DYNAmore Vortrag bei der NAFEMS European SDM Conference, 24. - 25. Noverber 2010 in Frankfurt. Autoren: Martin Liebscher, Marko Thiele, Heiner Müllerschön (DYNAmore GmbH)

The increasing demands with regard to the predictive capabilities and the exactness of crash simulations require more and more investigations into numerical models in order to capture the physical behaviour reliably. Steps towards this goal are the usage of finer meshes which allow for a better geometrical representation and more sophisticated material models which allow better prediction of failure scenarios. Another important playground towards improved crash models is the area of connection modelling. Validation in this area is usually closely related to very detailed models which cannot be easily translated into a crash environment due to time step restrictions. Therefore, representative substitute models have to be developed and foremost validated. The aspect that failure of the connections has to be considered as well adds another dimension to the complexity of the task. The present paper highlights the conflict between predictive capability, capture of physical reality and manageable numerical handling. Another aspect of the paper is the attempt to raise the awareness of the topics verification and validation of numerical models in general. This concept is illustrated using latest developments for modelling of spotwelds and adhesive bonding in LS-DYNA.

A finite element human model, THUMS (Total HUman Model for Safety), was developed in order to study human body responses to impact loads. This paper briefly describes the structure of the human model, as well as some of the results of the simulations conducted to validate the model.

Die DYNAmore GmbH – Gesellschaft für FEM-Ingenieurdienstleistungen – ist das Kompetenzzentrum für Beratung, Anwendung, Schulung, Support und Vertrieb der Finite-Elemente(FEM)-Software LS-DYNA. Das Produktportfolio umfasst LS-DYNA, LS-OPT, LS-PREPOST, zahlreiche Insassen- und Barrierenmodelle sowie ergänzende Zusatzprogramme.

In den vergangenen Jahren haben die zunehmenden Anforderungen im Bereich der passiven Sicherheit dazu geführt, dass den aus der Crash-Simulation gewonnen Aussagen immer höhere Bedeutung zugemessen wird. Dabei waren Vorgehensweisen und Modelliertechniken einem deutlichen Wandel unterzogen. Die Stärken der virtuellen und realen Techniken werden gleichermaßen genutzt, um die Entwicklungszeiten zu reduzieren und das technologische Potenzial moderner Materialien und innovativer Entwicklungskonzepte konsequent auszunutzen.

Aktuelle Entwicklungen bei der Bauteileherstellung aus hochfesten Werkstoffen im lückenlosen virtuellen und realen Prozesskreis

Many accidents with children or small adults, where the ignition of the airbag leads to dangerous and even fatal injuries for the passengers, have led to a number of efforts to analyze this so-called „Out-of-Position“ load cases more deeply within the development process of an airbag system. In the framework of simulation systems the fluid-structure interaction between the inflating gas and the airbag fabric has not been taken into account in the past. Recent developments in the LS-DYNA software package allow a fully coupled arbitrary Lagrange-Euler formulation and thus a more exact representation of the airbag deployment process within the simulation system. In the present contribution we will describe the standard procedure, based on the assumption of a uniform pressure distribution in the airbag and the recently achieved advances in LS-DYNA with respect to fluid-structure interaction of the expanding gas and the inflating airbag fabric.

Detailed finite element side impact dummy models of the USSID, EUROSID, and ES-2 have been developed in cooperation with the German Association for Automo- tive Research (FAT) during the last 5 years. All models are validated using tests at material and component levels as well as fully assembled models. The models are used by nearly all car manufacturers worldwide who use LS-DYNA for occupant safety simulations. The paper describes modeling aspects of the dummies and gives an overview of their performance in sled tests. Furthermore emphasis is put on difficulties and potential pitfalls that might arise during the everyday work with the models in predicting occupant injury risks. In addition to the knowledge gained during the development process, experiences from the support for and the consult- ing with the FAT dummy models are presented.

Detailed finite element side impact dummy models of the USSID and EUROSID have been developed in cooperation with the German Association for Automotive Research (FAT) dur- ing the last 5 years. Both models are validated using tests at material and component levels as well as fully assembled models. The development of the LS-DYNA dummy models has been performed by the authors. Both models are used by nearly all car manufacturers worldwide which use LS-DYNA for occupant safety simulations.

The purpose of this paper is to explore some interesting aspects of stochastic opti- mization and to propose a two-stage optimization process for highly nonlinear automotive crash problems. In the first stage of this process, a preliminary stochastic optimization is conducted with a large number of design variables. The stochastic optimization serves the dual purpose of obtaining a (nearly) optimal solution, which need not be close to the initial design, and of identifying a small set of design variables relevant to the optimization problem. In the second stage, a deterministic optimization using only the set of relevant design variables is conducted. The result of the preceding stochastic optimization is used as the starting point for the deterministic optimization. This procedure is demonstrated with a van-component model (previously introduced in [1]) used for crash calculations. LS-OPT [4] is used due to its ability to perform both stochastic (Latin Hypercube) and deterministic optimization.

Components for occupant restraint systems usually undergo structural analysis before hardware prototypes are made. In most cases the simulation is nonlinear in geometry, material and boundary conditions. Additionally, the load case often is highly dynamic. For this purpose explicit FEM is a suitable tool. It is well known, that the accuracy of deformations and especially stresses has to be checked carefully in some cases. Therefore, a comparison of different modeling approaches has been performed for basic analytical load cases. The examined variations included: Shell and solid mesh, different degrees of discretization, element formulations. All models have been run in LS-DYNA, some selected ones as well in PAMCRASH and ABAQUS Standard, for reasons of comparison.

Recently new materials were introduced to enhance different aspects of automotive safety while minimizing the weight added to the vehicle. Such foams are no longer isotropic but typically show a preferred strong direction due to their manufacturing process. Different stress/ strain curves are obtained from material testing in different directions. A new material model was added to the LS-DYNA code in order to allow a correct numerical simulation of such materials. Ease-of-use was a primary concern in the development of this user-subroutine: we required stress/ strain curves from material testing to be directly usable as input parameters for the numerical model without conversion. The user-subroutine is implemented as MAT_TRANSVERSELY_ANISOTROPIC_CRUSHABLE_FOAM, Mat law 142 in LS- DYNA Version 960-1106. In this paper we summarize the background of the material law and illustrate some applications in the field of interior head-impact. The obvious advantage of incorporating such detail in the simulation lies in the numerical assessment of impacts that are slightly offset with respect to the foam’s primary strength direction.

LS-DYNA has been applied to springback simulation by a large number of users, with generally mixed results. Some results have demonstrated 70% accuracy or better, while others have been entirely misleading. In order to eliminate inconsistent results, this report presents a standard procedure for conducting springback simulations with LS-DYNA. The “seamless” and “dynain” methods for springback are described, followed by a description of general implicit springback problem set-up. Recommendations are given for anticipating and improving springback prediction accuracy.

LS-DYNA has been widely used to study automotive crash. Default input parameters are generally chosen to give efficient, accurate crash simulation results. These defaults are not necessarily optimal for metal forming simulations. The following presents a standard procedure for conducting metal forming simulations with LS-DYNA.

Daimler-Chrysler in particular needs to model the behaviour of padding and dummy parts for the numerica1 simu1ation of vehicle side impact and FMVSS201 interior head-impact. A common problem is the geometrical complexity of the parts involved. In the quest for a faster and easier way to represent these bulky, complex geometries with finite elements, the use of the 4-node tetraeder element in LS-DYNA was systematically investigated. At first we examined the response of the T4 (4-node tetrahedron)-element under simple load cases such as pure shear and uniaxial compression. The behaviour of the classical hexagonal (H8) element was compared to the T4 element in different (regular and free) meshing configurations. The same procedure was applied in a second phase to a combined shear-compression load case and a simple impact load case with a cylindrical penetrator. The conclusion of this work was that although some care must be taken in the use of T4-elements, the element seems to be failsafe in conditions where compression is the dominant deformation mode. In a brief application overview, the important savings that can be achieved in the model preparation phase due to the use of T4 elements are illustrated. An example of FMVSS201 head-impact is used to show that the differences in results with respect to a hexagonal mesh are within a range that is acceptable for engineering applications. A summary and conclusions complete the paper.