Low cycle fatigue and cyclic plasticity bahaviour of Indian PHWR / AHWR primary piping materials

The integrity assessment of the primary piping components needs to be demonstrated under normal operation cyclic loadings as well as under complex cycling loadings of extreme magnitude as may come during a severe earthquake event. In order to understand material's cyclic plasticity and fatigue ratcheting behaviour, systematic experimental and analytical investigations have been carried out on specimens of SA333Gr.6 carbon steel and SS304LN stainless steel. The materials specification of SA333Gr.6 is same as used in Primary Heat transport (PHT) piping of Pressurized Heavy Water Reactors (PHWRs) and materials specification of SS304LN steel is same as proposed for Indian Advanced Heavy Water Recactor (AHWRs) Main Heat Transport (MHT) piping. The test program included the properties and cyclic plasticity behaviour. The results of these tests have been investigated in detals using few popular finite element cyclic plasticity models to understand and quantify the materials' cyclic plasticity behaviour. The studies revealed the need to modify the Chaboche model to simulate the LCF/cyclic plasticity and ratcheting under different stress/strain amplitude loading conditions. On accounting for modification, the Chaboche model nicely predicted the LCF and ratcheting response for all the tests. The tests, finite element analyses results and their interpretations have been presented in this paper.