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• An apropos kinematic framework for the numerical modelling of Friction Stir Welding

  N. Dialami, M. Chiumenti, M. Cervera, C. Agelet de Saracibar

  Computers and Structures (2013). (prepint) Vol. 117, pp. 48-57.

  
  

  Abstract

  This paper describes features of a fully coupled thermo-mechanical model for Friction Stir Welding (FSW) simulation. An apropos kinematic setting for different zones of the computational domain is introduced and an efficient coupling strategy is proposed. Heat generation via viscous dissipation as well as frictional heating is considered. The results of the simulation using the proposed model are compared with the experimental evidence. The effect of slip and stick condition on non-circular pin shapes is analyzed. Simulation of material stirring is also carried out via particle tracing, providing insight of the material flow pattern in the vicinity of the pin.

  Abstract
  This paper describes features of a fully coupled thermo-mechanical model for Friction Stir Welding (FSW) simulation. An apropos kinematic setting for different zones of the [...]

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• Capacidad límite última de disipación de energía de estructuras de hormigón armado sometidas a acciones sísmicas

  A. Benavent-Climent, F. López-Almansa, L. Pujades

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (2001). MIS44, ISBN: 84-899925-88-7

  
  

  Abstract

  El principal objetivo de esta monografía es la evaluación de la capacidad límite de disipación de energía de las estructuras sometidas a terremotos. En ella se expone, a través de su aplicación a varias estructuras tipo, una de las metodologías posibles para llevarla a cabo.

  Abstract
  El principal objetivo de esta monografía es la evaluación de la capacidad límite de disipación de energía de las estructuras sometidas a [...]

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• Espectros de input de energía de aplicación en el proyecto sismorresistente de estructuras en regiones de sismicidad moderada

  A. Benavent-Climent, L. Pujades, F. López-Almansa

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (2001). MIS43, ISBN: 84-89925-86-0

  
  

  Abstract

  Esta monografía se compone de seis capítulos. En el Capítulo 1 se introduce el concepto de la energía y se demuestra la dependencia que tiene el input de energía total, del periodo fundamental de vvibración y de la masa del edificio. En el capítulo 2 se hace una estimación indirecta de los espectros de input de energía implícitos en la normativa sísmica española vigente (CSE-94), a partir de la hipóyesis de Housner y de las relaciones conocidas entre la pseudo-velocidad máximarelativa y la aceleración máxima absoluta de respuesta en sistemas dinámicos de un grado de libertad. En el Capítulo 3 se determinan mediante cálculos dinámicos directos, los espectros de input de energía de más de 100 acelerogramas correspondientes a terremotos históricos registrados en España. El Capítulo 4 se dedica a la evolución del input de energía que contribuye a daños estructurales, a partir del input de energía total y se expone nuevas fórmulas propuestas recientemente en la literatura. Finalmente, los Capítulos 5 y 6 se ocupan de comparar los espectros de input de energía de proyecto propuestos en diversas áreas geográficas de diferente sismicidad. Estos espectros de proyecto se contrastan también con los correspondientes a los recientes de Turquía, Taiwán y Mula de 1999.

  Abstract
  Esta monografía se compone de seis capítulos. En el Capítulo 1 se introduce el concepto de la energía y se demuestra la dependencia que tiene el [...]

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• Continuum FE models for the analysis of a representative bay in Mallorca Cathedral

  P. Roca, M. Cervera, L. Pelà

  Engineering Structures (2013). (preprint) Vol. 46, pp. 653-670

  
  

  Abstract

  From the theoretical point of view, systems composed by masonry arches or vaults would require, during construction, the simultaneous activation of all structural elements in order to reach the optimum balance of thrusts. This is not obviously the case of complex ancient masonry constructions, whose long and gradual building process may have contributed to their deformed condition and even to damage.In this paper, the possible influence of the construction process as well as that of later long-term deformation on the final condition of the building is investigated in the case of a complex and large historical structure, namely Mallorca Cathedral. A FE code has been specifically developed for the present study. The code is able to account for construction processes through sequential-evolutionary analyses, with the description of masonry mechanical damage and long-term deformation. The representative bay of the cathedral is analyzed taking into account different construction phases, as emerged from historical research. The response of such substructure to transverse earthquake equivalent forces is then investigated. In this case, the damage model is improved with a local crack-tracking algorithm. This numerical strategy models the tensile damage as distinct cracks, leading to a better prediction of realistic collapsing mechanisms.

  Abstract
  From the theoretical point of view, systems composed by masonry arches or vaults would require, during construction, the simultaneous activation of all structural elements [...]

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• An orthotropic damage model for the analysis of masonry structures

  L. Pelà, M. Cervera, P. Roca

  Construction and Building Materials (2013). (preprint) Vol. 41, pp. 957-967.

  
  

  Abstract

  This paper presents a numerical model for nonlinear analysis of masonry structural elements based on Continuum Damage Mechanics. The material is described at the macro-level, i.e. it is modeled as a homogeneous orthotropic continuum. The orthotropic behavior is simulated by means of an original methodology, resulting from the concept of mapped tensors from the anisotropic field to an auxiliary workspace. The application of this idea to strain-based Continuum Damage Models is innovative and leads to several computational benefits. The suitability of the model for representing the behavior of different types of brickwork masonry is shown via the simulation of experimental tests.

  Abstract
  This paper presents a numerical model for nonlinear analysis of masonry structural elements based on Continuum Damage Mechanics. The material is described at the macro-level, [...]

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• Viscoelasticity and damage model for creep behaviour of historical masonry structures

  P. Roca, M. Cervera, L. Pelà, R. Clemente, M. Chiumenti

  The Open Civil Engineering Journal (2012). Vol. 6 (Suppl. 1-M7), pp. 188-199.

  
  

  Abstract

  This paper presents a continuum model for the simulation of the viscous effects and the long-term damage accumulation in masonry structures. The rheological model is based on a generalized Maxwell chain representation with a constitutive law utilizing a limited number of internal variables. Thanks to its computational efficiency, this approach is suitable for the analysis of large and complex structures. In the paper, the viscous and damage models are presented and their coupling is discussed. The FE simulation of the construction process of the representative bay of Mallorca Cathedral is presented, together with the analysis of the long-term effects. The parameters of the model are tentatively calibrated on the basis of the time-dependent viscous deformations detected during the cathedral monitoring.

  Abstract
  This paper presents a continuum model for the simulation of the viscous effects and the long-term damage accumulation in masonry structures. The rheological model is based [...]

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• Structural Analysis of Masonry Historical Constructions. Classical and Advanced Approaches

  P. Roca, M. Cervera, G. Gariup, L. Pelà

  Archives of Comp. Meths. Engng. (2010). 17 (3), pp. 299-325

  
  

  Abstract

  A review of methods applicable to the study of masonry historical construction, encompassing both classical and advanced ones, is presented. Firstly, the paper offers a discussion on the main challenges posed by historical structures and the desirable conditions that approaches oriented to the modeling and analysis of this type of structures should accomplish. Secondly, the main available methods which are actually used for study masonry historical structures are referred to and discussed. The main available strategies, including limit analysis, simplified methods, FEM macro- or micro-modeling and discrete element methods (DEM) are considered with regard to their realism, computer efficiency, data availability and real applicability to large structures. A set of final considerations are offered on the real possibility of carrying out realistic analysis of complex historic masonry structures. In spite of the modern developments, the study of historical buildings is still facing significant difficulties linked to computational effort, possibility of input data acquisition and limited realism of methods.

  Abstract
  A review of methods applicable to the study of masonry historical construction, encompassing both classical and advanced ones, is presented. Firstly, the paper offers a discussion [...]

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• A crack-tracking technique for localized damage in quasi-brittle materials

  M. Cervera, L. Pelà, R. Clemente, P. Roca

  Engineering Fracture Mechanics (2010). Vol. 77 (13), pp. 2431-2450.

  
  

  Abstract

  This work presents a procedure to simulate the growth and propagation of localized tensile cracks on quasi-brittle materials. The so-called smeared damage approach, which consists in standard finite elements and local nonlinear constitutive laws, is recovered and improved in order to represent crack localization and avoid spurious mesh-bias dependence in the discrete problem. This is achieved by means of the implementation of a local crack-tracking algorithm which can reproduce individual (discrete) cracks and ensure objectivity of the finite element problem solution. The performance of the localized damage model is stressed by means of the analyses of structural case-studies. Compared to the Smeared Crack Approach in its original form, the presented procedure shows clearly a better capacity to predict realistic collapse mechanisms. The proposed tracking technique is relatively inexpensive.

  Abstract
  This work presents a procedure to simulate the growth and propagation of localized tensile cracks on quasi-brittle materials. The so-called smeared damage approach, which [...]

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• Size effect and localization in J2 plasticity

  M. Cervera, M. Chiumenti

  Int. J. Solids and Structures (2009). Vol. 46 (17), pp. 3301-3312.

  
  

  Abstract

  This paper studies the phenomenon of structural size effect and strain localization in J2 plasticity. Size effect is here understood as the change in the response of a given structure when the spatial dimensions are scaled up or down while the geometry and other relevant properties of the structure are preserved. The work exploits the advantages of the mixed displacement–pressure formulation in incompressible or quasi-incompressible situations. Elasto-J2-plastic constitutive behaviour with regularized softening is considered. Stability issues are discussed to ensure existence and uniqueness of the solution of the corresponding discrete finite element formulation. Numerical examples show that the formulation derived is able to solve a wide range of structural scales, including real life engineering applications. The results obtained do not suffer from spurious mesh dependence. Furthermore, the formulation includes the classical theories of perfect plasticity and linear fracture mechanics as limit cases.

  Abstract
  This paper studies the phenomenon of structural size effect and strain localization in J2 plasticity. Size effect is here understood as the change in the response of a given [...]

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• On the Numerical modeling of the thermomechanical contact for metal casting analysis

  M. Chiumenti, C. Agelet de Saracibar, M. Cervera

  J. Heat Transfer (2008). Vol. 130 (6), 10 pp.

  
  

  Abstract

  The paper shows the intrinsic difficulties found in the numerical simulation of industrial casting processes using finite element (FE) analysis. Up until now, uncoupled pure thermal simulations have been mostly considered to model solidification and cooling phenomena. However, a fully coupled thermomechanical analysis provides a more complete insight of the casting process and the final outcome regarding the quality of the part. In this type of analysis, the thermomechanical model used plays a role of paramount importance, as the problem is coupled both ways through contact between part and mould. The paper presents the full statement of the problem regarding contact, and it considers the difficulties associated with FE mesh generation and time integration strategy. It also reviews soft and hard algorithms for mechanical contact presenting some new alternatives. Evaluation of coefficients used for thermal contact is also discussed, and a new proposal is presented. Finally, some numerical applications are presented to assess the performance of the proposed strategies both in benchmark and industrial problems.

  Abstract
  The paper shows the intrinsic difficulties found in the numerical simulation of industrial casting processes using finite element (FE) analysis. Up until now, uncoupled pure [...]

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