Mesoscale modelling of concrete – A review of geometry generation, placing algorithms, constitutive relations and applications

We investigate the dynamic behavior of concrete in relation to its composition within a computational framework (FEM). Concrete is modeled using a meso-mechanical approach in which aggregates and mortar are represented explicitly. Both continuum phases are considered to behave elastically, while nucleation, coalescence and propagation of cracks are modeled using the cohesive-element approach. In order to understand the loading-rate sensitivity of concrete, we simulate direct tensile-tests for strain rates ranging 1–1000 s−1. We investigate the influence of aggregate properties (internal ordering, size distribution and toughness) on peak strength and dissipated fracture energy. We show that a rate independent constitutive law captures the general increase of peak strength with strain rate. However, a phenomenological rate-dependent cohesive law is needed to obtain a better agreement with experiments. Furthermore, at low rates, peak strength is sensitive to the inclusions' toughness, while the matrix dominates the mechanical behavior at high rates.

Influence of Meso-structure on the Dynamic Fracture Simulation of Concrete Under Tensile Loading

Meso-scale modelling of compressive fracture in concrete with irregularly shaped aggregates

Meso-scale simulations of size effect on concrete dynamic splitting tensile strength: Influence of aggregate content and maximum aggregate size

3D mesoscale fracture analysis of concrete under complex loading

The mechanical performance of concrete is strongly influenced by the geometry and properties of its components (namely aggregate, mortar, and Interfacial Transitional Zone (ITZ)) from the mesoscale viewpoint, and analyzing the material at that level should be a powerful tool for understanding macroscopic behavior. In this paper, a simple and highly efficient method is proposed for constructing realistic mesostructures of concrete. A shrinking process based on 3D Voronoi tessellation was employed to generate aggregates with random polyhedron and grading size, and reversely, an extending procedure was applied for ITZ generation. 3D mesoscale numerical simulation was conducted under a quasi-static load using an implicit solver which demonstrated the good robustness and feasibility of the presented model. The simulated results resembled favorably the corresponding experiments both in stress–strain curves and failure modes. Damage evolution analysis showed that the ITZ phase has profound influence on the damage behavior of concrete as damage initially develops from here and propagates to mortar. In addition, it was found that tensile damage is the principal factor of mortar failure while compressive damage is the principal factor of ITZ failure under compression.

Validation and Investigation on the Mechanical Behavior of Concrete Using a Novel 3D Mesoscale Method.

Titanium Ti6Al4V alloy is a superior material that has extremely high strength, hardness and good anti-corrosion resistance. Dynamic shear-compression experiments were carried out on the alloy to investigate the micro-mechanisms of adiabatic shear banding (ASB) formation. The split Hopkinson pressure bar (SHPB) setup were used for the tests at high strain rates. It was found that the shear deformation localization (SDL) was considerably affected by the complex loading conditions. The micro-mechanisms for the ASB formation relied on different shear compressive proportion of loadings (SCLPs). Scanning electron microscope (SEM) observations showed that the ASB width was related with the SCLP and the fracture failure of alloy was induced by the nucleation and growth of microvoids. In transmission electron microscope (TEM) analysis, the microstructural changes of material within the ASB were characterized by dynamic recrystallization (DRX) and twining grain formation, dislocation migration, and stacking and grain refining processes. The results in this article demonstrates a complex image of microstructural evolution of alloy in the shear localization process.

Micro-Mechanisms of Shear Deformation Localization of Ti6Al4V Alloy under Shear-Compressive Loading Conditions.

In this work, we develop a high-temperature dynamic testing technology for characterizing the properties of Ti-1023 alloy The modified Hopkinson torsion bar system includes a high-temperature furnace subsystem and a water cooling subsystem High-temperature dynamic tests of the alloy are performed The dependence of the yield stress on the temperature and the shear strain rate is studied The scanning electron microscopy observations show that the microstructural evolution makes up of two steps: the first one is caused by thermal loading and the second one by the mechanical loading The high-temperature dynamic constitutive model is established based on the experimental results

/pdf/the-mechanical-behaviours-of-the-ti-10v-2fe-3al-alloy-under-395tvfz1gx.pdf

The mechanical behaviours of the Ti-10V-2Fe-3Al alloy under the high-temperature and dynamic loading conditions

Temperatures of −25 °C, +5 °C, and +35 °C were selected to study the creep behavior of high-density polyethylene (HDPE). The ultimate tensile strength of HDPE materials was obtained through uniaxial tensile experiments and the time–strain curves were obtained through creep experiments. When the loaded stress levels were lower than 60% of the ultimate strength, the specimens could maintain a longer time in the stable creep stage and were not prone to necking. In contrast, the specimens necked in a short time. Then, the time hardening form model was applied to simulate the time–strain curve and the parameter values were solved. The parameter values changed exponentially with the stresses, thereby expanding and transforming the time hardening model. The expanded model can easily and accurately predict creep behaviors of the initial and stable creep stages as well as the long-term deformations of HDPE materials. This study would provide a theoretical basis and reference value for engineering applications of HDPE.

Zhiqiang Li

Papers

3D mesoscale fracture analysis of concrete under complex loading

Validation and Investigation on the Mechanical Behavior of Concrete Using a Novel 3D Mesoscale Method.

Micro-Mechanisms of Shear Deformation Localization of Ti6Al4V Alloy under Shear-Compressive Loading Conditions.

The mechanical behaviours of the Ti-10V-2Fe-3Al alloy under the high-temperature and dynamic loading conditions

Investigation of Tensile Creep Behavior for High-Density Polyethylene (HDPE) via Experiments and Mathematical Model.