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• Continuum damage model for orthotropic materials: Application to masonry

  L. Pelà, M. Cervera, P. Roca

  Comput. Methods Appl. Mech. Engrg., (2011). Vol. 200 (9-12), pp. 917-930

  
  

  Abstract

  This paper contributes to the formulation of continuum damage models for orthotropic materials under plane stress conditions. Two stress transformation tensors, related to tensile and compressive stress states, respectively, are used to establish a one-to-one mapping relationship between the orthotropic behaviour and an auxiliary model. This allows the consideration of two individual damage criteria, according to different failure mechanisms, i.e. cracking and crushing. The constitutive model adopted in the mapped space makes use of two scalar variables which monitor the local damage under tension and compression, respectively. The model affords the simulation of orthotropic induced damage, while also accounting for unilateral effects, thanks to a stress tensor split into tensile and compressive contributions. The fundamentals of the method are presented together with the procedure utilized to adjust the model in order to study the mechanical behaviour of masonry material. The validation of the model is carried out by means of comparisons with experimental results on different types of orthotropic masonry at the material level.

  Abstract
  This paper contributes to the formulation of continuum damage models for orthotropic materials under plane stress conditions. Two stress transformation tensors, related to [...]

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• Mixed stabilized finite element methods in nonlinear solid mechanics: Part II: Strain localization

  M. Cervera, M. Chiumenti, R. Codina

  Comput. Methods Appl. Mech. Engrg., (2010). Vol. 199 (37-40), pp. 2571-2589

  
  

  Abstract

  This paper deals with the question of strain localization associated with materials which exhibit softening due to tensile straining. A standard local isotropic Rankine damage model with strain-softening is used as exemplary constitutive model. Both the irreducible and mixed forms of the problem are examined and stability and solvability conditions are discussed. Lack of uniqueness and convergence difficulties related to the strong material nonlinearities involved are also treated. From this analysis, the issue of local discretization error in the pre-localization regime is deemed as the main difficulty to be overcome in the discrete problem. Focus is placed on low order finite elements with continuous strain and displacement fields (triangular P1P1 and quadrilateral Q1Q1), although the presented approach is very general. Numerical examples show that the resulting procedure is remarkably robust: it does not require the use of auxiliary tracking techniques and the results obtained do not suffer from spurious mesh-bias dependence.

  Abstract
  This paper deals with the question of strain localization associated with materials which exhibit softening due to tensile straining. A standard local isotropic Rankine damage [...]

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• Mixed stabilized finite element methods in nonlinear solid mechanics: Part I: Formulation

  M. Cervera, M. Chiumenti, R. Codina

  Comput. Methods Appl. Mech. Engrg., (2010). Vol. 199 (37-40), pp. 2559-2570

  
  

  Abstract

  This paper exploits the concept of stabilized finite element methods to formulate stable mixed stress/displacement and strain/displacement finite elements for the solution of nonlinear solid mechanics problems. The different assumptions and approximations used to derive the methods are exposed. The proposed procedure is very general, applicable to 2D and 3D problems. Implementation and computational aspects are also discussed, showing that a robust application of the proposed formulation is feasible. Numerical examples show that the results obtained compare favorably with those obtained with the corresponding irreducible formulation.

  Abstract
  This paper exploits the concept of stabilized finite element methods to formulate stable mixed stress/displacement and strain/displacement finite elements for the solution [...]

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• Finite element modeling of multi-pass welding and shaped metal deposition processes

  M. Chiumenti, M. Cervera, A. Salmi, C. Agelet de Saracibar, N. Dialami, K. Matsui

  Comput. Methods Appl. Mech. Engrg., (2010). Vol. 199 (37-40), pp. 2343-2359

  
  

  Abstract

  This paper describes the formulation adopted for the numerical simulation of the shaped metal deposition process (SMD) and the experimental work carried out at ITP Industry to calibrate and validate the proposed model. The SMD process is a novel manufacturing technology, similar to the multi-pass welding used for building features such as lugs and flanges on fabricated components (see Fig. 1a and b). A fully coupled thermo-mechanical solution is adopted including phase-change phenomena defined in terms of both latent heat release and shrinkage effects. Temperature evolution as well as residual stresses and distortions, due to the successive welding layers deposited, are accurately simulated coupling the heat transfer and the mechanical analysis. The material behavior is characterized by a thermo-elasto-viscoplastic constitutive model coupled with a metallurgical model. Nickel super-alloy 718 is the target material of this work. Both heat convection and heat radiation models are introduced to dissipate heat through the boundaries of the component. An in-house coupled FE software is used to deal with the numerical simulation and an ad-hoc activation methodology is formulated to simulate the deposition of the different layers of filler material. Difficulties and simplifying hypotheses are discussed. Thermo-mechanical results are presented in terms of both temperature evolution and distortions, and compared with the experimental data obtained at the SMD laboratory of ITP.

  Abstract
  This paper describes the formulation adopted for the numerical simulation of the shaped metal deposition process (SMD) and the experimental work carried out at ITP Industry [...]

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• An orthotropic mesh corrected crack model

  M. Cervera

  Comput. Methods Appl. Mech. Engrg., (2008). Vol. 197 (17-18), 1603-1619

  
  

  Abstract

  This paper recovers the original spirit of the continuous crack approaches, where displacements jumps across the crack are smeared over the affected elements and the behaviour is established through a softening stress–(total) strain law, using standard finite element displacement interpolations and orthotropic localconstitutive models. The paper focuses on the problem of shear locking observed in the discrete problem when orthotropic models are used. The solution for this drawback is found in the form of a mesh corrected crack model where the structure of the inelastic strain tensor is linked to the geometry of the cracked element. The discrete model is formulated as a non-symmetric orthotropic local damage constitutive model, in which the softening modulus is regularized according to the material fracture energy and the element size. The resulting formulation is easily implemented in standard non-linear FE codes and suitable for engineering applications. Numerical examples show that the results obtained using this crack model do not suffer from dependence on the mesh directional alignment, comparing very favourably with those obtained using related standard isotropic or orthotropic damage models.

  Abstract
  This paper recovers the original spirit of the continuous crack approaches, where displacements jumps across the crack are smeared over the affected elements and the behaviour [...]

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• Mesh objective tensile cracking via a local continuum damage model and a crack tracking technique

  M. Cervera, M. Chiumenti

  Comput. Methods Appl. Mech. Engrg., (2006). Vol. 196 (1-3), pp. 304-320

  
  

  Abstract

  This paper describes a procedure for the solution of problems involving tensile cracking using the so-called smeared crack approach, that is, standard finite elements with continuous displacement fields and a standard local constitutive model with strain-softening. An isotropic Rankine damage model is considered. The softening modulus is adjusted according to the material fracture energy and the element size. The resulting continuum and discrete mechanical problems are analyzed and the question of predicting correctly the direction of crack propagation is deemed as the main difficulty to be overcome in the discrete problem. It is proposed to use a crack tracking technique to attain the desired stability and convergence properties of the corresponding formulation. Numerical examples show that the resulting procedure is well-posed, stable and remarkably robust; the results obtained do not seem to suffer from spurious mesh-size or mesh-bias dependence.

  Abstract
  This paper describes a procedure for the solution of problems involving tensile cracking using the so-called smeared crack approach, that is, standard finite elements [...]

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• On the orthogonal subgrid scale pressure stabilization of finite deformation J2 plasticity

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

  Comput. Methods Appl. Mech. Engrg., (2006). Vol. 195 (9-12), pp. 1224-1251

  
  

  Abstract

  The use of stabilization methods is becoming an increasingly well-accepted technique due to their success in dealing with numerous numerical pathologies that arise in a variety of applications in computational mechanics. In this paper a multiscale finite element method technique to deal with pressure stabilization of nearly incompressibility problems in nonlinear solid mechanics at finite deformations is presented. A J2-flow theory plasticity model at finite deformations is considered. A mixed formulation involving pressure and displacement fields is used as starting point. Within the finite element discretization setting, continuous linear interpolation for both fields is considered. To overcome the Babuška–Brezzi stability condition, a multiscale stabilization method based on the orthogonal subgrid scale (OSGS) technique is introduced. A suitable nonlinear expression of the stabilization parameter is proposed. The main advantage of the method is the possibility of using linear triangular or tetrahedral finite elements, which are easy to generate and, therefore, very convenient for practical industrial applications. Numerical results obtained using the OSGS stabilization technique are compared with results provided by the P1 standard Galerkin displacements linear triangular/tetrahedral element, P1/P1 standard mixed linear displacements/linear pressure triangular/tetrahedral element and Q1/P0 mixed bilinear/trilinear displacements/constant pressure quadrilateral/hexahedral element for 2D/3D nearly incompressible problems in the context of a nonlinear finite deformation J2 plasticity model.

  Abstract
  The use of stabilization methods is becoming an increasingly well-accepted technique due to their success in dealing with numerous numerical pathologies that arise in a variety [...]

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• Mixed linear/linear simplicial elements for incompressible elasticity and plasticity

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

  Comput. Methods Appl. Mech. Engrg., (2003). Vol. 192 (49-50), pp. 5249-5263

  
  

  Abstract

  This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed linear/linear simplicial elements (triangles and tetrahedra) in incompressible or nearly incompressible situations. Both incompressible elastic and J2-plastic constitutive behaviours have been considered. The different assumptions and approximations used to derive the method are exposed. Implementation and computational aspects are also discussed, showing that a robust application of the proposed formulation is feasible. Numerical examples show that the elements derived are free of volumetric locking and spurious oscillations of the pressure, and that the results obtained compare favourably with those obtained with the Q1P0 quadrilateral.

  Abstract
  This paper exploits the concept of orthogonal sub-grid scales to stabilize the behaviour of mixed linear/linear simplicial elements (triangles and tetrahedra) in incompressible [...]

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• Simulación numérica del comportamiento no lineal de presas de hormigón ante acciones sísmicas

  M. Galindo, J. Oliver, M. Cervera

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (1993). MIS03, ISBN: 84-87867-38-3

  
  

  Abstract

  Desde una perspectiva metodológica general, el presente estudio pretende desarrollar una herramienta basada en la utilización del diseño asistido por ordenador para el análisis numérico del comportamiento resistente de presas de hormigón, a la vez que una metodología de aplicación de la misma para el análisis de seguridad de las presas. Para este propósito, se ha intentado desarrollar un sistema genérico, modular y unificador, que permita tener en cuenta los más diversos factores como el comportamiento no-lineal del material, la interacción con el terreno y el fluido del embalse, la acción de cargas estáticas y dinámicas o la excitación sísmica.

  Abstract
  Desde una perspectiva metodológica general, el presente estudio pretende desarrollar una herramienta basada en la utilización del diseño asistido por [...]

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• Control predictivo en sistemas de protección sísmica de estructuras

  R. Andrade, J. Rodellar, F. Almansa

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (1993). MIS02, ISBN: 84-87867-37-5

  
  

  Abstract

  En este trabajo se propone una metodología para diseñar sistemas de control activo de estructuras utilizando un algoritmo de control basado en la estrategia de control predictivo. Se considera que el diseño del sistema de control cosiste en seleccionar el número, el tipo, las características y la posición de los sensores y actuadores, y en escoger los valores de los parámetros que definen la estrategia de control predictivo. La metodología propuesta puede aplicarse de forma numérica o experimental. En este trabajo se utiliza simulación numérica pero en aplicaciones reales el diseño final debe ir precedido de ensayos experimentales siguiendo la metodología descrita en este trabajo.

  Abstract
  En este trabajo se propone una metodología para diseñar sistemas de control activo de estructuras utilizando un algoritmo de control basado en la estrategia [...]

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