Finite element analysis of the free surface effects on the mechanical behavior of thin nickel polycrystals

in International Journal of Plasticity (2012), 29

The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The ... [more ▼]

The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The objective of this work is to provide new numerical results which explain the softening mechanisms on the mechanical behavior for nickel polycrystals which have been experimentally characterized by the authors in a previous published paper (Keller et al., 2011). Based on a strain gradient crystalline plasticity model identified for nickel, simulations of tensile tests were performed for samples with different thicknesses and grain sizes. The simulations correctly reproduce the softening effect linked to a decrease in the thickness and in the number of grains across the thickness. The analysis of the plasticity mechanisms shows that the softening is due to surface effects which are discussed in terms of grain orientations, dislocation mean free path and long-range back-stress. The model also predicts a hardening mechanism for further dimension reduction if the samples have only grain boundaries perpendicular to the tensile direction. In this case, the modification of the mechanical behavior is due to strain gradients formation. [less ▲]

A finite element code for subsidence problems: LAGAMINE

in Bulletin of Engineering Geology & the Environment (1993), 47(1 / avril), 5-11

Finite element computation of electromechanical micro-switches and micro-pump actuators

Conference given outside the academic context (2004)

a new methodology to model the electromechanical behavior of microscale system components is presented. The original approach proposed in this paper is based on a unified FE formulation of the strong ... [more ▼]

a new methodology to model the electromechanical behavior of microscale system components is presented. The original approach proposed in this paper is based on a unified FE formulation of the strong electromechanical interaction problem, in which both the electric and the mechanical fields are considered simultaneously. To this aim, finite elements based on the Mindlin shell theory are implemented. In order to illustrate the proposed methodology, numerical results are presented on the modelling and simulation of microscale electromechanical switches and microscale pump actuators. [less ▲]

Finite element computation of nonlinear normal modes of nonconservative systems

in Proceedings of the ISMA 2012 conference (2012, September)

Modal analysis, i.e., the computation of vibration modes of linear systems, is really quite sophisticated and advanced. Even though modal analysis served, and is still serving, the structural dynamics ... [more ▼]

Modal analysis, i.e., the computation of vibration modes of linear systems, is really quite sophisticated and advanced. Even though modal analysis served, and is still serving, the structural dynamics community for applications ranging from bridges to satellites, it is commonly accepted that nonlinearity is a frequent occurrence in engineering structures. Because modal analysis fails in the presence of nonlinear dynamical phenomena, the development of a practical nonlinear analog of modal analysis is the objective of this research. Progress in this direction has been made recently with the development of numerical techniques (harmonic balance, continuation of periodic solutions) for the computation of nonlinear normal modes (NNMs). Because these methods consider the conservative system, this study targets the computation of NNMs for nonconservative systems, i.e. defined as invariant manifolds in phase space. Specifically, a new finite element technique is proposed to solve the set of partial differential equations governing the manifold geometry. The algorithm is demonstrated using different two-degree-of-freedom systems. [less ▲]

Finite Element Computational Homogenization of Nonlinear Multiscale Materials in Magnetostatics

in 18th Conference on the Computation of Electromagnetic Fields (COMPUMAG2011) (2011)

This paper deals with the modelling of nonlinear multiscale materials in magnetostatics by means of a finite element computational homogenization method. The method couples a macroscale problem with many ... [more ▼]

This paper deals with the modelling of nonlinear multiscale materials in magnetostatics by means of a finite element computational homogenization method. The method couples a macroscale problem with many microscale problems. During the upscaling step, the homogenized magnetic permeability and its derivative with respect to the magnetic field are calculated from the microscale solution and transferred to the macroscale. The downscaling step consists in imposing proper boundary conditions for the microscale problems from the macroscale solution. Results are validated by comparison with those obtained with classical finite element brute force approach. [less ▲]

Finite element computations of hydro mechanical coupled problem using a local second gradient model

Conference (2005)

A finite element for thermo-mechanical problems.

in Proceedings Numiform Conference Göteborg (1986, August)

Finite element grid optimization with geometric approach

in The 33rd Aiaa/Asme/Asce/Ahs/Asc Structures, Structural Dynamics and Materials Conference: April 13-15, 1992/Dallas, Tx (1992)

Finite Element Magnetic Models via a Coupling of Subproblems of Lower Dimensions

in IEEE Transactions on Magnetics (2010), 46(8), 2827-2830

Model refinements of magnetic circuits are performed via a subdomain finite element method based on a perturbation technique. A complete problem is split into subproblems, some of lower dimensions, to ... [more ▼]

Model refinements of magnetic circuits are performed via a subdomain finite element method based on a perturbation technique. A complete problem is split into subproblems, some of lower dimensions, to allow a progression from 1-D to 3-D models. Its solution is then expressed as the sum of the subproblem solutions supported by different meshes. A convenient and robust correction procedure is proposed allowing independent overlapping meshes for both source and reaction fields, the latter being free of cancellation error in magnetic materials. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each model refinement on both local fields and global quantities. [less ▲]

A finite element method for thermomechanical simulation of materials submitted to high strain rates with an implicit approach

in 7th National Congress on Theoretical and Applied Mechanics (2006)