69 巻 (2013) 2 号 p. I_267-I_278
Bifurcation phenomenon is highlight as a source to diversify strain localization and shear band formation in sand specimens. Compression tests on various shapes of right-angled parallelepiped specimens under two types of conditions of plane strain and axisymmetric lateral confining stress were simulated by two- or three-dimensional nonlinear finite element analysis. The Cam-Clay plasticity model incorporating the subloading surface concept was employed to model the deformation property of sands. The inception and progress of localization breaking uniformity were analyzed as a bifurcation problem. Complex localization process accompanied by the formation and disappearance of shear bands simulated by the bifurcation analysis were compared with an experimental observation of dense dry sand specimens in a true-triaxial apparatus. Some unexpected three-dimensional localization modes were found in the analysis of plane strain test as a diffuse mode of bifurcation breaking out-of-plane uniformity, while the bifurcation point was not detected in the axisymmetric case. Effects of the testing condition and the aspect ratio of specimen on the bifurcation and failure mode were also examined.