Features of stress-strain state of thin-walled circular single-edge-notch specimen under eccentric tension

Features of deformation behavior and fracture resistance of a material of fuel element claddings are used to design and ensure their safe operation. To determine these features, JSC “Institute of Nuclear Materials” applies static eccentric tension tests of thin-walled circular specimens with a stress concentrator in the form of a single-edge-notch, which are cut from shell pipes. The tests were made in certain time intervals of fuel element cladding operation. The experiments show various dependences of the specimen loading force on the value of the test machine grip displacement. These dependences are influenced by the accumulated damage of a fuel element cladding. Loading curve behavior is explained by the test simulation. The paper presents the test scheme. We formulated the elastoplastic problem of stress-strain state simulation of a single-edge-notch circular specimen under eccentric tension. The plane strain state is considered. The finite element simulation is made using the specialized computer program for the considered type of tests. The program is developed in the Institute of Engineering Science, Ural Branch of the Russian Academy of Sciences. The load is applied gradually in small increments of the test machine grip motion. At each load step, the simulation algorithm is based on the principle of virtual power. Constitutive equations developed by the authors for the elastoplastic medium with large plastic deformations are used. The simulation results of loading processes are shown for the specimens made from the austenitic steel ChS86hd. It appears that the curve describing the dependence of tensile force in the specimen on the test machine grip displacement consists of two straight line segments with a smooth transition. The first straight segment is notoriously more inclined to horizontal axis compared to the second one. The change of the accumulated plastic strain in the region of the specimen notch in different points of the loading curve was analyzed. The features of the specimen at different points of the loading curve were explained taking into account the formation and development of a macrocrack at the top of the specimen notch. Fields of stress state indicator distributions in the region of the specimen notch are shown.