Oller Martinez, Sergio Horacio
Total activity: 558
Expertise
Prof. Structures and Continuum Mechanics
h index
26
Professional category
University professor
Doctoral courses
Dr. Ingeniero de Caminos, Canales y Puertos
University degree
Ingeniero en Construcciones (Homologado al Título de Ing. de Caminos)
Postgraduated qualification
Especialidad en Métodos Avanzados de Análisis y Diseño de Estructuras.
Research group
(MC)2 - Group of Computational Mechanics on Continuous Medium
Department
Department of Strength of Materials and Structural Engineering
School
Barcelona School of Civil Engineering (ETSECCPB)
Associated research bodies
CIMNE. Centre Internacional de Mètodes Numèrics en Enginyeria Open in new window
E-mail
sergio.ollerupc.edu
Contact details
UPC directory Open in new window
Orcid
0000-0002-5203-8903 Open in new window
Scopus Author ID
7003881173 Open in new window
Links of interest
Google Scholar Open in new window
ResearchGate Open in new window

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1 to 50 of 558 results
  • Impact damage identification in composite laminates using vibration testing

     Pérez Martínez, Marco Antonio; Gil Espert, Lluis; Oller Martinez, Sergio Horacio
    Composite structures
    Date of publication: 2014-02
    Journal article

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    Due to the problems arising from impact damage in composite laminates, there is a need to develop fast, accurate, cost-effective and non-destructive testing methods to identify this type of damage at an early stage and thus enhance the service life of composite structures. This paper presents the results of an extensive experimental campaign conducted to investigate the feasibility of using vibration-based meth- ods to identify damages sustained by composite laminates due to low-velocity impacts. The experimental programme included an evaluation of impact damage resistance and tolerance according to ASTM test methods, characterisation of induced damage by ultrasonic testing and quantification of the effects on the vibration response. The damage identification involved the detection, localisation, quantification and estimation of the remaining bearing capacity. Four damage indicators based on modal parameters were assessed by comparing pristine and damaged states. The results allowed for conclusions to be drawn regarding the capability and suitability of each damage indicator, including its ability to detect impact-induced damage, its precision in determining the location of damage, its sensitivity regarding damage extent and pertinent correlations with residual bearing capacity.

    Due to the problems arising from impact damage in composite laminates, there is a need to develop fast, accurate, cost-effective and non-destructive testing methods to identify this type of damage at an early stage and thus enhance the service life of composite structures. This paper presents the results of an extensive experimental campaign conducted to investigate the feasibility of using vibration-based methods to identify damages sustained by composite laminates due to low-velocity impacts. The experimental programme included an evaluation of impact damage resistance and tolerance according to ASTM test methods, characterisation of induced damage by ultrasonic testing and quantification of the effects on the vibration response. The damage identification involved the detection, localisation, quantification and estimation of the remaining bearing capacity. Four damage indicators based on modal parameters were assessed by comparing pristine and damaged states. The results allowed for conclusions to be drawn regarding the capability and suitability of each damage indicator, including its ability to detect impact-induced damage, its precision in determining the location of damage, its sensitivity regarding damage extent and pertinent correlations with residual bearing capacity.

  • Delamination in laminated plates using the 4-noded quadrilateral QLRZ plate element based on the refined zigzag theory

     Eijo, Ariel; Oñate Ibáñez de Navarra, Eugenio; Oller Martinez, Sergio Horacio
    Composite structures
    Date of publication: 2014-02
    Journal article

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    A numerical method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated plate/shell structures is presented. The originality of this method is the use of 4-noded quadrilateral plate finite elements whit only seven variables per node to discretize the plate/shell geometry. The ability to capture the relative displacement between consecutive layers in fracture mode II and III is the more important advantage of this element, denoted QLRZ. A continuum isotropic damage model is used to model the mechanical behavior of the plies. The material non-lineal problem is solved with the modified Newton¿Raphson method. The RZT plate theory, the QLRZ finite element and the isotropic damage model are described in this work. Also, the implicit integration algorithm is presented. The performance of the numerical model is analyzed by studying the delamination in a rectangular plate for two different laminates, using the 3D analysis as the reference solution.

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    Comparative experimental analysis of the effect caused by artificial and real induced damage in composite laminates  Open access

     Pérez Martínez, Marco Antonio; Gil Espert, Lluis; Sanchez Romero, Montserrat; Oller Martinez, Sergio Horacio
    Composite structures
    Date of publication: 2014-06-02
    Journal article

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    This paper presents the results of an extensive experimental campaign aimed to examine the effect upon the vibration response and on the residual load-bearing capacity caused by both: isolated artificially induced interlaminar damage and low-velocity impact induced damage in composite laminates. The experimental programme included modal testing, drop-weight impact testing, ultrasonic inspection, transverse quasi-static loading testing and compression testing conducted on a set of 72 carbon fibre-reinforced composite laminated coupons. Both types of damage caused measurable changes in laminate performance, however marked divergent trends were observed. The results allowed for conclusions to be drawn regarding the adequacy of the artificial damage approach and highlighted the importance and role of other forms of degradation upon damage tolerance of laminated composites containing damage.

    This paper presents the results of an extensive experimental campaign aimed to examine the effect upon the vibration response and on the residual load-bearing capacity caused by both: isolated artificially induced interlaminar damage and low-velocity impact induced damage in composite laminates. The experimental programme included modal testing, drop-weight impact testing, ultrasonic inspection, transverse quasi-static loading testing and compression testing conducted on a set of 72 carbon fibre-reinforced composite laminated coupons. Both types of damage caused measurable changes in laminate performance, however marked divergent trends were observed. The results allowed for conclusions to be drawn regarding the adequacy of the artificial damage approach and highlighted the importance and role of other forms of degradation upon damage tolerance of laminated composites containing damage.

  • A localized mapped damage model for orthotropic materials

     Pelà, Luca; Cervera Ruiz, Miguel; Oller Martinez, Sergio Horacio; Chiumenti, Michele
    Engineering fracture mechanics
    Date of publication: 2014-05-08
    Journal article

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    This paper presents an implicit orthotropic model based on the Continuum Damage Mechanics isotropic models. A mapping relationship is established between the behaviour of the anisotropic material and that of an isotropic one. The proposed model is used to simulate the failure loci of common orthotropic materials, such as masonry, fibre-reinforced composites and wood. The damage model is combined with a crack-tracking technique to reproduce the propagation of localized cracks in the discrete FE problem. The proposed numerical model is used to simulate the mixed mode fracture in masonry members with different orientations of the brick layers.

    This paper presents an implicit orthotropic model based on the Continuum Damage Mechanics isotropic models. A mapping relationship is established between the behaviour of the anisotropic material and that of an isotropic one. The proposed model is used to simulate the failure loci of common orthotropic materials, such as masonry, fibre-reinforced composites and wood. The damage model is combined with a crack-tracking technique to reproduce the propagation of localized cracks in the discrete FE problem. The proposed numerical model is used to simulate the mixed mode fracture in masonry members with different orientations of the brick layers.

  • Análisis no-lineal de materiales compuestos mediante la teoría de mezclas serie-paralelo

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Rastellini Canela, Fernando Gabriel
    Date of publication: 2014
    Book chapter

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    El propósito de esta obra es aportar una visión global del estado actual de la técnica y los recientes desarrollos sobre la aplicabilidad de los materiales compuestos en la obra civil y la edificación. El libro recoge una colección de trabajos de investigación de expertos nacionales e internacionales, que abordan los retos actuales y futuros en este campo, proporcionando, a través de una amplia variedad de casos de estudio, una hoja de ruta con las habilidades técnicas y los conocimientos prácticos necesarios para el empleo de materiales compuestos en nuevas aplicaciones. Los textos son ¿en la medida de lo posible¿ autocontenidos en sus partes, permitiendo una lectura acorde al interés particular de cada lector. En ellos se presentan fundamentos técnicos, resultados de investigaciones, y se revisan y compilan referencias bibliográficas actualizadas que complementan y permiten al lector adquirir un conocimiento más profundo de los temas expuestos, encaminándolo hacia posibles futuras líneas de investigación. Escrito por profesionales e investigadores con experiencia en este campo, este libro pretende ser un texto de referencia para los no iniciados en la temática y una herramienta de estudio e investigación para lectores de niveles más avanzados.

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    Análisis numérico de la reparación y refuerzo de estructuras con FRP  Open access

     Oller Martinez, Sergio Horacio; Molina, Maritzabel; Vielma Pérez, Juan Carlos; Martinez Garcia, Xavier; Barbat Barbat, Horia Alejandro; Nallim, Liz G.
    Date of publication: 2014
    Book chapter

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    El propósito de esta obra es aportar una visión global del estado actual de la técnica y los recientes desarrollos sobre la aplicabilidad de los materiales compuestos en la obra civil y la edificación. El libro recoge una colección de trabajos de investigación de expertos nacionales e internacionales, que abordan los retos actuales y futuros en este campo, proporcionando, a través de una amplia variedad de casos de estudio, una hoja de ruta con las habilidades técnicas y los conocimientos prácticos necesarios para el empleo de materiales compuestos en nuevas aplicaciones. Los textos son ¿en la medida de lo posible¿ autocontenidos en sus partes, permitiendo una lectura acorde al interés particular de cada lector. En ellos se presentan fundamentos técnicos, resultados de investigaciones, y se revisan y compilan referencias bibliográficas actualizadas que complementan y permiten al lector adquirir un conocimiento más profundo de los temas expuestos, encaminándolo hacia posibles futuras líneas de investigación. Escrito por profesionales e investigadores con experiencia en este campo, este libro pretende ser un texto de referencia para los no iniciados en la temática y una herramienta de estudio e investigación para lectores de niveles más avanzados.

    Este libro presenta una panorámica del estado actual de los materiales compuestos y sus aplicaciones más relevantes en la obra civil y la edificación.

  • Modelización del comportamiento de estructuras mediante la teoría de homogeneización

     Quinteros, Ricardo D.
    Defense's date: 2014-03-27
    National University of Salta
    Theses

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    Esta tesis se focaliza en el análisis y desarrollo de técnicas de homogenización ad-hoc para resolver el problema de representar el comportamiento estructural de muros de mampostería, aprovechando la configuración periódica que sus materiales y distribución le confieren. Mediante estas técnicas, es posible derivar el comportamiento global de la estructura a partir del comportamiento de los materiales constituyentes (ladrillo y mortero) adoptando modelos constitutivos diferentes para cada uno de ellos. Se realizan diversos ejemplos de validación para los modelos propuestos mediante la simulación de ensayos sencillos y curvas de falla del material compuesto. Se realizan además simulaciones de estructuras de paneles de mampostería con diversas configuraciones geométricas y mecánicas, sometidos a varias tipologías de cargas, para analizar el comportamiento mediante la comparación con resultados experimentales presentes en la bibliografía y/o otros modelos desarrollados por otros autores.

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    Impact damage prediction in carbon fiber-reinforced laminated composite using the matrix-reinforced mixing theory  Open access

     Pérez Martínez, Marco Antonio; Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Gil Espert, Lluis; Rastellini Canela, Fernando Gabriel; Flores, Fernando
    Composite structures
    Date of publication: 2013-10-01
    Journal article

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    The impact damage tolerance of fiber-reinforced laminated composite materials is a source of concern, mainly due to internal induced damage which causes large reductions on the strength and stability of the structure. This paper presents a procedure based on a finite element formulation that can be used to perform numerical predictions of the impact induced internal damage in composite laminates. The procedure is based on simulating the composite performance using a micro-mechanical approach named matrix-reinforced mixing theory, a simplified version of the serial/parallel mixing theory that does not require neither the iterative procedure nor the calculation of the tangent stiffness tensor. The numerical formulation uses continuum mechanics to simulate the phenomenon of initiation and propagation of interlaminar damage with no need to formulate interface elements, resulting in a computationally less demanding formulation. To demonstrate the capability of numerical procedure when applied to a low-velocity impact problem, numerical results are compared with the experimental ones obtained in a test campaign performed on 44 laminates specimens subjected to an out-of-plane and concentrated impact event, according to ASTM test method. Results are in good agreement with experimental data in terms of delamination onset and the internal spatial distribution of induced damage.

    The impact damage tolerance of fiber-reinforced laminated composite materials is a source of concern, mainly due to internal induced damage which causes large reductions on the strength and stability of the structure. This paper presents a procedure based on a finite element formulation that can be used to perform numerical predictions of the impact induced internal damage in composite laminates. The procedure is based on simulating the composite performance using a micro-mechanical approach named matrix-reinforced mixing theory, a simplified version of the serial/parallel mixing theory that does not require neither the iterative procedure nor the calculation of the tangent stiffness tensor. The numerical formulation uses continuum mechanics to simulate the phenomenon of initiation and propagation of interlaminar damage with no need to formulate interface elements, resulting in a computationally less demanding formulation. To demonstrate the capability of numerical procedure when applied to a low-velocity impact problem, numerical results are compared with the experimental ones obtained in a test campaign performed on 44 laminates specimens subjected to an out-of-plane and concentrated impact event, according to ASTM test method. Results are in good agreement with experimental data in terms of delamination onset and the internal spatial distribution of induced damage.

  • An integrated procedure for the structural design of a composite rotor-hydrofoil of a Water Current Turbine (WCT)

     Oller Aramayo, Sergio A.; Nallim, Liz G.; Oller Martinez, Sergio Horacio
    Applied composite materials
    Date of publication: 2013-12
    Journal article

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    This paper shows an integrated structural design optimization of a composite rotor-hydrofoil of a water current turbine by means the finite elements method (FEM), using a Serial/Parallel mixing theory (Rastellini et al. Comput. Struct. 86:879¿896, 2008, Martinez et al., 2007, Martinez and Oller Arch. Comput. Methods. 16(4):357¿397, 2009, Martinez et al. Compos. Part B Eng. 42(2011):134¿144, 2010) coupled with a fluid-dynamic formulation and multi-objective optimization algorithm (Gen and Cheng 1997, Lee et al. Compos. Struct. 99:181¿192, 2013, Lee et al. Compos. Struct. 94(3):1087¿1096, 2012). The composite hydrofoil of the turbine rotor has been design using a reinforced laminate composites, taking into account the optimization of the carbon fiber orientation to obtain the maximum strength and lower rotational-inertia. Also, these results have been compared with a steel hydrofoil remarking the different performance on both structures. The mechanical and geometrical parameters involved in the design of this fiber-reinforced composite material are the fiber orientation, number of layers, stacking sequence and laminate thickness. Water pressure in the rotor of the turbine is obtained from a coupled fluid-dynamic simulation (CFD), whose detail can be found in the reference Oller et al. (2012). The main purpose of this paper is to achieve a very low inertia rotor minimizing the start-stop effect, because it is applied in axial water flow turbine currently in design by the authors, in which is important to take the maximum advantage of the kinetic energy. The FEM simulation codes are engineered by CIMNE (International Center for Numerical Method in Engineering, Barcelona, Spain), COMPack for the solids problem application, KRATOS for fluid dynamic application and RMOP for the structural optimization. To validate the procedure here presented, many turbine rotors made of composite materials are analyzed and three of them are compared with the steel one.

    This paper shows an integrated structural design optimization of a composite rotor-hydrofoil of a water current turbine by means the finite elements method (FEM), using a Serial/Parallel mixing theory (Rastellini et al. Comput. Struct. 86:879–896, 2008, Martinez et al., 2007, Martinez and Oller Arch. Comput. Methods. 16(4):357–397, 2009, Martinez et al. Compos. Part B Eng. 42(2011):134–144, 2010) coupled with a fluid-dynamic formulation and multi-objective optimization algorithm (Gen and Cheng 1997, Lee et al. Compos. Struct. 99:181–192, 2013, Lee et al. Compos. Struct. 94(3):1087–1096, 2012). The composite hydrofoil of the turbine rotor has been design using a reinforced laminate composites, taking into account the optimization of the carbon fiber orientation to obtain the maximum strength and lower rotational-inertia. Also, these results have been compared with a steel hydrofoil remarking the different performance on both structures. The mechanical and geometrical parameters involved in the design of this fiber-reinforced composite material are the fiber orientation, number of layers, stacking sequence and laminate thickness. Water pressure in the rotor of the turbine is obtained from a coupled fluid-dynamic simulation (CFD), whose detail can be found in the reference Oller et al. (2012). The main purpose of this paper is to achieve a very low inertia rotor minimizing the start-stop effect, because it is applied in axial water flow turbine currently in design by the authors, in which is important to take the maximum advantage of the kinetic energy. The FEM simulation codes are engineered by CIMNE (International Center for Numerical Method in Engineering, Barcelona, Spain), COMPack for the solids problem application, KRATOS for fluid dynamic application and RMOP for the structural optimization. To validate the procedure here presented, many turbine rotors made of composite materials are analyzed and three of them are compared with the steel one.

  • A four-noded quadrilateral element for composite laminated plates/shells using the refined zigzag theory

     Eijo, Ariel; Oñate Ibáñez de Navarra, Eugenio; Oller Martinez, Sergio Horacio
    International journal for numerical methods in engineering
    Date of publication: 2013-05-20
    Journal article

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    A new bilinear four-noded quadrilateral element (called quadrilateral linear refined zigzag) for the analysis of composite laminated and sandwich plates/shells based on the refined zigzag theory is presented. The element has seven kinematic variables per node. Shear locking is avoided by introducing an assumed linear shear strain field. The performance of the element is studied in several examples where the reference solution is the 3D finite element analysis using 20-noded hexahedral elements.

    A new bilinear four-noded quadrilateral element (called quadrilateral linear refined zigzag) for the analysis of composite laminated and sandwich plates/shells based on the refined zigzag theory is presented. The element has seven kinematic variables per node. Shear locking is avoided by introducing an assumed linear shear strain field. The performance of the element is studied in several examples where the reference solution is the 3D finite element analysis using 20-noded hexahedral elements.

  • A numerical model of delamination in composite laminated beams using the LRZ beam element based on the refined zigzag theory

     Eijo, Ariel; Oñate Ibáñez de Navarra, Eugenio; Oller Martinez, Sergio Horacio
    Composite structures
    Date of publication: 2013-10
    Journal article

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    A method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated beam structures is presented. The novelty of this method is the use of one-dimensional finite elements to discretize the geometry of the beam. The key property of this beam element, named LRZ [1], is the possibility to capture the relative displacement between consecutive layers which occurs during delamination. The fracture mode that the LRZ element is capable to predict is mode II. In order to capture the relative displacement using the LRZ element it is necessary to adapt the RZT theory as presented in this paper. The mechanical properties of the layers are modeled using a continuum isotropic damage model [2]. The modified Newton-Raphson method is used for solving the non-linear problem.The RZT theory, the LRZ finite element and the isotropic damage model are described in the paper. Also, the implicit integrations algorithm is presented. The performance of the LRZ element is analyzed by studying the delamination in a beam for two different laminates, using the plane stress solution as a reference.

    A method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated beam structures is presented. The novelty of this method is the use of one-dimensional finite elements to discretize the geometry of the beam. The key property of this beam element, named LRZ [1], is the possibility to capture the relative displacement between consecutive layers which occurs during delamination. The fracture mode that the LRZ element is capable to predict is mode II. In order to capture the relative displacement using the LRZ element it is necessary to adapt the RZT theory as presented in this paper. The mechanical properties of the layers are modeled using a continuum isotropic damage model [2]. The modified Newton–Raphson method is used for solving the non-linear problem. The RZT theory, the LRZ finite element and the isotropic damage model are described in the paper. Also, the implicit integrations algorithm is presented. The performance of the LRZ element is analyzed by studying the delamination in a beam for two different laminates, using the plane stress solution as a reference.

  • Analytical and numerical analysis of human dental occlusal contact

     Bastos de Souza, FLAVIA; Casas, Estevam; Oller Martinez, Sergio Horacio
    Computer methods in biomechanics and biomedical engineering
    Date of publication: 2013
    Journal article

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    The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental enamel. The development of a numerical model for analysis of the occlusal contact between two antagonistic teeth is proposed, which includes three basic steps: the characterisation of the surface roughness, its homogenisation using an assumed distribution function and the numerical determination of the resulting forces. Finite element strain results for the main different asperities are statistically combined, deriving the predicted macroscopic behaviour of the interface. Axisymmetric and 3D numerical models with an elasto-plastic constitutive law are used to simulate micro-indentations and micro-contacts, respectively. The contact is allowed to occur locally in planes not necessarily parallel to the surface's mean plane, a problem for which there is no analytical solution. The three identified parameters, homogenised surface hardness (3.68 GPa), surface yield stress (3.08 GPa) and static friction coefficient (0.23), agree with the experimental values reported in the literature.

    The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental enamel. The development of a numerical model for analysis of the occlusal contact between two antagonistic teeth is proposed, which includes three basic steps: the characterisation of the surface roughness, its homogenisation using an assumed distribution function and the numerical determination of the resulting forces. Finite element strain results for the main different asperities are statistically combined, deriving the predicted macroscopic behaviour of the interface. Axisymmetric and 3D numerical models with an elasto-plastic constitutive law are used to simulate micro-indentations and micro-contacts, respectively. The contact is allowed to occur locally in planes not necessarily parallel to the surface's mean plane, a problem for which there is no analytical solution. The three identified parameters, homogenised surface hardness (3.68 GPa), surface yield stress (3.08 GPa) and static friction coefficient (0.23), agree with the experimental values reported in the literature.

  • Robust design optimisation of advance hybrid (fiber¿metal) composite structures

     Lee, Dong Seop; Morillo Carbonell, Carlos; Oller Martinez, Sergio Horacio; Bugeda Castelltort, Gabriel; Oñate Ibáñez de Navarra, Eugenio
    Composite structures
    Date of publication: 2013-05
    Journal article

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  • Characterization of mechanical properties of biological tissue: application to the FEM analysis of the urinary bladder

     Oñate Ibáñez de Navarra, Eugenio; Bellomo, Facundo J.; Monteiro, Virginia; Oller Martinez, Sergio Horacio; Nallim, Liz G.
    Date of publication: 2013
    Book chapter

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    This text presents an approach for the mechanical behavior of soft biological tissue using the finite elements method and a general constitutive model. Specifically we analyze the mechanical behavior of a urinary bladder starting from a procedure for obtaining the mechanical characterization of the biological tissue. Bladder tissue is modelled as a composite material formed by soft matrix reinforced with preferentially oriented fibres. In the first part of the text we present a procedure for identifying the mechanical properties of biological tissue main constituents by an inverse method. Then this information is used for the numerical simulation of the mechanical behavior of the bladder within the FEM. The formulation can be applied to various types of biological tissues, both in the field of material characterization, and in the numerical simulation of the tissue biomechanical behavior.

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    Stepwise advancing strategy for the simulation of fatigue problems  Open access

     Barbu, Lucia Gratiela; Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Barbat Barbat, Horia Alejandro
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2013-09-04
    Presentation of work at congresses

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    A time advance strategy for cyclic loading will be presented, applied to the fatigue formulation first proposed by [1].The coupling of both formulationsprovides a comprehensive approachto simulate high cycle fatigue problems accurately and with an important computational cost reduction. The capabilities of the proposed procedure are shown in a numerical example

    A time advance strategy for cyclic loading will be presented, applied to the fatigue formulation first proposed by [1].The coupling of both formulations provides a comprehensive approachto simulate high cycle fatigue problems accurately and with an important computational cost reduction. The capabilities of the proposed procedure are shown in a numerical example

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    Analysis of ultra low cycle fatigue problems with the Barcelona plastic damage model  Open access

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbu, Lucia Gratiela; Barbat Barbat, Horia Alejandro
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2013-09-05
    Presentation of work at congresses

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    This paper presents a plastic formulation based on the Barcelona plastic damage model capable of predicting the material failure due to Ultra Low Cycle Fatigue. This is achieved taking into account the fracture energy dissipated during the cyclic process. This approach allows the simulation of ULCF in regular cyclic tests, but also in non-regular cases such as seismic loads.

    This paper presents a plastic formulation based on the Barcelona plastic damage model capable of predicting the material failure due to Ultra Low Cycle Fatigue. This is achieved taking into account the fracture energy dissipated during the cyclic process. This approach allows the simulation of ULCF in regular cyclic tests, but also in non-regular cases such as seismic loads.

  • Computational Model of the Human Urinary Bladder  Open access

     Silva Araujo monteiro, Virginia
    Defense's date: 2013-06-10
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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    La propuesta de una vejiga artificial es un obstáculo a trasponer. El cáncer de vejiga está entrelos casos más frecuentes de enfermedades oncológicas en Estados Unidos y Europa. Ese cánceres considerado un problema médico importante una vez que esa enfermedad presenta altastasas de re-ocurrencia, muchas veces llevando a la remoción del órgano.La solución más sofisticada para remplazar ese órgano es la vejiga ileal, que consiste en una neovejigahecha de tejido intestinal del enfermo. Desafortunadamente, esa solución presenta no soloproblemas mecánicos funcionales, descritos en la literatura como problemas de vaciado y fuga,peo también problemas de orden biológica (como ejemplo pérdida ósea, debido a la absorciónpor el intestino de substancias que necesitan ser eliminadas del organismo).A través de la solicitación de la comunidad urológica del Hospital Clínico de Barcelona y con suexperiencia en modelos numéricos para estructuras biomédicas, el Centro de MétodosNuméricos en Ingeniería (CIMNE) ha tenido la iniciativa de proporcionar actividadinvestigadora de la mecánica de la vejiga urinaria y de la simulación de interacción fluidoestructurapara reproducir el llenado y vaciado de ese órgano con la orina.La simulación de la vejiga humana por el Método de los Elementos Finitos (FEM) y un completoentendimiento de la mecánica de ese órgano y de su interacción con la orina dará la posibilidadde proponer mejora en la geometría y de analizar materiales para la solución artificial en caso deremplazamiento de la vejiga.Para lograr ese objetivo, primeramente procedemos a una revisión bibliográfica de los modelosmatemáticos del aparato urinario y un estudio comprehensivo de la fisiología y dinámica de lavejiga. Presentamos una revisión de las principales estructuras urológicas, riñón, uréter y uretra.Las estructuras anexas también son consideradas para entender las condiciones de contorno delproblema estudiado.Posteriormente, proponemos el modelo constitutivo para estudiar la vejiga urinaria humana. Elcomportamiento del musculo detrusor durante llenado y vaciado de la vejiga con orina, suhabilidad de retención de orina a baja presión debe ser correctamente representada por mediode la implementación de un modelo constitutivo no-lineal. El modelo matemático necesitarepresentar las variables mecánicas que gobiernan ese órgano, y también las propiedades de laorina. El comportamiento no-lineal de tejidos vivos es implementado y validado con ejemplos dela literatura. La propiedad quasi-incompressible de la orina y las ecuaciones Navier-Stokes sonconsideradas para análisis del fluido.Para representar la geometría de la vejiga, implementamos un modelo computacional 3D apartir de imágenes de tomografía computadorizada de un cadáver adulto. Los datos son tratadospara considerar las condiciones de contorno. Hemos construido dos modelos de malla: ummallado com tetrahedos de quatro nodos y outro mallado com elementos de membrana de tresnodos.El esquema utilizado para calcular la interacción fluido-estructura debe ser adecuado paramateriales de densidad muy parecidas. La análisis numérica de llenado y vaciado de la vejigahumana es validada con testes urodinámicos estandarizados.La parte final de la tesis, presentamos una simulación de una neo-vejiga, siendo el primer pasopara representar numéricamente materiales artificiales para remplazamiento de la vejiga

    La propuesta de una vejiga artificial es un obstáculo a trasponer. El cáncer de vejiga está entre los casos más frecuentes de enfermedades oncológicas en Estados Unidos y Europa. Ese cáncer es considerado un problema médico importante una vez que esa enfermedad presenta altas tasas de re-ocurrencia, muchas veces llevando a la remoción del órgano. La solución más sofisticada para remplazar ese órgano es la vejiga ileal, que consiste en una neovejiga hecha de tejido intestinal del enfermo. Desafortunadamente, esa solución presenta no solo problemas mecánicos funcionales, descritos en la literatura como problemas de vaciado y fuga, peo también problemas de orden biológica (como ejemplo pérdida ósea, debido a la absorción por el intestino de substancias que necesitan ser eliminadas del organismo). A través de la solicitación de la comunidad urológica del Hospital Clínico de Barcelona y con su experiencia en modelos numéricos para estructuras biomédicas, el Centro de Métodos Numéricos en Ingeniería (CIMNE) ha tenido la iniciativa de proporcionar actividad investigadora de la mecánica de la vejiga urinaria y de la simulación de interacción fluidoestructura para reproducir el llenado y vaciado de ese órgano con la orina. La simulación de la vejiga humana por el Método de los Elementos Finitos (FEM) y un completo entendimiento de la mecánica de ese órgano y de su interacción con la orina dará la posibilidad de proponer mejora en la geometría y de analizar materiales para la solución artificial en caso de remplazamiento de la vejiga. Para lograr ese objetivo, primeramente procedemos a una revisión bibliográfica de los modelos matemáticos del aparato urinario y un estudio comprehensivo de la fisiología y dinámica de la vejiga. Presentamos una revisión de las principales estructuras urológicas, riñón, uréter y uretra. Las estructuras anexas también son consideradas para entender las condiciones de contorno del problema estudiado. Posteriormente, proponemos el modelo constitutivo para estudiar la vejiga urinaria humana. El comportamiento del musculo detrusor durante llenado y vaciado de la vejiga con orina, su habilidad de retención de orina a baja presión debe ser correctamente representada por medio de la implementación de un modelo constitutivo no-lineal. El modelo matemático necesita representar las variables mecánicas que gobiernan ese órgano, y también las propiedades de la orina. El comportamiento no-lineal de tejidos vivos es implementado y validado con ejemplos de la literatura. La propiedad quasi-incompressible de la orina y las ecuaciones Navier-Stokes son consideradas para análisis del fluido. Para representar la geometría de la vejiga, implementamos un modelo computacional 3D a partir de imágenes de tomografía computadorizada de un cadáver adulto. Los datos son tratados para considerar las condiciones de contorno. Hemos construido dos modelos de malla: un mallado con tetrahedos de cuatro nodos y otro mallado con elementos de membrana de tres nodos. El esquema utilizado para calcular la interacción fluido-estructura debe ser adecuado para materiales de densidad muy parecidas. El análisis numérico de llenado y vaciado de la vejiga humana es validada con tests urodinámicos estandarizados. La parte final de la tesis, presentamos una simulación de una neo-vejiga, siendo el primer paso para representar numéricamente materiales artificiales para remplazamiento de la vejiga.

    The proposal of an artificial bladder is still a challenge to overcome. Bladder cancer is among the most frequent cases of oncologic diseases in United States and Europe. It is considered a major medical problem once this disease has high rates of reoccurrence, often leading to the extirpation of this organ. The most refined solution to replace this organ is the ileal bladder, which consists of a neobladder made of the patient’s intestinal tissue. Unfortunately this solution presents not only functional mechanical problems, described on the literature as voiding and leaking problems, but also biological ones (i.e. bone loss, given the absorption by the intestine of substances that should be eliminated from the organism). Urged by the urological community of the Hospital Clinic de Barcelona and backgrounded by its experience in the numerical simulation of biomedical structures, the Center of Numerical Methods in Engineering (CIMNE) had the initiative to provide the research of the mechanics of the urinary bladder and the simulation of fluid structure interaction (FSI) to account for the filling and voiding of this organ with urine. The Finite Element Method (FEM) simulation of the real bladder and the comprehensive understanding of the mechanics of this organ and its interaction with urine will give the possibility to propose geometrical improvements and study suitable materials for an artificial solution to address the cases on which the bladder needs to be removed. To reach this goal, first we proceeded to the bibliographic review of mathematical models of the urinary apparatus and to a comprehensive study of the physiology and dynamics of the bladder. A review of the major urological structures, kidney, ureter and urethra, takes place. To consider boundary conditions other surrounding structures to the urinary system are also studied. In the second part of the thesis, we propose the numerical model to study the human urinary bladder. The behavior of the detrusor muscle during filling and voiding of the bladder with urine and its ability to promote the storage of urine under low pressure need to be accurately represented, requiring the implementation of a non-linear constitutive model. The mathematical model needs to be capable to simulate the mechanical variables that govern this organ and the properties of the urine. The nonlinear behavior of living tissues is implemented and validated with examples from the literature. The quasi-incompressibility property of urine and the navierstokes equations for the fluid are taken into account. The geometry of the bladder needs to be taken into account, and the implementation of a 3D computational model obtained from the computerized tomography of a cadaver male adult is considered. The data has been treated to consider boundary conditions. Two models have been conceived: one meshed with four nodes tetrahedral and another meshed with shell elements. FSI must work for the simulation of filling and voiding of the bladder. Due to the close densities of the materials the scheme used to solve fluid-structure needs to be carefully selected. The proposed numerical model and the filling and voiding analysis are finally validated with standardized urodynamic tests. The final part of the thesis, the simulation of a neobladder is presented, being the first step to simulate numerically artificial materials for bladder replacement.

  • Modelización numérica del comportamiento constitutivo del daño local y global y su correlación con la evolución de las frecuencias naturales en estructuras de hormigón reforzado  Open access

     Paredes Lopez, Jairo Andrés
    Defense's date: 2013-11-11
    Universitat Politècnica de Catalunya
    Theses

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    Esta tesis surge de la necesidad de establecer un método racional y práctico para identificar, a través del cambio de las frecuencias naturales , el daño en estructuras de hormigón armado. Por lo que se desarrolla un nuevo modelo constitutivo de daño diferenciado con dos variables internas de daño utilizando una única superficie de discontinuidad para tracción, compresión y cortante; asimismo, se plantea un procedimiento numérico para el cálculo de las frecuencias naturales con sus formas modales de vibración para diferentes estados de daño de estructuras de hormigón armado; se presenta una metodología para correlacionar daño global y frecuencias naturales . Esta tesis se desarrollará en el marco del análisis de estructuras y la mecánica computacional, particularmente, del análisis de materiales compuestos utilizando la teoría de mezclas serie/paralelo. Los resultados numéricos obtenidos se han comparado con resultados experimentales y numéricos obtenidos de la literatura, se ha observado buenos ajustes de los resultados.

    Esta tesis surge de la necesidad de establecer un método racional y práctico para identificar, a través del cambio de las frecuencias naturales , el daño en estructuras de hormigón armado. Por lo que se desarrolla un nuevo modelo constitutivo de daño diferenciado con dos variables internas de daño utilizando una única superficie de discontinuidad para tracción, compresión y cortante; asimismo, se plantea un procedimiento numérico para el cálculo de las frecuencias naturales con sus formas modales de vibración para diferentes estados de daño de estructuras de hormigón armado; se presenta una metodología para correlacionar daño global y frecuencias naturales . Esta tesis se desarrollará en el marco del análisis de estructuras y la mecánica computacional, particularmente, del análisis de materiales compuestos utilizando la teoría de mezclas serie/paralelo. Los resultados numéricos obtenidos se han comparado con resultados experimentales y numéricos obtenidos de la literatura, se ha observado buenos ajustes de los resultados

    This thesis emerges from the need to establish a rational and smart method to estimate the global damage through changes on eigenfrequency of concrete structures. Therefore, a new constitutive damage model is developed with two scalar inner variables and using only one surface of discontinuity to traction, compression and shear. Additionally, a numerical process has been proposed to calculate eigenfrequencies and eigenvectors of concrete structure with different levels of damage. A methodology to correlation ship between global damage and changes on e1genfrequencies has been proposed. This thesis is based on structural analysis and computational mechanics and, particularly, on analysis of composite materials using serial/parallel mix theory. The numerical results obtained in this thesis is have been compared with experimental and numerical results obtained of literature, and can be seen a good fit.

  • MODELO ANALÍTICO NUMÉRICO PARA EL ESTUDIO Y OPTIMIZACIÓN DE PLACAS GRUESAS LAMINADAS

     Rango, Rita-Fernanda
    Defense's date: 2013-03-26
    Universidad Nacional de Salta (UNSa)- Argentina.
    Theses

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  • Diseño óptimo multi-objetivo y ecológico de materiales con estructuras compuestas con nanotubos de carbono

     Morillo, Carlos; Lee, Dong Seop; Bugeda Castelltort, Gabriel; Oller Martinez, Sergio Horacio; Oñate Ibáñez de Navarra, Eugenio
    Congreso de Métodos Numéricos en Ingeniería
    Presentation's date: 2013-06-26
    Presentation of work at congresses

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  • Multi-objective green design optimization of carbon nanotube composite structures

     Morillo, Carlos; Lee, Dong Seop; Bugeda Castelltort, Gabriel; Oller Martinez, Sergio Horacio; Oñate Ibáñez de Navarra, Eugenio
    International Conference on Computational Methods for Coupled Problems in Science and Engineering
    Presentation's date: 2013-06-19
    Presentation of work at congresses

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  • Dimensionado sísmico de edificios porticados de hormigón armado mediante factores de amplificación con base en energía

     Vielma Pérez, Juan Carlos; Barbat Barbat, Horia Alejandro; Oller Martinez, Sergio Horacio
    Hormigon y acero
    Date of publication: 2012
    Journal article

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    El proyecto sismorresistente de estructuras actual se realiza mediante una serie de prescripciones normativas que persiguen garantizar su adecuado comportamiento. Los procedimientos actuales de análisis se realizan utilizando el comportamiento elástico, aplicando los factores de reducción de respuesta para obtener fuerzas sísmicas equivalentes, representativas del comportamiento inelástico que pueden alcanzar las estructuras al ser sometidas a la acción de sismos fuertes. A partir de los resultados del análisis elástico se obtienen los desplazamientos inelásticos, amplificados mediante factores que son función de los factores de reducción; sin embargo, se ha observado una amplia variación en los valores de los factores de amplificación prescritos en las normas a nivel mundial, por lo que se justifica profundizar en el estudio de dichos factores. En este trabajo se presenta un procedimiento de dimensionado sísmico con base en la respuesta no lineal. El procedimiento es aplicado a un conjunto de edificios regulares de hormigón armado de diferentes alturas, proyectados para niveles altos de amenaza sísmica y es evaluado aplicando análisis dinámico no lineal para tres Estados Límite, correlacionado con tres umbrales de daño que se definen a través de las derivas de planta. Los resultados demuestran que el procedimiento es adecuado para realizar el dimensionado sísmico de edificios, proporcionando al proyectista criterios de evaluación más cónsonos con las características de los edificios y de la amenaza sísmica.

  • An inverse approach for the mechanical characterisation of vascular tissues via a generalised rule of mixtures

     Bellomo, Facundo; Oller Martinez, Sergio Horacio; Nallim, Liz G.
    Computer methods in biomechanics and biomedical engineering
    Date of publication: 2012-12
    Journal article

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    Mechanical factors such as stresses and strains play a major role in the growth and remodelling of soft biological tissues. The main constituents of tissue undergo different processes reacting to mechanical stimulus. Thereby, the characterisation of growth and remodelling requires an accurate estimation of the stresses and strains of their main components. Many soft tissues can be considered as composite materials and can be analysed using an appropriate rule of mixtures. Particularly, arterial tissue can be modelled as an isotropic soft matrix reinforced with preferentially oriented collagen fibres. An inverse approach to obtain the mechanical characterisation of each main component is proposed in this work. The procedure is based on a rule of mixtures raised in a finite deformation framework and generalised to include kinematics and compatibility equations for serial–parallel behaviour. This methodology allows obtaining the stress–strain relationship of the components fitting experimental data.

  • Advanced models for finite element analysis of composite materials

     Oller Martinez, Sergio Horacio; Oñate Ibáñez de Navarra, Eugenio
    Date of publication: 2012
    Book chapter

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    Written by prominent international experts from industry and academia, the Wiley Encyclopedia of Composites, Second Edition presents over 265 new and revised articles addressing the new technological advances in properties, processing, formulation, design, analysis, evaluation, manufacture, testing, and reliability of composites. The entire range of industrial applications of composites is covered.

  • Estudio numérico-experimental de la interfaz hormigón-epoxi-FRP para una estructura reforzada sometida a doble corte

     Molina, Maritzabel; Cruz Solis, Juan Jose; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Gil Espert, Lluis
    Revista internacional de métodos numéricos para cálculo y diseño en ingeniería
    Date of publication: 2012-02
    Journal article

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  • Numerical-experimental study of the FRP-epoxy-concrete interface for reinforced structures under double shear

     Molina Herrera, Maritzabel; Cruz Solis, Juan Jose; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Gil Espert, Lluis
    Revista internacional de métodos numéricos para cálculo y diseño en ingeniería
    Date of publication: 2012
    Journal article

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  • Nonlinear homogenization techniques to solve masonry structures problems

     Quinteros, Ricardo D.; Oller Martinez, Sergio Horacio; Nallim, Liz G.
    Composite structures
    Date of publication: 2012-01
    Journal article

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  • A constitutive model for tissue adaptation: necrosis and stress driven growth

     Bellomo, Facundo; Armero, Francisco; Nallim, Liz G.; Oller Martinez, Sergio Horacio
    Mechanics research communications
    Date of publication: 2012-06
    Journal article

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  • Study and prediction of the mechanical performance of a nanotube-reinforced composite

     Otero, Fermin; Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Salomon, Ramon Omar
    Composite structures
    Date of publication: 2012-09
    Journal article

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  • Multilayered composite structure design optimisation using distributed/parallel multi-objective evolutionary algorithms

     Lee, Dong Seop; Morillo Carbonell, Carlos; Bugeda Castelltort, Gabriel; Oller Martinez, Sergio Horacio; Oñate Ibáñez de Navarra, Eugenio
    Composite structures
    Date of publication: 2012-02
    Journal article

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  • Simple and accurate two-noded beam element for composite laminated beams using a refined zigzag theory

     Oñate Ibáñez de Navarra, Eugenio; Eijo, A.; Oller Martinez, Sergio Horacio
    Computer methods in applied mechanics and engineering
    Date of publication: 2012-03
    Journal article

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  • Dynamical analysis of long fiber-reinforced laminated plates with elastically restrained edges

     Bellomo, Facundo; Quinteros, Ricardo D.; Oller Martinez, Sergio Horacio; Nallim, Liz G.
    Advances in Acoustics and Vibration
    Date of publication: 2012
    Journal article

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  • Puentes peatonales sostenibles (superbam)

     Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier
    Participation in a competitive project

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  • Regularización de la energía de fractura utilizando un modelo de fisura distribuida de Hillerborg y daño isotrópico mediante un método sin malla de puntos finitos

     Pérez Pozo, Luis; Valdivia, Fernado; Oller Martinez, Sergio Horacio
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-15
    Presentation of work at congresses

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    El fenómeno de fractura en materiales heterogéneos cuasi-frágiles ha sido estudiado extensivamente con modelación numérica basada en el Método de Elementos Finitos (MEF), mostrando dependencias en la orientación y tamaño de la malla en los resultados. Es por eso que el uso de técnicas sin malla junto con modelos de fisura distribuida surgen como alternativas a estas dependencias. En este trabajo, un modelo de fisura distribuida aplicado al fenómeno de daño isotrópico mediante un método sin malla de Puntos Finitos es presentado. Se propone el uso de una longitud geométrica dada por la dirección de los esfuerzos principales en reemplazo de una longitud característica, la cual se basa en el modelo de Fisura Ficticia de Hillerborg. El criterio de fluencia de Rankine y un esquema iterativo incremental de Newton-Raphson son usados para predecir el comportamiento no-lineal en la zona fracturada del material.

  • Simulación numérica del crecimiento hipertrófico de tejidos biológicos

     Bellomo, Facundo; Oller Martinez, Sergio Horacio; Nallim, Liz G.
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-15
    Presentation of work at congresses

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    El crecimiento de los tejidos biológicos blandos tiene un papel fundamental en una serie de procesos normales y patológicos de gran incidencia en la salud humana. Algunos de los factores que regulan estos procesos en los tejidos biológicos son fundamentalmente mecánicos, de allí la importancia del estudio de estos fenómenos en el marco de una formulación que permita estimar los campos de tensión y deformación, así como la interrelación con los fenómenos de crecimiento. En general, los modelos de crecimiento publicados hasta la fecha consideran el estímulo mecánico para el crecimiento a partir de las tensiones instantáneas a que está sometido el tejido en un determinado instante. Estos modelos, sin embargo, no resultan adecuados para el caso del crecimiento hipertrófico de tejidos biológicos blandos. El proceso de hipertrofia consiste en un incremento en el volumen del tejido, que se genera cuando las fibras dañadas del mismo son reparadas y por lo tanto esta asociado al daño que sufren las mismas. Este proceso es el responsable del crecimiento del tejido muscular, de allí la importancia de su estudio con miras a su aplicación en el estudio de metodologías de entrenamiento de alto rendimiento y patologías relacionadas con la hipertrofia muscular, como por ejemplo la hipertrofia cardiaca. Para la modelación del tejido se propone el empleo de un modelo constitutivo basado en la teoría de mezclas generalizada considerando crecimiento isótropo. En el modelo el crecimiento es controlado por una variable interna de daño reversible que constituye el estímulo mecánico para la reparación de las fibras del tejido. La capacidad de reparación del tejido y el crecimiento hipertrófico asociado dependerán, a su vez, de la capacidad del metabolismo para llevar adelante estos procesos. Esto se tiene en cuanta en el modelo a través de una variable de disponibilidad biológica. Finalmente, se presentan ejemplos de validación que permiten demostrar que el modelo resulta adecuado para el estudio del crecimiento hipertrófico, considerando la acción simultánea de los campos biológico y mecánico.

  • Simulación numérica del comportamiento mecánico en vivo de tejidos biológicos blandos

     Bellomo, Facundo Javier
    Defense's date: 2012-03-30
    Universidad Nacional de Salta
    Theses

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  • Formulación de elementos finitos para vigas de sección abierta en laminados compuestos

     Vargas Mendoza, Pablo Enrique
    Defense's date: 2012-01-27
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Numerial modelling based on the multiscale homogenization theory. Application in composite materials and structures  Open access

     Badillo Almaraz, Hiram
    Defense's date: 2012-04-16
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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    A multi-domain homogenization method is proposed and developed in this thesis based on a two-scale technique. The method is capable of analyzing composite structures with several periodic distributions by partitioning the entire domain of the composite into substructures making use of the classical homogenization theory following a first-order standard continuum mechanics formulation. The need to develop the multi-domain homogenization method arose because current homogenization methods are based on the assumption that the entire domain of the composite is represented by one periodic or quasi-periodic distribution. However, in some cases the structure or composite may be formed by more than one type of periodic domain distribution, making the existing homogenization techniques not suitable to analyze this type of cases in which more than one recurrent configuration appears. The theoretical principles used in the multi-domain homogenization method were applied to assemble a computational tool based on two nested boundary value problems represented by a finite element code in two scales: a) one global scale, which treats the composite as an homogeneous material and deals with the boundary conditions, the loads applied and the different periodic (or quasi-periodic) subdomains that may exist in the composite; and b) one local scale, which obtains the homogenized response of the representative volume element or unit cell, that deals with the geometry distribution and with the material properties of the constituents. The method is based on the local periodicity hypothesis arising from the periodicity of the internal structure of the composite. The numerical implementation of the restrictions on the displacements and forces corresponding to the degrees of freedom of the domain's boundary derived from the periodicity was performed by means of the Lagrange multipliers method. The formulation included a method to compute the homogenized non-linear tangent constitutive tensor once the threshold of nonlinearity of any of the unit cells has been surpassed. The procedure is based in performing a numerical derivation applying a perturbation technique. The tangent constitutive tensor is computed for each load increment and for each iteration of the analysis once the structure has entered in the non-linear range. The perturbation method was applied at the global and local scales in order to analyze the performance of the method at both scales. A simple average method of the constitutive tensors of the elements of the cell was also explored for comparison purposes. A parallelization process was implemented on the multi-domain homogenization method in order to speed-up the computational process due to the huge computational cost that the nested incremental-iterative solution embraces. The effect of softening in two-scale homogenization was investigated following a smeared cracked approach. Mesh objectivity was discussed first within the classical one-scale FE formulation and then the concepts exposed were extrapolated into the two-scale homogenization framework. The importance of the element characteristic length in a multi-scale analysis was highlighted in the computation of the specific dissipated energy when strain-softening occurs. Various examples were presented to evaluate and explore the capabilities of the computational approach developed in this research. Several aspects were studied, such as analyzing different composite arrangements that include different types of materials, composites that present softening after the yield point is reached (e.g. damage and plasticity) and composites with zones that present high strain gradients. The examples were carried out in composites with one and with several periodic domains using different unit cell configurations. The examples are compared to benchmark solutions obtained with the classical one-scale FE method.

    En esta tesis se propone y desarrolla un método de homogeneización multi-dominio basado en una técnica en dos escalas. El método es capaz de analizar estructuras de materiales compuestos con varias distribuciones periódicas dentro de un mismo continuo mediante la partición de todo el dominio del material compuesto en subestructuras utilizando la teoría clásica de homogeneización a través de una formulación estándar de mecánica de medios continuos de primer orden. La necesidad de desarrollar este método multi-dominio surgió porque los métodos actuales de homogeneización se basan en el supuesto de que todo el dominio del material está representado por solo una distribución periódica o cuasi-periódica. Sin embargo, en algunos casos, la estructura puede estar formada por más de un tipo de distribución de dominio periódico. Los principios teóricos desarrollados en el método de homogeneización multi-dominio se aplicaron para ensamblar una herramienta computacional basada en dos problemas de valores de contorno anidados, los cuales son representados por un código de elementos finitos (FE) en dos escalas: a) una escala global, que trata el material compuesto como un material homogéneo. Esta escala se ocupa de las condiciones de contorno, las cargas aplicadas y los diferentes subdominios periódicos (o cuasi-periódicos) que puedan existir en el material compuesto; y b) una escala local, que obtiene la respuesta homogenizada de un volumen representativo o celda unitaria. Esta escala se ocupa de la geometría, y de la distribución espacial de los constituyentes del compuesto así como de sus propiedades constitutivas. El método se basa en la hipótesis de periodicidad local derivada de la periodicidad de la estructura interna del material. La implementación numérica de las restricciones de los desplazamientos y las fuerzas derivadas de la periodicidad se realizaron por medio del método de multiplicadores de Lagrange. La formulación incluye un método para calcular el tensor constitutivo tangente no-lineal homogeneizado una vez que el umbral de la no-linealidad de cualquiera de las celdas unitarias ha sido superado. El procedimiento se basa en llevar a cabo una derivación numérica aplicando una técnica de perturbación. El tensor constitutivo tangente se calcula para cada incremento de carga y para cada iteración del análisis una vez que la estructura ha entrado en el rango no-lineal. El método de perturbación se aplicó tanto en la escala global como en la local con el fin de analizar la efectividad del método en ambas escalas. Se lleva a cabo un proceso de paralelización en el método con el fin de acelerar el proceso de cómputo debido al enorme coste computacional que requiere la solución iterativa incremental anidada. Se investiga el efecto de ablandamiento por deformación en el material usando el método de homogeneización en dos escalas a través de un enfoque de fractura discreta. Se estudió la objetividad en el mallado dentro de la formulación clásica de FE en una escala y luego los conceptos expuestos se extrapolaron en el marco de la homogeneización de dos escalas. Se enfatiza la importancia de la longitud característica del elemento en un análisis multi-escala en el cálculo de la energía específica disipada cuando se produce el efecto de ablandamiento. Se presentan varios ejemplos para evaluar la propuesta computacional desarrollada en esta investigación. Se estudiaron diferentes configuraciones de compuestos que incluyen diferentes tipos de materiales, así como compuestos que presentan ablandamiento después de que el punto de fluencia del material se alcanza (usando daño y plasticidad) y compuestos con zonas que presentan altos gradientes de deformación. Los ejemplos se llevaron a cabo en materiales compuestos con uno y con varios dominios periódicos utilizando diferentes configuraciones de células unitarias. Los ejemplos se comparan con soluciones de referencia obtenidas con el método clásico de elementos finitos en una escala.

  • Evaluación del daño por impacto en laminados de material compuesto mediante la respuesta dinámica

     Pérez Martínez, Marco Antonio
    Defense's date: 2012-02-06
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Simulación de los materiales compuestos como refuerzo en estructuras de hormigón armado

     Molina Herrera, Maritzabel
    Defense's date: 2012-01-12
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Evaluación del daño por impacto en laminados de material compuesto mediante la respuesta dinámica

     Pérez Martínez, Marco Antonio; Gil Espert, Lluis; Oller Martinez, Sergio Horacio
    Date of publication: 2012-04-23
    Book

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  • The Quadrants Method: a procedure to evaluate the seismic performance of existing buildings

     Vielma Pérez, Juan Carlos; Martínez, Y; Barbat Barbat, Horia Alejandro; Oller Martinez, Sergio Horacio
    World Conference on Earthquake Engineering
    Presentation's date: 2012-09-25
    Presentation of work at congresses

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    In this work a new simple procedure for the evaluation of the seismic performance is formulated. It combines the results of non-linear static analysis with a specific Limit State defined by inter-storey drift-based damage threshold and the seismic demand obtained from the inelastic design spectrum. With both values it is possible to define four zones in the capacity curve which characterizes four different seismic performances. The procedure is used to evaluate two reinforced concrete framed buildings, the first one consist in a typical lowrise building designed according to current Venezuelan codes; the second one is a four-storey building designed according to older code, whose had been damaged by fire. Results shown both cases do not meet the Quadrants Method criterion then they need to be redesigned. Redesigned buildings were submitted to a non-linear dynamic analysis, representative of three hazard levels associated with three Limit States. These redesigned buildings met all the objectives associated with the hazard levels, showing the efficiency of the method for the rapid evaluation of the seismic performance of existing buildings.

    In this work a new simple procedure for the evaluation of the seismic performance is formulated. It combines the results of non-linear static analysis with a specific Limit State defined by inter-storey drift-based damage threshold and the seismic demand obtained from the inelastic design spectrum. With both values it is possible to define four zones in the capacity curve which characterizes four different seismic performances. The procedure is used to evaluate two reinforced concrete framed buildings, the first one consist in a typical lowrise building designed according to current Venezuelan codes; the second one is a four-storey building designed according to older code, whose had been damaged by fire. Results shown both cases do not meet the Quadrants Method criterion then they need to be redesigned. Redesigned buildings were submitted to a non-linear dynamic analysis, representative of three hazard levels associated with three Limit States. These redesigned buildings met all the objectives associated with the hazard levels, showing the efficiency of the method for the rapid evaluation of the seismic performance of existing buildings.

  • Advanced hybrid composite structure design optimisation using robust multi-objective optimisation platform (RMOP)

     Lee, Dong Seop; Morillo Carbonell, Carlos; Oller Martinez, Sergio Horacio; Bugeda Castelltort, Gabriel; Oñate Ibáñez de Navarra, Eugenio
    International Conference on Mechanics of Nano, Micro and Macro Composite Structures
    Presentation's date: 2012-06
    Presentation of work at congresses

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  • Simulación numérica del flujo de un tramo fluvial con una turbina de paso situada en su lecho y los efectos en el comportamiento de su lámina libre

     Oller Aramayo, Sergio A.; Bateman Pinzon, Allen; Nallim, Liz G.; Oller Martinez, Sergio Horacio
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-14
    Presentation of work at congresses

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    Las turbinas de paso o WCT (Water Current Turbines) abren nuevas y mayores posibilidades, con grandes ventajas en cuanto al aprovechamiento hidroeléctrico. Éstas evitan las construcciones de costosas presas y reducen considerablemente el impacto medioambiental que producen otras soluciones de aprovechamiento energético. Pero a su vez esta solución plantea una serie de nuevos retos tecnológicos, debido a sus diseños sin todavía ningún tipo de estandarización y pocos antecedentes en su utilización. Además, a todo esto hay que agregar la complejidad que añade el estudio del comportamiento del flujo del río donde deben instalarse. El modelo que se analiza en el presente trabajo representa un tramo fluvial con una turbina de paso axial situada en su lecho. Dicho modelo se analiza mediante la técnica de simulación numérica CFD (Computational Fluid Dynamics) y la turbina de paso se representa introduciendo en el cauce del río un bloque constituido por un medio continuo poroso para representar las perturbaciones que esta introduce y sus intercambios energéticos con el flujo del cauce. En este artículo se analizan las velocidades alcanzadas en las distintas zonas del río, presiones, líneas de corriente, y el comportamiento de la lámina libre que resulte de la presencia de la turbina representada a través de un bloque de medio poroso. Con este trabajo se estudia un eslabón importante en la cadena de desarrollos necesarios para el diseño y factibilidad de aplicación y puesta en marcha de una turbina de paso que está actualmente en desarrollo por los autores. (Oller et al., Revista Iberoamericana de Ingeniería Mecánica, Vol.16 Nº1 pp. 03-16 (2012)).

  • Access to the full text
    Modelling viscoelastic behaviour of carbón nanotube-reinforced thermo-plastics  Open access

     Otero Gruer, Fermin Enrique; Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Salomon, Ramon Omar
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-15
    Presentation of work at congresses

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    Carbon nanotubes (CNTs), since their discovery by Lijima (S. Lijima, Nature, 354:56-58 (1991)), are considered a new generation of reinforcement. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties. There are two main nanotube types: single wall nanotubes (SWCNTs), which are made of a single wall tube; and multiwall nanotubes (MWCNTs), which consist in several concentric walls, one inside the other. A key factor for the reinforcement efficiency in a composite it is the interface bonding between the CNTs and the matrix. This work presents a new constitutive model to predict the mechanical performance of composites made of a thermo-plastic matrix reinforced with CNTs. The model takes into account explicitly the mechanical contribution of the interface between the matrix and the CNTs (F. Otero et. al., Comp Structures, 94:2920-2930 (2012)). The constitutive model is based in the mixing theory, which obtains the composite performance from the response of each constituent component, each one simulated with its own constitutive law. The model has been implemented into an in-house FEM code: PLCd. As an application example, this code is used to predict the mechanical properties of a straight beam with different material configurations. In this case, a viscoelastic constitutive model is proposed for the polymeric matrix. The viscous response within the elastic range of the materials is studied. This response shows a high capacity of energy dissipation in composites reinforced with MWCNTs.

  • Numerical modeling of a cervical spine discectomy

     Comellas Sanfeliu, Ester; Oller Martinez, Sergio Horacio; Poblete, José; Berenguer, Joan; Prats-Galino, Alberto
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-16
    Presentation of work at congresses

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    Cervical spine discectomy is a relatively common medical procedure which entails the surgical removal of a herniated intervertebral disc which is then replaced with an adequate prosthesis. Surgeons rely on their expertise to minimize the damage induced on the adjacent vertebrae and discs during this invasive procedure in order to reduce the patient's postsurgical distress. A typical cervical spine discectomy has been modelled and tested using the Finite Element Method (FEM) with the intention of contributing to better elucidate its immediate physical consequences on the vertebrae and intervertebral discs. Internal stresses, strains and damage levels can be obtained through the use of FE models, which can prove useful in improving surgical procedures or tailoring them to the need of particular patients. To this aim, a model of four cervical vertebrae with their corresponding discs has been built. Spinal ligaments, zygapophyseal joints and uncovertebral joints have also been included. The vertebrae have been modelled using a damage model whilst the intervertebral discs and ligaments have been treated as separate hyperelastic materials. Also, the nucleus and the annulus of the discs have been di erentiated. The problem has been solved following non-linear large deformation theory and considering prestress in the ligaments. The model's accuracy has been assessed through comparison of previously published results for di erent spinal movements (N. Kallemeyn et al., Med Eng Phys, 32(5):482-489 (2010)). Then, the model has been numerically tested for a load case representative of the discectomy procedure.

  • Advanced composite material simulation

     Oller Martinez, Sergio Horacio
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-13
    Presentation of work at congresses

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  • A comparative mechanical analysis of the effect caused by artificial and real induced interlaminar damage in composite laminates

     Pérez Martínez, Marco Antonio; Gil Espert, Lluis; Oller Martinez, Sergio Horacio
    International Conference on Experimental Mechanics
    Presentation's date: 2012-07-24
    Presentation of work at congresses

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  • Non-destructive evaluation of low velocity impact damage in composite laminates using dynamic response

     Pérez Martínez, Marco Antonio; Gil Espert, Lluis; Oller Martinez, Sergio Horacio
    International Conference on Mechanics of Nano, Micro and Macro Composite Structures
    Presentation's date: 2012-06-19
    Presentation of work at congresses

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  • Modelo de degradación diferenciada para materiales compuestos

     Quinteros, Ricardo D.; Oller Martinez, Sergio Horacio; Nallim, Liz G.
    Congreso Argentino de Mecánica Computacional
    Presentation's date: 2012-11-16
    Presentation of work at congresses

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    En este trabajo se presenta la formulación y validación de un modelo de degradación elástica diferenciado. El modelo propuesto permite degradar en forma diferenciada la parte volumétrica y desviadora del comportamiento constitutivo del material y está basado en una generalización del modelo de degradación simple de Kachanov. De esta manera, el modelo resulta especialmente apropiado para simular el comportamiento de materiales friccionales. En particular, este modelo se aplica a los materiales componentes de una mampostería de ladrillos homogeneizada mediante una técnica particular ad hoc¸ que permite su tratamiento como material compuesto anisótropo, partiendo de las características geométricas y mecánicas de los materiales constituyentes. Para el tratamiento de la anisotropía, se usa la técnica de mapeo de espacios a través del concepto de espacio isótropo ficticio. La metodología planteada brinda una gran potencia de simulación pudiéndose también utilizar, si fuera necesario, otras formulaciones constitutivas diferentes para el comportamiento de los materiales componentes de la mampostería. El modelo constitutivo propuesto, junto con la técnica de homogeneización se implementa en un programa general de elementos finitos. Finalmente, se muestran los resultados obtenidos en ejemplos simples de validación del modelo y luego se presentan ejemplos de aplicación que muestran la respuesta no lineal del compuesto y su comparación con resultados publicados por otros autores.