ASTM C1322-15(2019)

Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics

SIGNIFICANCE AND USE
5.1 This practice is suitable for monolithic and some composite ceramics, for example, particulate- and whisker-reinforced and continuous-grain-boundary phase ceramics. (Long- or continuous-fiber reinforced ceramics are excluded.) For some materials, the location and identification of fracture origins may not be possible due to the specific microstructure.  
5.2 This practice is principally oriented towards characterization of fracture origins in specimens loaded in so-called fast fracture testing, but the approach can be extended to include other modes of loading as well.  
5.3 The procedures described within are primarily applicable to mechanical test specimens, although the same procedures may be relevant to component fracture analyses as well. It is customary practice to test a number of specimens (constituting a sample) to permit statistical analysis of the variability of the material’s strength. It is usually not difficult to test the specimens in a manner that will facilitate subsequent fractographic analysis. This may not be the case with component fracture analyses. Component fracture analysis is sometimes aided by cutting test pieces from the component and fracturing the test pieces. Fracture markings and fracture origins from the latter may aid component interpretation.  
5.4 Optimum fractographic analysis requires examination of as many similar specimens or components as possible. This will enhance the chances of successful interpretations. Examination of only one or a few specimens can be misleading. Of course, in some instances the fractographer may have access to only one or a few fractured specimens or components.  
5.5 Successful and complete fractography also requires careful consideration of all ancillary information that may be available, such as microstructural characteristics, material fabrication, properties and service histories, component or specimen machining, or preparation techniques.  
5.6 Fractographic inspection and analysis can b...
SCOPE
1.1 The objective of this practice is to provide an efficient and consistent methodology to locate and characterize fracture origins in advanced ceramics. It is applicable to advanced ceramics that are brittle; that is, fracture that takes place with little or no preceding plastic deformation. In such materials, fracture commences from a single location which is termed the fracture origin. The fracture origin in brittle ceramics normally consists of some irregularity or singularity in the material which acts as a stress concentrator. In the parlance of the engineer or scientist, these irregularities are termed flaws or defects. The latter word should not be construed to mean that the material has been prepared improperly or is somehow faulty.  
1.2 Although this practice is primarily intended for laboratory test piece analysis, the general concepts and procedures may be applied to component fracture analyses as well. In many cases, component fracture analysis may be aided by cutting laboratory test pieces out of the component. Information gleaned from testing the laboratory pieces (for example, flaw types, general fracture features, fracture mirror constants) may then aid interpretation of component fractures. For more information on component fracture analysis, see Refs (1, 2).2  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Jun-2019
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.01 - Mechanical Properties and Performance

Relations

• Replaces: ASTM C1322-15 - Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM C162-23 - Standard Terminology of Glass and Glass Products
• Effective Date: 01-Oct-2023
• Refers: ASTM C242-20 - Standard Terminology of Ceramic Whitewares and Related Products
• Effective Date: 01-Feb-2020
• Refers: ASTM C242-19a - Standard Terminology of Ceramic Whitewares and Related Products
• Effective Date: 01-Oct-2019
• Refers: ASTM C242-19 - Standard Terminology of Ceramic Whitewares and Related Products
• Effective Date: 01-Aug-2019
• Refers: ASTM C1499-19 - Standard Test Method for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature
• Effective Date: 01-Jul-2019
• Refers: ASTM C1145-19 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM C1239-13(2018) - Standard Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• Effective Date: 01-Jul-2018
• Refers: ASTM C242-18 - Standard Terminology of Ceramic Whitewares and Related Products
• Effective Date: 01-Feb-2018
• Refers: ASTM C162-05(2015) - Standard Terminology of<brk type="line"/> Glass and Glass Products
• Effective Date: 01-Nov-2015
• Refers: ASTM C1499-15 - Standard Test Method for Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature
• Effective Date: 01-Jul-2015
• Refers: ASTM C242-15 - Standard Terminology of Ceramic Whitewares and Related Products
• Effective Date: 01-Mar-2015
• Refers: ASTM C242-14 - Standard Terminology of Ceramic Whitewares and Related Products
• Effective Date: 01-Feb-2014
• Refers: ASTM C1211-13 - Standard Test Method for Flexural Strength of Advanced Ceramics at Elevated Temperatures
• Effective Date: 01-Aug-2013
• Refers: ASTM C1161-13 - Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
• Effective Date: 01-Aug-2013

Overview

ASTM C1322-15(2019), the "Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics," offers a systematic approach for locating and characterizing fracture origins in brittle, advanced ceramic materials. Developed by ASTM International, this standard is applicable to laboratory specimens of monolithic and certain composite ceramics, specifically those prone to brittle fracture with little or no plastic deformation. The methodology helps identify critical flaws, or "fracture origins," which serve as stress concentrators in ceramic bodies.

Fractography, as outlined in the standard, supports quality control, failure analysis, materials development, and the design of ceramic components. By ensuring consistent characterization, it also enables robust statistical analysis and the construction of comprehensive data sets, essential for ongoing material improvement and product reliability.

---

Key Topics

• Scope and Applicability

  • Targets monolithic and some particulate- or whisker-reinforced ceramics; excludes long/continuous-fiber reinforced ceramics.
  • Suitable for brittle ceramics where fracture initiates from a single point.

• Fracture Origin Types

  • Details origins such as agglomerates, inclusions, grains, pores, cracks, pits, grain boundaries, machining and handling damage.
  • Emphasizes distinction between volume-distributed and surface-distributed flaws for effective Weibull statistical analysis.

• Fractography Procedures

  • Involves marking specimens, careful mechanical testing, and minimizing post-fracture handling damage.
  • Recommends both optical (10-300×) and scanning electron microscopy (SEM, up to 2000×) for fracture surface examination.
  • Stresses documentation, including photographic records and digital imaging, at every analysis stage.

• Statistical Analysis

  • Encourages testing multiple specimens to analyze material strength variability and reliability through consistent data reporting.

• Ancillary Information

  • Considers factors such as microstructure, manufacturing history, service environment, and specimen preparation methods for a holistic understanding of fracture origins.

---

Applications

ASTM C1322-15(2019) is highly relevant for industries using advanced ceramics, such as electronics, biomedical implants, aerospace, and energy. The standard’s methodology is valuable in:

• Quality Control:
  • Identifying prevalent flaw types and sources, supporting root cause analysis, and preventing recurring defects.
• Materials Development:
  • Comparing fracture patterns across processing variables to inform material improvements.
• Component Failure Analysis:
  • Applying laboratory-based characterization techniques to fractured components in service, often by extracting and testing representative test pieces.
• Design and Reliability Engineering:
  • Supplying statistically valid strength and flaw data for robust engineering design and lifetime prediction.
• Research and Standards Compliance:
  • Establishing consistent terminology and reporting procedures, facilitating data sharing and regulatory compliance.

---

Related Standards

Several international and ASTM standards complement or support the procedures in ASTM C1322-15(2019):

• ASTM C1161: Flexural Strength of Advanced Ceramics at Ambient Temperature
• ASTM C1211: Flexural Strength of Advanced Ceramics at Elevated Temperatures
• ASTM C1499: Monotonic Equibiaxial Flexural Strength of Advanced Ceramics at Ambient Temperature
• ASTM C1239: Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• ASTM C1678: Fractographic Analysis of Fracture Mirror Sizes in Ceramics and Glasses
• NIST SP 960-16: Guide to Practice for Fractography of Ceramics and Glasses
• CEN EN 843-6: Mechanical Properties of Monolithic Ceramics - Guidance for Fractographic Investigation

These documents collectively enable standardized material testing, interpretation of fracture surfaces, and international harmonization, ensuring advanced ceramics' reliability across industries.

---

By following ASTM C1322-15(2019), technical professionals can improve failure analysis accuracy, enhance product reliability, and contribute to the advancement of ceramic technologies through consistent and statistically robust fractography practices.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1322 − 15 (Reapproved 2019)
Standard Practice for
Fractography and Characterization of Fracture Origins in
Advanced Ceramics
This standard is issued under the fixed designation C1322; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 The objective of this practice is to provide an efficient 2.1 ASTM Standards:
and consistent methodology to locate and characterize fracture C162Terminology of Glass and Glass Products
origins in advanced ceramics. It is applicable to advanced C242Terminology of Ceramic Whitewares and Related
ceramics that are brittle; that is, fracture that takes place with Products
little or no preceding plastic deformation. In such materials, C1036Specification for Flat Glass
fracturecommencesfromasinglelocationwhichistermedthe C1145Terminology of Advanced Ceramics
fractureorigin.Thefractureorigininbrittleceramicsnormally C1161Test Method for Flexural Strength of Advanced
consists of some irregularity or singularity in the material Ceramics at Ambient Temperature
which acts as a stress concentrator. In the parlance of the C1211Test Method for Flexural Strength of Advanced
engineer or scientist, these irregularities are termed flaws or Ceramics at Elevated Temperatures
defects. The latter word should not be construed to mean that C1239Practice for Reporting Uniaxial Strength Data and
the material has been prepared improperly or is somehow EstimatingWeibull Distribution Parameters forAdvanced
faulty. Ceramics
C1499Test Method for Monotonic Equibiaxial Flexural
1.2 Although this practice is primarily intended for labora-
Strength of Advanced Ceramics at Ambient Temperature
tory test piece analysis, the general concepts and procedures
C1678Practice for Fractographic Analysis of Fracture Mir-
may be applied to component fracture analyses as well. In
ror Sizes in Ceramics and Glasses
many cases, component fracture analysis may be aided by
F109Terminology Relating to Surface Imperfections on
cutting laboratory test pieces out of the component. Informa-
Ceramics
tion gleaned from testing the laboratory pieces (for example,
2.2 NIST Standard:
flaw types, general fracture features, fracture mirror constants)
NIST Special Publication SP 960-16Guide to Practice for
may then aid interpretation of component fractures. For more
Fractography of Ceramics and Glasses (2)
information on component fracture analysis, see Refs (1, 2).
2.3 CEN Standard:
1.3 This standard does not purport to address all of the
EN 843-6 Advanced Technical Ceramics—Mechanical
safety concerns, if any, associated with its use. It is the
Properties of Monolithic Ceramics at Room
responsibility of the user of this standard to establish appro-
Temperature—Part 6: Guidance for Fractographic Inves-
priate safety, health, and environmental practices and deter-
tigation
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
3. Terminology
dance with internationally recognized principles on standard-
3.1 Definitions:
ization established in the Decision on Principles for the
3.1.1 General—Thefollowingtermsaregivenasabasisfor
Development of International Standards, Guides and Recom-
identifying fracture origins in advanced ceramics. It should be
mendations issued by the World Trade Organization Technical
recognized that origins can manifest themselves differently in
Barriers to Trade (TBT) Committee.
1 3
This practice is under the jurisdiction ofASTM Committee C28 on Advanced For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Ceramics and is the direct responsibility of Subcommittee C28.01 on Mechanical contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Properties and Performance. Standards volume information, refer to the standard’s Document Summary page on
CurrenteditionapprovedJuly1,2019.PublishedJuly2019.Originallyapproved the ASTM website.
in 1996. Last previous edition approved in 2015 as C1322–15. DOI: 10.1520/ Available from National Institute of Standards and Technology (NIST), 100
C1322-15R19. Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http://www.nist.gov.
2 5
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Available from European Committee for Standardization (CEN), Avenue
this standard. Marnix 17, B-1000, Brussels, Belgium, http://www.cen.eu.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1322 − 15 (2019)
various materials. The photographs in Appendix X1 show 3.2.3 crack (CK), n—as used in fractography, a volume- or
examples of the origins defined in 3.2.1 and 3.2.12.Terms that surface-distributed flaw that is a surface of fracture without
are contained in otherASTM standards are noted at the end of complete separation. C1145
the each definition. The specific origin types listed in 3.2.1 –
3.2.4 handling damage (HD), n—as used in fractography,
3.2.12 are the most common types in advanced ceramics, but
surface-distributed flaws that include scratches, chips, cracks,
by no means cover all possibilities. NIST Special Publication
etc., due to the handling of the specimen/component. C1145
SP960-16 (2)includesmanymoreorigintypes.Subsection3.3
3.2.5 inclusion (I), n—as used in fractography, a volume-
providesguidanceonhowtocharacterizeordefineotherorigin
distributed flaw that is a foreign body that has a composition
types. Some common origin types are identified in 3.2.1 –
different from the nominal composition of the bulk advanced
3.2.12. These origin flaws are distributed throughout the bulk
ceramic. C1145
(inherentlyvolumedistributed)oraredistributedonanexterior
3.2.6 large grain(s) (LG), n—as used in fractography, a
surface (inherently surface distributed). The distinction is very
important for Weibull statistical analysis and size scaling of volume- or surface-distributed flaw that is a single (or cluster
of) grain(s) having a size significantly greater than that
strength as discussed in Practice C1239. Subsection 7.2 pro-
vides guidance on interpretation encompassed by the normal grain size distribution. C1145
3.1.2 advanced ceramic, n—a highly engineered, high-
3.2.7 machining damage (MD), n—as used in fractography,
performance, predominately nonmetallic, inorganic, ceramic
a surface-distributed flaw that is a microcrack(s), chip(s),
material having specific functional attributes. C1145
striation(s), or scratch(es), or a combination of these, created
during the machining process.
3.1.3 brittle fracture, n—fracture that takes place with little
or no preceding plastic deformation. 3.2.7.1 Discussion—Machining may result in the formation
of surface or subsurface damage, or both. C1145
3.1.4 flaw, n—structural discontinuity in an advanced ce-
3.2.8 pit (PT), n—as used in fractography, a surface-
ramic body that acts as a highly localized stress raiser.
distributed flaw that is a cavity created on the specimen/
3.1.4.1 Discussion—The presence of such discontinuities
component surface during the reaction/interaction between the
does not necessarily imply that the ceramic has been prepared
material and the environment, for example, corrosion or
improperly or is faulty.
oxidation. C1145
3.1.5 fractography, n—means and methods for characteriz-
3.2.9 pore (P(V)), n—as used in fractography, a volume-
ing a fractured specimen or component. C1145
distributed flaw that is a discrete cavity or void in a solid
3.1.6 fracture mirror, n—as used in fractography of brittle
material. C1145
materials, a relatively smooth region in the immediate vicinity
3.2.10 porous region (PR), n—as used in fractography, a
of and surrounding the fracture origin.
volume-distributed flaw that is a three-dimensional zone of
3.1.7 fracture origin, n—the source from which brittle
porosity or microporosity. C1145
fracture commences. C1145
3.2.11 porous seam (PS), n—as used in fractography, a
3.1.8 grain boundary (GB), n—as used in fractography, a
volume-distributed flaw that is a two-dimensional area of
volume-distributed flaw that is a boundary facet between two
porosity or microporosity. C1145
or more grains.
3.2.12 surface void (SV), n—as used in fractography, a
3.1.8.1 Discussion—This flaw is most apt to be strength
surface-distributed flaw that is a cavity created at the surface/
limiting in coarse-grained ceramics.
exterior as a consequence of the reaction/interaction between
3.1.9 hackle, n—as used in fractography, a line or lines on
the material and the processing environment, for example,
the crack surface running in the local direction of cracking,
surface reaction layer or bubble that is trapped during
separating parallel but non-coplanar portions of the crack
processing. C1145
surface.
3.3 Miscellaneous Origins:
3.1.10 mist, n—as used in fractography of brittle materials,
3.3.1 unidentified origin (?), n—as used in this practice, an
markings on the surface of an accelerating crack close to its
uncertain or undetermined fracture origin.
effective terminal velocity, observable first as a misty appear-
3.4 Other terms or fracture origin types may be devised by
ance and with increasing velocity reveals a fibrous texture,
the user if those listed in 3.2.1 – 3.2.12 are inadequate. In such
elongated in the direction of crack propagation.
instances, the user shall explicitly define the nature of the
3.2 Common Origins:
fracture origin (flaw) and whether it is inherently volume or
3.2.1 agglomerate (A), n—as used in fractography, a
surface distributed.Additional terms for surface imperfections
volume-distributed flaw that is a cluster of grains, particles,
can be found inTerminology F109 and supplementary fracture
platelets, or whiskers, or a combination thereof, present in a
origin types for ceramics and glasses may be found in
larger solid mass. C1145
Terminologies C162 and C242 and in Specification C1036.
3.2.2 compositional inhomogeneity (CI), n—as used in Examples of additional terms are hard agglomerate, collapsed
fractography, a volume-distributed flaw that is a microstruc- agglomerate, hard agglomerate (CEN 843-6) poorly bonded
tural irregularity related to the nonuniform distribution of the region, glassy inclusion, chip, closed chip, chip (CEN 843-6),
primary constituents or an additive or second phase. C1145 delamination (CEN 843-6), grain boundary cracks, chatter
C1322 − 15 (2019)
cracks, sharp impact cracks, blunt impact cracks, C-cracks
(ballbearings),baselinemicrostructuralflaws(BMF),ormain-
stream microstructural flaws (MMF). See the “Guide to Prac-
tice for Fractography of Ceramics and Glasses” (2) for discus-
sion and examples.
3.5 Theword“surface”mayhavemultiplemeanings.Itmay
refer to the intrinsic spatial distribution of flaws. The word
“surface” also may refer to the exterior of a test specimen cut
fromabulkceramicorcomponent,oralternatively,theoriginal
surface of the component in the as-fired state. It is recom-
mended that the terms original-surface or as-processed surface
be used if appropriate.
4. Summary of Practice
4.1 Prior to testing, mark the specimen or component
orientation and location to aid in reconstruction of the
specimen/component fragments. Marker lines made with a
pencil or felt-tip marker may suffice. See Fig. 1.
4.2 Whenever possible, test the specimen(s)/component(s)
to fracture in a fashion that preserves the primary fracture
surface(s) and all associated fragments for further fracto-
graphic analysis.
4.3 Carefully handle and store the specimen(s)/
component(s)tominimizeadditionaldamageorcontamination
of the fracture surface(s), or both.
4.4 Visuallyinspectthefracturedspecimen(s)/component(s)
(1 to 10×) in order to determine crack branching patterns, any
evidence of abnormal fracture patterns (indicative of testing
misalignments), the primary fracture surfaces, the location of
the mirror and, if possible, the fracture origin. Specimen/
component reconstruction may be helpful in this step. Label
the pieces with a letter or numerical code and photograph the
assembly if appropriate.
4.5 Useanopticalmicroscope(10to200×)toexamineboth
matinghalvesoftheprimaryfracturesurfaceinordertolocate
and, if possible, characterize the origin. Repeat the examina-
tion of pieces as required. If the fracture origin cannot be
characterized, then conduct the optical examination with the
purpose of expediting subsequent examination with the scan-
ning electron microscope (SEM).
4.6 Inspect the external surfaces of the specimen(s)/
component(s) near the origin for evidence of handling or
machining damage or any interactions that may have occurred
Keep appropriate records, digital images, and photographs at each step to
between these surfaces and the environment.
assist in the origin characterization and for future reference.
4.7 Clean and prepare the specimen(s)/component(s) for
SEM examination, if necessary.
FIG. 1 Simplified Schematic Diagram of the Fractographic Analy-
4.8 Carry out SEM examination (10 to 2000×) of both sis Procedure
mating halves of the primary fracture surface.
4.9 Characterize the strength-limiting origin by its identity,
location and the general features of the fractured specimen/
location,andsize.Whenappropriate,usethechemicalanalysis
component, as well as for future reference.
capability of the SEM to help characterize the origin.
4.12 Compare the measured origin size to that estimated by
4.10 If necessary, repeat 4.6 using the SEM.
fracturemechanics.Ifthesesizesarenotingeneralagreement,
4.11 Keep appropriate records, digital images, and photo- then an explanation shall be given to account for the discrep-
graphs at each step in order to characterize the origin, show its ancy.
C1322 − 15 (2019)
4.13 For a new material, or a new set of processing or 5.8 The irregularities which act as fracture origins in ad-
exposureconditions,itishighlyrecommendedthatarepresen- vanced ceramics can develop during or after fabrication of the
tative polished section of the microstructure be photographed material.Largeirregularities(relativetotheaveragesizeofthe
to show the normal microstructural features such as grain size, microstructural features) such as pores, agglomerates, and
porosity, and phase distribution. inclusions are typically introduced during processing and can
(in one sense) be considered intrinsic to the manufacturing
5. Significance and Use
process. Other origins can be introduced after processing as a
5.1 This practice is suitable for monolithic and some com-
result of machining, handling, impact, wear, oxidation, and
posite ceramics, for example, particulate- and whisker-
corrosion.Thesecanbeconsideredextrinsicorigins.However,
reinforced and continuous-grain-boundary phase ceramics.
machining damage may be considered intrinsic to the manu-
(Long- or continuous-fiber reinforced ceramics are excluded.)
facturing procedure to the extent that machining is a normal
For some materials, the location and identification of fracture
step of producing a finished specimen or component.
origins may not be possible due to the specific microstructure.
5.9 Regardless of how origins develop, they are either
5.2 This practice is principally oriented towards character-
inherently volume distributed throughout the bulk (for
izationoffractureoriginsinspecimensloadedinso-calledfast
example, agglomerates, large grains, or pores) or inherently
fracture testing, but the approach can be extended to include
surface distributed (for example, handling damage, pits from
other modes of loading as well.
oxidation, or corrosion). The distinction is a consequence of
how the specimen or component is prepared. For example,
5.3 The procedures described within are primarily appli-
inclusions may be scattered throughout the bulk ceramic
cable to mechanical test specimens, although the same proce-
material (inherently volume distributed), but when a particular
dures may be relevant to component fracture analyses as well.
specimen is cut from the bulk ceramic material, the strength-
It is customary practice to test a number of specimens
limiting inclusion could be located at the specimen surface.
(constituting a sample) to permit statistical analysis of the
This may frequently occur if the specimen is very thin. Thus,
variabilityofthematerial’sstrength.Itisusuallynotdifficultto
in a particular specimen, a volume-distributed origin can be
test the specimens in a manner that will facilitate subsequent
volume located, surface located, near-surface located, or edge
fractographic analysis. This may not be the case with compo-
located. The distinction is important for Weibull analysis and
nent fracture analyses. Component fracture analysis is some-
strength scaling with size as discussed in Practice C1239.
times aided by cutting test pieces from the component and
fracturing the test pieces. Fracture markings and fracture
5.10 As fabricators improve materials by careful process
origins from the latter may aid component interpretation.
control, thus eliminating undesirable microstructural features,
advancedceramicswillbecomestrength-limitedbyoriginsthat
5.4 Optimumfractographicanalysisrequiresexaminationof
comefromthelarge-sizedendofthedistributionofthenormal
as many similar specimens or components as possible. This
microstructural features. Such origins can be considered main-
will enhance the chances of successful interpretations. Exami-
stream microstructural features. In other instances, regions of
nation of only one or a few specimens can be misleading. Of
slightly different microstructure (locally higher microporosity)
course,insomeinstancesthefractographermayhaveaccessto
or microcracks between grains (possibly introduced by ther-
only one or a few fractured specimens or components.
moelastic strains) may act as fracture origins. These origins
5.5 Successful and complete fractography also requires
will blend in well with the background microstructure and will
careful consideration of all ancillary information that may be
be extremely difficult or impossible to discern, even with
available, such as microstructural characteristics, material
carefulscanningelectronmicroscopy.Thispracticecanstillbe
fabrication, properties and service histories, component or
used to analyze such fracture origins, but specific origin
specimen machining, or preparation techniques.
definitions may need to be devised.
5.6 Fractographic inspection and analysis can be a time-
5.11 ThispracticeiscompatiblewithCENStandardEN843
consuming process. Experience will, in general, enhance the
Part 6.
chances of correct interpretation and characterization, but will
not obviate the need for time and patience. Repeat examina-
6. Apparatus
tions are often fruitful. For example, a particular origin type or
key feature may be overlooked in the first few test pieces of a 6.1 General—Examplesoftheequipmentdescribedin6.2–
6.6 are illustrated in Appendix X4 and also the NIST Special
sampleset.Asthefractographergainsexperiencebylookingat
multipleexamples,heorshemaybegintoappreciatesomekey Publication SP 960-16 (2).
feature that was initially overlooked.
6.2 Binocular Stereomicroscope,withadjustablemagnifica-
5.7 This practice is applicable to quality control, materials tion between 10 to 200× and directional light source (see Fig.
research and development, and design. It will also serve as a X4.1). A camera or video monitor system used with this
bridge between mechanical testing standards and statistical microscope is a useful option (see 6.6 and Fig. X4.2). Basic
analysis practices to permit comprehensive interpretation of binocular stereomicroscopes have magnification ranges to the
data for design. An important feature of this practice is the eyes of about 8 to 32× or 10 to 40×, but these limit one’s view
adoption of a consistent manner of characterizing fracture of a small fracture origin flaw and greater magnifications are
origins,includingoriginnomenclature.Thiswillfurtherenable needed. Stereomicroscopes with upper magnifications of 100×
the construction of efficient computer databases. orashighas300×(availablewithmanystereomicroscopes)are
C1322 − 15 (2019)
more suitable for fractographic analysis. On the other hand, series of digital images (e.g., 10 to 20 images). A series of
having a small magnification at the lowest limit (e.g., 5×) images are taken at slightly different z heights above a
facilitates taking an overall picture of a small component. specimen. The software takes the in-focus portions of each
Hence, a stereoptical microscope with a broad zoom range image and combines them into a single focused image in
(e.g., range of 10, 16, or even 20 power) is very advantageous. seconds.
A50/50beamsplitter(halfthelightissenttotheeyesandhalf
6.7 Digital Camera for Overall Macrophotography—
issenttothecamera)inthestereobinocularmicroscopeisvery
Simple consumer digital cameras or even cell phone cameras
desirable since it allows one to look through the eyepieces at
are very useful for photographing the overall component or
the same time an image is sent to the camera. The alternative,
specimen.
a lever which diverts light either to the eyes or to the camera,
6.8 Digital Microscope (also known as a USB
is cumbersome and less desirable. See the NIST Special
microscope)—This is a digital microscope that connects to a
Publication SP 960-16 (2) for additional information.
computer. They are a new technology that is becoming
6.3 Cleaning and Preparation Equipment, such as an ultra-
increasingly common. They can range from inexpensive,
sonic bath and a diamond cut-off wheel.
low-power, handheld models to elaborate, high-power, expen-
6.4 Scanning Electron Microscope (SEM), with energy or
sive models mounted on a rigid platform with z-axis control
wavelength dispersive spectroscopy (see Fig. X4.3).
and digital image stitching capabilities. It may be difficult to
obtain sharp, focused images with the simpler models that are
6.5 Peripheral Equipment, such as hand magnifying lens;
hand held or on simple stands. One limitation to all of them is
5×, 7×, or 10× inspection loupe; tweezers; grips; felt-tip pens;
illumination, which is usually provided by built-in light emit-
and compressed air, as shown in Fig. X4.4.
ting diodes surrounding the lens. This limits their ability to
6.6 Digital Camera for the Binocular Stereomicroscope—
highlight or even discern critical fracture surface features. For
Digital cameras have largely replaced older video cameras or
example,shadowing,orvicinalillumination,whichisessential
films and negatives. It is optimal to mount such a camera with
for ceramic examination and fracture mirror examination, is
adedicatedcameraportmoduleinthemicroscopebody,rather
difficultorimpossiblewithdigitalmicroscopes.Anothersevere
than an attachment directly onto an eyepiece.An adaptor lens
limitation is obtaining images with accurate magnifications or
at the camera port may be needed to ensure that the field of
magnification markers.
view as seen by the eyepieces is comparable to that imaged by
the camera. CCD or CMOS chip cameras are commonly used.
7. Detailed Procedures and Characterization
Experience has shown that a digital camera chip with 2 to 5
7.1 Procedure:
million pixels is adequate for most applications. The most
7.1.1 General—Location, identification, and characteriza-
common image formats in 2015 are JPEG and TIFF. Image
tionoffractureoriginsinadvancedceramicscansometimesbe
compression should be minimized or not used at all when
accomplished using simple optical microscopy techniques,
capturing and saving images. (Sometimes excessive emphasis
isplacedonhavinglargepixelcountsindigitalcameras.There though it more often requires scanning electron microscopy
(SEM). It may not be feasible, practical, or even necessary to
is no harm in having digital cameras with larger pixel counts,
but storing and handling very large files might become examine all fracture surfaces with the SEM. The extent of
fractographic analysis required will depend upon the purpose
cumbersome, especially if the images are embedded in docu-
ments. Nearly all the images in NIST Special Publication SP of the analysis and the fractographic conduciveness of the
material.Additional information on inspection techniques may
960-16 (2) were captured with a digital camera having a color
mosaic chip having 2 megapixels on the CCD chip.)Although be found in NIST Special Publication SP 960-16 (2).
stereoptical microscopes have good depth of field, it can even 7.1.1.1 The nature of the fractographic analysis will depend
be further enhanced by modern, effective, and inexpensive on whether the results will be used for quality control,
software that allows “focus stacking” or “z-axis stacking” of a materials research and development, or design. Table 1 gives
TABLE 1 Suggested Sampling Guidelines
Level 1 to 10× Visual 10 to 200× Optical 10 to 2000× SEM
Level 1
Quality control Specimens that fail to meet minimum Specimens that fail to meet minimum Optional
strength requirements strength requirements
Level 2
Quality control All specimens All specimens, if possible. Representative specimens, for example:
Materials development Always both fracture halves. —2 of each origin type
—the 5 lowest strength specimens
—at least 2 optically unidentifiable
origins, if present
Level 3
Materials development All specimens All specimens, if possible. All specimens, or as many specimens
Design Always both fracture halves. as necessary such that combined
optical and SEM characterize 90 %
(100 % for design) of all identifiable
origins
C1322 − 15 (2019)
suggested sampling guidelines for medium- to high-strength 7.1.6 Handling and Storage—Broken specimens shall be
advanced ceramics. handledandstoredsoastominimizethepossibilityofdamage
or contamination of the fracture surfaces, or both. Avoid
7.1.1.2 The fractographic analysis will also depend on the
handling the specimen, especially the fracture surface, with
conduciveness of the material to this analysis. Some ceramics
your hands. Body oils and skin fragments can easily change or
are easy to analyze; fracture origins are readily visible with an
obscure the character of the fracture surface. During recon-
optical microscope and the SEM is not needed. Alternatively,
struction of the specimen, minimize rubbing the fragments
originsmaybetoosmalltodiscernwithanopticalmicroscope,
together since this may abrade or chip the fracture surfaces,
difficult to differentiate from the normal microstructure, or too
and damage the fracture surface. Avoid picking or even
difficult to see in some translucent materials, thus, the SEM
touching the fracture surface with sharp instruments such as
examination is necessary. Coarse-grained or porous materials
tweezers, as this may alter or contaminate the fracture surface.
may have no fractographic markings that permit origin
The specimen shall be stored in a clean and orderly fashion, as
identification, and optical and SEM microscopy will prove
much time can be lost trying to sort out mixed-up specimens.
useless.
Store the specimen and fragments in containers that will
7.1.2 An origin type may not reveal itself clearly in some
minimize additional damage or contamination.
specimens and may only be detected after a number of
examplesareviewedandapatternbeginstoemerge.Itisoften
NOTE 1—The laboratory environment contains a myriad of materials
necessary to reexamine many of the specimens and reevaluate
such as ceramic-based clays, waxes, adhesives, and resins that should be
the initial appraisal. Fractographic interpretations based on avoidedwhereverpossible.Manyofthesematerials,oncetheyareaffixed
to the specimen, are very tenacious and often impossible to remove.
only one or a few specimens can be very misleading. The
examination of all specimens shall include the examination of
7.1.7 VisualInspectionandSpecimenorComponentRecon-
both mating halves of the primary fracture surface irrespective
struction (1 to 10×)—Visually examine the fragmented
of the purpose of the fractographic analysis.
specimen/component pieces in order to find the primary
7.1.3 Tomaximizetheamountofinformationobtainedfrom
fracture surfaces, the general region of the fracture origin, and
afractographicexercise,careshallbetakeninallstepsstarting
if possible, the fracture mirror. Hand magnifiers or inspection
with the initial testing of the specimen or component.
loupes can be helpful. Reconstruct the specimen if necessary,
7.1.4 Specimens that fail during machining, handling, or but take care to avoid damaging the fracture surfaces of pieces
without measurement of a fracture stress should be examined that have the prospective fracture origin. Reconstruction is
to determine the fracture origins. The fact that these types of valuableinobservingthecrack(s)andcrackbranchingpatterns
fracture occurred should be noted and reported. which, in turn, helps determine the primary fracture surfaces
and can help assess the stress state if it is not known. Special
7.1.5 MechanicalTesting—Afewsimpleprecautionsshould
emphasis should be on determining whether the fracture
betakenpriortobreakingthespecimen.Thetestsiteshouldbe
pattern indicates misalignments or breakages at test grips (in
kept clean to minimize pickup of contaminants. Markings of
tension), at stress concentrators (neck region in tension), or
somesortshouldbeplacedonthespecimentomaintainapoint
load application points (in flexure and disk tests).
of reference and to aid in the reconstruction of the specimen.
The markings shall not damage the specimen or lead to 7.1.7.1 Crack patterns can range from very simple to quite
contamination of the fracture surfaces.Afine pencil or felt-tip complexdependinguponthespecimenorcomponentgeometry
marker line is often sufficient to mark the inner gage length in andthestressstatesinthebody.Multiplefracturesarecommon
a flexural strength specimen. The tension and compression to high-strength ceramics that store large amounts of elastic
sides of the specimen may also be marked. A circular direct energy during testing. Upon fracture, this energy is released
tension strength specimen may be marked with a zero-degree and reflects from free surfaces back through the body of the
reference. Testing that allows the broken fragments of the material causing additional fractures. Appendix X6 shows
specimen to hurtle about shall be avoided. Incidental impact many potential fracture patterns in some common test speci-
damage to the fracture surfaces can destroy the origin, alter its mens.Ahierarchy or sequence of crack propagation can assist
appearance,orcausesecondaryfractures.Acompliantmaterial inbacktrackingtotheprimaryfracturesurfaces.Crackbranch-
that covers the hard surfaces of the fixture or prevents pieces ing can be used to determine the direction of crack
from flying about, or both, is sufficient to minimize this propagation, which may be denoted by “dcp.” A traveling
damage. All fragments from the broken specimen shall be macrocrackwilltypicallybranchintosuccessivelymorecracks
retained for reconstruction, unless it can be positively estab- and will rarely rejoin another crack to form a single crack (see
lished that some pieces are incidental or trivial. In some cases, Fig. 2).Acrack that intersects another crack at angles close to
tape may be applied to a test piece prior to testing in order to 90° and stops (does not continue into an adjacent piece) will
hold fragments together after fracture. Tapes shall not be usually be a secondary crack that can be quickly eliminated
applied to tensile-loaded specimen surfaces, nor shall they since it will not contain the fracture origin. For specimens that
interfere with the application of forces or loads on the test do not show macroscopic crack branching, incipient branching
piece.Forexample,portionsoftheback(compression)surface intheformofshallowcrackscanoftenbefoundalongtheedge
of a biaxial disk specimen for ring-on-ring testing may be of the main crack on the exterior surface. As with the
taped, but the annular region where the inner loading ring macroscopic cracks, the angle of these shallow cracks in
contacts the test piece should be left untaped. relation to the main crack indicate the local direction of crack
C1322 − 15 (2019)
(a) shows crack branching and the arrow shows the direction of crack propagation (dcp).
(b) shows a crack intersection with the first crack labeled 1, and the secondary crack, labeled 2, which ran over and stopped
at the intersection.
FIG. 2 Schematic of Typical Fracture Patterns
growth.Vicinalilluminationordyepenetrants,orboth,maybe origin on the primary fracture surfaces (Table 1, Levels 2–3)
used to make these cracks more easily discernible. andattempttocharacterizetheorigin.Ifcharacterizationisnot
7.1.7.2 Misalignment or deviation from the assumed stress possible during this step, the optical examination helps to
state can be discerned by fracture surfaces that are at an minimize the time spent during the subsequent SEM examina-
irregular angle (not 90°) to the anticipated maximum principal tion.
stress. Branching angles can be helpful in detecting multiaxial
7.1.8.1 Astereomicroscope is preferred for examining frac-
stress states. Frequent breakage at test grips (in tension), at
turesurfacesduetoitsexcellentdepthoffield.Viewingwillbe
stress concentrators (neck region in tension), or load applica-
most effective in the 10 to 300× range. A traversing stage
tion points (in flexure and disk tests) may indicate misalign-
coupled with crosshairs or a graduated reticule in the eyepiece
ment.
is useful for measuring the size or area, or both, of the mirror
7.1.7.3 The detection of the general region of the fracture
and, if possible, the origin. Illumination should be provided by
origin, and the fracture mirror if present, during visual exami-
a common microscope light source with adjustable intensity
nationdependsontheceramicmaterialbeinganalyzed.Dense,
and angle of incidence to provide a means of variable lighting.
fine-grained, or amorphous ceramics are conducive to fractog-
These variations can highlight aspects of the fracture surface
raphy and will leave distinct fracture markings (hackle and
that may be hidden if one is restricted to a single view.
mirror) which will aid in locating the origin (see Fig. 3).
Low-anglegrazingillumination(vicinal)isespeciallyvaluable
Hackle lines and ridges on the fracture surface are extremely
in highlighting ridges, valleys, hackle lines, and other features
helpfulinlocatingthegeneralvicinityofafractureorigin,even
on the fracture surface.
whenafracturemirrorisnotevident(Fig.4).Theywillradiate
7.1.8.2 The specimen should be mounted to view the
from, and thus point the way back to, the fracture origin.They
fracture and external surfaces. A holder, such as a simple
are best highlighted by low incident angle lighting which will
alligatorclipattachedtoastandwithaflexiblearmandhaving
createusefulshadows.Fracturemirrorsaretelltalefeaturesthat
a compliant coating or sheath covering the teeth, provides a
are typically centered on the strength-limiting origins. If the
sturdy grip (Item B in Fig. X4.4) for examination. Ceramic
specimen or component is highly stressed, and the material is
clays or organic waxes shall not be used because these
fine-grained and dense, a distinct fracture mirror will form as
materials can contaminate the fracture surface and are very
showninFig.3.Ontheotherhand,lowerenergyfracturesand
difficult to remove. Surface contaminants such as lint and dust
those in coarse-grained or porous ceramics will not leave
can be removed easily with canned or filtered compressed air.
distinct fracture markings (Fig. 4). Coarse hackle markings or
Viewing both of the mating primary fracture surfaces simulta-
ridgescanstillbeusedtodeterminethevicinityofthefracture
neously can expedite and improve the quality of the analysis
origin, especially with oblique lighting.
since what might appear to be a pore on one half may show an
agglomerate on the other (flexure specimens should be
NOTE 2—Coarse-grained or porous materials may have no fracto-
graphic markings that permit origin identification, and optical and SEM mountedtensilesurface-to-tensilesurface).Careshallbetaken
will prove useless.
so that extraneous damage is not created.
7.1.8 Optical Microscopy (10 to 300×)—Examine both
NOTE 3—Polymer-based clays may be used for mounting specimens,
mating halves of the primary fracture surface. This is often
providedthattheycanbeeasilyremovedwithsolventssuchasacetoneor
performed in conjunction with the visual inspection. The
ethanol. The polymer clay should have an easily recognizable color, so
purpose of the optical examination is to locate the fracture that if it inadvertently gets onto a fracture surface, it can be easily
C1322 − 15 (2019)
(A)Aschematicofaflawlocatedatthesurface.Theflawcouldeitherbeaninherentlysurface-distributedflaworaninherently
volume-distributed flaw.
(B)Anopticalmicrographofasurface-locatedflawinabiaxialborosilicatecrownglassdiscfracturedinabiaxialring-on-ring
strength test (σ = 118 MPa).
(C)A schematic of a volume-distributed flaw.
(D)An optical micrograph of a volume-distributed flaw in a tungsten carbide specimen tested in four-point flexure (σ = 724
MPa).
(E)Schematic of a volume-distributed flaw.
(F)An optical micrograph of a volume-distributed flaw in a siliconized silicon carbide tension specimen (σ = 350 MPa).
Themirrorcanbecenteredaroundaportionoftheoriginandnottheentireorigin.Inceramicterminology,smoothisarelative
term.
FIG. 3 Fracture Surfaces of Advanced Ceramics That Failed in a Brittle Manner
recognized and removed with the solvent. listed in X2.1.1 and NIST Special Publication SP 960-16 (2).
NOTE4—Additionalilluminationtechniquesandhelpfulproceduresare
7.1.8.3 At the lowest magnification, locate the fracture
mirror and origin site using the hackle on the fracture surface.
Sculpey III, Oven Baked Clay by Polyform Products Company, Elk Grove
In high-strength, fine-grained, and dense ceramics the origin
Village, IL, 60007, USA is particularly effective and is easily dissolvable by
will be approximately centered in the fracture mirror as shown
acetone. It should not be baked, but used in its soft form right out of the package.
C1322 − 15 (2019)
NOTE 1—The coarse hackle lines that emanate from the flaw can be used to locate the origin.
NOTE 2—The coarse hackle lines are obvious (arrows) and clearly indicate the location of the origin (a Knoop indentation-induced pre-crack), even
though a mirror is NOT readily visible.
FIG. 4 (A) Schematic of a Flaw in Which a Mirror Has Not Formed and (B) an Optical Micrograph of a Fracture Surface of a Sintered
Silicon Nitride Flexure Specimen (σ = 227 MPa)
in Fig. 3B and Fig. 3C. Hackle lines and ridges will be very height to view the external surfaces. This examination can be
helpful since they will radiate outward from the fracture origin
especially helpful if the origin is not evident on the fracture
and mirror. As discussed in 7.1.7 and shown in Fig. 4,
surface and handling or machining damage is suspected. It is
low-energy fractures or fractures in porous or coarse-grained
also helpful in ascertaining if any interaction/reaction has
ceramics may not lead to fracture mirror formation, but the
occurred between the material and the environment.
same principles of using the hackle lines apply. Twist hackle
7.1.8.5 Characterize the identity, location, and size of the
lines are especially helpful and occur when a crack encounters
strength-limiting origin in accordance with 7.2. Record obser-
a principal stress field that is not perpendicular to the original
vations pertaining to features specific to the lighting, such as
plane of fracture. Twist hackle commences as finely spaced
color and reflectivity.These records should include, but not be
parallel lines which usually merge in the direction of crack
limited to, notes, sketches, and photographs. Although this
propagation, giving rise to the well-known river pattern as
extra step may seem time consuming, it often leads to greater
shown in Fig. 5.
efficiency in the long run. These records are extremely useful
NOTE 5—The merger of twist hackle in the direction of crack propa-
for publication and minimizing the search time with the SEM.
gation is opposite to the tendency of macrocracks to diverge as discussed
The latter point can not be underestimated. Novices often lose
in 7.1.7.1.These features are usually well defined in glasses and very fine
grained, fully dense polycrystalline ceramics. Such twist hackle often much time searching for the origin or examining the wrong
occurs on individual grains in coarse-grained polycrystalline ceramics.
area with the SEM. The SEM images are quite different from
7.1.8.4 Examine the external surfaces of the specimen or optical images, and a reorientation time is sometimes neces-
component if the origin is surface or edge located.Aspecimen
sary. Appendix X1 and Appendix X9 may be consulted for
holder (parts C in Fig. X4.4) with a flat or vee groove can be
examples of fracture origins and typical signs of machining
used to hold the entire specimen at a convenient working
damage origins.
7.1.8.6 Reexamine the specimen fracture surfaces if neces-
sary.Thiswillbeimportantifanewmaterialisbeingexamined
or if a particular origin type becomes clear only after some or
all of the specimens have been examined.
7.1.8.7 Photograph the fracture surface, if appropriate (see
7.1.10). A digital camera directly mounted on the stereo
binocular microscope is especially valuable and a great time
saver. The camera is usually attached to the body of the
stereoptical microscope with a camera port, which diverts the
image from one or the other of the two light paths in the
microscope.Withbuilt-inzoomrangesfrom5to1(orgreater)
and beam splitters, it is possible to frame, focus, and shoot
NOTE 1—The direction of crack propagation is shown by the arrow.
quickly and efficiently.
NOTE 6—Appendix X2 and NIST Special Publication SP 960-16 (2)
FIG. 5 Schematic of Twist Hackle Lines That Form a “River Pat-
tern” have helpful tips on lighting techniques.
C1322 − 15 (2019)
7.1.8.8 For translucent ceramics, it may be useful to illumi- tial adjunct to SEM examination since telltale color, contrast,
nate the fracture surface from the side with low incident angle or reflectivity features, as well as subtle features such as mist,
illumination. An opaque card held next to the specimen side and Wallner lines, may be completely lost in electron-
can block the light entering the specimen bulk. This will microscope viewing. Once optical fractography is complete
minimize light scattering from inside the specimen. andtheoriginsarecharacterizedaswellaspossible,asubsetof
Alternately, it may be useful to coat the fracture surface with specimens should be prepared for SEM analysis. Determina-
evaporated carbon or sputtered gold-palladium prior to optical tion of the number of specimens which will comprise the
examination. This will often improve the visibility of some subset will depend on the intent of the analysis (see Table 1).
crack propagation patterns, eliminate subsurface reflections,
7.1.9.1 Preparation:
and improve the quality of the photographs taken of the
7.1.9.2 If necessary, the specimens should be cut to a
fracture surface. A simple, effective expedient is to stain or
consistent height that allows for ease of installation and
“paint” the fracture surface with a green felt-tip pen. The dye
movement in the SEM. Wet cutting should be done so as to
will mask internal reflections and run into valleys and
flushawaythespecimenandcuttingwheeldebris.Theyshould
depressions, highlighting and bringing out the texture in
becutasflataspossibletoeliminateproblemsduetoexcessive
fracturesurfacemarkings.Thedyemaybeeasilyremovedwith
tilt,althoughaslighttiltbackwardscanbebeneficialonflexure
acetoneoralcoholonacotton-tippedswab.Suchdyesmaynot
specimens (this allows for the simultaneous viewing of the
be advisable if chemical analysis o
...