Significance and Use
5.1 Advanced ceramics are candidate materials for high-temperature structural applications requiring high strength along with wear and corrosion resistance. In particular, ceramic tubes are being considered and evaluated as hermetically tight fuel containment tubes for nuclear reactors. These ceramic tubes require end-plugs for containment and structural integrity. The end-plugs are commonly bonded with high-temperature adhesives into the tubes. The strength and durability of the test specimen joint are critical engineering factors, and the joint strength has to be determined across the full range of operating temperatures and conditions. The test method has to determine the breaking force, the nominal joint strength, the nominal burst pressure, and the failure mode for a given tube/plug/adhesive configuration.
5.2 The EPPO test provides information on the strength and the deformation of test specimen joints under applied shear, tensile, and mixed-mode stresses (with different plug geometries) at various temperatures and after environmental conditioning.
5.3 The end-plug test specimen geometry is a direct analog of the functional plug-tube application and is the most direct way of testing the tubular joint for the purposes of development, evaluation, and comparative studies involving adhesives and bonded products, including manufacturing quality control. This test method is a more realistic test for the intended geometry than the current shear test of ceramic joints (Test Method ), which uses an asymmetric four-point shear test on a flat adhesive face joint.
5.4 The EPPO test method may be used for joining method development and selection, adhesive comparison and screening, and quality assurance. This test method is not recommended for adhesive property determination, design data generation, material model verification/validation, or combinations thereof.
1.1 This test method covers the determination of the push-out force, nominal joint strength, and nominal burst pressure of bonded ceramic end-plugs in advanced ceramic cylindrical tubes (monolithic and composite) at ambient and elevated temperatures (see ). The test method is broad in scope and end-plugs may have a variety of different configurations, joint types, and geometries. It is expected that the most common type of joints tested are adhesively bonded end-plugs that use organic adhesives, metals, glass sealants, and ceramic adhesives (sintered powders, sol-gel, polymer-derived ceramics) as the bonding material between the end-plug and the tube. This test method describes the test capabilities and limitations, the test apparatus, test specimen geometries and preparation methods, test procedures (modes, rates, mounting, alignment, testing methods, data collection, and fracture analysis), calculation methods, and reporting procedures.
1.2 In this end-plug push-out (EPPO) test method, test specimens are prepared by bonding a fitted ceramic plug into one end of a ceramic tube. The test specimen tube is secured into a gripping fixture and test apparatus, and an axial compressive force is applied to the interior face of the plug to push it out of the tube. (See .) The axial force required to fracture (or permanently deform) the joined test specimen is measured and used to calculate a nominal joint strength and a nominal burst pressure. Tests are performed at ambient or elevated temperatures, or both, based on the temperature capabilities of the test furnace and the test apparatus.
1.3 This test method is applicable to end-plug test specimens with a wide range of configurations and sizes. The test method does not define a standardized test specimen geometry, because the purpose of the test is to determine the nominal joint strength and nominal burst pressure of an application-specific plug-tube design. The test specimen should be similar in size and configuration with the intended application and product design.
1.4 Calculations in this test method include a nominal joint strength which is specific to the adhesives, adherends, configuration, size, and geometry of the test specimen. The nominal joint strength has value as a comparative test for different adhesives and plug configurations in the intended application geometry. When using nominal joint strength for comparison purposes, only values obtained using identical geometries should be compared due to potential differences in induced stress states (shear versus tensile versus mixed mode). The joint strength calculated in this test may differ widely from the true shear or tensile strength (or both) of the adhesive due to mixed-mode stress states and stress concentration effects. (True adhesive shear and tensile strengths are material properties independent of the joint geometry.)
1.5 In this test, a longitudinal failure stress is being calculated and reported. This longitudinal failure stress acts as an engineering corollary to the burst pressure value measured from a hydrostatic pressure test, which is a more difficult and complex test procedure. Thus this longitudinal failure stress is recorded as a nominal burst pressure. As a general rule, the absolute magnitude of the nominal burst pressure measured in this EPPO test is different than the absolute magnitude of a burst pressure from a hydrostatic burst pressure test, because the EPPO test does not induce the hoop stresses commonly observed in a hydrostatic pressure test.
1.6 The use of this test method at elevated temperatures is limited by the temperature capabilities of the loading fixtures, the gripping method (adhesive, mechanical clamping, etc.), and the furnace temperature limitations.
1.7 Values expressed in this test method are in accordance with the International System of Units (SI) and .
1.8 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 and health practices and determine the applicability of regulatory limitations prior to use.
1.9 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.