Integracion Numerica del Problema Viscoplastico

(2009)

En este trabajo se discute la integración numérica para el modelo viscoplástico de Perzyna, que conduce a una ecuación de consistencia viscoplástica no lineal, de acuerdo a un trabajo previo de Ponthot ... [more ▼]

En este trabajo se discute la integración numérica para el modelo viscoplástico de Perzyna, que conduce a una ecuación de consistencia viscoplástica no lineal, de acuerdo a un trabajo previo de Ponthot. Esta ecuación no lineal se resuelve mediante elMétodo de Newton Raphson y el algoritmo resultante se implementa en MATLAB. Los resultados obtenidos con el programa desarrollado ajustan muy bien con soluciones cerradas disponibles en la literatura para algunos casos particulares. En este trabajo además se propone una solución cerrada para el caso de sensitividad viscosa lineal (m=1) y exponente de endurecimiento viscoplástico lineal (n=1). Se estudia además la respuesta del algoritmo frente a la variación de diferentes parámetros como el coeficiente de viscosidad. El código obtenido en una etapa posterior del estudio se podrá utilizar para resolver otros problemas de interés y, además, permitirá su implmentación en un código de elementos finitos con capacidades no lineales. [less ▲]

Damage and fracture of materials submitted to high strain rates. A thermomechanically coupled approach with element erosion

in Proceedings of “Dynamic behaviour of materials”, Workshop in memory of Prof. J.R. Klepaczko (2009)

Etudes sur la simulation de la tenue thermo-mécanique d'assemblages complexes

Report (2008)

A continuum damage model for alveolar bone remodeling

in Fourth International Conference on Advance COmputational Methods in ENgineering - ACOMEN 2008 (2008, May)

Issues in FEM-based Modeling of Brain Shift in Neurosurgery

in Hogge, Michel; Van Keer, R.; Noels, Ludovic (Eds.) et al Proceedings of ACOMEN’2008, Advanced Computational Methods in Engineering (2008, May)

We consider the problem of improving outcomes for neurosurgery patients by enhancing intraoperative navigation and guidance. Current navigation systems do not accurately account for intraoperative brain ... [more ▼]

We consider the problem of improving outcomes for neurosurgery patients by enhancing intraoperative navigation and guidance. Current navigation systems do not accurately account for intraoperative brain deformation. In this work, we focus on the brain shift deformation that occurs just after the opening of the skull and dura, before any cut and subsequent deformation has happened. We test several algorithms and parameters in order to evaluate their impact on the modeling of the brain shift. [less ▲]

An Efficient Numerical Model for the Numerical Simulation of Forming Processes

in Khan, Akhtar; Farrokh, Babak (Eds.) Mechanics and Mechanisms of Finite Plastic Deformation : Proceedings of PLASTICITY'08, Fourteenth International Symposium on Plasticity and its Current Applications (2008, January)

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of a 2D metal cutting operation and a 3D U-shaped cold roll forming process. Compared to the Lagrangian case ... [more ▼]

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of a 2D metal cutting operation and a 3D U-shaped cold roll forming process. Compared to the Lagrangian case, this method allows the use of a refined mesh near the tools, leading to an accurate representation of the chip formation (metal cutting) and the bending of the sheet (roll forming) with a limited computational time. [less ▲]

The influence of friction on elasto-plastic material in nanoindentation

in Proceedings of ACOMEN’2008, Advanced Computational Methods in Engineering (2008)

A comprehensive computational study is undertaken to identify the influence of friction in nanoindentation of elasto-plastic materials, the impacts of friction on calculation results with conical and ... [more ▼]

A comprehensive computational study is undertaken to identify the influence of friction in nanoindentation of elasto-plastic materials, the impacts of friction on calculation results with conical and spherical indenters are shown in this paper. The results clearly demonstrate that, for some elasto-plastic materials, the P  h curves obtained either by spherical or conical indenters with different friction coefficients cannot be distinguished. However, if utilizing the parameter  (see text for details), to quantify the deformation of piling-up or sinking-in, it is easy to find that the influence of friction on piling-up or sinking-in in nanoindentation is significant. Therefore, the material parameters derived from the projected area will have a large error caused by the influence of friction. In this paper, the maximum error on hardness can reach 14% for some elastic materials. These results do not agree with those from researchers who stated that instrumented indentation experiments are not significantly affected by friction. Moreover, in conical indentation, friction can effectively restrain the slip on the interface between indenter and specimen, which leads to a decrease in the amount of piling-up or increase in the amount of sinking-in. However, when the half apex angle is large enough, the influence of friction becomes a minor factor in indentation. In spherical indentation, the amount of piling-up decreases or of sinking-in increases with an increasing friction coefficient. But the friction is independent of the radius of spherical indenter, the piling-up or sinking-in obtained by two different spherical indenters with varying friction coefficients are nearly identical. [less ▲]

An Improved Constitutive Model for the Numerical Simulation of Semi-Solid Thixoforming

in Proceedings of ACOMEN’2008, Advanced Computational Methods in Engineering (2008)

In order to model thixoforming processes, previous papers presented a thermo-mechanical one-phase modelling. This first version of constitutive model revealed several limitations: the model could not ... [more ▼]

In order to model thixoforming processes, previous papers presented a thermo-mechanical one-phase modelling. This first version of constitutive model revealed several limitations: the model could not degenerate properly to pure solid or liquid behaviour neither to free solid suspensions. The aim of this paper was to propose solutions to overcome these limitations. [less ▲]

Numerical simulation of cold roll-forming processes

in Journal of Materials Processing Technology (2008), 202(1-3), 275-282

3D finite element analysis is employed to simulate a cold roll-forming process. Numerical results of longitudinal strains and displacement trajectories are compared with experimental results available in ... [more ▼]

3D finite element analysis is employed to simulate a cold roll-forming process. Numerical results of longitudinal strains and displacement trajectories are compared with experimental results available in the literature. Through a parametri study, significant impacts of the yield limit and the work-hardening exponent on the product quality are observed, whereas forming speed and friction at roll-sheet interface appear to play a minor role. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

A first-order energy-dissipative momentum-conserving scheme for elasto-plasticity using the variational updates formulation

in Computer Methods in Applied Mechanics & Engineering (2008), 197(6-8), 706726

In a previous paper [L. Noels, L. Stainier, J.-P. Ponthot, An energy momentum conserving algorithm using the variational formulation of visco-plastic updates, Int. J. Numer. Methods Engrg. 65 (2006) 904 ... [more ▼]

In a previous paper [L. Noels, L. Stainier, J.-P. Ponthot, An energy momentum conserving algorithm using the variational formulation of visco-plastic updates, Int. J. Numer. Methods Engrg. 65 (2006) 904-942] the authors demonstrated the efficiency of the variational formulation of elasto-plastic updates to develop energy-momentum conserving time integration algorithms. Indeed, within such a framework, the stress tensor always derives from an incremental potential, even when plastic behavior is considered. Therefore the verification of the conservation of energy in the non-linear range can easily be demonstrated: the sum of the reversible stored energy and irreversible dissipated energy exactly corresponds to the work of the external forces applied to the structure. Although this formulation was shown to be accurate and robust, the introduction of numerical dissipation for high-frequency numerical modes can be necessary to simulate complex phenomena. In this work, we propose a modification of the variational updates framework to introduce this numerical property, leading to a new energy-dissipative momentum-conserving time-integration algorithm for elasto-plasticity. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]