The Brittle Ring Test: A method for measuring strength and young's modulus on coatings of HTR fuel particles

Abstract The Brittle Ring Test for the measurement of strength and Young's modulus on silicon carbide (SiC) and pyrocarbon (PyC) rings prepared out of the coatings of HTR fuel particles is described. The results for the strength are interpreted assuming Weibull statistics. The corresponding formalism for the transformation of the strength measured on rings into the equivalent strength of the coating shells on the fuel particle is derived. Typical values for the strengths of coating shells made from SiC and PyC are 500 and 200 MN/m 2 , respectively. The measured values for Young's modulus range between 200000 and 600000 MN/m 2 for SiC and between 10000 and 50000 MN/m 2 for PyC. The strength of SiC increases with decreasing deposition temperature, the strength of PyC is well correlated to its density. Various influences on the strength values are discussed, e.g. simplifications of the mathematical model describing the Brittle Ring Test, errors due to the practical limits on the number of specimens, influences of the specimen preparation and a sandwich effect on the SiC strength in PyC-SiC-PyC coatings.