of the notch tip, a0, below the test piece surface is about 20 % of the depth of the test piece, W; c) the positions of run-out of the notch throug
40、h the test piece sides, a11, a12are closely similar, and are in the range 90 % to 100 % of the test piece depth, W. NOTE 1 The use of a surface grinder or precision slicing saw permits straight-tipped cuts to be made. The use of a non-traversing saw, or a wire saw, is not recommended because the lin
41、e of the notch tip produced is not straight. This can introduce a considerable error in the use of the calibration equations. NOTE 2 The reproducibility and quality of machining of the notch can influence the reproducibility of the test result. In general, narrower and more precise cutting encourage
42、s more reproducible initial stable crack growth and reduces the scatter in results. 6.3.2 A simple method of obtaining the required precision of cutting is to prepare a V-block with an end stop against which the test piece can be registered. The test piece is clamped on one side to permit the first
43、cut, and is then rotated and clamped on the other side to allow the second cut of equal depth to be coplanar with the first. The angle of the V-block is the same as that required for the notch angle. 6.3.3 A minimum of five test pieces shall be prepared. 7 Procedure 7.1 Measure the external dimensio
44、ns of the test piece at the notch to the nearest 0,002 mm using the micrometer (5.3). 7.2 Measure the notch lengths a11and a12(to the points where the roots of the notch meet the external surfaces) to the nearest 0,002 mm using the calibrated device (5.4). The difference between the average value a1
45、and the individual values shall not be greater than 0,05 W, where W is the test piece thickness. 7.3 Adjust the sensitivity of the load recording device to permit an accuracy of subsequent measurement to better than 1 % of recorded values. Adjust the recording and plotting parameters of the recordin
46、g device to permit clear identification of the load/time or load/displacement behaviour (see Figure 2). 7.4 Insert the test piece in the strength test apparatus with the tip of the chevron notch facing the outer support rollers, and align it carefully to ensure that the support and loading spans are
47、 centralised to within 0,2 mm in accordance with EN 843-1:2006. 7.5 Select for the test machine displacement rate a value which achieves fracture in typically 2 min to 5 min. BS EN 14425-3:2010EN 14425-3:2010 (E) 7 NOTE Typically this requires a machine displacement rate of about 0,05 mm/min or slow
48、er. If the fracture force range is known, it is possible to use a faster rate up to about 75 % of the fracture force, before switching to the slower rate. 7.6 Measure and record the relative humidity and temperature of the atmosphere in the proximity of the test. 7.7 Load the test piece in the flexu
49、ral test apparatus and record the load/displacement curve produced as the test piece fractures. 7.8 Inspect the trace (see Figure 2). If the fracture exhibited stable characteristics with the load rising to a smooth maximum and then falling (Figure 2a), or if the crack popped-in prior to the load passing through a smooth maximum (Figure 2b), the test can be deemed to be valid. Determine the maximum test force, Pmax. If the load reached a sharp maximum from which it fell suddenly towards zero without a s
