BRITISH STANDARD BS EN 843-6:2009 Advanced technical ceramics — Mechanical properties of monolithic ceramics at room temperature Part 6: Guidance for fractographic investigation ICS 81.060.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 National foreword This British Standard is the UK implementation of EN 843-6:2009 It supersedes DD CEN/TS 843-6:2004 which is withdrawn The UK participation in its preparation was entrusted to Technical Committee RPI/13, Advanced technical ceramics A list of organizations represented on this committee 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 Standard cannot confer immunity from legal obligations `,,```,,,,````-`-`,,`,,`,`,,` - This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 January 2010 Amendments/corrigenda issued since publication Date Comments © BSI 2010 ISBN 978 580 63845 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EUROPEAN STANDARD EN 843-6 NORME EUROPÉENNE EUROPÄISCHE NORM August 2009 ICS 81.060.30 Supersedes CEN/TS 843-6:2004 English Version Advanced technical ceramics - Mechanical properties of monolithic ceramics at room temperature - Part 6: Guidance for fractographic investigation Céramiques techniques avancées - Propriétés mécaniques des céramiques monolithiques température ambiante Partie 6: Guide pour l'analyse fractographique Hochleistungskeramik - Mechanische Eigenschaften monolithischer Keramik bei Raumtemperatur - Teil 6: Leitlinie für die fraktographische Untersuchung This European Standard was approved by CEN on 16 July 2009 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 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 status as the official versions CEN members are the national standards bodies of Austria, Belgium, Bulgaria, 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 COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Management Centre: Avenue Marnix 17, B-1000 Brussels © 2009 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale Ref No EN 843-6:2009: E BS EN 843-6:2009 EN 843-6:2009 (E) Contents Page Foreword Scope Normative references 3.1 3.2 3.3 3.4 Terms and definitions General terms Terms classifying inherently volume-distributed fracture origins Terms classifying inherently surface-distributed fracture origins Terms classifying features on fracture surfaces Significance and use 5.1 5.2 Apparatus Preparation and cleaning facilities Observational facilities 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 Recommended procedure Outline Specimen storage and cleaning of fracture surfaces Visual inspection Optical microscope examination 10 Identification of major fracture surface features 10 Scanning electron microscope examination 12 Identification of fracture origin 12 Identification of chemical inhomogeneity at fracture origin 13 Drawing conclusions 13 Report 13 Annex A (informative) Crack patterns in ceramic bodies 14 Annex B (informative) Examples of general features of fracture surfaces 17 Annex C (informative) Examples of procedure for fracture origin identification 19 C.1 Single large pores 20 C.2 Agglomerates 22 C.3 Large grains 24 C.4 Compositional inhomogeneities 26 C.5 Delaminations 28 C.6 Handling damage 30 C.7 Machining damage 31 C.8 Oxidation pitting 33 C.9 Complex origins 35 C.10 No obvious origins 36 Annex D (informative) Use of fracture mechanical information to aid fractography 37 D.1 Fracture stress and origin size 37 D.2 Fracture stress and fracture mirror size 40 Annex E (informative) Example layout of reporting pro-forma 42 Bibliography 44 `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) Foreword This document (EN 843-6:2009) 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 endorsement, at the latest by February 2010, and conflicting national standards shall be withdrawn at the latest by February 2010 Attention 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 843-6:2004 EN 843 Advanced technical ceramics – Mechanical properties of monolithic ceramics at room temperature consists of six parts: Part 1: Determination of flexural strength Part 2: Determination of Young's modulus, shear modulus and Poisson's ratio Part 3: Determination of subcritical crack growth parameters from constant stressing rate flexural strength tests Part 4: Vickers, Knoop and Rockwell superficial hardness Part 5: Statistical analysis Part 6: Guidance for fractographic investigation `,,```,,,,````-`-`,,`,,`,`,,` - According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, 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 the United Kingdom Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) Scope This Part of EN 843 contains guidelines to be adopted when evaluating the appearance of the fracture surface of an advanced technical ceramic The purpose in undertaking this procedure can be various, for example, for material development or quality assessment, to identify normal or abnormal causes of failure, or as a design aid NOTE Not all advanced technical ceramics are amenable to fractography In particular, coarse-grained ceramics can show such rough surfaces that identifying the fracture origin may be impossible Similarly, porous materials, especially those of a granular nature, tend not to fracture in a continuous manner, making analysis difficult 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 amendments) applies EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories (ISO/IEC 17025:2005) Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1 General terms 3.1.1 crack distinct microstructural discontinuity arising during or after manufacture caused by the action of thermal and/or mechanical stress and leading to the generation of new surfaces which not completely separate 3.1.2 flaw inhomogeneity which, through stress concentration, can act as a strength defining feature NOTE The term flaw used in this sense does not imply that the component is defective 3.1.3 fracture process of propagation of a crack through a test-piece or component 3.1.4 fracture origin source from which failure commences 3.2 Terms classifying inherently volume-distributed fracture origins 3.2.1 agglomerate unintentional microstructural inhomogeneity usually of altered density, for example a cluster of grains of abnormal size, particles, platelets or whiskers, resulting from non-uniformity in processing `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) 3.2.2 compositional inhomogeneity local variations in chemical composition, usually manifest as agglomerates (3.2.1), or as areas denuded of or enriched in dispersed phases, or as changes in grain size 3.2.3 delamination generally planar crack within a material arising from the method of manufacture 3.2.4 inclusion discrete inhomogeneity, usually as a result of inorganic contamination by a foreign body not removed during firing 3.2.5 large grain grain which is of abnormally large size as a result of poor particle size control or accelerated grain growth, and which can act as a flaw (3.1.2) 3.2.6 pore cavity or void within a material, which may be isolated or continuously interconnected with others 3.2.7 porous region zone of enhanced porosity, usually three-dimensional in nature and resulting from inhomogeneity or organic contamination in processing 3.2.8 porous seam zone of enhanced porosity, usually linear or planar in nature and resulting from inhomogeneity or organic contamination in processing 3.3 Terms classifying inherently surface-distributed fracture origins 3.3.1 chip small flake of material removed from a surface or an edge of an item or its fracture surface 3.3.2 handling damage scratches, chips or other damage resulting from contact between items, test-pieces or fracture surfaces, not present normally 3.3.3 machining damage result of removal of small chips (see 3.3.1) or the formation of scratches at, or cracks near, the surface resulting from abrasive removal of material 3.3.4 open pore void connected to the external surface, usually by virtue of machining 3.3.5 pit surface depression or surface connected shallow pore, usually resulting from manufacturing conditions or interaction with the external environment `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) 3.4 Terms classifying features on fracture surfaces 3.4.1 fracture lines ridges or troughs running approximately parallel to the direction of propagation of a crack front, usually in the hackle (3.4.2) region NOTE In some cases, particularly with materials with low fracture toughness, additional lines can be found on fracture surfaces resulting from interactions of the crack with free surfaces or other features, including socalled Wallner lines, arrest lines, wake hackle, etc Definitions of such terms can be found in ASTM C1256 (see reference [1] in the Bibliography) 3.4.2 hackle region of rough fracture outside the mirror (3.4.3) and mist (3.4.4) regions, often with ridges or troughs emanating radially from the fracture origin (3.1.4) 3.4.3 mirror area of a fracture surface, usually approximately circular (or semicircular for near-edge fracture origins) and immediately surrounding a fracture origin (3.1.4), which is relatively flat and featureless compared with regions further removed from the fracture origin NOTE Not all materials or fractures show obvious fracture mirrors They tend to be visible most clearly in high-stress, accelerating fractures from small flaws 3.4.4 mist halo around the outer region of the mirror (3.4.3) where the roughness is enhanced with a texture elongated in the direction of fracture `,,```,,,,````-`-`,,`,,`,`,,` - NOTE The mist region is most clearly seen in glasses, glass-ceramics or ceramics with very fine grain sizes which produce smooth surfaces on fracture Significance and use Fractography is recommended as a routine diagnostic aid to the interpretation of fracture tests on testpieces or of failures in components Observation of the macroscopic features of fragments, such as cracks and their relative disposition, chips and scratches, provides information about the likely directions of stressing Observation of intermediate scale features on the fracture surface, such as the shape of hackle (3.4.2) and fracture lines (3.4.1) give indications of the approximate position of the fracture origin (3.1.4) Microscopic observations give information on the nature of the fracture origin, and thus may provide evidence of the reasons for fracture The accumulation of additional information about the conditions of fracture (stresses, forces, temperature, time under stress, likelihood of impact, etc.) is highly desirable for achieving justifiable conclusions Apparatus 5.1 5.1.1 Preparation and cleaning facilities Cutting wheel, for large specimens A diamond-bladed saw NOTE This is needed to cut small samples for microscope observation, particularly in the scanning electron microscope Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) 5.1.2 Ultrasonic bath, for cleaning the fracture surface 5.1.3 Compressed air supply, for drying specimens after cleaning and for removal of dust or lint The supply should be dry and oil-free 5.2 5.2.1 Observational facilities Small hand lens, with a magnification in the range to times 5.2.2 Optical microscope, preferably with photomicrographic facilities, and with variable magnification in the range to 50 times NOTE As an alternative to photomicrographic facilities, a camera with appropriate lenses and a macrophotography stand 5.2.3 Illumination system, a light source that can be positioned to the side of the test-piece to provide contrast on the fracture surface 5.2.4 Scanning electron microscope (SEM), preferably with energy-dispersive X-ray (EDX) analysis equipment fitted `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) Objection Location of origin Acton: Deduction: Collection and clean fragments History of fracture Visual inspection Primary fracture face Binocular macroscope inspection Identify features and locate origin Result: Tentative classification of origin More ? No Yes Mechanical nature of origin SEM inspection Origin size, fracture mechanics Mechanical circumstances of fracture More ? No Yes Chemical nature of origin EDX analysis Origin chemical inhomogeneity Chemical causes of failure Overall conclusions Report Figure — Flow chart for general fractographic procedure `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS 32 Key: Tensile surface, Fracture lines, Chip EXAMPLE C7.2: A sintered silicon carbide test-piece showing (Figure C7.2(a)) at low magnification an asymmetric fracture pattern with indistinct fracture markings, but with fracture originating from the right corner of the test-piece, and (Figure C7.2(b)) at higher magnification a chip removed from the fracture surface at the edge of chamfer suggesting that edge damage had been suffered in preparing the chamfer EN 843-6:2009 (E) `,,```,,,,````-`-`,,`,,`,`,,` - Key: Tensile surface, Chamfer surface, Machining flaw EXAMPLE C7.3: A Y-TZP test-piece showing (Figure C7.3(a)) a large elongated elliptical region on the chamfer at the fracture origin with clear radiating fracture lines, and (Figure C7.3(b)) the same area at higher magnification and rotated to illustrate the flaw BS EN 843-6:2009 Not for Resale o Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Key: Tensile surface `,,```,,,,````-`-`,,`,,`,`,,` - 33 EXAMPLE C8.1: A four-point bend fracture test was performed at room temperature on a sintered silicon nitride with alumina and yttria additives after oxidation at 1000 C for 60 h in combustion gas containing 0,01 wt% sulphur The fracture observed by SEM (Figure C8.1(a)) has a distinct mirror and radiating hackle which initiates from the oxidized surface layer At higher magnification using a backscattered electron image (Figure C8.1(b)), the origin is clearly seen as an oxidation pit underlying about 150 µm of glassy oxide surface layer containing gas bubbles C.8 Oxidation pitting EN 843-6:2009 (E) BS EN 843-6:2009 Not for Resale o Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS 34 Key: Tensile surface, Glass-filled pit EXAMPLE C8.2: A similar fracture surface to that in Example C8.1, after exposure to combustion gas containing 1% sulphur at 1000 C for 20 h Fracture markings (Figure C8.2(a), secondary electron image) indicate a near surface origin which, when examined at higher magnification (Figure C8.2(b), backscattered electron image), reveals a 70 µm deep corrosion pit containing sodium silicate glass `,,```,,,,````-`-`,,`,,`,`,,` - EN 843-6:2009 (E) BS EN 843-6:2009 Not for Resale Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Key: Tensile surface, Coating, Surface crack 35 EXAMPLE C9: A sintered silicon carbide flexural strength test-piece coated with CVD aluminium nitride before testing showing (Figure C9(a)) with tensile surface uppermost, much contortion of the fracture plane near the edges of the test-piece, but no clear fracture markings in the SiC However, closer examination of the surface region shows the AlN coating to be cracked through in a number of places, due presumably to thermal expansion/elastic mismatch The region shown in Figure C9(b) can conceivably be the fracture origin where the surface cracks may have penetrated into the silicon carbide in the roughly triangular area `,,```,,,,````-`-`,,`,,`,`,,` - C.9 Complex origins EN 843-6:2009 (E) BS EN 843-6:2009 Not for Resale Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Key: Tensile surfaces Key: Tensile surfaces, Chipped edge 36 EXAMPLE C10.2: Flexural strength test-piece of an Mg-PSZ type zirconia showing a rough fracture surface but with no obvious fracture markings which permit the observer to trace back to an origin EXAMPLE C10.1: A flexural strength test-piece of a silicon nitride composite material in which the origin is lost by impact between the test-piece and the testing jig The two halves not match, and there is extensive damage to the tensile edge This problem can be rectified by good test practice, but in field failures, loss of critical regions containing the origin happens frequently C.10 No obvious origins EN 843-6:2009 (E) BS EN 843-6:2009 `,,```,,,,````-`-`,,`,,`,`,,` - Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) Annex D (informative) Use of fracture mechanical information to aid fractography D.1 Fracture stress and origin size In order to provide an estimate of the stress, σ f, on a fracture origin at the moment of propagation, or conversely, a measure of the size of the origin, a, for a failure at a given stress, a simple relationship can be used: K lc K lc or = a Ya1 / Y 2σ 2f (D.1) where KIc is the critical stress intensity factor for fast fracture, and Y is a flaw shape factor This analysis requires an estimate of KIc which therefore presumes that it is known or can be assumed from other sources Values for Y can be estimated from Table D.1, in which the ellipticity of the origin is taken into account, with the axis perpendicular to the fracture direction being 2c and the axis parallel to the fracture direction being 2a (Figure D.1) It should be noted that Y depends on whether the flaw is intersected by the surface or is in the bulk of the test-piece, and for surface connected origins, the value at the centre remote from the surface is different from that where the flaw intersects the surface For surface connected origins, inspection of the fracture markings from the origin should be used to identify which value of Y to use c 2c 2a 2a Key Surface Surface edge initiation Central initiation Figure D.1 — (Left) elliptical bulk origin flaw and (right) semielliptical surface flaw types 37 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale `,,```,,,,````-`-`,,`,,`,`,,` - σf = BS EN 843-6:2009 EN 843-6:2009 (E) Table D.1 — Flaw shape correction factors, Y Bulk origins Surface origins Shape Y Shape Y Circle, c/a = 1,13 Semicircle, c/a = Centre: 1,17 Surface: 1,29 Ellipse, c/a = 1,4 1,26 Semiellipse, c/a = 1,4 Centre: 1,39 Surface: 1,29 Ellipse, c/a = 1,47 Semiellipse, c/a = Centre: 1,59 Surface: 1,24 Long ellipse, c/a >> 1,77 Long ellipse, c/a >>4 Centre: 1,99 NOTE Factors for intermediate shapes of flaw can be computed using the equations given in reference [3] in the Bibliography It should be noted that this analysis should be used only as a guide, not as a definitive way of computing either the stress at failure or the flaw size to expect In some cases, critical flaws can grow under stress from a small initial origin size to a larger critical size with little or no change in fracture surface appearance In others, a subcritical crack growth region can be visible as a distinct change in fracture surface morphology 38 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS `,,```,,,,````-`-`,,`,,`,`,,` - Not for Resale Key: Tensile surface, Initiation region, Pore with an effectively semi-elliptical boundary `,,```,,,,````-`-`,,`,,`,`,,` - EXAMPLE D1: Using an SEM, a flexural strength test-piece of a wt% yttria TZP zirconia shows a smooth fracture surface with fine radial fracture lines originating at the tensile surface (Figure D.2 (a)) At higher magnification, a large irregular pore intersected by the machined surface is found (Figure D.2 (b) and (c) show the sides A and B of the fracture) This should be identified as a pore of bulk type since the test-pieces have been machined after firing, but a surface connected type from a fracture mechanics 1/2 standpoint If KIc = 4,7 MPa m , and the origin is considered to be an elliptical crack about 160 µm major axis (2c) and depth about 35 µm (a), c/a is about 2,3 and the flaw shape factor Y can be estimated to be approximately 1,65 for central initiation by interpolation in Table D.1, and the strength at failure can be estimated as 481 MPa The actual failure strength was 728 MPa indicating that this type of analysis can give only an indication, not an accurate value, of stress EN 843-6:2009 (E) BS EN 843-6:2009 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) D.2 Fracture stress and fracture mirror size When studying the fracture surface at low magnification, some materials demonstrate a clear halo around the origin in which the fracture surface is smooth, surrounding which the fracture becomes much rougher and the fracture lines much more obvious The transition region is known as the "mist", and the rough area as the "hackle" (Figure D.1) The mirror radius, r, is related to the stress at failure, σf, through the relationship: σf = A r (D.2) where A is a constant for a given material The constant is found by experimental measurement Thus if the mirror radius is measured in an unknown case, the fracture stress can be estimated, and vice versa The similarity of form between Equations (D.1) and (D.2) suggests a relationship between origin size and mirror radius or outer mist radius The ratio is typically between 1:6 and 1:10 for the mirror radius and about 1:13 for the outer mist radius It should be noted that not all materials show such features clearly This is especially the case in medium to coarse-grained ceramics In Y-TZP, for example in Example D.1, the fracture surface appears to become steadily rougher from the origin outwards There can be no unambiguous definition of a mirror radius, and any assessment becomes somewhat subjective to the observation conditions and criteria employed In this respect, mirror analysis can be used only as a guide, not as a rigorous diagnostic tool The following table summarizes typical values for the mirror constant A, and a worked example is given in Example D2 Material class Range of values of fracture mirror 1/2 constant, A, MPa m Glasses 1,8 - 2,4 "Pyroceram" glass-ceramics 5,7 - 6,5 Aluminas 8,0 - 10,4 Dense silicon nitrides 5,9 - 18,1 Porous silicon nitrides 4,2 Silicon carbides 10,7 - 11,9 Zirconias 7,4 - 15,2 Mullite 6,1 Boron carbide 9,3 Source: ASTM C1322:1996 (see reference [2] in the Bibliography) EXAMPLE D2: A high purity alumina showing a distinct mirror at low magnification, but no clear origin at higher magnification (Figure D.3(a)) The mirror radius is about 0,8 mm Using Equation (D.2) and a value of the mirror constant 40 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale `,,```,,,,````-`-`,,`,,`,`,,` - Table D.2 — Typical fracture mirror constants BS EN 843-6:2009 EN 843-6:2009 (E) 1/2 of MPa m (Table D.2), the fracture stress must have been about 280 MPa For a typical short-crack fracture toughness 1/2 for this type of alumina of about 3,5 MPa m , the flaw depth at the origin can be estimated using Equation (D.1) as 93 µm for a semicircular flaw, or 57 µm for a semielliptical flaw with c/a = Examination of the higher magnification micrographs (Figures D.3(b) and (c)) shows no distinct evidence of an initiating crack boundary of this order of size, but a shallow pit can be seen at the apparent origin The calculated flaw dimensions have been added to Figure D.3(c) to provide an indication of likely origin size The most likely explanation is that there is surface machining damage which has caused local spalling and cracking and which has grown subcritically to cause failure Key: Tensile surface, Mirror/mist boundary, Shallow pit `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS 41 Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) Annex E (informative) Example layout of reporting pro-forma Date: Operator: Customer: Customer’s reference: Description of fragments (6.2) Known history of fragments Cleaning procedure if used (6.2) Visual inspection (6.3), sketches or photographs of fragments, identification of principal fracture Binocular microscopy (6.4), identification of location of origin (6.5), sketches and/or photographs of relevant features Tentative causes of fracture (6.5) Scanning electron microscopy (6.6); mounting, coating and conditions of viewing Identification of origin type and size (6.7) Application of fracture mechanics (Annex D); estimation of flaw size `,,```,,,,````-`-`,,`,,`,`,,` - 42 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) from mechanical data; estimation of fracture stress from apparent flaw or mirror sizes EDX analysis; identification of chemical nature of origin (6.8) Overall conclusions (6.9) `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS 43 Not for Resale BS EN 843-6:2009 EN 843-6:2009 (E) Bibliography ASTM C1256-93 (1998), Standard practice for interpreting glass fracture surface features [2] ASTM C1322-96, Standard practice for fractography and characterisation of fracture origins in advanced ceramics [3] Newman, J.C., Jr.; Raju, I.S.; “An empirical stress-intensity factor equation for the surface crack, Eng Fract Mech 1981, 15[1–2], 185–92 `,,```,,,,````-`-`,,`,,`,`,,` - [1] 44 Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS Not for Resale BS EN 843-6:2009 `,,```,,,,````-`-`,,`,,`,`,,` - Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS This page has been intentionally left blank Not for Resale BS EN 843-6:2009 BSI - 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