ASTM D7779-20
Standard Test Method for Determination of Fracture Toughness of Graphite at Ambient Temperature

Standard No.

ASTM D7779-20

Release Date

2020

Published By

American Society for Testing and Materials (ASTM)

Latest

ASTM D7779-20

Scope

1.1 This test method covers and provides a measure of the resistance of a graphite to crack extension at ambient temperature and atmosphere expressed in terms of stress-intensity factor, K, and strain energy release rate, G. These crack growth resistance properties are determined using beam test specimens with a straight-through sharp machined V-notch. 1.2 This test method determines the stress intensity factor, K, from applied force and gross specimen deflection measured away from the crack tip. The stress intensity factor calculated at the maximum applied load is denoted as fracture toughness, KIc, and is known as the critical stress intensity factor. If the resolution of the deflection gauge is sensitive to fracture behavior in the test specimen and can provide a measure of the specimen compliance, strain energy release rate, G, can be determined as a function of crack extension. 1.3 This test method is applicable to a variety of grades of graphite which exhibit different types of resistance to crack growth, such as growth at constant stress intensity (strain energy release rate), or growth with increasing stress intensity (strain energy release rate), or growth with decreasing stress intensity (strain energy release rate). It is generally recognized that because of the inhomogeneous microstructure of graphite, the general behavior will exhibit a mixture of all three during the test. The crack resistance behavior exhibited in the test is usually referred to as an “R-curve.” NOTE 1—One difference between the procedure in this test method and test methods such as Test Method E399, which measure fracture toughness, KIc, by one set of specific operational procedures, is that Test Method E399 focuses on the start of crack extension from a fatigue precrack for metallic materials. This test method for graphite makes use of a machined notch with sharp cracking at the root of the notch because of the nature of graphite. Therefore, fracture toughness values determined with this method may not be interchanged with KIc as defined in Test Method E399. 1.4 This test method gives fracture toughness values, KIc and critical strain energy release rate, GIc for specific conditions of environment, deformation rate, and temperature. Fracture toughness values for a graphite grade can be functions of environment, deformation rate, and temperature. 1.5 This test method is divided into two major parts. The first major part is the main body of the standard, which provides general information on the test method, the applicability to materials comparison and qualification, and requirements and recommendations for fracture toughness testing. The second major part is composed of annexes, which provide information related to test apparatus and test specimen geometry. Main Body Section Scope 1 Referenced Documents 2 Terminology 3 Summary of Test Method 4 Significance and Use 5 Apparatus 6 Test Specimen 7 Procedure 8 Specimen Dryness 9 Calculation of Results 10 Report 11 Precision and Bias 12 Keywords 13 Annex Annex A1 1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.6.1 Measurement units expressed in these test methods are in accordance with IEEE/ASTM SI 10. 1.7 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. 1.8 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. 1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee D02.F0 on Manufactured Carbon and Graphite Products. Current edition approved Oct. 1, 2020. Published December 2020. Originally approved in 2011. Last previous edition approved in 2015 as D7779 – 11 (2015). DOI:10.1520/D7779-20. *A Summary of Changes section appears at the end of this standard Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States 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. 2. Referenced Documents

ASTM D7779-20 Referenced Document

• ASTM C1161 Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
• ASTM C1421 Standard Test Methods for Determination of Fracture Toughness of Advanced Ceramics at Ambient Temperatures
• ASTM E177 Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• ASTM E1823 Standard Terminology Relating to Fatigue and Fracture Testing
• ASTM E2309 Standard Practices for Verification of Displacement Measuring Systems and Devices Used in Material Testing Machines*， 2024-04-22 Update
• ASTM E337 Standard Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
• ASTM E399 Standard Test Method for Plane-Strain Fracture Toughness of Metallic Materials
• ASTM E4 Standard Practices for Force Verification of Testing Machines
• ASTM E561 Standard Practice for R-Curve Determination
• ASTM E691 Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• IEEE/ASTM SI 10 American National Standard for Metric Practice

ASTM D7779-20 history

• 2020 ASTM D7779-20 Standard Test Method for Determination of Fracture Toughness of Graphite at Ambient Temperature
• 2011 ASTM D7779-11(2015) Standard Test Method for Determination of Fracture Toughness of Graphite at Ambient Temperature
• 2011 ASTM D7779-11 Standard Test Method for Determination of Fracture Toughness of Graphite at Ambient Temperature