SIST-TS CEN/TS 843-6:2004

SLOVENSKI STANDARD
SIST-TS CEN/TS 843-6:2004
01-september-2004
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Advanced technical ceramics - Monolithic ceramics. Mechanical properties at room
temperature - Part 6: Guidance for fractographic investigation
Hochleistungskeramik - Monolithische Keramik - Mechanische Eigenschaften bei
Raumtemperatur - Teil 6: Leitlinie für die fraktographische Untersuchung
Céramiques techniques avancées - Céramiques monolithiques -Propriétés mécaniques
a température ambiante - Partie 6: Guide pour l'analyse fractographique
Ta slovenski standard je istoveten z: CEN/TS 843-6:2004
ICS:
81.060.30 Sodobna keramika Advanced ceramics
SIST-TS CEN/TS 843-6:2004 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CEN/TS 843-6:2004

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SIST-TS CEN/TS 843-6:2004
TECHNICAL SPECIFICATION
CEN/TS 843-6
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
June 2004
ICS 81.060.30
English version
Advanced technical ceramics - Monolithic ceramics. Mechanical
properties at room temperature - Part 6: Guidance for
fractographic investigation
Céramiques techniques avancées - Céramiques Hochleistungskeramik - Monolithische Keramik -
monolithiques -Propriétés mécaniques à température Mechanische Eigenschaften bei Raumtemperatur - Teil 6:
ambiante - Partie 6: Guide pour l'analyse fractographique Leitlinie für die fraktographische Untersuchung
This Technical Specification (CEN/TS) was approved by CEN on 17 November 2003 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 843-6:2004: E
worldwide for CEN national Members.

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Contents Page
Foreword . 3
1 Scope. 4
2 Normative references. 4
3 Terms and definitions. 4
3.1 General terms . 4
3.2 Terms classifying inherently volume-distributed fracture origins . 5
3.3 Terms classifying inherently surface-distributed fracture origins . 5
3.4 Terms classifying features on fracture surfaces. 6
4 Significance and use. 6
5 Apparatus. 7
5.1 Preparation and cleaning facilities. 7
5.2 Observational facilities. 7
6 Recommended procedure. 9
6.1 Outline . 9
6.2 Specimen storage and cleaning of fracture surfaces . 9
6.3 Visual inspection. 9
6.4 Optical microscope examination. 10
6.5 Identification of major fracture surface features . 10
6.6 Scanning electron microscope examination. 12
6.7 Identification of fracture origin. 12
6.8 Identification of chemical inhomogeneity at fracture origin . 13
6.9 Drawing conclusions . 13
7 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
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Foreword
This document CEN/TS 843-6:2004 has been prepared by Technical Committee CEN/TC 184
“Advanced technical ceramics”, the secretariat of which is held by BSI.
This document has been prepared under a mandate given to CEN by the European Commission and
the European Free Trade Association.
Annexes A to E are informative.
This document includes a Bibliography.
EN 843 Advanced technical ceramics – Monolithic ceramics – Mechanical properties at room
temperature consists of six parts:
Part 1: Determination of flexural strength
Part 2: Determination of elastic moduli
Part 3: Determination of subcritical crack growth parameters from constant stressing rate flexural
strength tests
Part 4: Vickers, Knoop and Rockwell superficial hardness tests
Part 5: Statistical analysis
Part 6: Guidance for fractographic investigation
At the time of publication of this Technical Specification, Part 1 is a European Standard, while Parts 2
to 5 are European Prestandards.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to announce this Technical Specification: Austria, Belgium, 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
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1 Scope
This Technical Specification 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.
2 Normative references
This Technical Specification 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 Technical Specification only when incorporated in it by amendment
or revision. For undated references the latest edition of the publication referred to applies (including
amendments).
EN ISO/IEC 17025 General requirements for the competence of testing and calibration laboratories
(ISO/IEC 17025:1999).
3 Terms and definitions
For the purposes of this Technical Specification, 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 do 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
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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
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
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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
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 so-
called 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.
4 Significance and use
Fractography is recommended as a routine diagnostic aid to the interpretation of fracture tests on test-
pieces 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.
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5 Apparatus
5.1 Preparation and cleaning facilities
5.1.1 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
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 Observational facilities
5.2.1 Small hand lens, with a magnification in the range 3 to 8 times.
5.2.2 Optical microscope, preferably with photomicrographic facilities, and with variable
magnification in the range 5 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.
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Objection Acton: Deduction: Result:
Collection and clean
Location of origin
History of fracture
fragments
Primary fracture
Visual inspection
face
Binocular macroscope
Identify features and
inspection
locate origin
Tentative
classification of
origin
No
More ?
Yes
SEM inspection. Mechanical
Mechanical
Origin size, fracture circumstances
nature of origin
mechanics of fracture
No
More ?
Yes
EDX analysis.
Chemical Chemical causes Overall
Origin chemical
nature of origin of failure conclusions
inhomogeneity
Report
Figure 1 - Flow chart for general fractographic procedure
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6 Recommended procedure
6.1 Outline
The sequence of steps in undertaking fractography on a specimen is outlined in Figure 1. It should be
noted that not all the steps will be necessary on every occasion; for example, if only a check on
approximate position of failure is needed, SEM examination is not generally necessary. Thus, the
following series of paragraphs should be used as appropriate to the task, defined by the type of
investigation needed.
6.2 Specimen storage and cleaning of fracture surfaces
Fracture surfaces are rough and are prone to contamination in handling and storage. Contamination can
lead to misinterpretation of observed features, especially in the SEM. Where possible, store fractured
fragments separately in clean, dry, conditions in which the fracture surfaces cannot contact foreign
bodies.
NOTE Storage in paper or plastic containers can lead to pick-up of contamination. Glass vials minimise
risks, but can damage surfaces if the specimen is loose in the vial. It is recommended to avoid the use of tape or
mouldable compounds as the adhesive is difficult to remove once contaminating the fracture surface.
Avoid handling with naked hands; use tweezers or surgical gloves to avoid contamination from body oils.
Cleaning facilities are required to allow removal of such contamination without damaging further the
fracture surface. It is recommended that solvents such as acetone or ethyl alcohol are used in
conjunction with a laboratory ultrasonic bath to remove soluble or loose contamination.
Dry the specimens using compressed air.
6.3 Visual inspection
6.3.1 Examine visually all the available fragments using a good light source and a hand lens as
appropriate.
6.3.2 Label all fragments with an indelible marker at positions that are remote from the surfaces of
interest. Make a sketch of the labelled fragments for future reference.
6.3.3 Where there are several fragments, use the pattern of cracks to identify the originating
fracture surface (the primary fracture):
NOTE 1 Annex A contains some examples of crack patterns in test-pieces and components.
NOTE 2 It is recommended not to attempt to fit the fracture pieces tightly together since this may induce
further damage on the fracture surfaces which will impede subsequent investigations.
6.3.4 Examine the primary fracture surface for evidence of an origin of the fracture. This may be
identified by tracing back any radiating ridges or grooves.
NOTE 1 Annex B shows some examples of fracture surface patterns which may aid this step. However, it
should be noted that:
1) Not all ceramic materials show clear fracture markings. High strength fine-grained or amorphous
materials show fracture features the best. In contrast, the roughness of the fracture surface in coarse-
grained or weaker materials may be too great, and obscures the fracture markings.
2) Features such as mist or hackle can be absent as a consequence of the size of the test-piece or the
level of fracture stress. These features only develop if the crack reaches a sufficient velocity within the
test-piece cross-section. An example is the case of subcritical crack growth, or in the fracture of small
test-bars.
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NOTE 2 It can be useful to hold the fracture surface at grazing incidence to a light source and observe any
changes in apparent roughness, using a hand lens if necessary. The region surrounding the fracture origin can
be smoother than the remainder of the surface.
Note any evidence from the fragments.
6.4 Optical microscope examination
6.4.1 Using oblique illumination to highlight the roughness of the fracture surface, and hence the
fracture markings, examine the fragments under an optical microscope at low magnification (x3 to
x10) to confirm the visual findings concerning the approximate origin. Table 1 advises on the visibility
of origins using optical microscopy.
NOTE 1 Many ceramics are translucent, and the scattering or oblique illumination in the surface layer can
obscure fracture markings. It is recommended:
1) to place a height-adjustable light barrier parallel to the fracture surface to shield the side of the
specimen;
2) if appropriate, to rotate the specimen so that a clear impression is obtained of the fracture markings
under illumination from all directions;
3) if appropriate, to coat the fracture surface with a thin layer of an opaque substance, such as a metal,
e.g. gold. However, coating should be used with discretion if subsequent SEM/EDX analysis is to be
performed.
NOTE 2 It can be helpful to the identification of the fracture origin if the two mating halves of the fracture
surface are placed side by side with the respective halves of the fracture origin adjacent. It is sometimes easier to
see the radial pattern of marks in this way.
6.4.2 If appropriate, sketch or record the images photographically.
6.4.3 Increase the magnification in stages and examine the suspected origin. If possible, identify
any feature at the origin, including the detailed pattern of local marks, or any marks or damage on the
external surface which may have caused the failure. Take photomicrographs if appropriate.
NOTE 1 At magnifications above about x200 fracture surfaces are generally too non-planar for effective
optical microscope examination, and are difficult to illuminate adequately from the side. In some cases, mixed
normal and oblique lighting can reveal important features.
NOTE 2 The radiating pattern of fracture marks can often be traced back to the origin, but only if these are
clearly identifiable.
6.5 Identification of major fracture surface features
Identify the major features of the fracture surface in terms of fracture lines (3.4.1) emanating from a focal
point in an equivalent manner on the two fracture surfaces. Identify strongly hackled regions, and any
mirror and mist regions. Identify the position and tentative nature of the fracture origin in relation to the
component or test-piece geometry and likely stressing. Correlate these observations with any ancillary
observations of the surface condition.
NOTE 1 The interpretation of the visual observations may not necessarily be straightforward, and optical
microscopy may not have adequate resolution or clarity of image to allow positive identification of the cause of
failure. If higher magnification is required, or confirmation of the chemical nature of the origin, SEM/EDX
examination should be employed (6.6, 6.8). However, a number of possible types of feature can be identified (not
all in every case), which will provide evidence for the report.
NOTE 2 The radius of the mirror, if present, is linked to the fracture stress at the point of failure through an
empirical fracture mechanics relationship. If the fracture stress and the mirror constant are known (see annex D),
the mirror size can be calculated, which is a guide to interpretation of a fracture origin. Alternatively, if the mirror
radius and mirror constant are known, the fracture stress can be estimated.
NOTE 3 Particularly with regard to optical observations, it is important to describe the origin in terms of its
physical form, and not how it appears under particular observational conditions.
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Table 1 — Visibility of fracture origins
Origin name Comment
Identifiable by optical Examples in
microscopy or SEM annex C or D
Pore (3.2.6) Large single pores are often irregular in shape, and can act as Optical, although SEM C1.1, C1.2
fracture origins, especially when close to or connected to the surface, better for translucent
e.g. when exposed by virtue of machining. materials
Porous region A zone of closely spaced pores distributed in three dimensions can SEM unless large
(3.2.7) be difficult to identify positively except at high magnification.
Porous seam A zone of closely spaced pores distributed in a planar or near planar SEM unless large
(3.2.8) arrangement may result from incomplete compaction, or inadvertent
organic matter, or a closed delamination.
Delamination A planar or near planar open cavity resulting from fracture during Optical or SEM C5.2
(3.2.3) or green- pressing of the green shape, or during ejection from a die cavity,
body crack which does not heal completely in firing. Usually identifiable as being
(3.1.1), at an angle to the general plane of fracture, and as having a different
internal surface topography from a fractured region.
Inclusion (3.2.4) An inhomogeneity of different chemical composition from that of the SEM for chemical C4.2
ceramic material which is often linked with a pore or locally modified information, optical
grain size, but which may become obvious only with backscattered only if large and
electron SEM or energy dispersive X-ray imaging. discoloured
A single or a group of abnormally large grains is usually caused by a SEM or optical if large C3.1
Large grain(s)
compositional inhomogeneity, excessive firing temperature, or
(3.2.5)
occasionally from poor milling of powders.
SEM C2.1, C2.2
Agglomerate A dense cluster of grains distinguishable from the rest of the
(3.2.1) microstructure, but often surrounded by a porous seam created by
differential shrinkage on sintering.
Compositional A region where there is a local change in composition modifying the SEM for chemical C4.1
inhomogeneity microstructure or creating a void. information
(3.2.2)
Surface chip Damage at the external surface, often along an edge, can initiate Optical or SEM D2
(3.3.1) cracking, and is usually identified by additional local damage.
Fracture may initially be out of plane of final fracture.
Surface crack A pre-existing crack which can result from mechanical or thermal Optical or SEM C9
(3.1.1) damage or during handling in production can be hard to identify, but
is usually out of the plane of final fracture.
Surface pit A cavity at the surface resulting from external influences, e.g. Optical or SEM C8.1, C8.2
(3.3.5) oxidation, requires examination of the relationship between the
fracture origin and the external surface.
Open pore A cavity at the surface which results from the processing method Optical or SEM D1
(3.3.4) used to prepare the component or test-piece can typically be
distinguished from a pit by its depth or by surface morphology similar
to normal surface.
Machining Surface or sub-surface shallow damage such as chips or cracks can SEM C7.1, C7.2
damage (3.3.3) be produced by machining, leading to apparently extended fracture
origins, often of semi-elliptical shape.
Handling Scratches or other abnormal damage resulting
...