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Study on a unified criterion for preventing plastic strain accumulation due to long distance travel of temperature distribution

温度分布の長区間移動による塑性ひずみ累積の防止のための統一的基準に関する研究

岡島 智史; 若井 隆純; 川崎 信史

Okajima, Satoshi; Wakai, Takashi; Kawasaki, Nobuchika

The prevention of excessive deformation by thermal ratcheting is important in the design of high-temperature components of fast breeder reactors (FBR). As a result of experimental study that simulated the fast breeder reactor vessel nearby the coolant surface, it was reported that long distance traveling of temperature distribution causes new type of thermal ratcheting, even if there is no primary stress. In this paper, we propose a simple screening criterion to prevent continuous accumulation of plastic strain derived from long distance traveling of temperature distribution. The major cause of this ratcheting mechanism is lack of residual stress that brings shakedown behavior at the center of yielding area. Because the residual stresses are derived from constraint against the elastic part, we focused on the distance from the center of yielding area to the elastic region. So, the proposed criterion restricts the axial length of the area with full-section yield state, which is the double of the above distance. We validated the proposed criterion based on finite element analyses using elastic-perfectly plastic material. As the result of the validation analyses, we confirmed that the accumulation of the plastic strain saturates before 2nd cycles in the cases that satisfy the proposed criterion, regardless of the shape of temperature distribution.

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