Friction Corrections to Improve Accuracy of Cladding Strength Measurements from the Ring Tension Test

Evaluation and qualification of accident tolerant fuel (ATF) cladding concepts requires highly robust mechanical testing, particularly for assessing material property variation due to irradiation. The ring tension test (RTT) is a possible test used to provide hoop direction material properties for anisotropic cladding and other tubular materials. Several configurations of the RTT have been implemented, each with different advantages and challenges. The single gauge RTT configuration with a hemicylindrical mandrel is ideal because of excellent stress state uniformity in the gauge region compared to other configurations. However, the primary challenge for this configuration is sensitivity of measured forces to the friction between the ring and mandrel, which lead to inaccurate strength results. This has previously been mitigated through lubrication and assumed to be insignificant, but when testing irradiated cladding in hot cell conditions, these frictional effects should not be ignored. In this work, finite element modelling of the test configuration is used to investigate the relationship between applied mandrel force and the hoop tensile force carried at different locations in the ring. Several potential friction correction methods resulting from this investigation are presented, showing improved accuracy. An extended analysis of the sensitivity of corrections and associated parameters is given during simulated tests with a variety of test conditions and potential material properties. Ultimately, correcting for friction with these methods produces robust strength measurements with significant accuracy improvement, providing a method to obtain hoop direction properties from both fresh and irradiated cladding with high fidelity.