www bzfxw com BRITISH STANDARD BS EN 843 1 1995 Advanced technical ceramics — Monolithic ceramics — Mechanical properties at room temperature — Part 1 Determination of flexural strength The European S[.]
BRITISH STANDARD Advanced technical ceramics — Monolithic ceramics — Mechanical properties at room temperature — Part 1: Determination of flexural strength The European Standard EN 843-1:1995 has the status of a British Standard BS EN 843-1:1995 BS EN 843-1:1995 Cooperating organizations The European Committee for Standardization (CEN), under whose supervision this European Standard was prepared, comprises the national standards organizations of the following countries: Austria Belgium Denmark Finland France Germany Greece Iceland Ireland Italy Luxembourg Netherlands Norway Portugal Spain Sweden Switzerland United Kingdom This British Standard, having been prepared under the direction of the Refractory Products Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 March 1995 © BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference RPM/13 Draft for comment 92/45075 DC ISBN 580 23140 Oesterreichisches Normungsinstitut Institut belge de normalisation Dansk Standard Suomen Standardisoimisliito, r.y Association franỗaise de normalisation Deutsches Institut für Normung e.V Hellenic Organization for Standardization Technological Institute of Iceland National Standards Authority of Ireland Ente Nazionale Italiano di Unificazione Inspection du Travail et des Mines Nederlands Normalisatie-instituut Norges Standardiseringsforbund Instituto Portugs da Qualidade Asociación Espola de Normalización y Certificación Standardiseringskommissionen i Sverige Association suisse de normalisation British Standards Institution Amendments issued since publication Amd No Date Comments BS EN 843-1:1995 Contents Cooperating organizations National foreword Foreword Text of EN 843-1 National annex NA (informative) Committees responsible © BSI 12-1999 Page Inside front cover ii Inside back cover i BS EN 843-1:1995 National foreword This British Standard has been prepared under the direction of the Refractory Products Standards Policy Committee and is the English language version of EN 843-1:1995 Advanced technical ceramics — Monolithic ceramics — Mechanical properties at room temperature — Part 1: Determination of flexural strength, published by the European Committee for Standardization (CEN) No current British Standard is superseded EN 843-1 was produced as a result of international discussions in which the UK took an active part A British Standard does not purport to include all the necessary provisions of a contract Users of British Standards are responsible for their correct application Compliance with a British Standard does not of itself confer immunity from legal obligations Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the EN title page, pages to 12, an inside back cover and a back cover This standard has been updated (see copyright date) and may have had amendments incorporated This will be indicated in the amendment table on the inside front cover ii © BSI 12-1999 EUROPEAN STANDARD EN 843-1 NORME EUROPÉENNE January 1995 EUROPÄISCHE NORM ICS 81.060.10; 81.060.20 Descriptors: Ceramics, environmental tests, mechanical properties, determination, flexural strength English version Advanced technical ceramics — Monolithic ceramics — Mechanical properties at room temperature Part 1: Determination of flexural strength Céramiques techniques avancées — Céramiques monolithiques — Propriétés mécaniques température ambiante — Partie 1: Détermination de la résistance en flexion Hochleistungskeramik — Monolithische Keramik — Mechanische Eigenschaft bei Raumtemperatur — Teil 1: Bestimmung der Biegefestigkeit ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ This European Standard was approved by CEN on 1995-01-04 CEN members are 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 the Central Secretariat or to any CEN member The European Standards exist 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 Central Secretariat has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom CEN European Committee for Standardization Comité Européen de Normalisation Europäisches Komitee für Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels © 1995 Copyright reserved to CEN members Ref No EN 843-1:1995 E EN 843-1:1995 Foreword Contents This European Standard has been prepared by Technical Committee CEN/TC184, 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 endorsement, at the latest by July 1995, and conflicting national standards shall be withdrawn at the latest by July 1995 EN 843 consists of five Parts: — Part 1: Determination of flexural strength; — Part 2: Determination of elastic moduli; — Part 3: Determination of sub-critical crack growth; — Part 4: Determination of hardness; — Part 5: Statistical analysis of fracture data According to the CEN/CENELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom Foreword Scope Normative references Definitions Significance and use Apparatus Test pieces Test procedure Calculations Test report Annex A (informative) Bibliography Figure — Schematic diagrams of function of a) three-point bend test jig and b) four-point bend test jig indicating the articulation and rotation required for the rollers Figure — Test span dimensions and tolerances Figure — Dimensions and tolerances of machined test pieces Page 3 3 10 12 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ 11 © BSI 12-1999 EN 843-1:1995 Scope Definitions This Part of EN 843 describes methods for determining the nominal flexural strength of advanced monolithic technical ceramic materials at ambient temperature The available loading geometries are three- and four-point flexure, using rectangular section test pieces of two prescribed geometries: 20 mm support span (A) and 40 mm support span (B) The test prescribes four categories of surface finish applied to the test pieces: I: as-fired or annealed after machining; II: machined using agreed grinding procedures and material removal rates; III: standard finishing procedures: III.1: finishing by grinding; III.2: finishing by lapping/polishing For the purposes of this Part of EN 843, the following definitions apply: 3.1 nominal flexural strength the maximum nominal stress at the instant of failure supported by the material when loaded in elastic bending 3.2 three-point flexure a means of bending a beam test piece whereby the test piece is supported on bearings near its ends, and a central load is applied 3.3 four-point flexure a means of bending a beam test piece whereby the test piece is supported on bearings near its ends, and is loaded equally at two positions symmetrically disposed about the centre of the supported span NOTE The test may not give representative results if the mean linear intercept grain size exceeds % of the thickness of the test piece, with the exception of single crystals Normative references This European Standard incorporates by dated or undated reference, provisions from other publications These normative references are cited at the appropriate places in the text and the publications are listed hereafter For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision For undated references the latest edition of the publication referred to applies ENV 623-4, Advanced technical ceramics — Monolithic ceramics — General and textural properties — Part 4: Surface roughness EN 10002-2, Tensile testing of metallic materials — Part 2: Verification of the force measuring system of the tensile testing machine ISO 3611, Micrometer callipers for external measurement ISO 4677-1, Atmospheres for conditioning and testing — Determination of relative humidity — Part 1: Aspirated psychrometer method ISO 4677-2, Atmospheres for conditioning and testing — Determination of relative humidity — Part 2: Whirling psychrometer method NOTE The term “quarter-point flexure” is sometimes used for the four-point flexure geometry wherein the load positions are each one-quarter of the support span from the support bearings, as is the case in this standard ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ © BSI 12-1999 Significance and use This test is intended to be used for material development, quality control, characterization and design data acquisition purposes The strength level determined by the test is calculated on the basis of linear elastic bending of a thin beam on the assumption that the material being tested is elastically homogeneous and isotropic, and shows linear (Hookean) stress-strain behaviour The result obtained from a strength test is determined by a large number of factors associated with the microstructure of the material, the surface finishing procedure applied in preparation of the test pieces, the size and shape of the test piece, the mechanical function of the testing apparatus, the rate of load application and the relative humidity of the ambient atmosphere As a consequence of the brittle nature of ceramics, there is usually a considerable range of results obtained from a number of nominally identical test pieces These factors combined mean that caution in the interpretation of test results is required For many purposes, and as described in this standard, the results of strength tests may be described in terms of a mean value and a standard deviation Further statistical evaluation of results is required for design data acquisition, and may be desirable for other purposes EN 843-1:1995 This method places closely defined restrictions on the size and shape of the test piece and on the function of the test apparatus in order to minimize the errors that can arise as a consequence of the test method NOTE The basis for the choice of dimensions and tolerances of test pieces and of the requirements of the test jig may be found in A.1 All other test factors are required to be stated in the test report (see clause 9) in order to allow intercomparison of material behaviours It is not possible rigorously to standardize particular surface finishes, since these are not absolutely controllable in mechanical terms The inclusion of a standard preparation procedure (see 6.3) as one of the surface finish options in this method is intended to provide a means of obtaining a minimum amount of residual grinding damage in the test material The extrapolation of flexure strength data to other geometries of stressing, to multiaxial stressing, to other rates of stressing or to other environments should be viewed with caution The origin of fracture in a flexure test can be a valuable guide to the nature and position of strength-limiting defects Fractography of test pieces is highly recommended In particular, the test may identify fracture origins as being edge defects (caused by edge preparation), surface defects (caused by surface preparation), or internal defects (caused by manufacturing inhomogeneities such as pores, large grains, impurity concentrations) Not all advanced monolithic technical ceramics are amenable to clear fractography Apparatus 5.1 Test jig The test jig shall function as specified below in order to minimize misalignments, twist and frictional forces applied to the test piece NOTE The precise test jig design is not specified, only the function Schematic arrangements of the test jig function are shown in Figure a) for three-point flexure, and Figure b) for four-point flexure The test piece is supported on two bearing edges perpendicular to its length The outer support bearing edges shall be parallel rollers of diameter 2,5 mm ± 0,2 mm (test pieces for span A; see 6.2) or 5,0 mm ± 0,2 mm (test pieces for span B; see 5.2), and shall be capable of rolling outward on flat support surfaces (see Figure 2) One of the rollers shall additionally be capable of rotating about an axis parallel to the length of the test piece such that torsional loading is minimized The two rollers shall be positioned initially with their centres 20 mm ± 0,5 mm apart (span A) or 40 mm ± 0,5 mm apart (span B) with their axes parallel to within 1° The separation of the centres of the rollers in their starting positions shall be measured to the nearest 0,1 mm with the travelling microscope (see 5.3.2) The rollers shall be made from hardened steel or other hard material with a hardness greater than 40 HRC (Rockwell C scale) The rollers shall have a smooth burr-free surface finish with roughness less than 0.5 4m Ra, and shall have diameter uniform to ± 0,02 mm NOTE Particular care should be taken when testing very high strength materials (> GPa) that flattening of the rollers by the test piece or Hertzian indentation of the rollers into the supports does not restrict their rotation High hardness rollers (> 60 HRC) are recommended for testing such ceramics ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ For three-point flexure, a third roller is located at the mid-point between and parallel to the two support rollers This roller has the same diameter as the support rollers, and is similarly free to rotate about an axis parallel to the length of the test piece Its position relative to the midpoint between the support rollers shall be to better than 0,2 mm, measured to the nearest 0,1 mm in a direction parallel to the length of the test piece using the travelling microscope or other suitable device (see 5.3.2) For four-point flexure, two loading rollers are located at the quarter points (see 3.3), i.e with inner spans 10 mm ± 0,2 mm (outer span A) or 20 mm ± 0,2 mm (outer span B), and are free to roll inwards As with the three-point apparatus, the two rollers are also free to rotate separately about an axis parallel to the length of the test piece to allow alignment The loading rollers shall be symmetrically positioned to within ± 0,1 mm The distances between the centres of the support rollers and adjacent loading rollers shall be measured to the nearest 0,1 mm along the length of the test piece perpendicular to the direction of loading, using the travelling microscope or other suitable device (see 5.3.2) The arrangement for loading shall ensure that equal forces are applied to the two loading rollers © BSI 12-1999 EN 843-1:1995 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Figure — Schematic diagrams of function of a) three-point bend test jig and b) four-point bend test jig indicating the articulation and rotation required for the rollers © BSI 12-1999 EN 843-1:1995 ｗｗｗ．ｂｚｆｘｗ．ｃｏｍ Figure — Test span dimensions and tolerances NOTE The accurate and repeatable lateral positioning of loading rollers can best be achieved by ensuring that in the unloaded position, the support rollers are in lateral contact with stops which allow the rollers to roll outwards on their support planes towards the ends of the test piece, and the inner loading rollers (four-point flexure) are in contact with stops which allow rolling inwards towards the middle of the test piece The rotation of the rollers is thus unhindered when load is applied 5.2 Test machine The test apparatus shall be arranged in a suitable mechanical testing machine which shall be capable of applying a force to the loading roller (three-point flexure) or equally to the two loading rollers (four-point flexure) in order to stress the test piece The machine shall be capable of applying the force at a constant loading or displacement rate The test machine shall be equipped for recording the peak load applied to the test piece The accuracy of the test machine shall be in accordance with EN 10002-2, Grade (accuracy % of indicated load) Ensure that the force calibration on the test machine has been checked in accordance with EN 10002-2 5.3 Linear measuring devices 5.3.1 Micrometer A micrometer in accordance with ISO 3611, capable of recording to 0,01 mm and accurate to this level 5.3.2 Travelling microscope A travelling microscope or other suitable device accurate to 0,05 mm (used for measurement of distance between loading rollers) 5.4 Drying oven A drying oven capable of maintaining a temperature of 110 °C ± °C 5.5 Humidity measuring device A device for measuring relative humidity to an accuracy of ± %, e.g those in accordance with ISO 4677 © BSI 12-1999 EN 843-1:1995 Test pieces 6.1 General The test pieces shall be selected and prepared according to agreement between the parties They may either be specially processed to, or close to, the final required dimensions specified below, or may be machined from larger blocks or components NOTE All four long edges may be chamfered or rounded The machining direction during chamfering shall be performed parallel to the length of the test piece NOTE If the chamfer size exceeds that given above, the formulae employed for the calculation of fracture stress require modification in accordance with A.1 Reject any test pieces which not fulfil the above dimensional criteria NOTE On occasion it may be desirable to test specimen geometries that fall outside the scope of this method In such a case it is still advisable to follow the guidelines given in this standard concerning jig function to minimize errors of measurement NOTE The strength of many types of advanced monolithic technical ceramics is strongly influenced by the machining procedure adopted in the preparation of the test pieces Low strengths may be caused by grinding with coarse diamond grit sizes, and conversely, very high strengths may be obtained if care in polishing is taken Some materials, especially those containing transformable zirconia, may be markedly strengthened by appropriate grinding schedules Reporting of surface preparation conditions is therefore an important aspect of this test method 6.3 Surface finish 6.2 Dimensions and tolerances 6.3.2 II Machined For span A (see 5.1), the test pieces shall be U 25 mm in length, 2,5 mm ± 0,2 mm in width and 2,0 mm ± 0,2 mm in thickness, and for span B (see 5.1), the test pieces shall be U 45 mm in length, 4,0 mm ± 0,2 mm in width and 3,0 mm ± 0,2 mm in thickness The maximum tolerable variation in either cross-sectional dimension of each test piece shall be either: a) for test pieces which have been machined (see 6.3.2 and 6.3.3), ± 0,02 mm; or b) for as-fired test pieces (see 6.3.1), ± 0,1 mm along the test piece length, and ± 0,05 mm across the test piece width or thickness Accurate finishing of the test piece ends is not required The test pieces may be prepared by machining in any relevant manner If they are to be prepared from blocks of material and tested as-cut, they shall be carefully cut using a diamond saw (of grit size not greater than D1511): approximately 125 4m – 150 4m) in order to obtain a surface roughness Rmax not greater than 4m (ignoring obvious pores; see ENV 623-4) The test pieces may be tested with a sawn, ground and/or lapped surface finish using a sequence of abrasives, machining direction and material removal rates They may also be annealed or refired after grinding Full details of preparation procedures shall be appended to the test results NOTE This allows some flexibility on actual dimensions, but ensures that the test pieces are adequately uniform in cross section for accuracy of stress calculation The cross section of the test piece shall be rectangular to within conventional engineering practice Out-of-squareness of sides to faces of the test pieces shall be less than 5° as determined by vernier protractor or engineering shadowgraph For as-fired test pieces, the maximum tolerable twist along the length of the test piece shall be less than 2°, determined by use of a shadowgraph or other suitable arrangement The two long edges bounding the face of the test piece to be subjected to tensile stress in the flexure test shall be chamfered at approximately 45° to a distance of 0,12 mm ± 0,03 mm as measured along the face or side of the test piece Alternatively, if appropriate, the long edges may be rounded to 0,15 mm ± 0,05 mm 1) Federation Four surface conditions are categorized as follows 6.3.1 I As-fired The test pieces may be tested in the as-fired (ex-kiln) condition without further surface preparation provided that they have dimensions within the tolerances given in 6.1 above The long edge chamfer or radius (see 6.2) shall be applied before firing Test pieces which are outside these limits shall be rejected NOTE The use of a fine abrasive for a finishing process may not completely remove the effects of previous coarser grinding stages Caution is advised in the interpretation of strength data related to finishing processes 6.3.3 Standard preparation procedures 6.3.3.1 Introduction This procedure is recommended when there is no other specified method for the test The aim is to minimize the damage created in the test pieces due to the preparation method in order to examine strength more representative of the material than the machining The recommended procedures cannot be standardized in the conventional sense, because of variation between grinding machines and the different behaviours during grinding of different types of material The procedures below should thus be treated as guidelines Furthermore, since there are no methods of accurately measuring surface finish parameters of ceramic materials, special attention must be paid to the quality of the machining of European Abrasives Producers (FEPA) designation © BSI 12-1999 EN 843-1:1995 6.3.3.2 III.1 Finishing by grinding 6.3.4 General requirements The test pieces shall be subject to the following grinding procedure Rough grinding shall employ a continuous rim peripheral diamond grinding wheel which is round to within 0,03 mm and of grit size not exceeding 120 mesh (D126), using a depth of cut not exceeding 0,03 mm per pass Finish grinding shall employ a peripheral grinding wheel of grit size between 320 and 500 mesh (e.g D46 or finer), using a depth of cut not exceeding 0,002 mm per pass, and removing at least 0,06 mm of material The final pass shall have zero cut All grinding shall be performed parallel to the length of the test piece, and an adequate quantity of coolant shall be used at all times Approximately equal amounts of material shall be removed from opposite faces of test pieces Discontinuous rim grinding wheels shall not be used Alternatively, an appropriate creep-feed grinding process may be adopted employing the same diamond grit size wheels as above, and with the finish grinding procedure including removal of at least 0,06 mm of material with final passes of 0,002 mm and mm The surface roughness Rmax measured using a profilometer with a stylus tip radius of less than 4m shall be less than 4m (ignoring obvious pores; see ENV 623-4) Whichever surface finishing procedure is employed, the long edges of the test pieces shall be chamfered or radiused after the faces have been finished The machining technique used for chamfering or radiusing shall be similar to that applied to the surface, with the direction of grinding or lapping parallel to the length of the test piece The test pieces shall be cleaned after any machining process using water or appropriate solvent, and shall then be dried in an oven at 110 °C ± °C for h, followed by equilibration for at least h in the ambient test atmosphere Whichever surface finishing routine is applied, full details of the machining procedure shall be provided in the report (see clause 9), including wheel type, grit size and concentration, cut sequence, depth of cut or amount of material removed, and lubricant type 6.3.3.3 III.2 Finishing by lapping and/or polishing The test face and the adjacent chamfered edges of the test pieces shall be lapped and/or polished using abrasives of less than 30 4m grit size, progressively reducing in size A thickness of at least 50 4m must be removed from the test face during this operation in order to remove pre-existing damage from rough grinding or cutting operations At least 4m shall be removed using abrasives of less than 4m grit size NOTE The recommended depths of material removal are not always essential, and depend on the nature of the material, especially its fracture toughness It is essential that any departure from the above procedure is by agreement between parties, and is stated in the report The polished test pieces shall be free from scratches observed with a low-power microscope (e.g with a magnification of × 100) Furthermore, the surface roughness Rmax measured using a profilometer with a tip radius of less than 4m shall be less than 4m (ignoring obvious pores; see ENV 623-4) 6.4 Number of test pieces For material development, characterization or quality control, the minimum number of test pieces shall be 10 For statistical evaluation of strength data (e.g Weibull parameters) the minimum number shall be 30 NOTE Weibull parameters may be seriously in error if the number of nominally identical test pieces is less than 30 The uncertainty in the parameters is sufficient to render comparisons between materials meaningless 6.5 Precautions The prepared test pieces should be handled with care to avoid the introduction of damage subsequent to the machining process Test pieces should be kept separate at all times, and should be individually wrapped for transport Test procedure Record the ambient temperature of the test environment and the relative humidity (% RH) The temperature shall be between 15 °C and 30 °C, and shall not vary by more than °C, nor the relative humidity by more than 10 %, during the course of the test series Choose a recording range for force on the testing machine (when necessary) such that the expected average force at fracture is near the centre of the range Measure the width and thickness of each test piece at a minimum of three positions approximately equidistant along its length, using the micrometer (see 5.3.1) © BSI 12-1999 EN 843-1:1995 If all four long edges of the test pieces have been chamfered, mark the tensile face of the test piece with a pencil to identify it as such Ensure that the test jig is cleaned of fracture debris from previous tests, and that the rollers of the test jig are free from burrs and can roll freely in the jig Position each test piece in turn in the test jig, marking the position of the point(s) of load application and ensuring that the test piece is positioned centrally across the support rollers, that the rollers are in the correct starting position, and that the test piece is centralized under the loading axis Place a protective screen around the test piece to trap the fractured fragments for safety reasons and for subsequent examination Select a rate of load application such that fracture is obtained in a time period of between s and 15 s NOTE Selection of machine displacement rate may have to be determined by experiment, depending on the elastic compliance of the test machine, the stiffness of the test jig and the elastic properties of the test piece A machine displacement rate of typically 0,5 mm/min is a convenient starting point for most testing machines in cases where the expected strength of the material is 200 to 400 MN · m–2 For materials which are much weaker or much stronger than this, the displacement rate may have to be respectively decreased or increased by an appropriate factor NOTE The strength of advanced monolithic technical ceramics may be markedly affected by the testing rate The short time to failure required by this method is intended as a compromise between the elimination of test-rate effects and the ability of test machines and load recording equipment to provide an accurate measure of peak fracture load Apply the test force at the chosen rate and record the peak load supported by the test piece at the instant of failure Record the time to failure Retrieve and identify the fracture fragments for later examination Even if the test piece has failed away from the central loading roller in three-point bending, or outside the uniformly stressed zone between the two loading rollers in four-point bending, the result shall not be ignored, and shall be included in the report of the test series and in the calculation of nominal mean strength If the test pieces are in the as-fired condition, remeasure the thickness and width of the test piece at the fracture position Repeat the procedure for each test piece Calculations Calculate the nominal strength of each test piece from the formulae: for three-point flexure: 3Fm ⋅ Ö f = 2bh (1) for four-point flexure: 3Fm ⋅ d Ö f = bh (2) where: Öf = the fracture stress expressed as N · mm–2 (equivalent to MN · m–2); Fm = the peak force at fracture, expressed as Newtons; b = the test piece width, expressed in millimetres, the mean of three determinations; h = the test piece thickness, expressed in millimetres, the mean of three determinations; l = the distance between centres of the outer support rollers (three-point flexure), expressed in millimetres; d = the mean of the distances between centres of the inner and outer support rollers (four-point flexure), expressed in millimetres NOTE It is recognized that these formulae not necessarily give the true fracture stress at the point of failure, but a nominal maximum effective stress experienced by the most highly stressed region in the test piece For some purposes, e.g the statistical evaluation of results, it may be necessary to correct the formulae for the position of failure, either for distance inside the test piece from the surface under tensile stress, or for distance away from the central loading roller in three-point bending, or from the uniformly stressed zone between the loading rollers in four-point bending In such cases, the position of the test piece relative to the loading rollers should be identified before the test to allow accurate measurement of the position of failure-for the lateral correction to be made The measurement of x in the formulae below should be made with a travelling microscope or other suitable device along the tensile surface of the test piece to an accuracy of 0.1 mm or better The appropriate formulae for lateral correction are: for three-point flexure: 3F m ( – 2x ) Ö f = 2bh (3) where x is the distance of fracture from the position of maximum stress, expressed in millimetres for four-point flexure: 3F m ( d – x ) Ö f = -2 bh © BSI 12-1999 (4) EN 843-1:1995 where x is the distance of fracture from the nearer inner loading roller, expressed in millimetres Fractographic examination of the site of failure should be made to identify its through-thickness position, which can be used to correct h/2 in a similar manner These modified formulae should not be used for calculating the nominal flexure strength according to this test method NOTE If the number of test pieces in a batch is sufficiently high, e.g 30 or more, it is strongly recommended that statistical analysis is performed Test report The test report shall contain the following information: a) name and address of the testing establishment; b) date of the test, unique identification of report and of each page, customer name and address, and signatory; c) a reference to this standard, i.e determined in accordance with EN 843-1; d) the test jig geometry used, i.e whether three- or four-point bending, and the span size, i.e A or B; e) description of the test material (material type, manufacturing code, batch number, date of receipt); f) method of production of test pieces from supplied material, if appropriate; 10 g) the surface finish category appropriate to the preparation method, i.e I, II, III.1 or III.2; h) the exact method of test piece surface preparation, including details of the grinding machine, the grinding and finishing operations, grit sizes, directions of grinding and depths of cut, and any subsequent thermal treatment; i) average ambient test temperature and average relative humidity during the tests; j) the average time to failure of the test pieces, expressed in seconds; k) the number of test pieces tested; l) individual nominal strength values for each test piece tested, expressed in MN · m–2 to three significant figures, including those failing substantially away from the loading rollers; m) unless otherwise agreed, the mean nominal strength and the standard deviation; n) comments about the test or the test results, details of any necessary deviations from this standard, and any observations of the nature of the fracture, and the positions and identifications of the fracture origins © BSI 12-1999 EN 843-1:1995 Figure — Dimensions and tolerances of machined test pieces © BSI 12-1999 11 EN 843-1:1995 Annex A (informative) Bibliography A.1 Baratta, F.I., Quinn, G.D., and Matthews, W.T., Errors associated with flexure testing of brittle materials, US Army Report MTL TR 87-35, July 1987 12 © BSI 12-1999 BS EN 843-1:1995 National annex NA (informative) Committees responsible The United Kingdom participation in the preparation of this European Standard was entrusted by the Refractory Products Standards Policy Committee (RPM/-) to Technical Committee RPM/13, upon which the following bodies were represented: AEA Technology Aluminium Federation British Ceramic Research Ltd British Industrial Ceramic Manufacturers’ Association Department of Trade and Industry (National Physical Laboratory) Flat Glass Manufacturers’ Association GAMBICA (BEAMA Ltd.) Institute of Refractories Engineers Ministry of Defence Refractories Association of Great Britain Society of British Aerospace Companies Limited University of Manchester © BSI 12-1999 BS EN 843-1:1995 BSI — British Standards Institution BSI is the independent national body responsible for preparing British Standards It presents the UK view on standards in Europe and at the international level It is incorporated by Royal Charter Revisions British Standards are updated by amendment or revision Users of British Standards should make sure that they possess the latest amendments or editions It is the constant aim of BSI to improve the quality of our products and services We would be grateful if anyone finding an inaccuracy or ambiguity while using this British Standard would inform the Secretary of the technical committee responsible, the identity of which can be found on the inside front cover Tel: 020 8996 9000 Fax: 020 8996 7400 BSI offers members an individual updating service called PLUS which ensures that subscribers automatically receive the latest editions of standards Buying standards Orders for all BSI, international and foreign standards publications should be addressed to Customer Services Tel: 020 8996 9001 Fax: 020 8996 7001 In response to orders for international standards, it is BSI policy to supply the BSI implementation of those that have been published as British Standards, unless otherwise requested Information on standards BSI provides a wide range of information on national, European and international standards through its Library and its Technical Help to Exporters Service Various BSI electronic information services are also available which give details on all its products and services Contact the Information Centre Tel: 020 8996 7111 Fax: 020 8996 7048 Subscribing members of BSI are kept up to date with standards developments and receive substantial discounts on the purchase price of standards For details of these and other benefits contact Membership Administration Tel: 020 8996 7002 Fax: 020 8996 7001 Copyright Copyright subsists in all BSI publications BSI also holds the copyright, in the UK, of the publications of the international standardization bodies Except as permitted under the Copyright, Designs and Patents Act 1988 no extract may be reproduced, stored in a retrieval system or transmitted in any form or by any means – electronic, photocopying, recording or otherwise – without prior written permission from BSI This does not preclude the free use, in the course of implementing the standard, of necessary details such as symbols, and size, type or grade designations If these details are to be used for any other purpose than implementation then the prior written permission of BSI must be obtained BSI 389 Chiswick High Road London W4 4AL If permission is granted, the terms may include royalty payments or a licensing agreement Details and advice can be obtained from the Copyright Manager Tel: 020 8996 7070