Modeling and simulation of quasi-brittle failure with continuous anisotropic stress-based gradient-enhanced damage models

Two anisotropic stress-based gradient-enhanced damage models are proposed to address the issue of spurious damage growth typical of continuous standard gradient-enhanced damage models. Both models are based on a decreasing interaction length upon decreasing stresses and do not require additional model parameters or extra degrees of freedom when compared to standard gradient-enhanced models. It is observed that with the proposed models damage spreading is significantly reduced due to the occurrence of non-physical oscillations in the nonlocal strain field near the strain localization band. Model improvements to eliminate these strain oscillations upon vanishing length scale values are proposed. The capability of the models and their patched versions to correctly simulate damage initiation and propagation is investigated by means of mode-I failure, shear band and four-point bending tests.