Luc Papeleux

Finite element simulation of springback in sheet metal forming

Abstract Although finite element analysis (FEA) is successful in simulating complex industrial sheet forming operations, the accurate and reliable application of this technique to springback has not been widely demonstrated. Several physical parameters, as well as numerical, influence this phenomenon and its numerical prediction. In this paper, we investigate the impact of these parameters on the springback appearing in a 2D U-draw bending.

The Influence of Equivalent Contact Area Computation in 3D Extended Node to Surface Contact Elements

This paper extends the frictionless penalty-based node to contact formulation with area regularization to a 3D framework. Based on our previous work [1] focused on axisymmetric modeling, two computational methods are also considered for the determination of the slave node area. The first method, named as the geometrical approach, is based on a force equivalence system, while the second one, named as the consistent approach, is derived from a more sophisticated scheme elaborated upon the virtual work principle. Then, the extended contact elements are derived for the contact formulations with geometrical and consistent area regularization and a consistent linearization is provided accordingly, which guarantees a quadratic rate of convergence of the global Newton Raphson iterative procedure. Finally, two numerical examples assess the performance of both contact formulations with area regularization and demonstrates the robustness and the efficiency of the node to surface contact formulation with consistent area regularization in reproducing a constant contact pressure distribution across the interface between a deformable body and a analytically-defined rigid body, irrespective of the mesh. Our findings will certainly encourage further developments towards the design of a penaltybased node to surface contact algorithm passing the contact patch test, as was already done successfully in 2D contact problems [2].

Thermoviscoplasticity at Finite Strains: A Thermoelastic Predictor-Viscoplastic Corrector Algorithm

This paper proposes a fully-coupled thermomechanical analysis of multilayered plates and shells. In the proposed refined plate/shell models, the temperature is considered as a primary variable of the problem as the displacement and it is directly obtained from the governing equations. Such models are very promising for multilayered structures because they permit both equivalent single layer and layer wise approaches and they have the order of expansion in the thickness direction as a free parameter (from linear to fourth order). Three different problems can be analyzed: evaluation of temperature field effects in the free vibration analysis of multilayered plates and shells; evaluation of temperature field effects in the stress analysis of multilayered structures subjected to mechanical loads; thermal stress analysis of multilayered structures with imposed sovra-temperature.From the Contents: - Aero-Thermo-Elasticity, Aero-Magneto-Elasticity, Functionally Graded Plates, Shells and Beams.- Analytical (Computational) Thermomechanics.-Ceramics and Linear Fracture Mechanics.-Composites.-Contact Problems.-Coupled and Generalized Thermoelasticity.-Elastostatics and Thermoelastostatics.-Electro-Elastic Thermoelasticity and Smart Structures.-Electronics, Optoelectronics, Photonics, and MEMS (MOEMS) Packaging Engineering.-Fracture.-Heat Conduction-Direct, Inverse and Optimization.-Heat Treatment, Welding, and Shape Memory.-Linear and Nonlinear Viscoelasticity and Viscoplasticity.-Mathematical Preliminaries and Methods.-Methods of Complex Variables.-Nanotechnology, Special Methods in Thermal Stresses.-Plates.-Qualitive Properties of Thermoelastic Solutions.-Shells.-Simulation and Modeling-Thermal Stresses.-Stability.-Thermal Stress Resistance, Experimental Methods.-Thermal Stresses-Basic Problems.-Thermal Stresses Induced by Laser Heating.-Thermo-Inelasticity and Damage.-Thermodynamics of Thermodeformable Solids.-Thermoelastodynamics.-Transient Thermoelastic Waves and Dynamic Problems.-

A 3D Arbitrary Lagrangian Eulerian formulation for the numerical simulation of forming processes. Application to cold roll forming and metal cutting.

The paper deals with the numerical simulation of forming processes by the finite element method. In order to find the solution of steady state processes by numerical simulation with the classical Lagrangian formulation, very large and useless meshes have to be considered. For example, when dealing with rolling simulation, a large part of the sheet has to be discretized even if the results in the first finite elements, which are introduced between the rolls, are not important. However, these finite elements cannot be removed because they are required in order to reach the steady state solution. Consequently, the CPU time is very large. Another approach is the well-known Eulerian formulation: the media flows through the mesh, which is fixed in space. However, boundary conditions are rather difficult to handle particularly frictional contact and free surfaces.

Numerical Simulations of a Two Roll Round Bar Straightener

A finite element model of a two-roll round bar straightener has been developed to study the influence of key parameters on the straightening process. The present model already allows a better understanding of the process and the effects of straightening on the bar. A dedicated post-treatment is also proposed. It is particularly focused on the defect of the bar before and after straightening as well as rotation speed of the bar in order to validate the model. Other quantities are available : equivalent cumulated plastic strain and longitudinal stress for instance. This model is also the first step towards further analysis of the process such as, for example, parametric studies.

A General Arbitrary Lagrangian Eulerian Formulation for the Numerical Simulation of 3D Forming Processes

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. The main problem of this kind of simulation is the rezoning of the nodes on the free surfaces of the sheet. A modified iterative isoparametric smoother is used to manage this geometrically complex and CPU expensive task.

An ALE Model for Numerical Simulation of Cold Roll Forming Process

In this paper, the Arbitrary Lagrangian Eulerian formalism is used to compute the steady state of 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 bending of the sheet with a limited computational time. The main problem of this kind of simulation is the rezoning of the nodes on the free surfaces of the sheet. A modified iterative isoparametric smoother is used to manage this geometrically complex and CPU expensive task.