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1 to 31 of 31 results
  • Reliability design methodology for confined high pressure inflatable structures

     Barbero, Ever; Sosa, Eduardo M.; Martinez Garcia, Xavier; Gutierrez, J.M.
    Engineering structures
    Date of publication: 2013-02-19
    Journal article

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    A design methodology for high pressure, inflatable structures is proposed. The inflatable structure may be partially confined inside large diameter conduits and tunnels. The design addresses the main structural requirements of the system, namely, fabric strength, geometric stability, and axial stability. The proposed design methodology is based on the concept of limit states. Load and resistance factors are identified for all the stochastic variables participating in the structural design equations. A formal methodology is used to estimate the load and resistance factors from known distributions of data for each of the stochastic variables. The concepts of basis values, coverage, and confidence are used along with the analytical treatment necessary to estimate the load and resistance factors. The analysis is applied to the cases of Normal, Log-normal, and Weibull distributions of data. Material characterization and data analysis are presented for fabric strength and friction coefficient between the inflatable and the confining conduit material. The system reliability is also evaluated.

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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.

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

     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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    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.

  • 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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    Numerical modelling of behaviour of carbon nanotube-reinforced composites  Open access

     Otero-Gruer, Fermín; Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Salomon, Ramon Omar
    International Conference on Computational Plasticity Fundamentals and Applications
    Presentation's date: 2011-09-08
    Presentation of work at congresses

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    Since their discovery by Lijima in 1991[1], carbon nanotubes (CNTs), are considered a new generation of reinforcement [2]. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties [3,4]. There are two main nanotube types: single wall nanotubes (SWNT) and multi wall nanotubes (MWNT). These last ones consist in several concentric walls, one inside the other. In a composite, one the most important factors that condition their mechanical performance is the interfacial tension between matrix and reinforcement. In general, the loads in a composite structure are introduced to the matrix and then are transferred to the reinforcement through the interface [5]. Therefore, the interface can be defined as the region, surrounding the reinforcement, where this stress transfer takes place. The properties of the composite depend on the properties of this region and its ability to transfer the load efficiently. This work proposes a new formulation to predict the mechanical properties and mechanical behaviour of nanotube-reinforced composites. The formulation is based on the mixing theory [6]. It obtains the behaviour of the composite from the mechanical performance of its constitutive materials: matrix, carbon-nanotube and the interface that bonds both of them.

  • Modelling the elastic behaviour of carbon nanotube-reinforced composites

     Otero-Gruer, Fermín; Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Salomon, Ramon Omar
    ECCOMAS Thematic Conference on Mechanical Response of Composites
    Presentation's date: 2011-09-22
    Presentation of work at congresses

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    Carbon nanotubes (CNTs), since their discovery by Lij ima in 1991 [1], are considered a new generation of reinforcement [2]. Their "nano" size structure makes them potentially free of defects, which provides them with excellent physical properties [3,4]. There are two main nanotube types: single wall nanotubes (SWNT), which are made of a single wall tube; and multiwall nanotubes (MWNT), which consist in several concentric walls, one inside the other. In a composite, one the most important factor is the interfacial tension between matrix and reinforcement. In general, the loads in a composite structure are introduced through the matrix and then are transferred to the reinforcement through the interface [5]. Therefore, the interface can be defined as the region surrounding the reinforcement where this stress transfer takes place. The properties of the composite depend on the properties of this regíon and its ability to transfer the load efficiently. This work proposes a new formulation to predict the mechanical properties of nanotube-reinforced composites. The formulation is based on the mixing theory [6]. It obtains the properties of the composite from the mechanical performance of its constitutive materials: matrix, carbon-nanotube and the interface that bonds both of them.

  • Modelling of behaviour of carbon nanotube-reinforced composites

     Otero, Fermin; Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Salomon, Ramon Omar
    Congreso Nacional de Materiales Compuestos
    Presentation's date: 2011-07-06
    Presentation of work at congresses

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  • Computationally optimized formulation for the simulation of composite materials and delamination failures

     Martinez Garcia, Xavier; Rastellini Canela, Fernando Gabriel; Oller Martinez, Sergio Horacio; Flores, Fernando G; Oñate Ibáñez de Navarra, Eugenio
    Composites Part B: Engineering
    Date of publication: 2011-03-01
    Journal article

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  • A discrete constitutive model for transverse and shear damage of symmetric laminates with arbitrary stacking sequence

     Barbero, Ever; Sgambitterra, Girolamo; Adumitroaie, Adi; Martinez Garcia, Xavier
    Composite structures
    Date of publication: 2011-01-01
    Journal article

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  • Simulation of delamination in composite materials using the serial/parallel mixing theory

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbero, Ever
    Revista internacional de métodos numéricos para cálculo y diseño en ingeniería
    Date of publication: 2011
    Journal article

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  • Valoración numérica del daño en estructuras de hormigón armado: análisis numérico de la reparación/ refuerzo con FRP de estructuras dañadas

     Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Molina, Maritzabel; Vielma, Juan Carlos; Martinez Garcia, Xavier
    Simposio Técnico Iberoamericano sobre Estructuras y Materiales para la Construcción
    Presentation's date: 2010-09-30
    Presentation of work at congresses

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    En este trabajo se presenta un procedimiento para evaluar la magnitud del daño local (en cada punto de la estructura) y el daño global en estructuras sometidas a acciones estáticas y dinámicas, con especial énfasis en el problema sísmico. Además de la formulación para la evaluación del daño, se introduce el concepto de refuerzo y reparación estructural mediante laminados compuestos de matriz epoxi con refuerzo de fibras de carbono (CFRP). Para está finalidad, se menciona la utilización de la teoría de mezclas, para componer un material compuesto a partir de sus componentes básicas. También se evalúa el daño en estas estructuras reforzadas y/o reparadas y se comenta la influencia de estas mejoras en la valoración del daño global de la estructura.

  • Numerical analisys of concrete structures strengthened with FRP using the serial/parallel mixing theory

     Molina Herrera, Maritzabel; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Martinez Garcia, Xavier
    Revista internacional de métodos numéricos para cálculo y diseño en ingeniería
    Date of publication: 2010
    Journal article

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  • Análisis numérico de estructuras de hormigón reforzadas con FRP por medio de la teoría de mezclas serie/paralelo

     Molina, Maritzabel; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Martinez Garcia, Xavier
    Revista internacional de métodos numéricos para cálculo y diseño en ingeniería
    Date of publication: 2010-05-01
    Journal article

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    Estudio de estructuras de hormigón reforzadas con FRP mediante la teoría de mezclas serie/paralelo  Open access

     Molina, Maritzabel; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Martinez Garcia, Xavier
    Revista internacional de ingeniería de estructuras
    Date of publication: 2009-09
    Journal article

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  • Numerical Simulation of Matrix Reinforced Composite Materials Subjected to Compression Loads

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio
    Archives of computational methods in engineering
    Date of publication: 2009-12
    Journal article

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  • A numerical procedure simulating RC structures reinforced with FRP using the serial/parallel mixing theory

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Rastellini Canela, Fernando Gabriel
    Computers & structures
    Date of publication: 2008-08
    Journal article

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  • Advanced composite material simulation

     Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Barbat Barbat, Horia Alejandro; Rastellini Canela, Fernando Gabriel
    Portuguese Conference on Fracture
    Presentation's date: 2008-02-13
    Presentation of work at congresses

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    A computational methodology is presented for modelling the material non-linear mechanical behaviour of composite structures made of FRP (Fibre-Reinforced Polymers) laminates. The model is based on the appropriate combination of the constitutive models of component materials, considered to behave as isolated continua, together with additional ‘closure equations’ that characterize the micromechanics of the composite from a morphological point of view. To this end, any appropriate constitutive model may be selected for each phase. Each component is modelled separately and the global response is obtained by assembling all contributions taking into account the interactions between components in a general phenomenological way. To model the behaviour of a single unidirectional (UD) composite lamina, a Serial-Parallel continuum approach has been developed assuming that components behave as parallel materials in the fibres alignment direction and as serial materials in orthogonal directions. Taking into account the internal morphology of the composite material, it is devised a strategy for decoupling and coupling component phases. This methodology [Rastellini 2006], named “compounding of behaviours”, allows to take into consideration local degradation phenomena (in the constituents materials), like plasticity, etc. in a coupled manner. It is based on the proper management of homogenous constitutive models, already available for each component. In this way, it is used all developments achieved in constitutive modelling of plain materials, what makes possible the transference of this technology to composites. A lamination theory complemented with the proposed UD model is employed to describe the mechanical behaviour of multidirectional laminates. A specific solution strategy for the general non linear case is proposed. It provides quick local and global convergences, what makes the model suitable for large scale structures. The model brings answers on the non-linear behaviour of composites, where classical micro-mechanics formulas are restricted to their linear elastic part. The methodology is validated through several numerical analyses and contrasted against experimental data and benchmark tests.

  • Study of delamination in composites by using the serial/parallel mixing theroy and a damage formulation

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbero, Ever
    Date of publication: 2008
    Book chapter

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  • Micro Mechanical Simulation of Composite Materials Using the Serial/Parallel Mixing Theory

     Martinez Garcia, Xavier
    Defense's date: 2008-06-20
    Department of Strength of Materials and Structural Engineering, Universitat Politècnica de Catalunya
    Theses

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    Advanced composite material simulation  Open access

     Oller Martinez, Sergio Horacio; Martinez Garcia, Xavier; Barbat Barbat, Horia Alejandro; Rastellini Canela, Fernando Gabriel
    Ciência e tecnologia dos materiais
    Date of publication: 2008-01
    Journal article

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    A computational methodology is presented for modeling the non-linear mechanical behavior of composite structures made of FRP (Fiber-Reinforced Polymers) laminates. The model is based on the appropriate combination of the constitutive models of compounding materials, considered to behave as isolated continua, together with additional “closure equations” that characterize the micro-mechanics of the composite from a morphological point of view. To this end, any appropriate constitutive model may be selected for each phase. Each component is modeled separately and the global response is obtained by assembling all contributions taking into account the interactions between components in a general phenomenological way. To model the behavior of a single uni-directional (UD) composite laminated, a Serial-Parallel continuum approach has been developed assuming that components behave as parallel materials in the fibers alignment direction and as serial materials in orthogonal directions. Taking into account the internal morphology of the composite material, it is devised a strategy for decoupling and coupling component phases. This methodology [Rastellini 2006], named "compounding of behavior", allows to take into consideration local non linear phenomenon in the compounding materials, like damage, plasticity, etc. in a coupled manner. It is based on the proper management of homogenous constitutive models, already available for each component. In this way, it is used all developments achieved in constitutive modeling for plain materials, what makes possible the transference of this technology to composites. A laminated theory complemented with the proposed UD model is employed to describe the mechanical behavior of multi-directional laminates. A specific solution strategy for the general non linear case is proposed. It provides quick local and global convergences, what makes the model suitable for large scale structures. The model brings answers on the non-linear behavior of composites, where classical micro-mechanics formulas are restricted to their linear elastic part. The methodology is validated through several numerical analyses and contrasted against experimental data and benchmark tests.

  • Study of delamination in composites by using the serial/parallel mixing theory and a damage formulation

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbero, Ever
    ECCOMAS Thematic Conference on Mechanical Response of Composites
    Presentation's date: 2007-09-13
    Presentation of work at congresses

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  • Numerical tool to study RC structures under seismic loads using fiber reinforced polymers

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro
    Intersections = Intersectii
    Date of publication: 2007
    Journal article

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  • Seismic upgrading of structures using fibre reinforced polymers

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Mata Almonacid, Pablo; Barbat Barbat, Horia Alejandro
    Date of publication: 2007-07
    Book chapter

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  • Seismic design and retrofit of structures using dissipative devices

     Barbat Barbat, Horia Alejandro; Oller Martinez, Sergio Horacio; Mata Almonacid, Pablo; Martinez Garcia, Xavier
    Date of publication: 2007-07
    Book chapter

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  • RC structures

     Barbat Barbat, Horia Alejandro; Oller Martinez, Sergio Horacio; Mata, Pablo; Martinez Garcia, Xavier
    Date of publication: 2007-07
    Book chapter

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  • Integration of knowledge on FRP retrofitted structures

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Mata, Pablo
    Date of publication: 2007-07
    Book chapter

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  • Herramienta numérica para el estudio de refuerzos de estructuras de hormigón mediante polímeros reforzados con fibras (FRP)

     Martinez Garcia, Xavier; Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro
    National Congress of Seismic Engineering
    Presentation of work at congresses

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  • Guidelines for seismic vulnerability reduction in the urban environment: LESSLOSS report no. 2007/04

     Oller Martinez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Mata Almonacid, Pablo; Martinez Garcia, Xavier
    Date of publication: 2007-07
    Book

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  • INNOVATIVE FINITE ELEMENT METHODS FOR NON LINEAR ANALYSIS OF COMPOSITE STRUCTURES

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

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