The Comparison of the Criteria for Ratcheting in ASME VIII-2 and Methods Given by C-TDF

Abstract

Ratcheting assessment by elastic-plastic stress analysis is presented in ASME VIII-2, paragraph 5.5.7. There are three criteria. The first one is strict in engineering design. It’s hard for most of structures to satisfy it. If the plastic strain in the structure is zero, it means that the material is not fully utilized and maybe the structure is unreasonable. Therefore, the second and third criteria are used much more. The first one and the third one can be observed directly and judged accurately by the finite element analysis results. The second one demands an elastic core in the primary-load-bearing boundary. It could be easily observed when the structure is axisymmetric, but hard to judge in the 3D structure. Okamoto in Committee on Three Dimensional Finite Element Stress Evaluation (C-TDF) has studied two thermal stress ratchet criteria: evaluating variations in the plastic strain increments and evaluating variations in the elastic core region, which can accurately assess ratcheting. Recent years, based on the criteria above, more researches have been performed by engineers not only from C-TDF but from all over the world. In this work, several two-dimensional structures and three-dimensional structures under particular load and displacement boundaries are performed by using finite element software ANSYS, aiming to compare the similarities and differences between the criteria in ASME VIII-2, 5.5.7.2 and those given by C-TDF. The assessment of these structures presented in this work will help engineers understand the realization of the criteria and methods in engineering design, especially how to utilize the results from ANSYS.