Experimental and Numerical Investigation of a Ring Tensile Test for Evaluation of Mechanical and Fracture Properties of Thin-Walled Fuel-Clad Tubes

Abstract Thin-walled fuel clad tubes of Zircaloy-4 material are used in nuclear reactors to hold fuel pellets. The design and safety analysis of these tubes requires estimation of the transverse mechanical and fracture properties at un-irradiated as well as service-exposed conditions. These thin-walled tubes are subjected to radial loading conditions due to expansion of fuel pellets during reactor operation. This loading condition exhibits the presence of combined tensile as well as bending stresses due to the curvature of the specimen and, as such, the tensile properties cannot be directly evaluated from the experiments on ring tensile specimens. In this work, ring tension tests were carried out on specimens machined from fuel-clad tubes. Both the specimen and the loading mandrel were modeled using the finite element (FE) method to evaluate the load–displacement behavior of the test. Rousselier's micro-mechanical model for ductile fracture was applied in order to simulate the crack growth in these specimens. The method was also validated by testing a ring–tension specimen (machined from alloy steel material) of similar dimension as that of the Zircaloy fuel pin specimen and then comparing the stress–strain curve with that of a standard round tensile specimen. The micro-mechanical parameters of the damage model were used to simulate the crack propagation in a standard double-edged notched tensile (DENT) specimen. The J–R curve of the DENT specimen has also been compared with that of a cracked pin–loading–tension (PLT) specimen. It was observed that the parameters of the Rousselier's model are able to predict the fracture resistance behavior of cracked fuel pins specimens satisfactorily, which have been obtained through a combined experiment and FE analysis of the ring tensile specimens. Thus, this method can be used to determine the material properties of irradiated and service-aged fuel pins as obtained from the nuclear reactors after different periods of reactor operation.