Assessment of Contact Laws Accounting for Softening in 3D Rigid Concrete Particle Models

To obtain predictions closer to concrete behaviour, it is necessary to employ a particle model (PM) that considers contact softening. A bilinear softening contact model (BL) has been adopted in PM studies. Several limitations in PM predictions have been identified that may be due to BL assumptions. For this reason, this paper compares BL predictions with those obtained with more complex models to assess if PM predictions can be improved. As shown, it is possible to calibrate each contact model to reproduce the complex behaviour observed in concrete in uniaxial and biaxial loading. The predicted responses are similar, and the known PM limitations still occur independently of the adopted model. Under biaxial loading, it is shown that a response closer to that observed in concrete can be obtained (higher normal-to-stiffness ratio of ≈0.50, maximum contact compressive strength of ≈60 MPa, and 30% reduction in the number of working contacts). The BL contact model for PM concrete DEM-based simulations is shown to have (i) lower associated computational costs (15% to 50% lower); (ii) a reduced number of contact strength parameters; and (iii) similar responses to those predicted with more complex models. This paper highlights that the BL contact model can be used with confidence in PM fracture studies.