Development of a miniaturized ring notched bend specimen for the assessment of the fracture toughness of ODS steel fuel claddings

A miniaturized Ring Notched Bend test (mRNB) was developed as a means to assess the fracture toughness of thin-walled tubes. The fracture resistance curve (J–R curve) was derived from both the load-CMOD curve and the load-LLD curve, utilizing a single specimen technique. Following the procedures proposed in the ASTM E1820 standard [1], the elastic unloading methods were employed for the load-CMOD curve. Alternatively, the normalization method was utilized to analyze the load-LLD curve when CMOD measurements was not possible. However, for the application of this methodology to the mRNB test, the standard lacks the necessary functions, including the compliance function, the geometric stress intensity function, and the plastic factor, to process the test results. In this study, the finite element analysis was used to determine the geometric functions required for crack length evaluation during the test, as well as the elastic and plastic components of the J-integral, whether derived from the load—CMOD or load—LLD curve. This methodology was applied to experimentally investigate the crack growth resistance and damage of two types of ODS (Oxide Dispersion Strengthened) steel tubes, (containing specifically 9%Cr and 14%Cr), which are considered candidate materials for fuel claddings of future fast-neutron reactors.