Failure prediction of smeared crack formulations

The smeared-crack approach of strain-softening is a popular engineering concept for the numerical simulation of tensile failure processes in concrete and rock. Despite numerous publications on the equivalent constitutive formulation of cracked solids, very little is known about the predictive value of the smeared-crack approach, particularly when nonproportional load histories are considered. To this end, two failure indicators are examined at the constitutive level in order to assess the predicted failure mode of fixed and rotating crack concepts. The directional stiffness parameter is used to examine singularities of smeared-crack formulations, which signal continuous failure due to material branching. In contrast, the localization indicator is used to examine the formation of weak discontinuities, which precede incipient failure process when the continuum degrades into a discontinuum. In this paper both failure indicators will be used to assess the failure modes of the fixed and rotating crack formulations for two loading scenarios involving pure shear and combined tension with shear.