Compression testing of tri-isotropic (TRISO) carbon/silicon carbide-coated fuel
particles between anvil materials with a wide range of hardnesses was investigated.
During compression testing, the particle produces a hardness impression before it fractures. For subsequent measurements, the same position can therefore not be used. A special testing machine was designed to use the same set of anvils for testing more than one specimen. By each time positioning a particle at a slightly different
position between the anvils, a large number of measurements could be made. The load required for fracture is almost independent of anvil hardness for very hard or very soft anvils. Finite element stress analysis showed that when the anvil hardness is very high, fracture occurs because of high local contact bending stresses at the
point of contact. In the case of very soft anvils, a tensile stress develops along a latitudinal direction along the perimeter of the particle over a large volume in between the contact zones with the anvils. The particle then fractures by the development of cracks at right
angles to the direction of the tensile stress. From the fracture load, the ability of the
particle to withstand internal pressure can be assessed. The advantages of using
compression testing of full particles between soft anvils without prior preparation to
complement previous test methods are highlighted.