ASTM D8255-19
(Guide)Standard Guide for Work of Fracture Measurements on Small Nuclear Graphite Specimens
Standard Guide for Work of Fracture Measurements on Small Nuclear Graphite Specimens
SIGNIFICANCE AND USE
5.1 Structural integrity assessments typically use values of strength and elastic modulus to predict crack initiation in graphite components and there is a suite of ASTM standards (Section 2, Test Methods C651, C695, C747, C749, C769, and D7775) to cover the measurement of these properties.
5.2 The graphite component behavior after crack initiation depends on fracture mechanics parameters, such as fracture toughness and the work of fracture. Test Method D7779 provides the specification and requirements for measuring the fracture toughness of graphite based on linear-elastic stress analysis. Moreover, Test Method D7779 applies to cases where there are no restrictions on specimen size and on applicable machining and specimen preparation techniques.
5.3 Most polycrystalline graphites are non-linear elastic, non-uniform, quasi-brittle materials. For such materials, an effective approach for the determination of fracture properties is the analysis of the global energy balance associated with crack extension, similar to Griffith's theory of brittle fracture. This approach does not have the mathematical complexity of the non-linear elastic fracture and is easier to implement in practice.
5.4 Work of Fracture, γf (J/m2), is defined as the energy required to form a crack divided by the cross sectional area of the crack. It is assumed that the energy per unit area is constant during crack propagation. In general, components that have an excess of strain energy to the point of fracture, compared to the work needed to extend the crack to full dimension, fail by fast fracture. Any excess energy is converted into kinetic energy through a process that generates stress waves. If the amount of excess energy is sufficiently large, the stress waves will have peak magnitudes greater than the material strength, leading to the initiation and propagation of secondary cracks that could result in the fragmentation of the component.
5.5 However, some components that have less str...
SCOPE
1.1 This guide provides general tutorial information and best practice for measuring the work of fracture on manufactured graphite and carbon specimens. Although applicable to all carbon and graphite materials, this guide is aimed specifically at measurements required on nuclear graphites, where there may be constraints on the geometry and/or volume of the test specimen.
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.
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
Relations
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: D8255 − 19
Standard Guide for
Work of Fracture Measurements on Small Nuclear Graphite
1
Specimens
This standard is issued under the fixed designation D8255; 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 C747TestMethodforModuliofElasticityandFundamental
Frequencies of Carbon and Graphite Materials by Sonic
1.1 This guide provides general tutorial information and
Resonance
best practice for measuring the work of fracture on manufac-
C749Test Method for Tensile Stress-Strain of Carbon and
tured graphite and carbon specimens. Although applicable to
Graphite
all carbon and graphite materials, this guide is aimed specifi-
C769Test Method for Sonic Velocity in Manufactured
cally at measurements required on nuclear graphites, where
Carbon and Graphite Materials for Use in Obtaining an
there may be constraints on the geometry and/or volume of the
Approximate Value of Young’s Modulus
test specimen.
D7775Guide for Measurements on Small Graphite Speci-
1.2 The values stated in SI units are to be regarded as
mens
standard. The values given in parentheses after SI units are
D7779Test Method for Determination of Fracture Tough-
provided for informationonlyandarenotconsideredstandard.
ness of Graphite at Ambient Temperature
1.3 This standard does not purport to address all of the
D7972Test Method for Flexural Strength of Manufactured
safety concerns, if any, associated with its use. It is the Carbon and GraphiteArticles Using Three-Point Loading
responsibility of the user of this standard to establish appro-
at Room Temperature
priate safety, health, and environmental practices and deter- E4Practices for Force Verification of Testing Machines
mine the applicability of regulatory limitations prior to use.
E399Test Method for Linear-Elastic Plane-Strain Fracture
1.4 This international standard was developed in accor- Toughness of Metallic Materials
dance with internationally recognized principles on standard-
3. Terminology
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
3.1 Definitions:
mendations issued by the World Trade Organization Technical 2
3.1.1 work of fracture, γ (J/m ),n—the total energy re-
f
Barriers to Trade (TBT) Committee.
quired to produce a unit area of fracture surface.
3.2 Definitions of Terms Specific to This Standard:
2. Referenced Documents
3.2.1 absorbed energy, n—the plastic energy absorbed by
2
2.1 ASTM Standards:
the system.
C559Test Method for Bulk Density by Physical Measure-
3.2.1.1 Discussion—This is primarily the work done to
ments of Manufactured Carbon and Graphite Articles
extend the crack but can also include other plastic strains
C651Test Method for Flexural Strength of Manufactured
related to the specimen, such as microcracking, or the entire
CarbonandGraphiteArticlesUsingFour-PointLoadingat
system, usually related to the stiffness of the loading frame.
Room Temperature
These cases are discussed in detail in Section 10.
C695Test Method for Compressive Strength of Carbon and
3.2.2 total (consumed) energy, n—the total energy calcu-
Graphite
lated by the load-displacement trace in this type of test.
3.2.2.1 Discussion—This is the sum of the elastic energy
1
This guide is under the jurisdiction of ASTM Committee D02 on Petroleum thatleadstoelasticdeformationofthespecimenandtheplastic
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
energy, which is primarily the work done to extend the crack.
mittee D02.F0 on Manufactured Carbon and Graphite Products.
Current edition approved May 1, 2019. Published June 2019. DOI: 10.1520/
4. Summary of Guide
D8255-19.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
4.1 An introduction is provided on the characteristics of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
nuclear graphite that restrict the number of test methods that
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. are applicable for measuring the Work of Fracture (WoF),
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D8255 − 19
3,4
especially with regard to testing of small irradiated specimens in the cross-section. Because the crack is initiated at the tip
in a shielded facility. This gu
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