A Study on plastic strain accumulation caused by traveling of temperature distribution synchronizing with temperature rise

Okajima, Satoshi 

Repeating of long range traveling of temperature distribution brings continuous accumulation of the plastic strain, even if there is no primary stress. In contrast, in the case with short range traveling, residual stress is caused by constraint against elastic part, and finally it results in shakedown. Because of this mechanism, limit for the shakedown behavior depends on distance from the elastic part (i.e. half length of region with plastic deformation). In the actual design of the fast reactor vessel nearby liquid sodium surface, the temperature distribution moves up synchronizing with the temperature rise, without any intentional control. In this paper, we examined characteristics of the accumulation of the plastic strain caused by realistic heat transients, namely, traveling of temperature distribution synchronizing with temperature rise. As a result, we confirmed that the shakedown limit depends on not the traveling range of the temperature distribution but the plastic deformation range, which was predicted by the elastic analysis. We can control the plastic deformation range by changing rate of the moving-up of liquid sodium surface.