10 R. W. L. Fong and J. Patrick Fig. 2.2 Photographs showing the online biaxial burst test facility at CNL Fig. 2.3 (a) Fuel sheath burst specimen, (b) flat (dog-bone) uniaxial tensile specimen 2.2.3 Test Procedure For biaxial burst test of a fuel sheath sample, a controlled axial loading on the tube allows different magnitudes of axial to hoop stressing ratios to be applied to deform the tube during pressurization. The different stress states (or end restraints) are useful to study the effects on ballooning deformation. For testing a flat tensile specimen, the axial loading applied will simply generate a uniaxial stress to elongate the specimen along the loading direction. The following preparation is typically used to setup a fuel sheath sample ready for biaxial burst test. 1. Open the cover of test chamber and install a test sample on the tensile machine. 2. Install the pressuring gas lines to the sample inlet and outlet fittings. 3. Spot weld thermocouples and a Zr tab on the sample. 4. Check for electrical continuity on the sample and electrical isolation from the remainder of the test apparatus. 5. Close the cover, and install a rupture disk on the bottom box. 6. Evacuate the test chamber and purge (backfill) with argon, and repeat this step several times. 7. Purge the inside of the sample with argon and close the bleed valve.
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