COLLECTIONS

Documents published in Scipedia

• On micro-to-macro connections in domain decomposition multiscale methods

  O. Lloberas-Valls, D. Rixen, A. Simone, L. Sluys

  Computer Methods in Applied Mechanics and Engineering (2012). Vol. 225-228, pp. 177-196

  
  

  Abstract

  Micro-to-macro connection techniques constitute a key ingredient in the formulation of multiscale strategies. In this contribution several connection methods are explored for the concurrent multiscale analysis of brittle heterogeneous materials. Particularly, these techniques are investigated in a domain decomposition strong coupling multiscale framework. The structural component under analysis is partitioned into a number of non-overlapping domains and a fine scale resolution is assigned therein in an adaptive manner exploiting a zoom-in technique. Mesh refinement is employed in the domains where crack coalescence and growth take place. The original contribution presented in this manuscript consists in the study of different strong and weak locality constraints that connect coarse and fine resolution domains. Standard collocation and average compatibility are considered and serve as a basis for the development of two new interscale links. The influence of different locality constraints is studied in terms of the mechanical response and the error distribution is compared to a full fine scale analysis

  Abstract
  Micro-to-macro connection techniques constitute a key ingredient in the formulation of multiscale strategies. In this contribution several connection methods are explored [...]

  • 2
  •  read

• Multiscale domain decomposition analysis of quasi-brittle heterogeneous materials

  O. Lloberas-Valls, D. Rixen, A. Simone, L. Sluys

  International Journal for Numerical Methods in Engineering (2012). Vol. 89 (11), pp. 1337-1366

  
  

  Abstract

  A hybrid multiscale framework is presented, which processes the material scales in a concurrent manner, borrowing features from hierarchical multiscale methods. The framework is used for the analysis of nonlinear heterogeneous materials and is capable of tackling strain localization and failure phenomena. Domain decomposition techniques, such as the finite element tearing and interconnecting method, are used to partition the material in a number of non-overlapping domains and adaptive refinement is performed at those domains that are affected by damage processes. This refinement is performed in terms of material scale and finite element size. It is verified that the results are independent of the chosen domain decomposition. Moreover, the multiscale analyses are validated with reference solutions obtained with a full fine-scale solution procedure.

  Abstract
  A hybrid multiscale framework is presented, which processes the material scales in a concurrent manner, borrowing features from hierarchical multiscale methods. The framework [...]

  • 1
  •  read

• Computational homogenization for multiscale crack modeling: implementational and computational aspects

  V. Nguyen, O. Lloberas-Valls, L. Sluys, M. Stroeven

  International Journal for Numerical Methods in Engineering (2012). Vol. 89 (2), pp. 192-226 (Preprint)

  
  

  Abstract

  A computational homogenization procedure for cohesive and adhesive crack modeling of materials with a heterogeneous microstructure has been recently presented in Computer Methods in Applied Mechanics and Engineering (2010, DOI:10.1016/j.cma.2010.10.013). The macroscopic material properties of the cohesive cracks are obtained from the inelastic deformation manifested in a localization band (modeled with a continuum damage theory) at the microscopic scale. The macroscopic behavior of the adhesive crack is derived from the response of a microscale sample representing the microstructure inside the adhesive crack. In this manuscript, we extend the theory presented in Computer Methods in Applied Mechanics and Engineering (2010, DOI:10.1016/j.cma.2010.10.013) with implementation details, solutions for cyclic loading, crack propagation, numerical analysis of the convergence characteristics of the multiscale method, and treatment of macroscopic snapback in a multiscale simulation. Numerical examples including crack growth simulations with extended finite elements are given to demonstrate the performance of the method.

  Abstract
  A computational homogenization procedure for cohesive and adhesive crack modeling of materials with a heterogeneous microstructure has been recently presented in Computer [...]

  • 3
  •  read

• Domain decomposition techniques for the efficient modeling of brittle heterogeneous materials

  O. Lloberas-Valls, D. Rixen, A. Simone, L. Sluys

  Computer Methods in Applied Mechanics and Engineering (2011). Vol. 200 (13-16), pp. 1577-1590

  
  

  Abstract

  This paper describes a computational tool for the efficient study of failure in brittle heterogeneous materials. By means of several examples, it is demonstrated that the proposed tool is adequate for the analysis of materials that show localized failure modes. This case is particular since the main non-linearities concentrate in a small area compared to the whole specimen. The use of the method is preferred when the mesoscopic structure plays a crucial role during failure processes and needs to be fully taken into account in order to accurately tackle damage growth and propagation in the material. The present strategy is based on a Domain decomposition technique. Its performance is improved by selectively processing inelastic regions and reducing the number of operations in the remaining elastic areas. A four point bending test and the fracturing of a heterogeneous concrete specimen are presented as illustrations. They demonstrate that computational costs can be significantly reduced when the proposed strategy is applied to damage analysis.

  Abstract
  This paper describes a computational tool for the efficient study of failure in brittle heterogeneous materials. By means of several examples, it is demonstrated that [...]

  • 0
  •  read

• Homogenization-based multiscale crack modelling: from micro-diffusive damage to macro-cracks

  V. Nguyen, O. Lloberas-Valls, M. Stroeven, L. Sluys

  Computer Methods in Applied Mechanics and Engineering (2011). Vol. 200 (9-12), pp. 1220-1236

  
  

  Abstract

  The existence of a representative volume element (RVE) for a class of quasi-brittle materials having a random heterogeneous microstructure in tensile, shear and mixed mode loading is demonstrated by deriving traction–separation relations, which are objective with respect to RVE size. A computational homogenization based multiscale crack modelling framework, implemented in an FE2 setting, for quasi-brittle solids with complex random microstructure is presented. The objectivity of the macroscopic response to the micro-sample size is shown by numerical simulations. Therefore, a homogenization scheme, which is objective with respect to macroscopic discretization and microscopic sample size, is devised. Numerical examples including a comparison with direct numerical simulation are given to demonstrate the performance of the proposed method

  Abstract
  The existence of a representative volume element (RVE) for a class of quasi-brittle materials having a random heterogeneous microstructure in tensile, shear and mixed mode [...]

  • 3
  •  read

• On the existence of representative volumes for softening quasi-brittle materials: a failure zone averaging scheme

  V. Nguyen, O. Lloberas-Valls, M. Stroeven, L. Sluys

  Computer Methods in Applied Mechanics and Engineering (2010). Vol. 199 (45-48), pp. 3028-3038

  
  

  Abstract

  The concept of the representative volume element (RVE) for softening materials is revised in this contribution. It is demonstrated by means of numerical simulations that there exists a sample which is statistically representative for quasi-brittle materials with random microstructure like concrete. This finding is an important ingredient for homogenization-based multiscale modelling of softening materials.

  Abstract
  The concept of the representative volume element (RVE) for softening materials is revised in this contribution. It is demonstrated by means of numerical simulations that there [...]

  • 2
  •  read

• Increasing understanding and confidence in THM simulations of engineered barrier systems

  A. Schäfers, A. Gens, A. Rodríguez-Dono

  Environmental geotechnics (2020). Vol. 7 (1), pp. 59-71

  
  

  Abstract

  Previous studies on the modelling of coupled thermo-hydro-mechanical (THM) processes in bentonite-based engineered barrier systems (EBSs) showed the sensitivity of the output quantities to changes in the input parameters. To investigate the effects of uncertainties on the modelling results, to improve the understanding of the coupled processes active in the repository near field and to gain in-depth understanding of model uncertainties of different codes, a sensitivity analysis and code comparison of EBS simulations was performed within the Task Force on Engineered Barrier Systems. The analysis included variations in material parameter values, boundary and initial conditions, considered physical processes and model geometries, amounting to 60 different cases. This in-depth analysis helped evaluate the influence of parameter and conceptual uncertainties on the results of coupled THM simulations and to identify key parameters and processes. The cross-code comparison encouraged a fruitful exchange among modelling teams and led to very good agreements between the results of the different codes. Serving as a benchmark example for THM-coupled simulations of bentonite-based EBSs, the study helped increase the confidence in the modelling capabilities of several codes used for safety evaluations of repositories for spent fuel and high-level radioactive waste

  Abstract
  Previous studies on the modelling of coupled thermo-hydro-mechanical (THM) processes in bentonite-based engineered barrier systems (EBSs) showed the sensitivity of the output [...]

  • 1
  •  read

• Characterisation of the multi-scale fabric features of high plasticity clays

  F. Cotecchia, S. Guglielmi, F. Cafaro, A. Gens

  Géotechnique Letters (2019). Vol. 9 (4), pp. 361-368

  
  

  Abstract

  An investigation of the microstructural features of a high-plasticity clay, in both its natural conditions and reconstituted in the laboratory, is described. Scanning electron microscopy is used here to characterise the fabric at different magnifications, while image processing of the micrographs delivers a quantitative assessment of the fabric orientation. The results of energy-dispersive X-ray spectroscopy and swelling tests, as reported in a previous study by the authors, are used to characterise the bonding nature and strength, as well as mercury intrusion porosimetry to investigate clay porosimetry. Despite their identical composition, the natural and the reconstituted clay have experienced different deposition and loading history, generating different microstructural features that are shown to underlie their differences in state. For both clays, one-dimensional (1D) compression to medium–high pressures is seen to determine a well-oriented medium magnification fabric. However, larger-scale observations and the corresponding image processing results reveal non-uniform local fabric features, hence making fabric characterisation dependent on the scale of analysis and bringing about the issue of identifying the clay micro-scale representative element volume relating to the clay macro-behaviour. The micro-REV is identified for the clays under study and its connection with the macro-behaviour characterised. The microstructural evolution induced by 1D compression to very high pressures is shown to concern mainly the clay porosity and porosimetry, the fabric orientation being steady, thus explaining the isotropic hardening observed in laboratory tests.

  Abstract
  An investigation of the microstructural features of a high-plasticity clay, in both its natural conditions and reconstituted in the laboratory, is described. Scanning [...]

  • 2
  •  read

• Discussion on 'Effects of particle breakage and stress reversal on the behaviour of sand around displacement piles'

  F. Altuhafi, R. Jardine, V. Georgiannou, W. Moinet, M. Ciantia, M. Arroyo, A. Gens

  Géotechnique (2019). Vol. 69 (11), pp. 1029-1030

  
  

  • 2
  •  read

• Micromechanical inspection of incremental behaviour of crushable soils

  M. Ciantia, M. Arroyo, C. O'Sullivan, A. Gens

  Acta Geotechnica (2019). Vol. 14 (5), pp. 1337-1356

  
  

  Abstract

  In granular soils grain crushing reduces dilatancy and stress obliquity enhances crushability. These are well-supported specimen-scale experimental observations. In principle, those observations should reflect some peculiar micromechanism associated with crushing, but which is it? To answer that question the nature of crushing-induced particle-scale interactions is here investigated using an efficient DEM model of crushable soil. Microstructural measures such as the mechanical coordination number and fabric are examined while performing systematic stress probing on the triaxial plane. Numerical techniques such as parallel and the newly introduced sequential probing enable clear separation of the micromechanical mechanisms associated with crushing. Particle crushing is shown to reduce fabric anisotropy during incremental loading and to slow fabric change during continuous shearing. On the other hand, increased fabric anisotropy does take more particles closer to breakage. Shear-enhanced breakage appears then to be a natural consequence of shear-enhanced fabric anisotropy. The particle crushing model employed here makes crushing dependent only on particle and contact properties, without any pre-established influence of particle connectivity. That influence does not emerge, and it is shown how particle connectivity, per se, is not a good indicator of crushing likelihood

  Abstract
  In granular soils grain crushing reduces dilatancy and stress obliquity enhances crushability. These are well-supported specimen-scale experimental observations. In principle, [...]

  • 2
  •  read