Unified instability criterion for quasibrittle material in uniaxial tension, direct shear and uniaxial compression subjected to shear failure

摘要

Structural stability is closely related to the failure of geomaterials, such as rocks, soils and concretes. The unstable failure leads to seriously hazards, such as earthquake, rockburst, landslide and collapses of tunnel, dam and borehole. Strain localization is assumed to be initiated just as peak stress. Beyond the occurrence of strain localization, the load-carrying capacity of localized band is decreased due to the considerable accumulation of plastic strain or damage in localized band, leading to the decrease of load-carrying capacity of the specimen. In strain-softening stage, if the decrease of elastic strain is faster than the increase of average plastic strain of entire specimen, then the instability (or snap-back) will take place. Three unstable criterions for rock or concrete specimen in uniaxial tension, direct shear and uniaxial compression subjected to shear failure are derived, respectively. The derived three unstable conditions can be written as a unified inequality. It is found from the unified unstable criterion that the unstable failure of the specimen easily takes place for thinner localized band (or smaller characteristic length of material based on gradient-dependent plasticity), larger specimen, higher softening modulus and lower elastic modulus.