Constitutive formulation and numerical validation of mechanical behavior of unsaturated soils

En este trabajo se presenta un modelo constitutivo elastoplástico para suelos parcialmente saturados. El modelo se formula en el marco general de la teoría de medios porosos y de la teoría del flujo de la plasticidad. La formulación constitutiva se basa en el conocido modelo de MRS Lade en el que se incorpora la succión como componente adicional independiente del estado de tensiones. Consecuentemente, las superficies de fluencia de cono y capa del modelo asi como la evolución de las variables internas de endurecimiento y ablandamiento muestran dependencias con el valor de la succión. Para el proceso de integración numérica de tensiones del modelo se propone el método de proyección al punto más cercano que es extendido en esta formulación para el caso de cuatro invariantes tensionales. Los resultados numéricos demuestran la capacidad de predicción del Modelo Extendido de MRS Lade para simular el comportamiento de los suelos parcialmente saturados tanto en régimen de prepico como en pospico bajo distintos niveles de saturación. Para la validación del modelo constitutivo formulado se realiza la simulación numérica de ensayos experimentales edométricos con succión controlada experimentales publicados por Gens et al 1 y ensayos de compresión triaxial convencional con succión controlada publicados por Macari et al 2.Peer Reviewe

Formulación elastoplástica para el análisis computacional de pórticos planos de hormigón armado

Se presenta una formulación de endurecimiento-ablandamiento en términos de resultantes de tensiones y desplazamientos para aplicar la teoría de elastoplasticidad a elementos de barra. Los factores se calibran con respecto a relaciones momento-curvatura de las secciones, obtenidas a partir de ecuaciones constitutivas realistas del hormigón y del acero. Ejemplos muestran la capacidad del modelo y la importancia del ablandamiento en la respuesta estructural hasta los estados límites considerados.A formulation of hardening and softening is presented in terms of stress resultants and displacements to apply the elastic-plastic theory to bar elements. The factors are adjusted with regard to moment-curvature relations of sections, obtained from realistic constitutive equations of confined concrete and steel. Examples shown the model capacity and the importance of softening in the structural response up to the limit states considered.Peer Reviewe

Thermodynamic Framework of Multiscale Homogenization Schemes for Dissipative Materials

The prediction of failure processes in composite, heterogeneous materials require multiscale analysis to account for the complex mechanisms and features taking place. Between the different multiscale schemes the more commonly used are those based on homogenization procedures, due to their versatility. In this work a thermodynamically consistent homogenisation based multiscale approach is formulated for modelling thermo-plastic materials. The proposal is valid for arbitrary multiscale procedures, including local or nonlocal methods, and continuum or discontinuum methods in either scale. The necessary and sufficient conditions for fulfilling the thermodynamic consistency are defined. It is demonstrated that the Hill-Mandel variational criterion for homogenization scheme is a necessary, but not a sufficient condition when dissipative material responses are involved at any scale. On this point, the additional condition that needs to be fulfilled is established. The general case of temperature-dependent, higher order elastoplasticity is considered as theoretical framework to account for the material dissipation at micro and macro scales of observation. Additionally, it is shown that the thermodynamic consistency enforces the homogenization of the nonlocal terms of the micro scale’s free energy density; however, this does not necessarily lead to nonlocal effects on the macro scale. Finally, the particular cases of local isothermal elastoplasticity and continuum damage are considered for the purpose of the proposed approach for multiscale homogenizations.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí

Thermodynamic Framework of Multiscale Homogenization Schemes for Dissipative Materials

The prediction of failure processes in composite, heterogeneous materials require multiscale analysis to account for the complex mechanisms and features taking place. Between the different multiscale schemes the more commonly used are those based on homogenization procedures, due to their versatility. In this work a thermodynamically consistent homogenisation based multiscale approach is formulated for modelling thermo-plastic materials. The proposal is valid for arbitrary multiscale procedures, including local or nonlocal methods, and continuum or discontinuum methods in either scale. The necessary and sufficient conditions for fulfilling the thermodynamic consistency are defined. It is demonstrated that the Hill-Mandel variational criterion for homogenization scheme is a necessary, but not a sufficient condition when dissipative material responses are involved at any scale. On this point, the additional condition that needs to be fulfilled is established. The general case of temperature-dependent, higher order elastoplasticity is considered as theoretical framework to account for the material dissipation at micro and macro scales of observation. Additionally, it is shown that the thermodynamic consistency enforces the homogenization of the nonlocal terms of the micro scale’s free energy density; however, this does not necessarily lead to nonlocal effects on the macro scale. Finally, the particular cases of local isothermal elastoplasticity and continuum damage are considered for the purpose of the proposed approach for multiscale homogenizations.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí

On mesh coarsening procedures for the virtual element method

In the context of adaptive remeshing, the virtual element method provides significant advantages over the finite element method. The attractive features of the virtual element method, such as the permission of arbitrary element geometries, and the seamless permission of 'hanging' nodes, have inspired many works concerning error estimation and adaptivity. However, these works have primarily focused on adaptive refinement techniques with little attention paid to adaptive coarsening (i.e. de-refinement) techniques that are required for the development of fully adaptive remeshing procedures. In this work novel indicators are proposed for the identification of patches/clusters of elements to be coarsened, along with a novel procedure to perform the coarsening. The indicators are computed over prospective patches of elements rather than on individual elements to identify the most suitable combinations of elements to coarsen. The coarsening procedure is robust and suitable for meshes of structured and unstructured/Voronoi elements. Numerical results demonstrate the high degree of efficacy of the proposed coarsening procedures and sensible mesh evolution during the coarsening process. It is demonstrated that critical mesh geometries, such as non-convex corners and holes, are preserved during coarsening, and that meshes remain fine in regions of interest to engineers, such as near singularities

Thermodynamic gradient-based poroplastic theory for concrete under high temperatures

Concrete materials subjected to long term exposures to high temperatures suffer severe degradations in its mechanical properties (cohesion, friction, strength and stiffness) and changes in their failure mechanisms. These degradations may lead to irreversible damage or sudden collapse of the related structures. From the predictive analysis stand point, accurate constitutive theories are required to simulate the variations of concrete mechanical failure behavior under high and durable temperature fields. In the realm of the smeared crack approach, non-local model strategies are required to objectively reproduce failure behaviors under coupled thermo-mechanical loading conditions, while realistic descriptions of the involved characteristic lengths are needed to objectively reproduce the variation from ductile to brittle failure modes depending on the acting confining pressure and temperature. In this work, a thermodynamically consistent gradient poroplastic model for concrete subjected to high temperatures is proposed. A particular and simple form of gradient-based poroplasticity is considered whereby the state variables are the only ones of non-local character. The degradations of these variables due to coupled thermo-mechanical effects are described in the framework of the thermodynamic approach. After describing the material formulation, numerical analyses are presented which demonstrate the predictive capabilities of the proposed constitutive theory for different stress paths and thermal conditions.Fil: Ripani, Marianela. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Construcciones y Estructuras. Laboratorio de Materiales y Estructuras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Etse, Jose Guillermo. Universidad de Buenos Aires. Facultad de Ingenieria. Departamento de Construcciones y Estructuras. Laboratorio de Materiales y Estructuras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Vrech, Sonia Mariel. Universidad de Buenos Aires. Facultad de Ingenieria. Laboratorio de Metodos Numericos En Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mroginski, Javier Luis. Universidad de Buenos Aires. Facultad de Ingenieria. Laboratorio de Metodos Numericos En Ingenieria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

An RVE-Based Multi-Scale Approach for Concrete Affected by Alkali–Silica Reaction

The alkali-silica reaction (ASR) is a deleterious reaction that occurs in cementitious mixtures like concrete due to the combination of the alkaline solution of the cement paste with the amorphous silica of the aggregates. As a consequence of this reaction a gel is generated that expands through water absorption, leading to pore filling and pore pressure increment. Experimentally, the consequences of ASR are observed in both the micro-cracking path around the aggregate and the stiffness reduction of the overall skeleton or solid phase. To get a proper prediction of the aforementioned effect, it is necessary to consider the kinetics of the chemical reaction and its effect on the mechanical behavior. In this paper, the ASR is modeled introducing a variable that quantifies its progress through a first order kinetic law. This variable affects the volumetric component of the Helmholtz free energy which now shall account for the chemo-mechanical behavior of the material. Thus, an additional term is introduced in the microscopic free energy density related to the chemical reaction process. The proposed free energy equation is implemented in a thermodynamically consistent multi-scale framework accounting for the chemo-mechanical degradation of the micro-structure due to the volumetric expansion of the gel. The cement mortar constitutive relation is reformulated using Biot’s poromechanics theory to include the pore pressure in the mechanical description, and a damage model to reproduce the solid phase degradation. Finally, some numerical examples showing the potential of the presented formulation are discussed.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí

An RVE-Based Multi-Scale Approach for Concrete Affected by Alkali–Silica Reaction

The alkali-silica reaction (ASR) is a deleterious reaction that occurs in cementitious mixtures like concrete due to the combination of the alkaline solution of the cement paste with the amorphous silica of the aggregates. As a consequence of this reaction a gel is generated that expands through water absorption, leading to pore filling and pore pressure increment. Experimentally, the consequences of ASR are observed in both the micro-cracking path around the aggregate and the stiffness reduction of the overall skeleton or solid phase. To get a proper prediction of the aforementioned effect, it is necessary to consider the kinetics of the chemical reaction and its effect on the mechanical behavior. In this paper, the ASR is modeled introducing a variable that quantifies its progress through a first order kinetic law. This variable affects the volumetric component of the Helmholtz free energy which now shall account for the chemo-mechanical behavior of the material. Thus, an additional term is introduced in the microscopic free energy density related to the chemical reaction process. The proposed free energy equation is implemented in a thermodynamically consistent multi-scale framework accounting for the chemo-mechanical degradation of the micro-structure due to the volumetric expansion of the gel. The cement mortar constitutive relation is reformulated using Biot’s poromechanics theory to include the pore pressure in the mechanical description, and a damage model to reproduce the solid phase degradation. Finally, some numerical examples showing the potential of the presented formulation are discussed.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí

An RVE-Based Multi-Scale Approach for Concrete Affected by Alkali–Silica Reaction

The alkali-silica reaction (ASR) is a deleterious reaction that occurs in cementitious mixtures like concrete due to the combination of the alkaline solution of the cement paste with the amorphous silica of the aggregates. As a consequence of this reaction a gel is generated that expands through water absorption, leading to pore filling and pore pressure increment. Experimentally, the consequences of ASR are observed in both the micro-cracking path around the aggregate and the stiffness reduction of the overall skeleton or solid phase. To get a proper prediction of the aforementioned effect, it is necessary to consider the kinetics of the chemical reaction and its effect on the mechanical behavior. In this paper, the ASR is modeled introducing a variable that quantifies its progress through a first order kinetic law. This variable affects the volumetric component of the Helmholtz free energy which now shall account for the chemo-mechanical behavior of the material. Thus, an additional term is introduced in the microscopic free energy density related to the chemical reaction process. The proposed free energy equation is implemented in a thermodynamically consistent multi-scale framework accounting for the chemo-mechanical degradation of the micro-structure due to the volumetric expansion of the gel. The cement mortar constitutive relation is reformulated using Biot’s poromechanics theory to include the pore pressure in the mechanical description, and a damage model to reproduce the solid phase degradation. Finally, some numerical examples showing the potential of the presented formulation are discussed.Publicado en: Mecánica Computacional vol. XXXV, no. 23Facultad de Ingenierí