Influence of specimen type and loading configuration on the fracture strength of SiC layer in coated particle fuel

Internal pressurization and diametrical loading techniques were developed to measure the fracture strength of chemically vapor-deposited (CVD) silicon carbide (SiC) coating in nuclear fuel particles. Miniature tubular and hemispherical shell specimens were used for both test methods. In the internal pressurization test, an expansion load was applied to the inner surface of a specimen by use of a compressively loaded elastomeric insert (polyurethane). In the crush test, a diametrical compressive load was applied to the outer surface(s) of a specimen. The test results revealed that the fracture strengths from four test methods obeyed Weibull's two-parameter distribution, and the measured values of the Weibull modulus were consistent for different test methods. The fracture strengths measured by crush test techniques were larger than those by internal pressurization tests. This is because the internal pressurization produces uniform stress distribution while the diametrical loading technique produces severely localized stress distribution, causing the tremendous reduction of effective surface. The test method dependence of fracture strength was explained by the size effect predicted by effective surface.