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Documents published in Scipedia

• Numerical validation of the incremental launching method of a steel bridge through a small-scale experimental study

  R. Chacon, N. Uribe, S. Oller

  Experimental Techniques (2016). (preprint) Vol. 40 (1), pp. 333-346

  
  

  Abstract

  The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0037-5 This article presents an experimental and a numerical study of an incremental launching process of a steel bridge. The former is deployed in a scale-reduced laboratory,whereas the latter is performed using the finite elementmethod. The numerical simulation is based upon realistic transient boundary conditions and accurately reproduces the elastic response of the steel bridge during launching. This numerical approach is validated experimentally with the scale-reduced test performed at the laboratory. The properly validated numerical model is subsequently systematically employed as a simulation tool of the process. The proposed simulation protocol might be useful for design and monitoring purposes of steel bridges to be launched. Results concerning strains, stresses, and displacements might be inferred from the model and thus compared to field measurements obtained in situ. The conditions presented at the end of the article are potentially useful for researchers and practice engineers alike.

  Abstract
  The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0037-5 This article presents an experimental and a numerical study of an incremental [...]

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• Micro-mechanical approach for the vibration analysis of CFRP laminates under impact-induced damage

  M. Perez, S. Oller, C. Felippa, L. Gil

  Composites Part B: Enginnering (2015). (preprint) Vol. 83, pp. 306-316

  
  

  Abstract

  This paper deals with modelling the effect of low-velocity impact damage upon the vibration response of CFRP laminates through a micro-mechanical description of the induced internal damage. The serial-parallel (SP) continuum approach is used to estimate the map of induced internal damage by considering the micro-structural interaction between the composite constituents and modifying their constitutive performance through a continuum damage formulation. An eigenvalue analysis is then done to determine the modal response of impacted laminates. The validity of the modelling approach to successfully reproduce the vibration response of impacted coupons is assessed through a comparison with an experimental test series conducted on a set of 48 CFRP laminated coupons. The results confirm the ability of the described approach in comparison to competing ones used to reproduce the experimentally observed behaviour.

  Abstract
  This paper deals with modelling the effect of low-velocity impact damage upon the vibration response of CFRP laminates through a micro-mechanical description of the induced [...]

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• Regularization of first order computational homogenization for multiscale analysis of masonry structures

  M. Petracca, L. Pelà, S. Oller, G. Camata, E. Spacone

  Computational Mechanics (2015). (preprint) Vol. 57 (2), pp. 257-276

  
  

  Abstract

  The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-015-1230-6 This paper investigates the possibility of using classical first order computational homogenization together with a simple regularization procedure based on the fracture energy of the micro-scale-constituents. A generalized geometrical characteristic length takes into account the size of the macro-scale element as well as the size of the RVE (and its constituents). The proposed regularization ensures objectivity of the dissipated energy at the macro-scale, with respect to the size of the FE in both scales and with respect to the size of the RVE. The proposed method is first validated against benchmark examples, and finally applied to the numerical simulation of experimental tests on in-plane loaded shear walls made of periodic masonry.

  Abstract
  The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-015-1230-6 This paper investigates the possibility of using classical first order computational [...]

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• An efficient multi-scale method for non-linear analysis of composite structures

  F. Otero, X. Martinez, S. Oller, R. Salomon, R. Omar

  Composite Structures (2015). (preprint) Vol. 131, pp. 707-719

  
  

  Abstract

  The use of multi-scale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a non-linear analysis of real composite structures without the aid of large computers. This work proposes a strategy to conduct non-linear multi-scale analysis in an efficient way. The proposed method considers that in a large structure, in general, material non-linear processes only take place in a localized region (or in a reduced number of finite elements, if a FE method is used). The strategy determines the elements that require a non-linear analysis defining of a non-linear activation function that accounts for the failure of the most critical point in the microstructure. The procedure conserves the dissipated energy through the scales, being mesh independent as the mesh objectivity concept is extended to the microstructure. The validity of the strategy proposed is proved with the analysis of academic examples showing not only the mesh independency but also the reduction of computational cost. Finally, an industrial composite component is solved using a standard computer, showing that the proposed strategy is capable of reducing the computational cost from 32 days and 14 hours (required by a classical multi-scale method) to less than 12 hours.

  Abstract
  The use of multi-scale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a non-linear analysis of real [...]

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• High cycle fatigue simulation: A new stepwise load-advancing strategy

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

  Engineering Structures (2015). (preprint) Vol. 97, pp. 118-129

  
  

  Abstract

  A stepwise load-advancing strategy for cyclic loading will be presented in this paper that yields convergence in reasonable computational time for highly nonlinear behaviour occurring past the S–N curve. The algorithm is also effective when dealing with combinations of cyclical loads. The strategy is coupled to a continuum damage model for mechanical fatigue analysis. A brief overview of the constitutive model is also presented although it is not the main focus of this work. The capabilities of the proposed procedure are shown in two numerical examples. The model is validated by comparison to experimental results.

  Abstract
  A stepwise load-advancing strategy for cyclic loading will be presented in this paper that yields convergence in reasonable computational time for highly nonlinear behaviour [...]

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• Numerical homogenization for composite materials analysis: comparison with other micro mechanical formulations

  F. Otero, S. Oller, X. Martinez, R. Salomon

  Composite Structures (2015). (preprint) Vol. 122, pp. 405-416

  
  

  Abstract

  This work presents a two-scale homogenization procedure to analyze three dimension composite structures by FEM. The theory implemented is compared with other micro-structural formulations: micro models and serial parallel mixing theory, in terms of result accuracy and computational cost. The comparison shows that for linear analysis, the homogenization is an excellent alternative to the other formulations. Its computational cost is substantially lower than the one required by the micro-model and it is able to capture several micro-structural phenomena that it is not automatically recorded by the serial parallel methodology. It will also be shown that the extension of the proposed theory to the non-linear range stills represents a challenge. The major limitation is its computational cost because it requires to solve the sub scale at each gauss point and load step. However, the comparison shows that this cost is in terms of CPU time but not in terms of memory. Based on the results obtained, it can be concluded that the homogenization is an excellent alternative for simulation of materials with complex micro structures. The method is also very promising for non linear simulations, when coupled with a threshold criteria to decide whether it is necessary to analyze the RVE or not.

  Abstract
  This work presents a two-scale homogenization procedure to analyze three dimension composite structures by FEM. The theory implemented is compared with other micro-structural [...]

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• Optimization method for the determination of material parameters in damaged composite structures

  E. Comellas, S. P, S. Oller, S. Botello

  Composite Structures (2015). (preprint) Vol. 122, pp. 417-424

  
  

  Abstract

  An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with their numerical reproduction using the finite element method in order to obtain an estimation of the error between the results. This error estimation is then used by an evolutionary optimizer to determine, in an iterative process, the value of the material parameters which result in the best numerical fit. The novelty of the method is in the coupling between the simple genetic algorithm and the mixing theory used to numerically reproduce the composite behavior. The methodology proposed has been validated through a simple example which illustrates the exploitability of the method in relation to the modeling of damaged composite structures.

  Abstract
  An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with [...]

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• Formulation of enriched macro elements using trigonometric shear deformation theory for free vibration analysis of symmetric laminated composite plate assemblies

  R. Rango, L. Nallim, S. Oller

  Composite Structures (2015). Vol. 119, pp. 38-49

  
  

  Abstract

  The formulation of an enriched macro element suitable to analyze the free vibration response of composite plate assemblies is presented in this article. Based on the Trigonometric Shear Deformation Theory (TSDT) and the use of Gram–Schmidt orthogonal polynomials as enrichment functions a finite macro element is developed. In the TSDT framework, shear stresses are vanished at the top and bottom surfaces of the plates and shear correction factors are no longer required. The Principle of Virtual Work is applied to derive the governing equations of motion. A special connectivity matrix is obtained; so that hierarchically enriched global stiffness matrix and mass matrix of general laminated plate structures are derived, allowing to study generally coplanar plate assemblies by combining two or more macro elements. This procedure gives a matrix-eigenvalue problem that can be solved with optimum efficiency. Results of free vibration analysis for symmetric laminated plates of different thickness ratios, geometrical planform shapes and boundary conditions are presented. The accuracy of the formulation is ensured by comparing some numerical examples with those available in the literature.

  Abstract
  The formulation of an enriched macro element suitable to analyze the free vibration response of composite plate assemblies is presented in this article. Based on the Trigonometric [...]

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• A finite points method approach for strain localization using the gradient plasticity formulation

  L. Pérez, A. Campos, S. Lascano, S. Oller, A. Rodríguez-Ferran

  mathematical problems in engineering (2014). Vol. 2014, p. 782079-1-782079-12

  
  

  Abstract

  The softening elastoplastic models present an unsuitable behavior after reaching the yield strength: unbounded strain localization. Because of the material instability, which is reflected in the loss of ellipticity of the governing partial differential equations, the solution depends on the discretization. The present work proposes to solve this dependency using the meshless Finite Points Method. This meshfree spatial discretization technique allows enriching the governing equations using gradient’s plasticity and introducing an internal length scale parameter at the material model in order to objectify the solution.

  Abstract
  The softening elastoplastic models present an unsuitable behavior after reaching the yield strength: unbounded strain localization. Because of the material instability, which [...]

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

  M. Perez, L. Gil, M. Sánchez, S. Oller

  Composite Structures (2014). (preprint) Vol. 112, pp. 169-178

  
  

  Abstract

  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.

  Abstract
  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 [...]

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