Improvements in FE-analysis of real-life sheet metal forming

An overview will be presented of recent developments concerning the application\ud and development of computer codes for numerical simulation of sheet metal forming\ud processes. In this paper attention is paid to some strategies which are followed to improve the\ud accuracy and to reduce the computation time of a finite element simulation. Special attention\ud will be paid to the mathematical modeling of the material deformation and friction, and the\ud effect of these models on the results of simulations. An equivalent drawbead model is\ud developed which avoids a drastic increase of computation time without significant loss of\ud accuracy. The real geometry of the drawbead is replaced by a line on the tool surface. When\ud an element of the sheet metal passes this drawbead line an additional drawbead restraining\ud force, lift force and a plastic strain are added to that element. A commonly used yield\ud criterion for anisotropic plastic deformation is the Hill yield criterion. This description is not\ud always sufficient to accurately describe the material behavior. This is due to the\ud determination of material parameters by uni-axial tests only. A new yield criterion is\ud proposed, which directly uses the experimental results at multi-axial stress states. The yield\ud criterion is based on the pure shear point, the uni-axial point, the plane strain point and the\ud equi-biaxial point

HYBRID PARALLELISATION OF AN ALGORITHMICALLY DIFFERENTIATED ADJOINT SOLVER

This research has been supported by the European Commission under the HORIZON 2020 Marie Curie fellowship (grant no. 642959

Mechanical properties of the cellular structures based on the isotruss unit cell^®

Summary. The present work aims to investigate the mechanical properties of the cellular structure based on the Isotruss unit cell by implementing the finite element method (FEM) introducing a representative elementary volume (REV). As an orthotropic cellular structure, the three principal Young’s modulus along the longitudinal and transversal directions are evaluated. The influence of the geometrical parameters on the elastic properties is studied in detail. Results reveal that Young’s modulus in two transverse directions are almost close, showing a 12% difference. Besides, the proposed unit cell presents the ability to tune the elasticity along with the main directions. It is seen that increasing the angle of helical pitch, increases the longitudinal Young’s modulus while decreases the transverse ones that suggest a considerable possibility for optimal designs. As an example, mimicking Young’s modulus of the human cortical bone as an orthotropic material is explored and it is seen that the presented cellular structure based on the Isotruss unit cell can successfully fit

Multi-physics Modelling of a Compliant Humanoid Robot

In this paper, we discuss some very important features for getting exploitable simulation results for multibody systems, relying on the example of a humanoid robot. First, we provide a comparison of simulation speed and accuracy for kinematics modeling relying on relative vs. absolute coor- dinates. This choice is particularly critical for mechanisms with long serial chains (e.g. legs and arms). Compliance in the robot actuation chain is also critical to enhance the robot safety and en- ergy efficiency, but makes the simulator more sensitive to modeling errors. Therefore, our second contribution is to derive the full electro-mechanical model of the inner dynamics of the compliant actuators embedded in our robot. Finally, we report our reasoning for choosing an appropriate contact library. The recommended solution is to couple our simulator with an open-source contact library offering both accurate and fast full-body contact modeling

Geometrically exact multi-layer beams with a rigid interconnection

Abstract. In this work, a finite-element formulation for geometrically exact multi-layer beams without considering the interlayer slip and uplift is proposed. Numerical examples indicate that, in comparison with the existing geometrically non-linear sandwich beam models, the 2D plane-stress elements and the analytical results from the theory of elasticity, the multi-layer beam model is very efficient for modelling thick beams where warping of cross-sections has to be considered

Simulation of the Aerodynamic Effects on an Actuated Pendulum with the Actuator Volume Method

This paper presents the Actuator Volume method applied to a simplified problem (unsteady with complex three-dimensional geometries) in order to validate it. Another goal is to make the junction between multibody dynamics and aerodynamics, that could be coupled for different situations

Solving the muscle redundancy problem with EMG input: application to back muscles for the Sorensen test posture

When solving inverse dynamics in the human body with a pure mathematical approach such as optimisation, the problem of muscle redundancy occurs. To solve this problem, cost functions can be found in the literature for the optimisation process to give the most physiological solution. Another approach is to use relevant information such as electromyography (EMG) from an upfront experiment prior to the quantification of muscle forces via a multibody (MBS) model. The idea is to make the most of EMG signals in the MBS model and in the subsequent computation process. In this work, such an EMG-based approach is used to predict muscle forces and intervertebral efforts in the lumbar spine for a static configuration in the Sorensen test posture. Muscles forces and the resulting intervertebral efforts are compared with these from a purely mathematical approach. One male subject was asked to produce three different muscle strategies in the Sorensen test posture. EMG signals of back and abdominal muscles were recorded during the experiment. Each configuration was performed without and with an external mass equal to 20% of the bodymass. An equivalent MBS model of the trunk in the Sorensen test posture including only back muscles was developed. Muscle forces for the EMG-based approach were quantified based on a deterministic muscle force distribution. On the other hand, muscle forces for the optimisation computation were computed with a trust-region algorithm with a constrained optimisation technique with two different cost functions classically used in the literature. As expected, varied muscle strategies were obtained for the different configurations on the basis of recorded EMG amplitudes. These different muscle strategies were obviously not caught by the optimisation computation. In conclusion, EMG seemed to be a valuable input to study different muscle strategies for a same subject that could not be differentiated by optimisation computations

A Scaled-Bogie Test Bench to Understand and Demystify Wheel-Rail Contact Dynamics

It is a well-known fact that railway dynamics is far from being trivial, mostly because of the wheel/rail contact phenomenon. Except for specialists in this field who are obviously familiar with notions like wheelset equivalent conicity, hunting motion, limit cycles, etc., most of people, including engineers, have no or few idea about the guidance principle of railway vehicles equipped with standard bogies with rigid wheelsets. The present project has been initiated at the Center for Research in Mechatronics of the Université catholique de Louvain within the framework of a master thesis under our supervision. The main objective is essentially educational and led us to build an experimental bench to highlight the wheel/rail guidance phenomenon of railway vehicles