Assessment of a Thermal Fatigue Test Conducted Under Cyclic Non-proportional Loading Using Open Source CAE and Finite Element Analysis Methods

Thermal fatigue assessment is often required for high temperature components such as those in thermal power and chemical plants. The procedures used to evaluate fatigue life consumption of a component subjected to cyclic non-steady thermal loading are rather complicated and, in many cases, difficult to carry out. In addition, experimental validation of a thermal fatigue assessment by using FEM is rarely carried out due to the high cost and length of time required to perform tests that subjected a specimen to cyclic thermal loading. The authors herein propose simplified fatigue assessment methods and undertake their experimental validation by comparing the FEA assessment with the result of a previously reported thermal fatigue test performed by JAEA (Japan Atomic Energy Agency) on a tapered cylindrical specimen. In the test considered, the loading was almost proportional, and thus the validity of these methods for general non-proportional loading remained to be solved. This paper describes the fatigue assessment of components subjected to cyclic thermal loading, in which simulation was undertaken of a previously conducted thermal fatigue test that used an axisymmetric specimen with three different types of structural discontinuities. The test was also performed by JAEA in their sodium flow test facility. The specimen was subjected to cyclic thermal loading by alternating liquid metal flows injection at different temperatures. In this study finite element analyses, non-steady-state thermal transient and stress analyses were performed using commercial FEA software (MSC.Marc) and open source FEA software (Salome-Meca, Code-Aster) to evaluate change in thermal stress, and the two FEAs were compared. The FEA results indicate non-proportional stress histories. The simplified assessment methods previously proposed for determining the pair of time steps that define the maximum stress range were applied and subsequently compared. The simplified assessments made using the methods in this study are consistent with those made based on ASME Section III Division 5.