A DIRECT METHOD FOR RATCHETING ANALYSIS OF NUCLEAR PRESSURE COMPONENTS UNDER THERMO-MECHANICAL LOADING

Ratcheting failure is a typical failure mode of nuclear pressure components, such as pressure vessels and piping systems, subjected to cyclic thermo-mechanical loading. Determining the safe load domain that prevents ratcheting failure through ratcheting analysis is of great significance for structural design and integrity assessment. In this work, a direct method for ratcheting analysis of elastoplastic structures is proposed within the framework of the Stress Compensation Method (SCM). First, the conventional SCM is extended to facilitate the capability of steady cyclic analysis for elastoplastic structures. Second, a lower-bound theorem is derived for the determination of ratcheting boundary based on the elastoplastic steady cyclic analysis minimum theorem. The lower-bound theorem indicates that, when the applied cyclic load can be decomposed into a constant component and a cyclic component, the ratcheting boundary can be directly determined by performing a single steady cyclic analysis together with a single shakedown analysis. Based on the lower-bound theorem and the established capabilities of SCM for steady cyclic analysis and lower-bound shakedown analysis, the procedure for ratcheting analysis is developed. In addition, a line search algorithm is introduced to further improve the computational efficiency of the proposed method. Finally, the proposed method is validated through numerical examples. For the square plate with a circular hole, the accuracy and effectiveness of the method are verified by comparisons with results reported in the literature and reference solutions obtained by commercial finite element software, while the efficiency improvement achieved by the line search algorithm is demonstrated through iteration convergence curves. For the pipe joint subjected to thermal-mechanical loads, the mesh sensitivity of the algorithm is analyzed, and the applicability of the proposed approach to practical engineering problems is verified. The proposed method extends the methodological framework of SCM, and provides an effective approach for ratcheting analysis and structural integrity assessment of nuclear pressure components under thermo-mechanical loading.