OS1418 Study on Fundamental Mechanism of Stress Redistribution and Thermal Ratchet Phenomena of Cylindrical Vessels

Under elevated temperature condition, thermal ratchet phenomena, namely the cyclic accumulation of plastic deformation, is one of the typical failure modes. Ratchet phenomena occurs when the structures are subjected to uniform primary stress with cyclic secondary stresses. ASME boiler & pressure vessel code provides an evaluation method for thermal ratchet. However, this method is so focused on protecting thermal ratchet, that it could be too conservative under some conditions. Therefore, the rational evaluation method for thermal ratchet phenomena is needed based on its mechanism. In this paper, rational simplified evaluation method for cylindrical vessels is proposed using simplified model called "two bar model", which express stress redistribution mechanism of cylindrical vessels. This evaluation method enables simple prediction of both thermal ratchet occurrence and thermal ratchet deformation.