Formulation of plastic strain distribution derived from long-distance travel of temperature distribution based on residual stress required for elastic shakedown behavior

摘要

In an experimental study that simulated a fast breeder reactor (FBR) vessel near the coolant surface, it was reported that the long distance travel of temperature distribution causes a new type of thermal ratcheting, even in the absence of primary stress. When the distance of temperature travel is moderate, the accumulation of the plastic strain due to this mechanism is finally saturated. Through the large number of Finite Element Analysis, we have found the strong relationship between hoop-membrane distributions of accumulated plastic strain and residual stress in this saturated case. Focusing on this relationship, we have aimed to predict the saturated distribution of the plastic strain based on the residual stress distribution that is required for the elastic shakedown behavior. In this paper, based on classical shell theory, we formulated the plastic strain distribution that brings uniform hoop-membrane stress in the given region. And then, we compared the formulated strain distribution with the accumulated plastic strain distribution obtained by finite element analyses using an elastic-perfectly plastic material. As a result, we confirmed that the formulated strain distribution can be used as the prediction of the plastic strain distribution for the cases with moderate distance of temperature travel. For the cases with long-distance travel of temperature, the region with plastic strain expanded with the repetition of temperature travel. By considering the effect of this expansion, the formulated strain distribution can be used as conservative prediction of the accumulated plastic strain also for the cases with long distance temperature travel.