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    Continuum approach to computational multi-scale modeling of fracture  Open access

     Oliver Olivella, Fco. Javier; Caicedo Silva, Manuel Alejandro; Roubin, Emmanuel; Huespe, Alfredo Edmundo
    Key engineering materials
    Vol. 627, p. 349-352
    DOI: 10.4028/www.scientific.net/KEM.627.349
    Date of publication: 2014-09
    Journal article

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    This paper presents a FE2 multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application to cementitious materials. Using the Continuum Strong Discontinuity Approach (CSD), innovative numerical tools, such as strain injection and crack path field techniques, provide a robust, and mesh-size, mesh-bias and RVE-size objective, procedure to model crack onset and propagation at the macro-scale.

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    High-performance model reduction techniques in computational multiscale homogenization  Open access

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Caicedo Silva, Manuel Alejandro; Cante Teran, Juan Carlos
    Computer methods in applied mechanics and engineering
    Vol. 276, p. 149-189
    DOI: 10.1016/j.cma.2014.03.011
    Date of publication: 2014-07-01
    Journal article

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    A novel model-order reduction technique for the solution of the fine-scale equilibrium problem appearing in computational homogenization is presented. The reduced set of empirical shape functions is obtained using a partitioned version that accounts for the elastic/inelastic character of the solution - of the Proper Orthogonal Decomposition (POD). On the other hand, it is shown that the standard approach of replacing the nonaffine term by an interpolant constructed using only POD modes leads to ill-posed formulations. We demonstrate that this ill-posedness can be avoided by enriching the approximation space with the span of the gradient of the empirical shape functions. Furthermore, interpolation points are chosen guided, not only by accuracy requirements, but also by stability considerations. The approach is assessed in the homogenization of a highly complex porous metal material. Computed results show that computational complexity is independent of the size and geometrical complexity of the Representative Volume Element. The speedup factor is over three orders of magnitude - as compared with finite element analysis - whereas the maximum error in stresses is less than 10%. (C) 2014 Elsevier B.V. All rights reserved.

    A novel model-order reduction technique for the solution of the fine-scale equilibrium problem appearing in computational homogenization is presented. The reduced set of empirical shape functions is obtained using a partitioned version that accounts for the elastic/inelastic character of the solution - of the Proper Orthogonal Decomposition (POD). On the other hand, it is shown that the standard approach of replacing the nonaffine term by an interpolant constructed using only POD modes leads to ill-posed formulations. We demonstrate that this ill-posedness can be avoided by enriching the approximation space with the span of the gradient of the empirical shape functions. Furthermore, interpolation points are chosen guided, not only by accuracy requirements, but also by stability considerations. The approach is assessed in the homogenization of a highly complex porous metal material. Computed results show that computational complexity is independent of the size and geometrical complexity of the Representative Volume Element. The speedup factor is over three orders of magnitude - as compared with finite element analysis - whereas the maximum error in stresses is less than 10%.

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    Crack-path field and strain-injection techniques in computational modeling of propagating material failure  Open access

     Oliver Olivella, Fco. Javier; Dias, I.F.; Huespe, Alfredo Edmundo
    Computer methods in applied mechanics and engineering
    Vol. 274, p. 289-348
    DOI: 10.1016/j.cma.2014.01.008
    Date of publication: 2014-06
    Journal article

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    The work presents two new numerical techniques devised for modeling propagating material failure, i.e. cracks in fracture mechanics or slip-lines in soil mechanics. The first one is termed crack-path-field technique and is conceived for the identification of the path of those cracks, or slip-lines, represented by strain-localization based solutions of the material failure problem. The second one is termed strain-injection, and consists of a procedure to insert, during specific stages of the simulation and in selected areas of the domain of analysis, goal oriented specific strain fields via mixed finite element formulations. In the approach, a first injection, of elemental constant strain modes (CSM) in quadrilaterals, is used, in combination of the crack-path-field technique, for obtaining reliable information that anticipates the position of the crack-path. Based on this information, in a subsequent stage, a discontinuous displacement mode (DDM) is efficiently injected, ensuring the required continuity of the crack-path across sides of contiguous elements. Combination of both techniques results in an efficient and robust procedure based on the staggered resolution of the crack-path-field and the mechanical failure problems. It provides the classical advantages of the "intra-elemental" methods for capturing complex propagating displacement discontinuities in coarse meshes, as E-FEM or X-FEM methods, with the non-code-invasive character of the crack-path-field technique. Numerical representative simulations of a wide range of benchmarks, in terms of the type of material and the failure problem, show the broad applicability, accuracy and robustness of the proposed methodology. The finite element code used for the simulations is open-source and available at http://www.cimne.com/compdesmat/. (C) 2014 Elsevier B.V. All rights reserved.

    The work presents two new numerical techniques devised for modeling propagating material failure, i.e. cracks in fracture mechanics or slip-lines in soil mechanics. The first one is termed crack-path-field technique and is conceived for the identification of the path of those cracks, or slip-lines, represented by strain-localization based solutions of the material failure problem. The second one is termed strain-injection, and consists of a procedure to insert, during specific stages of the simulation and in selected areas of the domain of analysis, goal oriented specific strain fields via mixed finite element formulations. In the approach, a first injection, of elemental constant strain modes (CSM) in quadrilaterals, is used, in combination of the crack-path-field technique, for obtaining reliable information that anticipates the position of the crack-path. Based on this information, in a subsequent stage, a discontinuous displacement mode (DDM) is efficiently injected, ensuring the required continuity of the crack-path across sides of contiguous elements. Combination of both techniques results in an efficient and robust procedure based on the staggered resolution of the crack-path-field and the mechanical failure problems. It provides the classical advantages of the “intra-elemental” methods for capturing complex propagating displacement discontinuities in coarse meshes, as E-FEM or X-FEM methods, with the non-code-invasive character of the crack-path-field technique. Numerical representative simulations of a wide range of benchmarks, in terms of the type of material and the failure problem, show the broad applicability, accuracy and robustness of the proposed methodology. The finite element code used for the simulations is open-source and available at http://www.cimne.com/compdesmat/.

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    Multi-scale (FE2) analysis of material failure in cement/aggregate-type composite structures  Open access

     Oliver Olivella, Fco. Javier; Caicedo Silva, Manuel Alejandro; Roubin, Emmanuel; Hernandez Ortega, Joaquin Alberto; Huespe, Alfredo Edmundo
    Computational Modelling of Concrete and Concrete Structures
    p. 39-49
    Presentation's date: 2014-03-24
    Presentation of work at congresses

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    The work propases a FP multiscale approach to computational modeling of material failure in concreteMlike structures, made of cement/aggregate-type composite materials. Keeping the approach in a classical homogenization setting, a multiscale model is proposed, which naturally provides a microscopic length-scale to be exported to the macrostructure. There, this length scale is used as regularization parameter in the context of the Continuum Strong Discontinuity Approach to material failure, and finite elements with embedded strong discontinuities (E~ FE M). The resulting technique allows robust modeling of crack propagation at the structural scale, accounting for the mesostructure morphology, supplies proper energy dissipation and solutions independent of the finite element and RVE sizes. Application toa number of examples, in the range from light-aggregate concrete to regular concrete, shows the potentiality of the method.

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    A two-scale failure model for heterogeneous materials: numerical implementation based on the finite element method  Open access

     Toro, Sebastian; Sánchez, Pablo J.; Huespe, Alfredo Edmundo; Giusti, Sebastian Miguel; Blanco, Pedro J.; Feijóo, R.A.
    International journal for numerical methods in engineering
    p. 1-39
    DOI: 10.1002/nme.4576
    Date of publication: 2013-07
    Journal article

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    In the first part of this contribution, a brief theoretical revision of the mechanical and variational foundations of a Failure-Oriented Multiscale Formulation (FOMF) devised for modeling failure in heterogeneous materials is described. The proposed model considers two well separated physical length scales, namely: (i) the ¿macro¿ scale where nucleation and evolution of a cohesive surface is considered as a medium to characterize the degradation phenomenon occurring at the lower length scale, and (ii) the ¿micro¿ scale where some mechanical processes that lead to the material failure are taking place, such as strain localization, damage, shear band formation, etc. These processes are modeled using the concept of Representative Volume Element (RVE). On the macro scale, the traction separation response, characterizing the mechanical behavior of the cohesive interface, is a result of the failure processes simulated in the micro scale. The traction separation response is obtained by a particular homogenization technique applied on specific RVE subdomains. Standard, as well as, Non-Standard boundary conditions are consistently derived in order to preserve ¿objectivity¿ of the homogenized response with respect to the micro-cell size. In the second part of the paper, and as an original contribution, the detailed numerical implementation of the two-scale model based on the Finite Element Method is presented. Special attention is devoted to the topics which are distinctive of the FOMF, such as: (i) the finite element technologies adopted in each scale along with their corresponding algorithmic expressions, (ii) the generalized treatment given to the kinematical boundary conditions in the RVE and (iii) how these kinematical restrictions affect the capturing of macroscopic material instability modes and the posterior evolution of failure at the RVE level. Finally, a set of numerical simulations is performed.

    The proposed model considers two well separated physical length scales, namely: (i) the macroscale where nucleation and evolution of a cohesive surface is considered as a medium to characterize the degradation phenomenon occurring at the lower length scale, and (ii) the microscale where some mechanical processes that lead to the material failure are taking place, such as strain localization, damage, shear band formation, and so on. These processes are modeled using the concept of Representative Volume Element (RVE). On the macroscale, the traction separation response, characterizing the mechanical behavior of the cohesive interface, is a result of the failure processes simulated in the microscale. The traction separation response is obtained by a particular homogenization technique applied on specific RVE sub-domains. Standard, as well as, Non-Standard boundary conditions are consistently derived in order to preserve objectivity of the homogenized response with respect to the micro-cell size. In the second part of the paper, and as an original contribution, the detailed numerical implementation of the two-scale model based on the finite element method is presented. Special attention is devoted to the topics, which are distinctive of the Failure-Oriented Multiscale Formulation, such as: (i) the finite element technologies adopted in each scale along with their corresponding algorithmic expressions, (ii) the generalized treatment given to the kinematical boundary conditions in the RVE, and (iii) how these kinematical restrictions affect the capturing of macroscopic material instability modes and the posterior evolution of failure at the RVE level. Finally, a set of numerical simulations is performed in order to show the potentialities of the proposed methodology, as well as, to compare and validate the numerical solutions furnished by the two-scale model with respect to a direct numerical simulation approach.

  • Two-scale modeling of material failure based on the continuum strong discontinuity approach

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Hernandez Ortega, Joaquin Alberto; Caicedo Silva, Manuel Alejandro
    International Conference on Computational Modeling of Fracture and Failure of Materials and Structures
    p. 224
    Presentation's date: 2013-06-05
    Presentation of work at congresses

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    Computational modeling of high-performance steel fiber reinforced concrete using a micromorphic approach  Open access

     Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier; Mora, Diego Fernando
    Computational Mechanics
    p. 1-22
    DOI: 10.1007/s00466-013-0873-4
    Date of publication: 2013-06
    Journal article

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    A finite element methodology for simulating the failure of high performance fiber reinforced concrete composites (HPFRC), with arbitrarily oriented short fibers, is presented. The composite material model is based on a micromorphic approach. Using the framework provided by this theory, the body configuration space is described through two kinematical descriptors. At the structural level, the displacement field represents the standard kinematical descriptor. Additionally, a morphological kinematical descriptor, the micromorphic field, is introduced. It describes the fiber¿matrix relative displacement, or slipping mechanism of the bond, observed at the mesoscale level. In the first part of this paper, we summarize the model formulation of the micromorphic approach presented in a previous work by the authors. In the second part, and as the main contribution of the paper, we address specific issues related to the numerical aspects involved in the computational implementation of the model. The developed numerical procedure is based on a mixed finite element technique. The number of dofs per node changes according with the number of fiber bundles simulated in the composite. Then, a specific solution scheme is proposed to solve the variable number of unknowns in the discrete model. The HPFRC composite model takes into account the important effects produced by concrete fracture. A procedure for simulating quasi-brittle fracture is introduced into the model and is described in the paper. The present numerical methodology is assessed by simulating a selected set of experimental tests which proves its viability and accuracy to capture a number of mechanical phenomenon interacting at the macro- and mesoscale and leading to failure of HPFRC composites.

    A finite element methodology for simulating the failure of High Performance Fiber Reinforced Concrete composites (HPFRC), with arbitrarily oriented short fibers, is presented. The composite material model is based on a micromorphic approach. Thus, using the framework provided by this theory, the body configuration space is described through two kinematical descriptors. At the structural level, the displacement field represents the standard kinematical descriptor. Additionally, a morphological kinematical descriptor, the micromorphic field, is introduced that describes the fibermatrix relative displacement, or slipping mechanism of the bond, observed at the mesoscale level. In this work, we address specific issues related to the numerical aspects involved in the computational implementation of the model. The developed numerical procedure is based on a mixed finite element technique. The number of d.o.f.’s per node changes according with the number of fiber bundles simulated in the composite. Then, a specific solution scheme is proposed to solve the variable number of unknowns in the discrete model. The HPFRC composite model takes into account the important effects produced by concrete fracture. A procedure for simulating quasi-brittle fracture is introduced into the model. It is described in the paper. The present numerical methodology is assessed by means of a selected set of experiments that prove its viability and accuracy to simulate a number of mechanical phenomenon interacting at the macro and mesoscale and leading to failure of HPFRC composites.

  • Multifield-based modeling of material failure in high performance reinforced cementitious composites  Open access

     Mora Mendez, Diego Fernando
    Universitat Politècnica de Catalunya
    Theses

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    Materiales fabricados a partir del cemento, tales como morteros y hormigones se comportan de forma frágil bajo tracciones. La adición de fibras cortas a tales matrices mejora de forma drástica su tenacidad. Generalmente, se acepta que las fibras contribuyen principalmente a la respuesta postcrítica del material compuesto debido al ¿bridging effect¿ y también al aumento de la resistencia ante la apertura de las fisuras. Por otro lado, la teoría multicampo es una herramienta matemática que permite describir materiales qe contienen subestructuras complejas. Esta subestructura influye en comportamiento macroestructural de modo drástico. Bajo este marco de referencia matemático, materiales como los compuesto hormigón pueden ser considerados un continuo con microestructura. Por lo tanto la teoría de la mecánica de daño continuo es aplicable a este tipo de materiales. Una formulación basada en la teoría del medio continuo con microestructura se desarrolla para modelizar el comportamiento mecánico de los compuestos de hormigón de alto desempeño con fibras orientadas de modo aleatorio. Esta formulación considera al continuo con microestructura, en el cual la microestructura tiene en cuenta el proceso de adherencia entre la fibra y la matriz, que ha sido reconocido por varios autores como el principal mecanismo responsable del incremento de la ductilidad del materiales cuasi-frágiles. En efecto, Las intercaras entre la matriz y la fibra son un factor condicionante en el diseño de materiales compuestos sometidos a tracción. Sin embargo, una intercara muy resistente puede generar concentración de tensiones en el frente de una fisura que se aproxima a esta. De acuerdo con Namaan, Las propiedades de la intercara fibra-matrix pueden ser mejoradas, modificando la rugosidad de la fibra a largo de su longitud o induciendo en esta deformaciones mecánicas. Por lo cual, la premisa del modelo es tener en consideración un microcampo que represente el desplazamiento fibra-matriz. Esta tesis incluye los aspectos computacionales del modelo que describe el compuesto de hormigón reforzado con fibras cortas (HPFRCC). Para simular el material compuesto, se utiliza una discretización mediante elementos finitos para resolver el sistema de ecuaciones dado por la aproximacion multicampo empleada en este caso particular. Dos discretizaciones son incluidas: El desplazamiento macroestructural estándar y el desplazamiento micromórfico. Adicionalmente, se presenta el procedimiento desacoplado propuesto para la integración del sistemas de ecuaciones. La iniciación del proceso de fractura en el HPFRCC, se identifica, desde el punto de vista constitutivo, como el comienzo de la localización de las deformaciones. En este caso particular, la localización depende de las propiedades mecanicas de todos los componentes. Como criterio de localizacion se considera el análisis de bifurcación en combinación con la técnica de inyección de modos de deformación presentado por Oliver et al. Este consiste en inyectar modos específicos de localización, mediante una formulación mixta, a aquellos elementos pertenecientes a la trayectoria que capturará la fisura. De este modo, es posible remediar problemas de dependencia respecto a la malla. La validación del modelo se realiza contrastando los resultados de la simulaciones con datos experimentales. Los resultados numéricos de la formulación propuesta permiten ilustrar dos aspectos relevantes de esta: 1) El papel que desempeña el mecanismo de adherencia en el comportamiento de endurecimiento presente en HPFRCC después de la fisuración y 2) El papel que desempeña la formulación de elementos finitos al capturar la localización de los desplazamientos en el estado postcrítico.

    Cementitious materials such as mortar or concrete are brittle and have an inherent weakness in resisting tensile stresses. The addition of discontinuous fibers to such matrices leads to a dramatic improvement in their toughness and remedies their deficiencies. It is generally agreed that the fibers contribute primarily to the post-cracking response of the composite by bridging the cracks and providing resistance to crack opening. On the other hand, the multifield theory is a mathematical tool able to describe materials which contain a complex substructure. This substructure is endowed with its own properties and it interacts with the macrostructure and influences drastically its behavior. Under this mathematical framework, materials such as cement composites can be seen as a continuum with a microstructure. Therefore, the whole continuum damage mechanics theory, incorporating a new microstructure, is still applicable. A formulation, initially based on the theory of continua with microstructure Capriz, has been developed to model the mechanical behavior of the high perfor-mance fiber cement composites with arbitrarily oriented fibers. This formulation approaches a continuum with microstructure, in which the microstructure takes into account the fiber-matrix interface bond/slip processes, which have been recognized for several authors as the principal mechanism increasing the ductility of the quasi-brittle cement response. In fact, the interfaces between the fiber and the matrix become a limiting factor in improving mechanical properties such as the tensile strength. Particularly, in short fiber composites is desired to have a strong interface to transfer effectively load from the matrix to the fiber. However, a strong interface will make difficult to relieve fiber stress concentration in front of the approaching crack. According to Naaman, in order to develop a better mechanical bond between the fiber and the matrix, the fiber should be modified along its length by roughening its surface or by inducing mechanical defor-mations. Thus, the premise of the model is to take into account this process considering a micro field that represents the slipping fiber-cement displacement. The conjugate generalized stress to the gradient of this micro-field verifies a balance equation and has a physical meaning. This contribution includes the computational modeling aspects of the high fiber rein-forced cement composites (HFRCC) model. To simulate the composite material, a finite element discretization is used to solve the set of equations given by the multifield approach for this particular case. A two field discretization: the standard macroscopic and the micro-scopic displacements, is proposed through a mixed finite element methodology. Furthermore, a splitting procedure for uncoupling both fields is proposed, which provides a more convenient numerical treatment of the discrete equation system. The initiation of failure in HPFRCC at the constitutive level identified as the onset of strain localization depends on the mechanical properties of the all compounds and not only on the matrix ones. As localization criteria is considered the bifurcation analysis in combination with the localized strain injection technique presented by Oliver et al. It consists of injecting a specific localization mode during the localization stage, via mixed finite element formulations, to the path of elements that are going to capture the cracks, and, in this way, the spurious mesh orientation dependence is removed. Model validation was performed using a selected set of experiments that proves the via-bility of this approach. The numerical examples of the proposed formulation illustrated two relevant aspects, namely: 1) the role of the bonding mechanism in the strain hardening be-havior after cracking in the HPFRCC and 2) the role that plays the finite element formulation in capturing the displacement localization in the localization stage.

  • Robustness of corroded reinforced concrete structures: a structural performance approach

     Cavaco, E. S.; Casas Rius, Joan Ramon; Neves, L. A. C.; Huespe, Alfredo Edmundo
    Structure and infrastructure engineering
    Vol. 9, num. 1, p. 42-58
    DOI: 10.1080/15732479.2010.515597
    Date of publication: 2013
    Journal article

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    A micromorphic model for steel fiber reinforced concrete  Open access

     Oliver Olivella, Fco. Javier; Mora Mendez, Diego Fernando; Huespe, Alfredo Edmundo; Weyler Perez, Rafael
    International journal of solids and structures
    Vol. 49, num. 21, p. 2990-3007
    DOI: 10.1016/j.ijsolstr.2012.05.032
    Date of publication: 2012-10-15
    Journal article

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    A new formulation to model the mechanical behavior of high performance fiber reinforced cement composites with arbitrarily oriented short fibers is presented. The formulation can be considered as a two scale approach, in which the macroscopic model, at the structural level, takes into account the mesostructural phenomenon associated with the fiber-matrix interface bond/slip process. This phenomenon is contemplated by including, in the macroscopic description, a micromorphic field representing the relative fiber-cement displacement. Then, the theoretical framework, from which the governing equations of the problem are derived, can be assimilated to a specific case of the Material Multifield Theory. The balance equation derived for this model, connecting the micro stresses with the micromorphic forces, has a physical meaning related with the fiber-matrix bond slip mechanism. Differently to previous procedures in the literature, addressed to model fiber reinforced composites, where this equation has been added as an additional independent ingredient of the methodology, in the present approach it arises as a natural result derived from the multifield theory. Every component of the composite is defined with a specific free energy and constitutive relation. The mixture theory is adopted to define the overall free energy of the composite, which is assumed to be homogeneously constituted, in the sense that every infinitesimal volume is occupied by all the components in a proportion given by the corresponding volume fraction. The numerical model is assessed by means of a selected set of experiments that prove the viability of the present approach.

  • Strain Injection Techniques in Numerial Modeling of Propagating Material Failure

     Baixinho Figueiredo dias, Ivo Miguel
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
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  • Strain localization, strong discontinuities and material fracture: matches and mismatches

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Dias, I. F.
    Computer methods in applied mechanics and engineering
    Vol. 241-244, p. 323-336
    DOI: 10.1016/j.cma.2012.06.004
    Date of publication: 2012-10-01
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    High-performance model reduction procedures in multiscale simulations  Open access

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Caicedo Silva, Manuel Alejandro
    Date of publication: 2012-03-01
    Book

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    Technological progress and discovery and mastery of increasingly sophisticated structural materials have been inexorably tied together since the dawn of history. In the present era ¿ the so-called Space Age ¿-, the prevailing trend is to design and create new materials, or improved existing ones, by meticulously altering and controlling structural features that span across all types of length scales: the ultimate aim is to achieve macroscopic proper- ties (yield strength, ductility, toughness, fatigue limit . . . ) tailored to given practical applications. Research efforts in this aspect range in complexity from the creation of structures at the scale of single atoms and molecules ¿ the realm of nanotechnology ¿, to the more mundane, to the average civil and mechanical engineers, development of structural materials by changing the composition, distribution, size and topology of their constituents at the microscopic/mesoscopic level (composite materials and porous metals, for instance).

    Technological progress and discovery and mastery of increasingly sophisticated structural materials have been inexorably tied together since the dawn of history. In the present era — the so-called Space Age —-, the prevailing trend is to design and create new materials, or improved existing ones, by meticulously altering and controlling structural features that span across all types of length scales: the ultimate aim is to achieve macroscopic proper- ties (yield strength, ductility, toughness, fatigue limit . . . ) tailored to given practical applications. Research efforts in this aspect range in complexity from the creation of structures at the scale of single atoms and molecules — the realm of nanotechnology —, to the more mundane, to the average civil and mechanical engineers, development of structural materials by changing the composition, distribution, size and topology of their constituents at the microscopic/mesoscopic level (composite materials and porous metals, for instance).

  • Strain localization, strong discontinuities and material failure: a strain injection procedure

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Baixinho Figueiredo Dias, Ivo Miguel
    International Conference on Computational Plasticity Fundamentals and Applications
    p. 1
    Presentation's date: 2011-09-08
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  • Computational modelling of fiber reinforced cement composites as a complex material

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Mora Mendez, Diego Fernando
    International Conference on Computational Plasticity Fundamentals and Applications
    p. 1
    Presentation's date: 2011-09-08
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  • Strong discontinuities, mixed finite element formulations and localized strain injection, in fracture modeling of quasi-brittle materials

     Oliver Olivella, Fco. Javier; Baixinho Figueiredo Dias, Ivo Miguel; Huespe, Alfredo Edmundo
    International Conference on Computational Modeling of Fracture and Failure of Materials and Structures
    p. 274
    Presentation's date: 2011-06-06
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  • Simulación numérica del proceso de fractura en concreto reforzado mediante la metodología de discontinuidades fuertes de continuo. Parte II: Aplicación a páneles sometidos a cortante

     Linero Segrera, Dorian Luis; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Ingeniería e investigación
    Vol. 30, num. 3, p. 16-26
    Date of publication: 2010-12
    Journal article

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    En este trabajo se presentan los resultados de la simulación numérica del proceso de fractura en páneles de concreto reforzado sometidos a cortante, utilizando un modelo basado en la metodología de discontinuidades fuertes de continuo (CSDA) y la teoría de mezclas. La CSDA describe la localzación de la deformación y la formación de una discontinuidad asociada con la aparición de una fisura. En cambio, la teoría de mezclas representa el comportamiento de un material compuesto, constituido por una matriz de concreto simple y uno o dos paquetes de barras largas de acero de refuerzo. El comportamiento del concreto simple y el acero se representan mediante un modelo de daño bidimensional y un modelo de plasticidad unidimensional, respectivamente. El modelo se implementa en el método de los elementos finitos considerando estado plano de esfuerzos, deformaciones infinitesimales y cargas estáticas. Se simularon tres páneles reforzados en una o en dos direcciones, los cuales estaban y sometidos principalmente a fuerzas cortantes. Los resultados de la simulación numérica, como la respuesta estructural y el patrón de fisuración, fueron satisfactorios. // The numerical simulation results of the fracture process in reinforced concrete shear panels are presented in this work. The simulation used a model based on the continuum strong discontinuity approach (CSDA) and mixing theory. CSDA describes strain localization and formation of discontinuity associated with the appearance of a crack. On the other hand, mixing theory represents composite material behaviour which is formed by a simple concrete matrix and one or two bundles of long reinforcement bars. The behaviour of simple concrete and steel is represented by a two-dimensional damage model and one-dimensional plasticity model, respectively. The model has been implemented in the finite element method which considers plane stress, infinitesimal strain and static loads. Three panels are simulated, reinforced in one or two ways; they are mainly subjected to shear forces. The numerical simulation results as well as structural response and cracking patterns were satisfactory.

  • Simulación numérica del proceso de fractura en concreto reforzado mediante la metodología de discontinuidades fuertes de continuo. Parte I: formulación

     Linero Segrera, Dorian Luis; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Ingeniería e investigación
    Vol. 30, num. 2, p. 5-15
    Date of publication: 2010-08-02
    Journal article

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    En general, las estructuras de concreto reforzado como vigas, columnas y muros están conformadas por entramados complejos de barras de acero embebidas en una matriz de concreto, las cuales exhiben múltiples fisuras ante la aplicación de cargas externas elevadas. Este artículo presenta la formulación de un modelo numérico cuyo objetivo es describir el proceso de fractura en elementos de concreto reforzado a partir de la fracción volumétrica del concreto y del acero. El modelo utiliza un campo enriquecido de la deformación para describir la formación y propagación de fisuras en un material compuesto, tal como lo establecen la metodología de discontinuidades fuertes de continuo y la teoría de mezclas. El material compuesto está constituido por una matriz de concreto y uno o dos paquetes de barras de acero ortogonales entre sí. El acero y el concreto se representan con modelos de plasticidad unidimensional y de daño escalar con tracción y compresión diferenciada, respectivamente. La acción pasador y los efectos del deslizamiento entre las barras y la matriz, se describen con modelos adicionales que relacionan el esfuerzo y la deformación de los materiales componentes. Finalmente, se concluye que el modelo propuesto se puede implementar con facilidad en el método de los elementos finitos, dado que permanecen muchas características del procedimiento numérico no lineal convencional. Asimismo, el modelo permite analizar el problema en la escala macroscópica, lo cual elude la construcción de mallas de elementos finitos de cada material componente y de sus efectos de interacción, reduciendo así el costo computacional. // Reinforced concrete structures generally refers to beams, columns and walls which are constituted by complex lattices of steel bars embedded in a concrete matrix, exhibiting multiple cracks due to high external loads. This paper presents the formulation of a numerical model aimed at describing the fracture process in reinforced concrete, from the volumetric ratio of concrete and steel. Crack formation and propagation in a composite material is described in the model by an enhanced strain field, such as that established in the continuum strong discontinuity approach and mixture theory. The composite material is constituted by a concrete matrix and one or two steel bar orthogonal packages. The steel and concrete are represented by a one-dimensional plasticity model and a scalar damage model having different tension and compression strength, respectively. The dowel action and the bond-slip effects between the bars and the matrix are described with additional models relating component material stress and strain. It is concluded that the proposed model can easily be implemented in the finite element method, due to several conventional nonlinear numerical process characteristics which remain. The model would also allow the problem to be analysed at macroscopic scale, thereby avoiding a finite element mesh having to be constructed for each component material and its interaction effects and reducing computational costs.

  • A framework for robustness assessment in the context of corroded RC structures

     Cavaco, E. S.; Neves, L. A. C.; Casas Rius, Joan Ramon; Huespe, Alfredo Edmundo
    International Conference on Bridge Maintenance, Safety and Management
    p. 2157-2164
    Presentation's date: 2010-07-13
    Presentation of work at congresses

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    Structural robustness is an emergent concept related to the structural response to damage. At the present time, robustness is not well defined and much controversy still remains around this subject. Even if robustness has seen growing interest as a consequence of catastrophic consequences due to extreme events, the fact is that the concept can also be very useful when considered on more probable exposure scenarios such as deterioration, among others. This paper intends to be a contribution to the definition of structural robustness, especially in the analysis of reinforced concrete structures subjected to corrosion. To achieve this, first of all, several proposed robustness definitions and indicators and misunderstood concepts will be analyzed and compared. From this point and regarding a concept that could be applied to most type of structures and damage scenarios, a robustness definition is proposed. To illustrate the proposed concept, an example of corroded reinforced concrete structures will be analyzed using nonlinear analysis numerical methods based on a continuum strong discontinuities approach and isotropic damage models for concrete. Finally the robustness of the presented example will be assessed.

  • Strong discontinuities, mixed finite element formulations and localized strain injection, in fracture modeling of quasi-brittle materials

     Oliver Olivella, Fco. Javier; Dias, I. F.; Huespe, Alfredo Edmundo
    Computational Modelling of Concrete and Concrete Structures
    p. 381-389
    Presentation's date: 2010-03-18
    Presentation of work at congresses

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  • Mesoscopic model to simulate the mechanical behavior of reinforced concrete members affected by corrosion

     Sánchez, P.J.; Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier; Toro, S.
    International journal of solids and structures
    Vol. 47, num. 5, p. 559-570
    DOI: 10.1016/j.ijsolstr.2009.10.023
    Date of publication: 2010-03
    Journal article

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  • On the numerical resolution of the discontinuous material bifurcation problem

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Cante Teran, Juan Carlos; Díaz, G.
    International journal for numerical methods in engineering
    Vol. 83, p. 786-804
    DOI: 10.1002/nme.2870
    Date of publication: 2010
    Journal article

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    The work focuses on the numerical resolution of the discontinuous material bifurcation problem as a relevant ingredient in computational material failure mechanics. The problem consists of finding the conditions for the strain localization onset in terms of the so-called bifurcation time, localization directions and localization modes. A numerical algorithm, based on the iterative resolution of a coupled eigenvalue problem in terms of the localization tensor, is proposed for such purpose. The algorithm is shown to be always convergent to the exact solution for the symmetric case (major and minor symmetries of the tangent constitutive operator). In the unsymmetric case (only minor symmetries), the solution is no longer exact, although it is shown that using the symmetric part of the localization tensor in the proposed algorithms provides enough accurate solutions for most of cases. Numerical examples illustrate the benefits of the proposed methodology in terms of accuracy and savings in the computational cost associated with the problem.

  • Access to the full text
    A finite thickness band method for ductile fracture analysis  Open access

     Huespe, Alfredo Edmundo; Needleman, Alan; Oliver Olivella, Fco. Javier; Sánchez, Pedro J
    International journal of plasticity
    Vol. 25, p. 2349-2365
    DOI: 10.1016/j.ijplas.2009.03.005
    Date of publication: 2009
    Journal article

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    We present a finite element method with a finite thickness embedded weak discontinuity to analyze ductile fracture problems. The formulation is restricted to small geometry changes. The material response is characterized by a constitutive relation for a progressively cavitating elastic–plastic solid. As voids nucleate, grow and coalesce, the stiffness of the material degrades. An embedded weak discontinuity is introduced when the condition for loss of ellipticity is met. The resulting localized deformation band is given a specified thickness which introduces a length scale thus providing a regularization of the post-localization response. Also since the constitutive relation for a progressively cavitation solid is used inside the band in the post-localization regime, the traction-opening relation across the band depends on the stress triaxiality. The methodology is illustrated through several example problems including mode I crack growth and localization and failure in notched bars. Various finite element meshes and values of the thickness of the localization band are used in the calculations to illustrate the convergence with mesh refinement and the dependence on the value chosen for the localization band thickness.

    Postprint (author’s final draft)

  • Desarrollo de herramientas para la simulación numérica de procesos de fractura, fragmentación e inestabilidad de materiales sólido o granulares mediante métodos de elementos finitos de partículas

     Cante Teran, Juan Carlos; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Weyler Perez, Rafael; Hernandez Ortega, Joaquin Alberto
    Competitive project

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  • Three-dimensional analysis of reinforced concrete members via embedded discontinuity finite elements

     Manzoli, O L; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    IBRACON structures and materials journal
    Vol. 1, num. 1, p. 71-83
    Date of publication: 2008-03
    Journal article

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  • A model of material failure for reinforced concrete via continuum strong discontinuity approach and mixing theory

     Linero, D L; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Date of publication: 2007-11-30
    Book

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  • Contribuciones a la simulación numérica del fallo material en medios tridimensionales mediante la metodología de discontinuidades fuertes de continuo.

     Blanco Ibañez, Sergio
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Un modelo del fallo material en el hormigón armado, mediante la metodología de discontinuidades fuertes de continuo y la teoría de mezclas.

     Linero Segrera, Dorian Luis
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • A comparative study on finite elements for capturing strong discontinuities: E-FEM vs. X-FEM

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Sánchez, P J
    Computer methods in applied mechanics and engineering
    num. 195, p. 4732-4752
    Date of publication: 2006-06
    Journal article

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  • On the fracture models determined by the continuum-strong discontinuity approach

     Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier; Gómez Pulido, María Dolores; Blanco, S; Linero, D
    International journal of fractures
    Vol. 137, p. 211-229
    Date of publication: 2006-04
    Journal article

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  • Modeling material failure in large concrete structures: recent computational developments

     Blanco, S; Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier; Gómez Pulido, María Dolores
    Computational Modelling of Concrete Structures
    p. 129-138
    Presentation of work at congresses

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  • Numerical modelling of fracture in fiber-reinforced composite structures. Application to reinforced concrete

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Gómez Pulido, María Dolores; Linero, D L
    Challenges in Computational Mechanics
    p. 109-110
    Presentation of work at congresses

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  • Cracking modelling in reinforced concrete via the strong discontinuity approach

     Linero, D L; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Gómez Pulido, María Dolores
    Computational Modelling of Concrete Structures
    p. 173-182
    Presentation of work at congresses

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  • Formulación de discontinuidades fuertes en la fractura de materiales compuestos conformados por fibras orientadas en una dirección

     Linero, D L; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Gómez Pulido, María Dolores
    Congreso de Métodos Numéricos en Ingeniería
    p. 1-16
    Presentation of work at congresses

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  • Strong discontinuity appoach to fracture of composite materials

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Linero, D
    11th International Conference on Fracture
    p. 1-6
    Presentation of work at congresses

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  • On a finite element with embedded discontinuities for numerical modeling of fracture

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Blanco Ibañez, Sergio
    11th International Conference on Fracture
    p. 1-6
    Presentation of work at congresses

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  • Modelado tridimensional del fallo material mediante la formulación de discontinuidad fuerte de contínuo

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Blanco Ibañez, Sergio
    Encuentro del Grupo Español de Fractura
    p. 47-52
    Presentation of work at congresses

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  • Fractura de materiales compuestos en elementos sometidos a tracción uniforme mediante la formulación de discontinuidades fuertes

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Linero Segrera, Dorian Luis; Gómez Pulido, María Dolores
    Encuentro del Grupo Español de Fractura
    p. 14-46
    Presentation of work at congresses

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  • Aplicación de la aproximación de contínuo de la discontinuidad fuerte al análisi del fallo material de estructuras tridimensionales

     Blanco Ibañez, Sergio; Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier
    Congreso de Métodos Numéricos en Ingeniería
    p. 1-20
    Presentation of work at congresses

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  • Fractura de materiales compuestos en elementos finitos sometidos a tracción uniforme mediante la formulación de discontinuidades fuertes

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Linero Segrera, Dorian Luis; Gómez Pulido, María Dolores
    Encuentro del Grupo Español de Fractura
    p. 1-6
    Presentation of work at congresses

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  • Modelado tridimensional del fallo material mediante la formulación de discontinuidad fuerte de continuo

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Blanco Ibañez, Sergio
    Encuentro del Grupo Español de Fractura
    p. 1-6
    Presentation of work at congresses

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  • Modelado de continuo de discontinuidades fuertes en grandes deformaciones

     Gómez Pulido, María Dolores; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Date of publication: 2004-11-30
    Book

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  • New developments in Computational Material Failure Mechanics

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Gómez Pulido, María Dolores; Blanco, S; Linero, D
    World Congress on Computational Mechanics
    p. 108-119
    Presentation's date: 2004-09-05
    Presentation of work at congresses

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  • Theoretical and computational issues in modelling material failure in strong discontinuity scenarios

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Computer methods in applied mechanics and engineering
    Vol. 193, num. 27-29, p. 2987-3014
    Date of publication: 2004-08
    Journal article

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  • Continuum approach to the numerical simulation of material failure in concrete

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Samaniego, E; Chaves, E W V
    International journal for numerical and analytical methods in geomechanics
    Vol. 28, p. 609-632
    Date of publication: 2004-07
    Journal article

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  • Continuum approach to material failure in strong discontinuity settings

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Computer methods in applied mechanics and engineering
    Vol. 193, p. 3195-3220
    Date of publication: 2004-06
    Journal article

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  • Computational modeling of cracking of concrete in strong discontinuity settings

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Gómez Pulido, María Dolores; Blanco, S
    Computers and concrete
    Vol. 1, num. 1, p. 61-76
    Date of publication: 2004-01
    Journal article

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