An explicit methodology of random fibre modelling for FRC fracture using non-conforming meshes and cohesive interface elements

The failure mechanisms of fibre reinforced concrete (FRC) are complicated and governed by random phases at meso-scale, typically including fibres, mortar and fibre-mortar interfaces. This work develops an efficient nu-merical method using non-conforming meshes between the fibres and mortar. Their interfacial bond-slip behaviour is explicitly modelled by inserting zero-thickness cohesive interface elements between fibres and their replicas, i.e. the proposed "shadow fibres". The shadow fibres are then constrained by the background mortar through a coupling technique proposed in the literature to ensure the displacement compatibility and force transmission. The damage and fracture of the mortar are captured by the concrete damage plasticity model, and the fibres are modelled by finite beam elements with elastoplastic constitutive relations. The proposed approach is validated by single fibre pullout tests, single fibre-bridged notched tension test-pieces, and direct tensile tests of ultra-high performance fibre reinforced concrete samples with random fibres. After comprehen-sive analyses of the key material and geometric parameters, the presented framework proves capable of capturing the major failure mechanisms at meso-scale, such as fibre pullout, bending and yielding, mortar cracking and spalling and fibre-mortar interfacial debonding, which can be used to enhance the understanding of FRC damage and fracture behaviour.