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• Effect of the tool tilt angle on the material flow and heat generation in Friction Stir Welding

  N. Dialami, M. Cervera, M. Chiumenti

  Metals (2019). Vol. 9 (1), pp. 28-45

  
  

  Abstract

  This work studies the effect of the tool tilt angle on the generated heat and the material flow in the work pieces joint by Friction Stir Welding (FSW). An apropos kinematic framework together with a two-stage speed-up strategy is adopted to simulate the FSW problem. The effect of tilt angle on the FSWelds is modeled through the contact condition by modifying an enhanced friction model. A rotated friction shear stress is proposed, the angle of rotation depending on the process parameters and the tilt angle. The proposed rotation angle is calibrated by the experimental data provided for a tilt angle 2.5◦ . The differences of generated heat and material flow for the cases of tool with tilt angle of 0◦ and 2.5◦ are discussed. It is concluded that due to the higher temperature, softer material and greater frictional force in the trailing side of the tool, the material flow in the rear side of the FSW tool with the title angle is considerably enhanced, which assists to prevent the generation of defect. 

  Abstract
  This work studies the effect of the tool tilt angle on the generated heat and the material flow in the work pieces joint by Friction Stir Welding (FSW). An apropos kinematic [...]

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• Finite Element Analysis of Membrane Structures

  R. Taylor, E. Oñate, P. Ubach de Fuentes

  (2005). Recent Advances in Textile Membranes and Inflatable Structures, Springer Verlag, pp. 47 - 68

  
  

  Abstract

  This paper summarizes the development for a large displacement formulation of a membrance composed of three-node triangular elements. A formulation in terms of the deformation gradient is first constructed in terms of nodal variables. In particular, the use of the right Cauchy-Green deformation tensor is shown to lead to a particulary simple representation in terms of nodal quantities. This may then be used to construct general models for use in static and transient analyses.

  Abstract
  This paper summarizes the development for a large displacement formulation of a membrance composed of three-node triangular elements. A formulation in terms of the deformation [...]

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• Stabilization via finite calculus in finite element computations

  E. Oñate

  (2004). Finite Element Methods: 1970's and Beyond, Franca L.P., Tezduyar T.E. and Masud A. (Eds.),CIMNE, Barcelona, Spain

  
  

  Abstract

  The expression “finite calculus” refers to the derivation of the governing differential equations in mechanics by invoking balance of fluxes, forces, etc. in a space-time domain of finite size. The governing equations resulting from this approach are different from those of infinitesimal calculus theory and they incorporate new terms which depend on the dimensions of the balance domain. The new governing equations allow to derive naturally stabilized numerical schemes using any discretization procedure. The paper discusses the possibilities of the finite calculus method for the finite element solution of convection-diffusion problems with sharp gradients and incompressible fluid flow.

  Abstract
  The expression “finite calculus” refers to the derivation of the governing differential equations in mechanics by invoking balance of fluxes, forces, etc. in a [...]

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• FE Analysis of membrane systems including wrinkling and coupling

  R. Rossi, R. Vitaliani, E. Oñate

  (2005). Recent Advances in Textile Membranes and Inflatable Structures, Springer Verlag, pp. 89 - 108

  
  

  Abstract

  Current work summarizes the experience of the writer in the modeling of membrane systems. A first subsection describes an efficient membrane model, together with a reliable solution procedure. The following section addresses the simulation of the wrinkling phenomena providing details of a new solution procedure. The last one proposes an efficient technique to obtain the solution of the fluid structural interaction problem.

  Abstract
  Current work summarizes the experience of the writer in the modeling of membrane systems. A first subsection describes an efficient membrane model, together with a reliable [...]

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• Enhanced Rotation-Free Basic Shell Triangle. Applications to Sheet Metal Forming

  E. Oñate, F. Flores, L. Neamtu

  (2007). Computational Plasticity, E. Oñate and R. Owen (Eds.), pp. 239-265

  
  

  Abstract

  An enhanced rotation-free three node triangular shell element (termed EBST) is presented. The element formulation is based on a quadratic interpolation of the geometry in terms of the six nodes of a patch of four triangles associated to each triangular element. This allows to compute an assumed constant curvature field and an assumed linear membrane strain field which improves the in-plane behaviour of the element. A simple and economic version of the element using a single integration point is presented. The implementation of the element into an explicit dynamic scheme is described. The efficiency and accuracy of the EBST element and the explicit dynamic scheme are demonstrated in many examples of application including the analysis of a cylindrical panel under impulse loading and sheet metal stamping problems.

  Abstract
  An enhanced rotation-free three node triangular shell element (termed EBST) is presented. The element formulation is based on a quadratic interpolation of the geometry in [...]

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• A unified symmetrical formulation for interactions between elastic solids and incompressible fluids

  S. Idelsohn, E. Oñate, J. Marti

  (2007). Variational Formulations in Mechanics: Theory and Applications, E. Taroco, E.A. de Souza Neto and A.A. Novotny (Eds.), CIMNE, Barcelona, Spain

  
  

  Abstract

  We present a general Lagrangian formulation for treating elastic solids and quasi/fully incompressible fluids in a unified form. The formulation allows to treat solid and fluid subdomains in a unified manner in fluid-structure interaction (FSI) situations. The use for both fluid and solid of a Lagrangian formulation avoid convective terms allowing to approximate the problem via a Variational Formulation. In our work the FSI problem is solved via the Particle Finite Element Method (PFEM). The PFEM is an effective technique for modeling complex interactions between floating and submerged bodies and free surface flows, accounting for splashing of waves, large motions of the bodies and frictional contact conditions. Applications of the unified Lagrangian formulation to a number of FSI problems are given.

  Abstract
  We present a general Lagrangian formulation for treating elastic solids and quasi/fully incompressible fluids in a unified form. The formulation allows to treat solid and [...]

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• Fluid-soil-structure interaction analysis with the particle finite element method

  E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, B. Suarez

  (2012). Bytes and Science, G. Zavarise and D. Boso (Eds.), pp. 119 - 130, CIMNE, Barcelona Spain

  
  

  Abstract

  We present some developments and applications of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction.

  Abstract
  We present some developments and applications of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure [...]

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• Experiences in the Design Analysis and Construction of Low Pressure Inflatable Structures

  J. Marcipar, E. Oñate, J. Canet

  (2005). Recent Advances in Textile Membranes and Inflatable Structures, Springer Verlag, pp. 241 - 257

  
  

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• Applications of a Rotation-Free Triangular Element for Finite Strain Analysis of Thin Shells and Membranes

  F. Flores, E. Oñate

  (2005). Recent Advances in Textile Membranes and Inflatable Structures, Springer Verlag, pp. 69 - 88

  
  

  Abstract

  This paper shows applications of a recently developed shell element to the analysis of thin shell and membrane structures. The element is a three node triangle with only translational DOFs (rotation free) that uses the configuration of the three adjacent elements to evaluate the strains. This allows to compute (constant) bending strains and (linear) membrane strains. A total Lagrangian formulation is used. Strains are defined in terms of the principal stretches. This allows to consider rubber materials and other type of materials using the Hencky stress-strain pair. An explicit central difference scheme is used to integrate the momentum equations. Several examples, including inflation and deflation of membranes show the excellent convergence properties and robustness of the element for large strain analysis of thin shells and membranes.

  Abstract
  This paper shows applications of a recently developed shell element to the analysis of thin shell and membrane structures. The element is a three node triangle with only translational [...]

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• Membrane Structures Formed by Low Pressure Inflatable tubes. New Analysis Methods and Recent Constructions

  E. Oñate, F. Flores, J. Marcipar

  (2008). Textile Composites and Inflatable Structures II, E. Oñate and B. Kröplin (eds.), pp. 163-196

  
  

  Abstract

  This paper shows applications of a recently developed thin shell element adequate for the analysis of membrane and inflatable structures. The element is a three node triangle with only translational degrees of freedom that uses the configuration of the three adjacent elements to evaluate the strains in terms of the nodal displacements only. This allows to compute (constant) bending strains and (linear) membrane strains using a total Lagrangian formulation. Several examples, including inflation and deflation of membranes and some practical applications to the analysis, design and construction of membrane structures formed by low pressure inflatable tubes are presented.

  Abstract
  This paper shows applications of a recently developed thin shell element adequate for the analysis of membrane and inflatable structures. The element is a three node triangle [...]

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