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• Análisis numérico de la reparación y refuerzo de estructuras con FRP

  S. Oller, M. Molina, J. Vielma-Perez, X. Martinez

  (2014). Omnia Publisher. Capítulo 11 - p. 261-291. Aplicaciones avanzadas de los materiales compuestos en la obra civil y la edificación, ISBN: 978-84-941872-9-2

  
  

  Abstract

  En este capítulo se presenta un procedimiento para evaluar la magnitud del daño local 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 epóxica con refuerzo de fibras de carbono. Para esta 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

  Abstract
  En este capítulo se presenta un procedimiento para evaluar la magnitud del daño local y el daño global en estructuras sometidas a acciones estáticas [...]

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• Study of Delamination in Composites by Using the Serial/Parallel Mixing Theory and a Damage Formulation

  X. Martinez, S. Oller, E. Barbero

  (2008). Mechanical response of composites. Ed. Pedro Camanho et al. pp. 119 - 140. Springer. ISBN 978-1-4020-8583-3

  
  

  Abstract

  This work presents a new procedure to deal with the delamination problem found in laminated composites, based in a continuum mechanics formulation. The procedure proposed obtains the composite constitutive performance with the Serial/Parallel mixing theory, developed by F. Rastellini. This theory characterizes composite materials by coupling the constitutive behaviour of the composite components, imposing an iso–strain relation among the components in the fibre (or parallel) direction and an iso–stress relation in the remaining directions (serial directions). The proposed procedure also uses a damage formulation to characterize the constitutive behaviour of matrix component in order to obtain the stress–strain performance of this material. With these two formulations, the delamination phenomenon is characterized naturally by the numerical simulation, being unnecessary the definition of special elements or computationally expensive techniques like the definition of contact elements or mesh separation. Matrix failure, as a result of the stress state found in it, leads to a reduction of the stiffness and strength capacity of the composite in its serial direction. This reduction provides a composite performance equivalent to what is found in a delaminated material. To prove the ability of the formulation proposed to solve delamination problems, the End Notch Failure test is numerically simulated and the results obtained are compared with experimental ones. The agreement found in the results with both simulations, numerical and experimental, validate the proposed methodology to solve the delamination problem.

  Abstract
  This work presents a new procedure to deal with the delamination problem found in laminated composites, based in a continuum mechanics formulation. The procedure proposed [...]

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• Nuevo Modelo Discreto Multiescala (DM) para análisis no-lineales de materiales compuestos

  S. Zaghi, X. Martinez, R. Rossi

  Materiales Compuestos (2018). Vol. 2 (4), pp. 70-79

  
  

  Abstract

  En los últimos años el estudio del comportamiento de los materiales a nivel microscópico ha aumentado significativamente en términos de diseño de materiales de altas prestaciones. A pesar de los recientes avances de ordenadores de elevado rendimiento, la aplicación de métodos numéricos multiescala para simular grandes estructuras aún requiere costes computacionales prohibitivos. Éste trabajo presenta un procedimiento capaz de predecir la respuesta mecánica no-lineal de los materiales compuestos con el fin de reducir el coste computacional necesario para el análisis numérico de estructuras complejas. La solución de la estructura macroscópica a través del método multiescala de primer orden (FE2) se sustituirá por un modelo discreto obtenido de un análisis del comportamiento de un Volumen Representativo Elemental (RVE) del material. A través de las definiciones de un parámetro de daño equivalente (deq), función del esfuerzo global en la microescala, se realizarán una serie de ensayos virtuales en control de deformación, almacenando el estado de tensión-deformación alcanzado por ciertos niveles de deq en una base de datos. Analizando la evolución de la fractura en los materiales compuestos se puede observar como el régimen no-lineal se alcanza solo en algunos elementos de la estructura. Es por ello que se plantea un procedimiento, el Discrete Multiscale Threshold Surface (DMTS), en el que el análisis del RVE sirve para obtener la superficie en la que empieza el daño (deq >0). Esta ley permite saber si para un determinado estado tenso-deformacional el material ha dañado, sin necesidad de resolver el micro-modelo. Una vez iniciado el daño, se propone de generar de forma adaptiva un RVE con el que obtener el comportamiento dañado del material. Luego, el método FE2 se utilizará solo en los puntos de integración que hayan dañado. Este trabajo demuestra que el método FE2 puede ser remplazado por un Modelo Discreto Multiescala, representativo del material compuesto, obteniendo mejoras computacionales significativas.

  Abstract
  En los últimos años el estudio del comportamiento de los materiales a nivel microscópico ha aumentado significativamente en términos de diseño [...]

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• Numerical analysis of interlaminar stresses in open-hole laminates under compression

  A. Solis, S. Sanchez-Saez, X. Martinez, E. Barbero-Pozuelo

  Composite Structures (2019). Vol. 217, pp. 89-99

  
  

  Abstract

  In this paper, the interlaminar stresses in open-hole laminates subjected to compressive loads are analysed using a numerical model. This model implements the Serial/Parallel Mixing Theory (S/PMT) and a Continuum Damage Mechanics (CDM) approach. The S/PMT estimates the global stiffness in the laminate from fibre and matrix properties. The CDM approach models the damage initiation due to fibre microbuckling. The global response estimated by the model was verified with experimental data from the literature. The model predicts that the damage initiates in the laminate middle-plane where the thickest block of plies oriented in the load direction is located, and progressively propagates to the nearest block of layers with the same orientation. Two laminate stacking sequences were analysed. The interlaminar stresses around the hole presented symmetry with respect to the load direction and the perpendicular axis, being located the maximum and minimum values in different angular positions for each stress component and laminate.

  Abstract
  In this paper, the interlaminar stresses in open-hole laminates subjected to compressive loads are analysed using a numerical model. This model implements the Serial/Parallel [...]

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• Adaptive and off-line techniques for non-linear multiscale analysis

  S. Zaghi, X. Martinez, R. Rossi, M. Petracca

  Composite Structures (2018). (preprint) Vol. 206, pp. 215-233

  
  

  Abstract

  This paper presents two procedures, based on the numerical multiscale theory, developed to predict the mechanical non-linear response of composite materials under monotonically increasing loads. Such procedures are designed with the objective of reducing the computational cost required in these types of analysis. Starting from virtual tests of the microscale, the solution of the macroscale structure via Classical First-Order Multiscale Method will be replaced by an interpolation of a discrete number of homogenized surfaces previously calculated. These surfaces describe the stress evolution of the microscale at fixed levels of an equivalent damage parameter (). The information required for these surfaces to conduct the analysis is stored in a Data Base using a json format. Of the two methods developed, the first one uses the pre-computed homogenized surface just to obtain the material non-linear threshold, and generates a Representative Volume Element (RVE) once the material point goes into the nonlinear range; the second method is completely off-line and is capable of describing the material linear and non-linear behavior just by using the discrete homogenized surfaces stored in the Data Base. After describing the two procedures developed, this manuscript provides two examples to validate the capabilities of the proposed methods

  Abstract
  This paper presents two procedures, based on the numerical multiscale theory, developed to predict the mechanical non-linear response of composite materials under monotonically [...]

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• Identification of Fracture Toughness for Discrete Damage Mechanics Analysis of Glass-Epoxy Laminates

  E. Barbero, F. Cosso, X. Martinez

  Applied Composite Materials (2014). Vol. 21, pp. 633-650

  
  

  Abstract

  A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental data. DDM is constitutive model that, when incorporated into commercial finite element software via user material subroutines, is able to predict intralaminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the composite. The applicability of the DDM model is studied by comparison to available experimental data for Glass-Epoxy laminates. Sensitivity of the DDM model to h- and p-refinement is studied. Also, the effect of in-situ correction of strength is highlighted.

  Abstract
  A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental [...]

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• Reliability design methodology for confined high pressure inflatable structures

  E. Barbero, E. Sosa, X. Martinez, J. Gutierrez

  Engineering Structures (2013). Vol. 51, pp. 1-9

  
  

  Abstract

  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.

  Abstract
  A design methodology for high pressure, inflatable structures is proposed. The inflatable structure may be partially confined inside large diameter conduits and tunnels. The [...]

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

  E. Barbero, G. Sgambitterra, A. Adumitroaie, X. Martinez

  Composite Structures (2011). Vol. 93 (2), pp. 1021-1030

  
  

  Abstract

  A damage constitutive model in conjunction with a 2-D finite element discretization is presented for predicting onset and evolution of matrix cracking and subsequent stiffness reduction of symmetric composite laminates with arbitrary stacking sequence subjected to membrane loads. The formulation uses laminae crack densities as the only state variables, with crack growth driven by both mechanical stress and residual stress due to thermal expansion. The formulation is based on fracture mechanics in terms of basic materials properties, lamina moduli, and critical strain energy release rates GIC and GIIC, only. No additional adjustable parameters are needed to predict the damage evolution. Spurious strain localization and mesh size dependence are intrinsically absent in this formulation. Thus, there is no need to define a characteristic length. Comparison of model results to experimental data is presented for various laminate stacking sequences. Prediction of crack initiation, evolution, and stiffness degradation compare very well to experimental data.

  Abstract
  A damage constitutive model in conjunction with a 2-D finite element discretization is presented for predicting onset and evolution of matrix cracking and [...]

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• Analysis of the mock-up of a reactor containment building: comparison with experimental results

  S. Jiménez, A. Cornejo Velázquez, L. Barbu, S. Oller, A. Barbat

  Nuclear Engineering and Design (2020). Vol. 359, pp. 110454:1-110454:13

  
  

  Abstract

  The results of a predictive analysis of the mock-up of a reactor containment building, based on computer numerical simulation, are presented in this paper and compared with the results obtained in the context of the VeRCoRs project during the 2015–2018 experimental campaign. The analysis is based on the Serial-Parallel Rule of Mixtures theory applied on a three-dimensional finite element model of the building. All the singular parts of the structure (two buttresses, the main penetrations, the gusset, etc.) and the complete prestressing tendons system are included in the structural model. The non-linear constitutive models used to describe the behaviour of the concrete, reinforcing steel and the tendons are formulated. A description of the Serial-Parallel Rule of Mixtures algorithm is also given. The structural response computed for the successive pressure tests applied on the mock-up are compared with the monitored structural behaviour. Finally, results for a simulation considering the aging of the tendon system during 40 years are shown and discussed.

  Abstract
  The results of a predictive analysis of the mock-up of a reactor containment building, based on computer numerical simulation, are presented in this paper and compared with [...]

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• High-cycle fatigue constitutive model and a load-advance strategy for the analysis of unidirectional fiber reinforced composites subjected to longitudinal loads

  L. Barbu, S. Oller, X. Martinez, A. Barbat

  Composite Structures (2019). Vol. 220, pp. 622-641

  
  

  Abstract

  A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel mixing theory that is also used as a constitutive equation manager. The constitutive formulation is coupled with a load advancing strategy in order to reduce the computational cost of the numerical simulations. Validation of the constitutive formulation is done on pultruded glass fiber reinforced polymer profiles. Special emphasis is made on the comparison between the experimental and the numerical failure mode.

  Abstract
  A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel [...]

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