Numerical modeling of the tension stiffening in reinforced concrete members via discontinuum models

[prova tipográfica]This study presents a numerical investigation on the fracture mechanism of tension stiffening phenomenon in reinforced concrete members. A novel approach using the discrete element method (DEM) is proposed, where three-dimensional randomly generated distinct polyhedral blocks are used, representing concrete and one-dimensional truss elements are utilized, representing steel reinforcements. Thus, an explicit representation of reinforced concrete members is achieved, and the mechanical behavior of the system is solved by integrating the equations of motion for each block using the central difference algorithm. The inter-block interactions are taken into consideration at each contact point with springs and cohesive frictional elements. Once the applied modeling strategy is validated, based on previously published experimental findings, a sensitivity analysis is performed for bond stiffness, cohesion strength, and the number of truss elements. Hence, valuable inferences are made regarding discontinuum analysis of reinforced concrete members, including concrete-steel interaction and their macro behavior. The results demonstrate that the proposed phenomenological modeling strategy successfully captures the concrete-steel interaction and provides an accurate estimation of the macro behavior

3D Voronoi Tessellation for the Study of Mechanical Behavior of Rocks at Different Scales

Numerical investigation of crack damage development and microfracturing in brittle rocks is a widely studied topic, given the number of applications involved. In the framework of the Discrete Element Method (DEM) formulation, the grain-based distinct element model with random polygonal blocks can represent an alternative to the Bonded-Particle Model (BPM) based on particles. Recently, a new engine called Neper has been made available for generating 3D Voronoi grains. The aim of this study is to investigate the applicability of a Neper-based 3D Voronoi tessellation technique for the simulation of the mechanical macro response of rocks. Simulation of unconfined compression tests on synthetic specimens is conducted and a calibration procedure tested. The issue related to scale effects is also addressed, with an application to the case study of a deep geothermal reservoir

A full-field crystal-plasticity analysis of bimodal polycrystals

International audienceA full field crystal plasticity modelling of bimodal polycrystals is presented. Bimodal polycrystals are generated using a controlled Laguerre–Voronoi algorithm, and a modified phenomenological law is used to take into account the grain size effect through a Hall–Petch term. A focus is particularly made on the effects of grain size and of grain size ratio between ultrafine grains and coarse grains populations on local and global mechanical responses. The effect of the spatial distribution of the coarse grains (clustered or isolated) is also analysed in terms of strain localisation and stress concentration at the local scale

A full-field crystal-plasticity analysis of bimodal polycrystals

International audienceA full field crystal plasticity modelling of bimodal polycrystals is presented. Bimodal polycrystals are generated using a controlled Laguerre–Voronoi algorithm, and a modified phenomenological law is used to take into account the grain size effect through a Hall–Petch term. A focus is particularly made on the effects of grain size and of grain size ratio between ultrafine grains and coarse grains populations on local and global mechanical responses. The effect of the spatial distribution of the coarse grains (clustered or isolated) is also analysed in terms of strain localisation and stress concentration at the local scale

New Grain Interaction Models for Deformation Texture Simulations

Publication suite au congrès : 5th International Conference on Processing and Manufacturing of Advanced Materials Vancouver 2007International audienceTwo relatively simple schemes are described for the interactions of grain deformations during large plastic deformations with the aim of evaluating their influence on texture development. The stress transfer model basically assumes that there is some degree of stress transfer across the boundaries proportional to the boundary area. The reduced stress incompatibility model minimizes the stress incompatibilities between each grain and their surrounding grains These models assume 3D topological schemes using evolving truncated octahedra for the spatial distributions of the grains. They are applied to the cases of hot rolled and cross forged Al alloys. Both give quite similar predictions for texture development which are moderate improvements on the Taylor models, confirming that the incorporation of grain interaction effects can be useful for texture modeling without major modifications. Moreover, they can yield interesting results for local orientation effects and their influence on orientation stability; an example of cube grains hot rolled in different crystallographic surroundings is also treated

Dislocation-driven recrystallization in AZ31B magnesium alloy imaged by quasi-in situ EBSD in annealing experiments

International audienceWe led a series of annealing experiments with quasi-in situ electron backscattered diffraction (EBSD) measurements to characterize the effect of the deformation microstructure on static recrystallization. Six samples of commercial purity AZ31B magnesium alloy were deformed under different temperature and strain rate conditions to produce microstructures with variable dislocation densities and arrangements, and then heated at 300°C (0.64 T m) for up to 6 h in several steps. All samples recrystallized by the growth of substructure-free grains, with nuclei mainly inherited from the deformed state. Recrystallization proceeded rapidly (minutes to hours), but remained incomplete in all cases. Using textural and microstructural proxies, we show that, under the studied experimental conditions, the stored energy associated with the dislocations controls the recrystallization ki-netics. We observe a positive correlation between the initial average kernel average misorientation (KAM) and the recrystallization kinetics of each sample and, to a lesser extent, the recrystallized fraction at a given time. We also present direct evidence on how the stored energy in the vicinity of the recrystallization front controls grain boundary migration kinetics. Yet, the reduction in the stored energy alone cannot explain the stagnation of the recrystallization front and incomplete recrystallization

(0) Save to: more options Evaluation of microstructure-based transformation plasticity models from experiments on 100C6 steel

International audienceThe main characteristics of quasi-isothermal diffusive transformation from austenite to pearlite in a 100C6 steel have been determined from experimental tests. The parameters of constitutive laws and kinetics of phase transformation of different micromechanical models of phase transformation could then be identified. The models are classified according to the prevailing assumptions: mean- or full-field approach, regular or heterogeneous microstructural morphology, macro-homogeneous constitutive laws or crystal plasticity. A comparative analysis in terms of transformation-induced plasticity (TRIP) is performed in order to conclude on the relevance of the different models as regards experiments and to show how the principal assumptions of TRIP modelling can affect the prediction

(0) Save to: more options Evaluation of microstructure-based transformation plasticity models from experiments on 100C6 steel

International audienceThe main characteristics of quasi-isothermal diffusive transformation from austenite to pearlite in a 100C6 steel have been determined from experimental tests. The parameters of constitutive laws and kinetics of phase transformation of different micromechanical models of phase transformation could then be identified. The models are classified according to the prevailing assumptions: mean- or full-field approach, regular or heterogeneous microstructural morphology, macro-homogeneous constitutive laws or crystal plasticity. A comparative analysis in terms of transformation-induced plasticity (TRIP) is performed in order to conclude on the relevance of the different models as regards experiments and to show how the principal assumptions of TRIP modelling can affect the prediction