船体構造用多結晶金属材料の繰返し塑性変形挙動の数値シミュレーションに関する研究(その2) : 面心立方3次元モデルの計算

抄録

In this report, we analyze cyclic plastic 3-dimensional deformation of f.c.c. polycrystalline by infinitesimal deformation FEM analysis, and evaluate the assumption on the characteristics of dislocation movement under cyclic loading condition, which was obtained by the 2-dimensional FEM analysis in the previous report by the authors. Furthermore, we investigate the effect of grain size on the local deformation of polycrystallines. Results of the analysis are summarized as follows. 1)As in the 2-dimensional analysis, it is possible to represent cyclic plastic behavior of real materials qualitatively if c.r.s.s. mainly raise by long-range stress field by dislocation structures, or the increment of c.r.s.s. vanishes during unloading and backward loading process. Most of dislocation movement model for cyclic plastic deformation under fatigue process meet the requirements mentioned above. 2)As in the 2-dimensional analysis, there exists plastic strain localization on free surface of the FEM model. The ratio of maximum localized plastic strain to mean plastic strain is more than 15 on the beginning of plastic deformation, but it reduces to an asymptotic value of 3 to 5 as plastic deformation develops. It shows that there exists stress level where finite local strain occurs but not observed as macroscopic plastic deformation, and it is assumed that such stress level corresponds to the fatigue limit. 3)In the cases calculated in this report, there is a tendency that a model of which grain size is larger shows higher maximum and mean plastic strain.