True stress measurement of nuclear fuel rod cladding material subjected to DSA regime

Austenitic stainless steel (ASS) grade 304 is being extensively used in various high-temperature applications, which makes it important to study their properties at elevated temperatures, especially the flow stress behavior. The literature reveals flow stress of the material depends on influence of various input parameters, the important ones being the strain, strain rate and temperature. It is often noticed that these process parameters are determined by trial-and-error approach, which results in increased material failure and power losses. Constitutive models have also been developed to find the relationships between them, but these models have computational limitations and cannot capture the true stress behavior at elevated temperatures. Therefore, there is a need for formulation of a generalized explicit model/expression that can predict accurately the behavior ASS 304 at elevated temperatures. Therefore, this work proposed a new variant of genetic programming, gene expression programming (GEP), to formulate a model for true stress of ASS 304. True stress model formulated based on M-MGGP methodology has outperformed the GEP approach. Further investigation is carried out by sensitivity and parametric analyses to determine the relationships between process parameters, and it was found that the temperature has highest impact on the true stress of ASS 304 steel.