Conference Agenda

This contribution revisits the homogenization techniques applied to discrete models incorporating rotational degrees of freedom. The theoretical framework extends previous work on the homogenization of Cosserat continua, demonstrating how these models can be homogenized to a Cauchy continuum under realistic assumptions. The formulation is developed within the context of linear elasticity and validated through simulations of a bent cantilever.

The impact of aggregate fragmentation, free water, and strain rate content on the dynamic behavior of concrete under the uniaxial compression state at the mesoscale was examined in this study. Extensive two-dimensional (2D) dynamic investigations were conducted to examine the impact of aggregate fragmentation and strain rate on concrete's dynamic strength and fracture patterns. The behavior of fully and partially fluid-saturated concrete was simulated using a mesoscopic pore-scale hydro-mechanical model based on a unique fully coupled DEM/CFD approach wherein a DEM-based breakage model was used. Concrete was simulated as a four-phase material consisting of aggregate, mortar, ITZs, and macropores. The concrete mesostructure was obtained from laboratory micro-CT tests. Collections of small spherical particles were used to imitate aggregate breakage of different sizes and shapes by enabling intra-granular fracturing between them. The dynamic compressive strength increased with the strain rate, fluid saturation, and aggregate fragmentation.

This paper presents a computational approach for simulating the fracture behavior of reinforced concrete. Cracks are discretely modeled using zero-thickness cohesive interface elements, while the reinforcement is explicitly represented by elastoplastic Timoshenko beam elements. The interaction between reinforcement and concrete is captured through specially developed coupling elements. To demonstrate the performance of the proposed computational approach, two series of experiments on reinforced concrete beams without shear reinforcement subjected to four-point bending were numerically analyzed in a 3D setting. In the first series of tests, the SL series performed by Syroka-Korol and Tejchman, the beam size was scaled in two dimensions while the span-to-depth and reinforcement ratios were kept constant. The distinct feature of these tests is that the failure mode was consistent across all sizes, enabling size-effect analysis. In the second series, the S1 series by Suchorzewski et al., only the beam depth was scaled, while the span, load location, and reinforcement ratios remained unchanged. This series exhibited markedly different failure modes for each size, allowing the assessment of the capabilities of the proposed modeling approach to capture the effects of the shape and size on the mechanical response of reinforced concrete beams. The proposed computational approach effectively captures size-dependent peak loads, failure modes, and fracture patterns in all investigated tests.

Mesoscale discrete lattice models offer a direct way to incorporate the heterogeneous microstructure of concrete and other geomaterials efficiently, using vector-based constitutive laws with homogeneous material parameters. These models exhibit stress oscillations, which, if deemed nonphysical, can be suppressed using methods such as auxiliary stress projection or deviatoric-volumetric decomposition to produce homogeneous elastic stress fields. This study examines the elastic behavior of the homogenized models with controlled heterogeneity introduced via spatial randomization of material parameters, with an emphasis on the replication of the oscillations in the non-homogenized discrete model. Simulations with varying degrees of spatial correlation under different macroscopic loading conditions reveal that the original stress oscillations are best replicated with spatially independent randomization. However, none of the techniques fully reproduce the original oscillations.

In this study, a Multiphysics-Lattice Discrete Particle Model (M-LDPM) framework that deals with coupled-fracture-poroflow problems has been introduced. The M-LDPM framework uses two lattice systems, the LDPM tessellation and the Flow Lattice Element (FLE) network, to represent the heterogeneous internal structure of typical quasi-brittle materials like concrete and rocks, and to simulate the material’s mechanical behavior and mass transport at the coarse aggregate scale. In this study, the LDPM governing equations are revisited and modified to include the influence of fluid pore pressure. The governing equations of the Flow Lattice Model (FLM) for pore pressure flow are derived using mass conservation balances for both uncracked and cracked specimens. The proposed M-LDPM framework was implemented using Abaqus user element subroutine VUEL for mechanical behavior within the explicit dynamic procedure and user subroutine UEL for mass transport within the implicit transient procedure. The coupling of the two models was achieved using Interprocess Communication (IPC) between Abaqus solvers. The M-LDPM framework can simulate the variation of permeability induced by fracturing processes by relating the transport properties of flow elements with local cracking behaviors. The proposed model is validated by comparing the numerical results with analytical solutions of classical benchmarks found in poromechanics literature.