Multiscale method for the simulation of the resilience and the fracture behaviour of heterogeneous structures

The aim of this subproject is to simulatively predict the behaviour of thin-walled carbon concrete structures under different load combinations and to ensure their sufficient robustness. Focus is the investigation of cracks in concrete at the mesoscale, including their initiation, propagation, branching and coalescence, and how these affect the macroscale behaviour. These phenomena can result in complex crack patterns which discrete reproduction within the finite-element (FE) method is difficult. Therefore, the Phase-Field Method is applied, in which cracks are represented in a smeared manner. However, the accurate representation of the phase field and the high displacement gradients across the crack requires very fine FE-meshes, which leads to a considerable computational effort. For this reason, the Extended Phase-Field Method (XPFM) is developed within the scope of this subproject. By transforming the phase-field approach and enriching the displacement field, significantly coarser meshes can be used with the XPFM and thus the computational effort can be reduced.

In order to also capture the macroscopic behaviour, efficient numerical multiscale methods are required, with which the inhomogeneous and both materially and geometrically non-linear behaviour can be taken into account. Therefore, the Multiscale Projection Method suitable for the localisation effects that occur is extended to account for heterogeneities and cracks in shell-like structures with finite deformations.

The combination of the Multiscale Projection mMethod with the XPFM for three-dimensional elements enables a realistic and locking-free representation of the macroscopic structural behaviour with moderate numerical effort. Thus, the resilience of carbon concrete structures designed with the strategies developed in CRC/Transregio 280 can be reliably evaluated against different combined external loads.

Within the framework of C05, the seed fund project "Simulation of the fatigue behaviour of carbon reinforced concrete components under changing cyclic loads" (1^st round 2022) was carried out. Furthermore, in the seed fund project "Numerical modelling and experimental validation of fibre pull-out behaviour in carbon reinforced concrete" (2nd round 2022), methods were developed to investigate fibre pull-out numerically.