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See detailThe adapted augmented Lagrangian method: a new method for the resolution of the mechanical frictional contact problem
Bussetta, Philippe ULg; Daniel, Marceau; Ponthot, Jean-Philippe ULg

in Computational Mechanics (2012), 49(2), 259-275

The aim of this work is to propose a new numerical method for solving the mechanical frictional contact problem in the general case of multi-bodies in a three dimensional space. This method is called ... [more ▼]

The aim of this work is to propose a new numerical method for solving the mechanical frictional contact problem in the general case of multi-bodies in a three dimensional space. This method is called adapted augmented Lagrangian method (AALM) and can be used in a multi-physical context (like thermo-electro-mechanical fields problems). This paper presents this new method and its advantages over other classical methods such as penalty method (PM), adapted penalty method (APM) and, augmented Lagrangian method (ALM). In addition, the efficiency and the reliability of the AALM are proved with some academic problems and an industrial thermo-electromechanical problem. [less ▲]

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See detailForming forces in single point incremental forming: prediction by finite element simulations, validation and sensitivity
Henrard, Christophe; Bouffioux, Chantal ULg; Eyckens, P. et al

in Computational Mechanics (2011), 47

The aim of this article is to study the accuracy of finite element simulations in predicting the tool force occurring during the single point incremental forming (SPIF) process. The forming of two cones ... [more ▼]

The aim of this article is to study the accuracy of finite element simulations in predicting the tool force occurring during the single point incremental forming (SPIF) process. The forming of two cones in soft aluminum was studied with two finite element (FE) codes and several constitutive laws (an elastic–plastic law coupled with various hardening models). The parameters of these laws were identified using several combinations of a tensile test, shear tests, and an inverse modeling approach taking into account a test similar to the incremental forming process. Comparisons between measured and predicted force values are performed. This article shows that three factors have an influence on force prediction: the type of finite element, the constitutive law and the identification procedure for the material parameters. In addition, it confirms that a detailed description of the behavior occurring across the thickness of the metal sheet is crucial for an accurate force prediction by FE simulations, even though a simple analytical formula could provide an otherwise acceptable answer. [less ▲]

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See detailForming Forces in Single Point Incremental Forming, Prediction by Finite Element Simulations
Henrard, Christophe; Bouffioux, Chantal ULg; Eyckens, P. et al

in Computational Mechanics (2010)

The aim of this article is to study the accuracy of the nite element simulations to predict the tool force during the Single Point Incremental Forming process. The forming of two cones in soft aluminum ... [more ▼]

The aim of this article is to study the accuracy of the nite element simulations to predict the tool force during the Single Point Incremental Forming process. The forming of two cones in soft aluminum was studied with two Finite Element (FE) codes and several constitutive laws (an elastic-plastic model coupled with different hardening approaches). The parameters of these laws were identi ed using tensile and shear tests, as well as an inverse approach taking into account a test similar to the incremental forming process. Comparisons between measured and predicted force values are performed. This article shows that three factors have an in uence on the force prediction: the type of nite element, the constitutive law and the identi cation procedure for the material parameters. In addition, it con rms that a very detailed description of the behavior occurring across the thickness of the metal sheet is crucial for an accurate force prediction by FE simulations, even though a simple analytical formula could provide an otherwise acceptable answer. [less ▲]

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See detailConvergence and conditionning issues with X-FEM in fracture mechanics
Béchet, Eric ULg; Minnebo, Hans; Moës, Nicolas

in Computational Mechanics (2004)

Numerical crack propagation schemes were augmented in an elegant manner by the X-FEM method applied to fracture mechanics. The use of special tip enrichment functions, as well as a discontinuous function ... [more ▼]

Numerical crack propagation schemes were augmented in an elegant manner by the X-FEM method applied to fracture mechanics. The use of special tip enrichment functions, as well as a discontinuous function along the sides of the crack allows one to do a complete crack analysis virtually without modifying the underlying mesh, which is of an evident industrial interest. The conventional approach for crack tip enrichment (described in [2,3]) is that only a specific layer of elements are enriched around the crack tip. We show that this “topological” approach does not yield an increase of the order of the asymptotic convergence rate when compared to unenriched finite elements, as when the crack is part of the mesh. It rather modifies the proportionality factor of the asymptotic convergence rate. In this study, we propose another enrichment scheme which yields a convergence rate that appears to be close to that of regular finite elements used when the solution field does not show singularities. The enriched basis in X-FEM degrades the rigidity and mass matrices condition numbers (the mass matrix typically appears in case of time dependent problems such as wave propagation in cracked bodies). To recover the condition number of non enriched matrices, we introduce a preconditioning strategy which acts block-wise on the set of enriched degrees of freedom associated to each node. This strategy uses a local (nodal) Cholesky based decomposition. Another issue is brought by the integration scheme used to build the matrices. The nature of the asymptotic functions are such that any Gauss-Legendre based integration scheme will only poorly converge with respect of the order of the quadrature. We propose a modified integration scheme to handle that issue. We apply the new technique developed to the estimation of stress intensity factors along the crack front of 3D cracks and use these SIFs for crack propagation using a Paris type fatigue law. [less ▲]

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