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• A continuum mechanics model for mechanical fatigue analysis

  S. Oller, O. Salomon, E. Oñate

  Computational Materials Science (2005). Vol. 32 (2), pp. 175-195

  
  

  Abstract

  In this paper, a thermo-mechanical constitutive model for the predictions of fatigue in structures using the finite element method is formulated. The model is based on the damage mechanics of the continuous medium and allows the treatment in a unified way of coupled phenomena such as fatigue with damage, plasticity, viscosity and temperature effects. Basically it is gotten sensitive models to cyclic loads starting from classical non-linear constitutive formulations incorporating the special variable influenced by the characteristics of the cyclic load. A formulation based on the theories of damage and plasticity is developed. The necessary modifications of these theories are outlined in order to include the fatigue phenomena. A brief description of the finite element implementation is given. Finally, results of the performance of the proposed model are shown through the simple fatigue test and the fatigue analysis of an aluminium engine alternator support.

  Abstract
  In this paper, a thermo-mechanical constitutive model for the predictions of fatigue in structures using the finite element method is formulated. The model is based on the [...]

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• A Lagrangian Panel Method in the Time Domain for Moving Free-surface Potential Flows

  J. D'ELIA, M. Storti, E. Oñate, S. Idelsohn

  Int. J. Computational Fluid Dynamics (2002). Vol. 16 (4), pp. 263-275

  
  

  Abstract

  A Lagrangian-type panel method in the time domain is proposed for potential flows with a moving free surface. After a spatial semi-discretization with a low-order scheme, the instantaneous velocity-potential and normal displacement on the moving free surface are obtained by means of a time-marching scheme. The kinematic and dynamic boundary conditions at the free surface are non-linear restrictions over the related Ordinary Differential Equation (ODE) system and, in order to handle them, an alternative Steklov-Poincaré operator technique is proposed. The method is applied to sloshing like flow problems.

  Abstract
  A Lagrangian-type panel method in the time domain is proposed for potential flows with a moving free surface. After a spatial semi-discretization with a low-order scheme, [...]

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• A finite element formulation for the analysis of marine pipelines during laying operations

  J. Oliver, E. Oñate

  Journal of Pipelines (1985). Vol. 5 (1), pp. 15-35

  
  

  Abstract

  In this paper a finite element formulation for the deformation analysis of submarine pipelines during laying operations is presented. The formation allows for large displacement/rotations and the effect of nonconservative water loads. An iterative procedure to deal with the changing boundary conditions at the seafloor is also presented. Numerical results for two pipeline laying cases, obtained using three noded isoparametrical one-dimensional curved elements, are given.

  Abstract
  In this paper a finite element formulation for the deformation analysis of submarine pipelines during laying operations is presented. The formation allows for large displacement/rotations [...]

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• A finite point method for incompressible flow problems

  E. Oñate, C. Sacco, S. Idelsohn

  Computing and Visualization in Science (2000). Vol. 3 (1), pp. 67-75

  
  

  Abstract

  A stabilized finite point method (FPM) for the meshless analysis of incompressible fluid flow problems is presented. The stabilization approach is based in the finite increment calculus (FIC) procedure developed by Oñate [14]. An enhanced fractional step procedure allowing the semi-implicit numerical solution of incompressible fluids using the FPM is described. Examples of application of the stabilized FPM to the solution of two incompressible flow problems are presented.

  Abstract
  A stabilized finite point method (FPM) for the meshless analysis of incompressible fluid flow problems is presented. The stabilization approach is based in the finite increment [...]

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• A methodology for adaptive mesh refinement in optimum shape design problems

  G. Bugeda, E. Oñate

  Computing Systems in Engineering (1994). Vol. 5 (1), pp. 91-102

  
  

  Abstract

  This work presents a methodology based on the use of adaptive mesh refinement (AMR) techniques in the context of shape optimization problems analyzed by the Finite Element Method (FEM). A suitable and very general technique for the parametrization of the optimization problem using B-splines to define the boundary is first presented. Then, mesh generation using the advancing front method, the error estimation and the mesh refinement criteria are dealt with in the context of a shape optimization problems. In particular, the sensitivities of the different ingredients ruling the problem (B-splines, finite element mesh, design behaviour, and error estimator) are studied in detail. The sensitivities of the finite element mesh coordinates and the error estimator allow their projection from one design to the next, giving an “a priori knowledge” of the error distribution on the new design. This allows to build up a finite element mesh for the new design with a specified and controlled level of error. The robustness and reliability of the proposed methodology is checked out with some 2D examples.

  Abstract
  This work presents a methodology based on the use of adaptive mesh refinement (AMR) techniques in the context of shape optimization problems analyzed by the Finite Element [...]

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• Reliability estimation of the sheet stamping process using support vector machines

  J. Hurtado, F. Zarate, E. Oñate

  Int. J. of Vehicle Design (2005). Vol. 39 (1-2), pp. 110–124

  
  

  Abstract

  An important concern in sheet stamping is the risk of obtaining brittle final products that can be affected by fracture. Monte Carlo simulations presented herein show that this is governed by two main factors, namely static and dynamic friction coefficients. Whereas the latter correlates in a non-linear manner with minimum and maximum end thickness, the relationship of these design parameters to the former exhibits a bifurcation that is typical of highly non-linear phenomena, in which there is a sensitivity to small perturbations of the input values (chaos). In order to estimate the reliability of the process (i.e., the probability of obtaining brittle products due to low minimum and maximum thicknesses) with a reduced number of Monte Carlo runs, it is proposed to assimilate the problem to a pattern recognition task, due to the existence of two classes, namely robust and brittle. Among many pattern recognition algorithms that are useful to this end, use is made of support vector machines, as this incorporates the powerful tool of class margins that allow a drastic reduction of the number of simulations.

  Abstract
  An important concern in sheet stamping is the risk of obtaining brittle final products that can be affected by fracture. Monte Carlo simulations presented herein show that [...]

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• A viscous shell formulation for the analysis of thin sheet metal forming

  E. Oñate, O. Zienkiewicz

  Int. J. Mechanical Sciences (1983). Vol. 25 (5), pp. 305-335

  
  

  Abstract

  A finite element method to analyse large plastic deformations of thin sheets of metal is presented. The formulation is based on an extension of the general viscoplastic flow theory for continuum problems to deal with thin shells. Axisymmetric situations are considered first and here the simple two noded reduced integration element is used. Numerical results for the stretch forming and deep drawing of circular sheets are presented and comparison with experimental results is made. The second part of the paper deals with the deformation of sheets of arbitrary shape. The general viscous shell element is derived from the standard reduced integration, “thick shell element. Numerical results for simple 3-D sheet forming problems are given.

  Abstract
  A finite element method to analyse large plastic deformations of thin sheets of metal is presented. The formulation is based on an extension of the general viscoplastic flow [...]

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• Numerical analysis of stereolithography processes using the finite element method

  G. Bugeda, M. Cervera, G. Lombera, E. Oñate

  Rapid Prototyping Journal (1995). Vol. 1 (2), pp. 13-23

  
  

  Abstract

  Stereolithography (SLA) is one of the most important techniques used in rapid prototyping processes. It has a great industrial interest because it allows for dramatic time savings with respect to traditional manufacturing processes. One of the main sources of error in the final dimensions of the prototype is the curl distortion effect owing to the shrinkage of the resin during the SLA process. Presents a study of the influence of different constructive and numerical parameters in the curl distortion, an analysis which was made using the computer code stereolithography analysis program, developed to model SLA processes using the finite element method. Also briefly presents this code.

  Abstract
  Stereolithography (SLA) is one of the most important techniques used in rapid prototyping processes. It has a great industrial interest because it allows for dramatic time [...]

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• Fatigue analysis of materials and structures using a continuum damage model

  O. Salomon, S. Oller, E. Oñate

  International Journal of Forming Processes (2002). Vol. 5 (2-3-4), pp. 493-503

  
  

  Abstract

  The scatter in the fatigue life of the metallic structures seems to be mainly caused by internal defects of the material (porosity, inclusions as oxide films and carbon layers, grain boundaries, etc.). As discontinuities in geometry, defects cause stress concentration and are therefore prone to fatigue crack initiation. Here, a fatigue model based in continuum mechanic with its general expressions for the elasto-plastic-damage constitutive equations, previously developed by the authors, is extended to include the effects of material internal defects. In this stress life approach the material is considered to be non-homogenous. The material strength is randomly assigned and Stress-Nº of cycles curves are scaled down according to material strength of each point. Limit values for material strength are based on experimental tests of samples with different degree of porosity.  

  Abstract
  The scatter in the fatigue life of the metallic structures seems to be mainly caused by internal defects of the material (porosity, inclusions as oxide films and carbon layers, [...]

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• Finite element nonlinear analysis of concrete structures using a “plastic-damage model”

  S. Oller, E. Oñate, J. Oliver, J. Lubliner

  Engineering Fracture Mechanics (1990). Vol. 35 (1-2-3), pp. 219-231

  
  

  Abstract

  In this paper a plastic damage model for nonlinear finite element analysis of concrete is presented. The model is based on standard plasticity theory for frictional materials. Details of the expressions of a new yield function proposed and of the evolution laws of the model parameters are given. The model allows to include elastic and plastic stiffness degradation effects. This is also discussed in the paper together with the problem of mesh objectivity, and the a posteriori determination of cracks. Finally, one example of application which shows the accuracy of the model is also given.

  Abstract
  In this paper a plastic damage model for nonlinear finite element analysis of concrete is presented. The model is based on standard plasticity theory for frictional [...]

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