Influence of aggregate deformation and contact behaviour on discrete particle modelling of fracture of concrete

The discrete element method, DEM, has been used in fracture studies of non-homogeneous continuous media adopting circular or spherical particles. A 2D circular rigid DEM formulation developed with the purpose of modelling concrete is described and evaluated in uniaxial tensile and compression tests. According to this model, the aggregate can be modelled either as a rigid macro-particle or as a deformable group of particles. The inter-particle contacts can either be assumed as brittle or follow a given bilinear softening curve. It is shown that aggregate deformability, together with the consideration of pure friction contacts working under compression, increases the fracture energy in compression, leading to a better agreement with concrete tests. The softening contact model, by adding a higher capability of load redistribution, is shown to give a better agreement than the brittle model under tensile loading. The recognized crack mechanisms of the brittle model (tensile splitting, branching, bridging) are also present with softening.