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  • Numerical modeling of metal cutting processes using the Particle Finite Element Method

     Rodríguez Prieto, Juan Manuel
    Defense's date: 2014-03-06
    Universitat Politècnica de Catalunya
    Theses

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    El mecanizado de metal es un proceso en el que una capa delgada de metal se retira por una herramienta en forma de cuña de un cuerpo grande . El corte es un complejo de fenómenos físicos en los que la fricción, bandas de cizalla adiabáticas , calentamiento excesivo , grandes deformaciones y de alta velocidad de las herramientas están presentes. La geometría de la herramienta , ángulo de ataque y la velocidad de corte juegan un papel importante en la morfología de la viruta , las fuerzas , el consumo de energía y desgaste de la herramienta de corte. El objetivo principal del trabajo es contribuir precisamente a resolver algunos de los problemas descritos anteriormente a través de la extensión del PFEM a los problemas termo-mecánicos en mecánica de sólidos que implican grandes deformaciones y rotaciones , múltiples contactos y generación de nuevas superficies, con el foco principal en la simulación numérica de procesos de corte de metal . El problema termomecánico, formulado en el marco de la mecánica de medios continuos , se integra usando un esquema isotérmico junto con esquemas implícitos , semi-explícito y Implex. La herramienta ha sido discretizado utilizando un elemento finito triangular de tres nodos estándar. La pieza se discretizado utilizando un elemento finito desplazamiento presión mixta para hacer frente a la condición de incompresibilidad impuesto por la plasticidad . El elemento finito mixto se ha estabilizado mediante la proyección polinómica Presión, aplicado inicialmente en la literatura para la ecuación de Stokes. El comportamiento de la herramienta se describe usando un modelo constitutivo hiperelástico Neo Hookean . El comportamiento de la pieza de trabajo se describe usando un modelo isotrópico , con elastoplasticidad j2 y con tres funciones diferentes que se utilizan para describir el endurecimiento por deformación , endurecimiento de la velocidad de deformación y el ablandamiento térmico de diferentes materiales bajo una amplia variedad de condiciones de corte . La fricción en la interfaz de la herramienta-viruta se modela utilizando la fricción ley Norton- Hoff . La transferencia de calor en la interfase herramienta-viruta incluye la transferencia de calor por conducci{on y por fricción. Para validar la formulación desplazamiento presión mixto propuesto, se presentan tres problemas de referencia (la membrana de la tensión normal de Cook, la prueba de impacto Taylor y una prueba de tracción termomecánica ). La división isotérmica - IMPLEX presentada en este trabajo ha sido validado mediante un ensayo de tracción termomecánica . Además , con el fin de explorar las posibilidades del modelo como una herramienta para ayudar en el análisis de los procesos de corte de metal, un conjunto de simulaciones se presentan en este trabajo, entre ellas : corte de una material con tensión de fluencia independiente de la tasa de deformación , cortando utilizando diferentes ángulos de ataque , corte con herramientas de corte deformables incluyendo la fricción y la transferencia de calor , la transición de la continua para la formación de viruta dentada aumento de la velocidad de corte . Además, nuestros resultados muestran que la selección adecuada del esquema global de integración de tiempo puede suponer un ahorro en el tiempo de cálculo hasta 9 veces. Por otra parte, este trabajo presenta un análisis de sensibilidad a las condiciones de corte mediante un diseño de experimentos (DOE) . El diseño de experimentos con el llevado a cabo PFEM ha sido comparada con la llevada a cabo con el DoE AdvantaEdge , deforme, Abaqus y experimentos.. Los resultados obtenidos con PFEM y otras simulaciones numéricas son muy similares, mientras que , en comparación de las simulaciones numéricas y experimentos muestran algunas diferencias en las variables de salida que dependen de los fenómenos de fricción. Los resultados sugieren que es necesario mejorar la modelización de la fricción en la interfaz de la herramienta-viruta.

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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
    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
    Defense's date: 2013-04-26
    Universitat Politècnica de Catalunya
    Theses

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    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.

  • Continuous-discontinuous modelling for quasi-brittle failure: propagating cracks in a regularised bulk.

     Tamayo Mas, Elena
    Defense's date: 2013-12-05
    Universitat Politècnica de Catalunya
    Theses

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    En aquesta tesi, presentem una nova estratègia per tal de descriure el procés de fallida de materials quasi-fràgils, com ara el formigó. Típicament la simulació numèrica d'aquest procés s'ha dut a terme mitjançant models de dany o models de fractura. Els primers -models continus- descriuen la fractura com un procés de localització de deformacions on el dany creix i es propaga. Els models de fractura, en canvi, són models discontinus que introdueixen de manera explícita discontinuïtats en el camp de desplaçaments. Recentment s'han proposat estratègies que combinen aquestes dues teories clàssiques. Tot i que aquestes formulacions alternatives permeten simular millor el procés de fallida, encara queden alguns aspectes per aclarir, especialment pel que fa al canvi de models -de l'estratègia contínua a la discontínua.En aquesta tesi es presenta una nova estratègia contínua-discontínua. El nostre principal objectiu és proposar nous mètodes per tal de resoldre tres de les dificultats que presenten aquests models combinats: (1) solucionar la dependència patológica de la malla d'elements finits que presenten els models locals amb reblaniment; (2) determinar la trajectòria de la fissura i (3) assegurar-se que el canvi de models -delcontinu al discontinu- es fa de manera que les dues estratègies siguin energèticament equivalents.En primer lloc, ampliem l'ús -per tal de poder simular problemes dos i tres dimensionals- d'una estratègia alternativa que regularitza el reblaniment de les lleis de tensió-deformació. Aquí la no-localitat s'introdueix a nivell del camp de desplaçaments i no a través d'una variable interna com succeeix en les formulacions estàndards. Per aquest motiu, proposem noves condicions de contorn combinades per l'equació de regularització (pel camp de desplaçaments suavitzat). Tal com s'observa en diferents exemples dos i tres dimensionals, aquestes condicions permeten simular de manera físicament realista les primeres etapes del procés de fallida.En segon lloc, presentem una nova formulació combinada on les fissures es propaguen a través del medi regularitzat. Per tal de definir la trajectòria d'aquestes fissures, utilitzem un criteri geomètric, a diferència dels criteris mecànics clàssics. En particular, sigui D(x) un camp regularitzat de dany, les discontinuïtats es propaguen seguint la direcció marcada per l'eix mitjà de la isolínia (o isosuperfície mitjana en 3D) D(x) = D*. És a dir, utilitzem aquí aquesta eina geomètrica -molt emprada en d'altres aplicacions com ara l'anàlisi d'imatges, la visió artificial o la generació de malles- per tal de propagar les fissures. En aquest cas, donem també exemples dos i tres dimensionals.Finalment, proposem un nou criteri per tal d'estimar l'energia que l'estructura encara no ha dissipat en el moment en que canviem de model, per tal que pugui ser transferida a la fissura cohesiva. D'aquesta manera, s'assegura que l'estratègia contínua i la contínua-discontínua siguin energèticament equivalents. En comparació amb d'altres tècniques, aquesta estratègia té en compte les diferents branques de descàrrega dels models de dany i permet estimar de manera més precisa l'energia que cal transmetre. Per tal de mostrar aquest balanç energètic es duen a terme diferents exemples en una i dues dimensions.

  • A comparative study on homogenization strategies for multi-scale analysis of materials

     ORTOLANO, JOSÉ MARÍA; Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier
    Date of publication: 2013-02-01
    Book

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    One of the most important engineering tasks over the years has been the design and manufacture of increasingly sophisticated structural materials as a result of the requirements related to the technological progress. In the last decades, the growing needs for improved properties of products have been partially solved through the development of composite materials. A key to the success of many modern structural components is the tailored behavior of the material to given applications.

  • A finite strain, finite band method for modeling ductile fracture

     Huespe, Alfredo Edmundo; Needleman, Alan; Oliver Olivella, Fco. Javier; Sánchez, Pedro J
    International journal of plasticity
    Date of publication: 2012-01
    Journal article

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  • Numerical Approach For Modeling Steel Fiber Reinforced Concrete  Open access

     Pros Parés, Alba
    Defense's date: 2012-02-06
    Universitat Politècnica de Catalunya
    Theses

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    One alternative to overcome the main drawbacks of plain concrete in tension (its brittleness and weakness) is Steel Fiber Reinforced Concrete (SFRC), a technique introduced in the 70's, which consists of adding steel fibers into the concrete matrix. Due to the presence of the steel fibers into the concrete matrix, the residual strength and the energy dissipation of the material increase. Moreover, once a crack appears in the concrete, the steel fibers sew this fissure. The shape, the length and the slenderness of the fibers influence on the SFRC behavior. Moreover, the distribution and the orientation of the fibers into the concrete domain must be taken into account for characterizing the material. In order to characterize the behavior of SFRC, a numerical tool is needed. The aim is to simulate the most standard and common tests (direct and indirect tension tests, flexural test, double punch tes,¿) and more complex setups. This thesis proposes a numerical tool for modeling SFRC avoiding homogenized models (not accurate enough) and conformal meshes (too expensive). Therefore, the numerical tool accounts for the actual geometry of the fibers, discretized as 1D bars nonconformal with the concrete bulk mesh (2D or 3D domains). The two materials, corresponding to the concrete bulk and the fiber cloud, are defined independently, but coupled by imposing displacement compatibility. This compatibility is enforced following the ideas of the Immersed Boundary methods. Two different models are considered for modeling the concrete bulk (a continuous one and a discontinuous one). The parametric study of each model is done for only plain concrete, before the addition of the steel fibers. A phenomenological mesomodel is defined for modeling steel fibers, on the basis of the analytical expressions describing the pullout tests. This phenomenological mesomodel not only describes the behavior of the steel fibers, but also accounts for the concrete-fiber interaction behavior. For each fiber, its constitutive equation is defined depending on its shape (straight or hooked) and the angle between the fiber and the normal direction of the failure pattern. Both 2D and 3D examples are reproduced with the proposed numerical tool. The obtained results illustrate the presence of the steel fibers into the concrete matrix. The shape of the fiber influences of the SFRC behavior: the residual strength is higher for hooked fibers than for straight ones. Moreover, increasing the quantity of fibers means increasing the residual strength of the material. The obtained numerical results are compared to the experimental ones (under the same hypothesis). Therefore, the proposed numerical approach of SFRC is validated experimentally.

  • Phase-field modeling of fracture in ferroelectric materials.

     Abdollahi Hosnijeh, Amir
    Defense's date: 2012-10-18
    Universitat Politècnica de Catalunya
    Theses

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  • Strain Injection Techniques in Numerial Modeling of Propagating Material Failure

     Baixinho Figueiredo dias, Ivo Miguel
    Defense's date: 2012-10-10
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • High-performance model reduction procedures in multiscale simulations

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Caicedo, 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).

  • Advanced Grant European Research Council (convocatòria 2012)

     Oliver Olivella, Fco. Javier
    Award or recognition

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  • On the contact domain method: a comparison of penalty and Lagrange multiplier implementations

     Weyler Perez, Rafael; Oliver Olivella, Fco. Javier; Sain, Trisha; Cante Teran, Juan Carlos
    Computer methods in applied mechanics and engineering
    Date of publication: 2012-01-15
    Journal article

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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
    Date of publication: 2012-10-01
    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
    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.

  • Finite element modelling of ejection cracks in powder metallurgy die compaction processes: case study

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Cante Teran, Juan Carlos; Weyler Perez, Rafael
    Powder metallurgy
    Date of publication: 2012
    Journal article

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  • Crack models with embedded discontinuities

     Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier
    Date of publication: 2011
    Book chapter

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  • Strain injection, mixed formulations and strong discontinuities in fracture modeling of quasi-brittle materials

     Baixinho Figueiredo Dias, Ivo Miguel; Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo
    Congreso en Métodos Numéricos em Engenharia
    Presentation's date: 2011-06-15
    Presentation of work at congresses

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  • Computational modeling of fiber reinforced concrete as a composite complex material

     Oliver Olivella, Fco. Javier; Huespe, Alfredo Edmundo; Mora Mendez, Diego Fernando
    International Conference on Recent Advances in Nonlinear Models
    Presentation's date: 2011-11-24
    Presentation of work at congresses

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  • On the proper characterization of tooling motions and initial conditions in powder die compaction modeling

     Hernandez Ortega, Joaquin Alberto; Cante Teran, Juan Carlos; Oliver Olivella, Fco. Javier; Weyler Perez, Rafael
    Journal of materials processing technology
    Date of publication: 2011-08
    Journal article

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    Flow regime analyses during the filling stage in powder metallurgy processes: experimental study and numerical modelling  Open access

     Cante Teran, Juan Carlos; Riera Colom, Maria Dolores; Oliver Olivella, Fco. Javier; Prado Pozuelo, Jose Manuel
    Granular matter
    Date of publication: 2011-01
    Journal article

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    Experimental and numerical studies of powder flow during the die filling stage in powder metallurgy cold compaction processes are presented. An experimental setting consisting of a horizontal pneumatically activated shoe, a vertical die and high-speed video system has been designed. The experiments show the existence of three flow regimes: continuous, transitory and discrete, which are identified in terms of the particle size, the morphology and the speed of the shoe. In the continuous regime the powder flows in a progressive manner but in the discrete one some perturbations appear as a consequence of a shear band formation that forms discrete avalanches. A numerical model, based on a ratedependent constitutive model, via a flow formulation, and in the framework of the particle finite element method (PFEM) is also proposed. For the purpose of this study, the use of the PFEM assumes that the powder can be modelled as a continuous medium. The model, provided with the corresponding characterisation of the parameters, is able to capture the two fundamental phenomena observed during the filling process: (1) the irreversibility of most of the deformation experienced by the material and (2) the quick dissipation of the potential gravitatory energy of the granular system through the inter-particle friction processes, modelled by the plastic dissipation associated with the material model. Experimental and numerical results have been compared in order to study the viability of the proposed model.

  • A robust approach to model densification and crack formation in powder compaction processes

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Cante Teran, Juan Carlos; Weyler Perez, Rafael
    International journal for numerical methods in engineering
    Date of publication: 2011-08-26
    Journal article

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    This paper deals with the question of how to efficiently integrate a constitutive model that describes the densification of powders and the potential formation of cracks in Powder Metallurgy (P/M) cold compaction processes. The analyzed model is a large strain, elastoplastic model of the Drucker–Prager/Cap type, refined to cover also the prediction of crack formation, and featuring non-conventional elements such as a density-dependent Von Mises yield surface; a parabolic plastic potential function for the Drucker–Prager envelope; and a softening law whose softening modulus is dependent on the level of densification. The employed integration procedure is a non-conventional hybrid or IMPLicit–EXplicit (IMPL-EX) scheme, whose essence is to solve explicitly for some variables and implicitly for others, with the peculiarity of the ‘explicit’ variables being but extrapolated values of the same quantities computed, at previous time steps, by means of a fully implicit scheme. The return-mapping equations stemming from this implicit scheme are solved using an unconditionally convergent, fractional step method-based iterative procedure. The performance of the IMPL-EX integration algorithm is critically assessed in two different situations: the densification of a cylindrical specimen, and the fracture process in a diametral compression test. Results obtained show conclusively that the proposed hybrid integration strategy offers an efficient solution to the trade-off between robustness and computational time requirements.

  • Recent developments on computational modeling of material failure in plain and reinforced concrete structures

     Huespe, Alfredo Edmundo; Oliver Olivella, Fco. Javier; Diaz, Guillermo; Sánchez, Pablo J.
    Computational Modelling of Concrete Structures
    Presentation's date: 2010-03-18
    Presentation of work at congresses

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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; Dias, I. F.; Huespe, Alfredo Edmundo
    Computational Modelling of Concrete Structures
    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
    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
    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.

  • A 3D Frictionless Contact Domain Method for Large Deformation Problems

     Hartmann, S.; Weyler Perez, Rafael; Oliver Olivella, Fco. Javier; Cante Teran, Juan Carlos; Hernandez Ortega, Joaquin Alberto
    CMES: computer modeling in engineering and sciences
    Date of publication: 2010-01
    Journal article

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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
    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.

  • El método PFEM . Aplicación a problemas industriales de pulvimetalúrgia

     González Ferrari, Carlos
    Defense's date: 2010-02-05
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Aplicación del método PFEM a la simulación de procesos de transferencia propios de la industria pulvimetalúrgica

     González Ferrari, Carlos; Cante Teran, Juan Carlos; Oliver Olivella, Fco. Javier
    Date of publication: 2010-04-01
    Book

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  • 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
    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.

  • Numerical modeling of crack formation in powder forming processes

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Cante Teran, Juan Carlos; Weyler Perez, Rafael
    International journal of solids and structures
    Date of publication: 2010-01-15
    Journal article

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  • On particle finite element methods (PFEM) in dynamic solid mechanics problems

     Oliver Olivella, Fco. Javier; Cante Teran, Juan Carlos; Weyler Perez, Rafael; Hartmann, S.; Hernandez Ortega, Joaquin Alberto
    International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering
    Presentation's date: 2009
    Presentation of work at congresses

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    The work presents the most relevant features of a numerical simulation setting based on the Particle Finite Element Method. The method is especially suitable for dynamic problems in computational solid mechanics where a fluid-like behavior is experienced by the solid i.e.: metal forming processes, powder compaction processes and granular flows, characterized by large strains and distortions, and those displaying new appearances and changes of existing solid boundaries, like in machining processes. The main elements of the method are: a) the updated Lagrange description of the motion, b) an automatic boundary recognition procedure (the alpha-shape method), c) appropriated constitutive models and integration algorithms and 4) a specific contact-domain based method to impose the contact constraints.

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    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
    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)

  • A contact domain method for large deformation frictional contact problems. Part 2: Numerical aspects

     Hartmann, S; Oliver Olivella, Fco. Javier; Weyler Perez, Rafael; Cante Teran, Juan Carlos; Hernandez Ortega, Joaquin Alberto
    Computer methods in applied mechanics and engineering
    Date of publication: 2009-07
    Journal article

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    This second part of the work describes the numerical aspects of the developed contact domain method for large deformation frictional contact problems. The theoretical basis of this contact method is detailed in the first part of this work. Starting from this, the present contribution focuses on describing important algorithmic details that go along with the finite element implementation for two-dimensional problems. Important aspects are the construction of the contact domain mesh, via a constraint Delaunay triangulation, the linearization of the discretized contact contributions and some important technical aspects about the extrapolation procedure used for the predictive active set strategy. Finally a set of numerical examples is presented to demonstrate the performance of the developed contact strategy. Demanding static and dynamic contact problems in the context of large deformations, including frictional effects as well as self contact, show the wide applicability and the robustness of the proposed method.

    Continuació de l'article "A contact domain method for large deformation frictional contact problems. Part 1: Theoretical basis" publicat a la revista Computer Methods in Applied Mechanics and Engineering, Vol. 198, #33-36, July 2009, p. 2591-2606

  • Numerical modeling of crack formation in powder compaction based manufacturing processes

     Hernandez Ortega, Joaquin Alberto
    Defense's date: 2009-09-23
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Modeling of ground excavation with the particle finite element method

     Carbonell Puigbo, Josep Maria
    Defense's date: 2009-12-17
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • GRUP DE RESISTÈNCIA DE MATERIALS I ESTRUCTURES A L'ENGINYERIA

     Chiumenti, Michele; Hernandez Ortega, Joaquin Alberto; Oller Martinez, Sergio Horacio; Agelet de Saracibar Bosch, Carlos; Badia Rodriguez, Santiago I.; González Lopez, Jose Manuel; Weyler Perez, Rafael; Codina Rovira, Ramon; Bugeda Castelltort, Gabriel; Barbat Barbat, Horia Alejandro; Cante Teran, Juan Carlos; Baiges Aznar, Joan; Davalos Chargoy, Cesar Emilio; Miquel Canet, Juan; Suarez Arroyo, Benjamin; Cervera Ruiz, Miguel; Pelà, Luca; Oliver Olivella, Fco. Javier
    Participation in a competitive project

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  • A new approach in computational contact mechanics: the contact domain method

     Oliver Olivella, Fco. Javier; Hartmann, S; Cante Teran, Juan Carlos; Weyler Perez, Rafael; Hernandez Ortega, Joaquin Alberto
    Date of publication: 2009-02-28
    Book

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    Numerical modeling of crack formation in powder compaction processes  Open access

     Hernandez Ortega, Joaquin Alberto; Oliver Olivella, Fco. Javier; Cante Teran, Juan Carlos
    Date of publication: 2009
    Book

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    Powder metallurgy (P/M) is an important technique of manufacturing metal parts from metal in powdered form. Traditionally, P/M processes and products have been designed and developed on the basis of practical rules and trial-and-error experience. However, this trend is progressively changing. In recent years, the growing efficiencies of computers, together with the recognition of numerical simulation techniques, and more specifically, the finite element method , as powerful alternatives to these costly trial-and-error procedures, have fueled the interest of the P/M industry in this modeling technology. Research efforts have been devoted mainly to the analysis of the pressing stage and, as a result, considerable progress has been made in the field of density predictions. However, the numerical simulation of the ejection stage, and in particular, the study of the formation of cracks caused by elastic expansion and/or interaction with the tool set during this phase, has received less attention, notwithstanding its extreme relevance in the quality of the final product. The primary objective of this work is precisely to fill this gap by developing a constitutive model that attempts to describe the mechanical behavior of the powder during both pressing and ejection phases, with special emphasis on the representation of the cracking phenomenon. The constitutive relationships are derived within the general framework of rate-independent, isotropic, finite strain elastoplasticity. The yield function is defined in stress space by three surfaces intersecting nonsmoothly, namely, an elliptical cap and two classical Von Mises and Drucker-Prager yield surfaces. The distinct irreversible processes occurring at the microscopic level are macroscopically described in terms of two internal variables: an internal hardening variable, associated with accumulated compressive (plastic) strains, and an internal softening variable, linked with accumulated (plastic) shear strains. The innovative part of our modeling approach is connected mainly with the characterization of the latter phenomenological aspect: strain softening. Incorporation of a softening law permits the representation of macroscopic cracks as high gradients of inelastic strains (strain localization). Motivated by both numerical and physical reasons, a parabolic plastic potential function is introduced to describe the plastic flow on the linear Drucker-Prager failure surface. A thermodynamically consistent calibration procedure is employed to relate material parameters involved in the softening law to fracture energy values obtained experimentally on Distaloy AE specimens. The discussion of the algorithmic implementation of the model is confined exclusively to the time integration of the constitutive equations. Motivated by computational robustness considerations, a non-conventional integration scheme that combines advantageous features of both implicit and explicit method is employed. The basic ideas and assumptions underlying this method are presented, and the stress update and the closed-form expression of the algorithmic tangent moduli stemming from this method are derived. This integration scheme involves, in turn, the solution at each time increment of the system of equations stemming from a classical, implicit backward-Euler difference scheme. An iterative procedure based on the decoupling of the evolution equations for the plastic strains and the internal variables is proposed for solving these return-mapping equations. It is proved that this apparently novel method converges unconditionally to the solution regardless of the value of the material properties. To validate the proposed model, a comparison between experimental results of diametral compression tests and finite element predictions is carried out. The validation is completed with the study of the formation of cracks due to elastic expansion during ejection of an overdensified thin cylindrical part. Both simulations demonstrate the ability of the model to detect evidence of macroscopic cracks, clarify and provide reasons for the formation of such cracks, and evaluate qualitatively the influence of variations in the input variables on their propagation. Besides, in order to explore the possibilities of the numerical model as a tool for assisting in the design and analysis of P/M uniaxial die compaction (including ejection) processes, a detailed case study of the compaction of an axially symmetric multilevel part in an advanced CNC press machine is performed. Special importance is given in this study to the accurate modeling of the geometry of the tool set and the external actions acting on it (punch platen motions). Finally, the potential areas for future research are identified.

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    Particle finite element method applied to granular material flow  Open access

     Cante Teran, Juan Carlos; Oliver Olivella, Fco. Javier; Weyler Perez, Rafael; Cafiero, Mailhyn E.; Dávalos, C.
    International Conference on Particle-Based Methods
    Presentation's date: 2009-11-25
    Presentation of work at congresses

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    A numerical model, based on a rate-dependent constitutive model, via a flow formulation, and in the framework of the particle finite element method (PFEM) is proposed. It is settled on the assumption that the powder can be modelled as a continuous medium. The model, provided with the corresponding characterization of the parameters, is able to capture the two fundamental phenomena observed during the granular material flow: 1) the irreversibility of most of the deformation experienced by the material and 2) the energy dissipation of the granular system through the inter-particle friction processes, modelled by the plastic dissipation associated with the material model. Experimental and numerical results have been compared in order to study the viability of the proposed model.

  • A contact domain method for large deformation frictional contact problems. Part 1: Theoretical basis

     Oliver Olivella, Fco. Javier; Hartmann, S; Cante Teran, Juan Carlos; Weyler Perez, Rafael; Hernandez Ortega, Joaquin Alberto
    Computer methods in applied mechanics and engineering
    Date of publication: 2009-03
    Journal article

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    In the first part of this work, the theoretical basis of a frictional contact domain method for two-dimensional large deformation problems is presented. Most of the existing contact formulations impose the contact constraints on the boundary of one of the contacting bodies, which necessitates the projection of certain quantities from one contacting surface onto the other. In this work, the contact constraints are formulated on a so-called contact domain, which has the same dimension as the contacting bodies. This contact domain can be interpreted as a fictive intermediate region connecting the potential contact surfaces of the deformable bodies. The introduced contact domain is subdivided into a non-overlapping set of patches and is endowed with a displacement field, interpolated from the displacements at the contact surfaces. This leads to a contact formulation that is based on dimensionless, strain-like measures for the normal and tangential gaps and that exactly passes the contact patch test. In addition, the contact constraints are enforced using a stabilized Lagrange multiplier formulation based on an interior penalty method (Nitsche method). This allows the condensation of the introduced Lagrange multipliers and leads to a purely displacement driven problem. An active set strategy, based on the concept of effective gaps as entities suitable for smooth extrapolation, is used for determining the active normal stick and slip patches of the contact domain.

    Continua a l'article "A contact domain method for large deformation frictional contact problems. Part 2: Numerical aspects" publicat a la revista "Computer methods in applied mechanics and engineering", 2009, vol. 198, p. 2607-2631.

  • An implicit/explicit integration scheme to increase computability of non-linear material and contact/friction problems

     Oliver Olivella, Fco. Javier; Huespe, A E And J C Cante; Cante Teran, Juan Carlos
    Computer methods in applied mechanics and engineering
    Date of publication: 2008-04
    Journal article

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  • A mixture theory based method for three-dimensional modeling of reinforced concrete members with embedded crack finite elements

     Manzoli, O L; Oliver Olivella, Fco. Javier; Huespe, A E; Diaz, G
    Computers and concrete
    Date of publication: 2008-08
    Journal article

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  • Numerical simulation of crack formation during pressing and ejection in axial die compaction processes

     Hernandez Ortega, Joaquin Alberto; Cante Teran, Juan Carlos; Oliver Olivella, Fco. Javier
    Congreso de Pulvimetalurgia
    Presentation of work at congresses

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  • IACM Award for excel.lence in research on Computational Mechanics

     Oliver Olivella, Fco. Javier
    Award or recognition

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  • Premio Internacional AMCA 2008

     Oliver Olivella, Fco. Javier
    Award or recognition

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  • Computers and concrete

     Oliver Olivella, Fco. Javier
    Collaboration in journals

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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
    Date of publication: 2008-03
    Journal article

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  • Two-dimensional modelling of material failure in reinforced concrete by means of a continuum strong discontinuity approach

     Oliver Olivella, Fco. Javier; Linero, D L; Huespe, A E; Manzoli, O L
    Computer methods in applied mechanics and engineering
    Date of publication: 2008-01
    Journal article

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