Theoretical and experimental bifurcation analysis of rock under plane strain compression

A new plane strain apparatus for rock testing was designed and built, and a series of plane strain tests on sandstone was performed. The formation and orientation of localization in sandstone were studied theoretically within the framework of equilibrium bifurcation theory. Corresponding elastoplastic constitutive models with nonlinear yield and potential functions were developed and fitted on the plane strain test data. The inclination of the shear band and the bifurcation point were predicted using the acoustic tensor method. The comparison of the computational and experimental results indicates that the initiation of a shear band predicted by a two-dimensional model could occur within the strain hardening region (i.e. prior to the peak stress), and the predicted orientations of the shear bands agreed qualitatively with those measured.