Phase field and gradient enhanced damage models for quasi-brittle failure: a numerical comparative study

This paper presents a comparative study of the gradient-enhanced damage models (GED) of Peerlings et al. (1996), Vandoren and Simone (2018) and the phase field damage/fracture model (PFM) of Wu (2017), Wu and Nguyen (2018) within the context of the computational modeling of the fracture of quasi-brittle materials (concrete, ceramic, rock, ice, etc.). Being continuous damage/fracture models, these two models enjoy the simplicity of modeling the fracture process on a fixed finite element mesh. The similarities and differences of the two models are discussed by examining governing equations and conducting numerical simulations of some mode I and mixed-mode fracture benchmark tests. The most worthy findings are: (i) both classes of models can handle the initiation and propagation of cohesive cracks, (ii) they are totally different–PFM behaves like a cohesive zone model (a sub-class of fracture mechanics) when the length scale is sufficiently small and the response is insensitive to this length scale whereas GED is a non-local damage model (a sub-class of continuum damage mechanics) of which response obviously depends on the length scale.