Significance and Use 4.1 By definition, the tensile strength of manufactured graphite is obtained by the direct uniaxial tensile test (Test Method C749). The C749 tensile test specimen is relatively large and is frequently incompatible with available irradiation capsule volumes, or oxidation apparatus (Test Method D7542). The splitting tensile test provides an alternate means of testing tensile properties on specimens that have severe geometric constraints and otherwise cannot meet the prescribed testing geometries of Test Method C749. By loading a disc-shaped specimen, on edge, under a compressive load, the resulting tensile stresses transverse to the loading axis provide an indication of the tensile strength properties of graphite. To obtain consistent and meaningful values of a splitting tensile strength, it is vital that the fracture initiate in the center of the disk and not along an edge. This standard test helps to ensure that the disk specimens break diametrally along the loading diameter due to tensile stresses that are perpendicular to the loading axis and that the fracture initiates at the center of the disk. 4.2 The stress determined using the diametral compression test is the maximum tensile stress at the center of the disk when loaded under the prescribed conditions and the fracture initiates at the center of the disk. It should be understood that this tensile stress value is obtained with the specimen in a complex biaxial stress condition. When the test is performed carefully and consistently these tensile stress values are comparable to each other, but the performers of this test should validate the values obtained. Any bias when comparing values with this standard to the uniaxial tensile stress values obtained using Test Method C749 should be identified and reported. Validation shall be performed on the same material and may not be applicable to other states of the same material (for example, oxidized, irradiated). Guidance on small specimen testing can be found in Guide D7775.Scope 1.1 This test method covers testing apparatus, specimen preparation, and testing procedures for determining the splitting tensile strength of graphite by diametral line compression of a disk. This small specimen geometry (Test Method D7779) is specifically intended for irradiation capsule use. Users are cautioned to use Test Method C749 if possible for measuring tensile strength properties of graphite. 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 All dimension and force measurements and stress calculations shall conform to the guidelines for significant digits and rounding established in Practice D6026. 1.4 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. 1.5 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.
