Michael Kriescher

Bending Collapse Behaviour of Polyurethane Foam-Filled Rectangular Magnesium Alloy AZ31B Tubes

Quasi-static/dynamic three-point bending tests were conducted to assess the crash performance of magnesium alloy AZ31B extruded and sheet tubes at the German Aerospace Centre (DLR) – Institute of Vehicle Concepts in Stuttgart. Different foam-filled AZ31B beams with a variation of foam density and thickness were fabricated through several manufacturing processes: cold bending, tungsten inert gas welding, cathodic dip painting and polyurethane foam injection. The experimental results were compared with those from mild steel DC04 tubes. It shows that empty magnesium alloy AZ31B outperforms steel DC04 in terms of specific energy absorption for the empty tubes with equivalent volume when subjected to bending loads. It was found that the foam-filled tubes achieved much higher load carrying capacity and specific energy absorption than the empty tubes. Moreover, there is a tendency showing that a foam-filled beam with a higher foam density reaches higher load carrying capacity, but fractures earlier. The foam-filled AZ31B tube with 0.20 g/cm3 foam obtained the highest specific energy absorption, but this outperformance was weakened due to the earlier fracture. In addition, the numerical simulation utilising material model MAT_124 in LS-DYNA explicit FEA package was performed. The simulation results indicate that using calibrated stress-strain curves and failure parameters, material model MAT_124 yields a general good agreement with the experimental results.

Sandwich Lightweight Design in Automotive Usage

State of the Art

Kostenattraktiver Leichtbau in der Vorderwagenstruktur

Zur Senkung des CO2-Ausstoses spielt die Reduzierung der Fahrzeugmasse eine wichtige Rolle. Am Beispiel eines Magnesiumgussteils fur die Vorderwagenstruktur zeigt das DLR-Institut fur Fahrzeugkonzepte, wie durch Anwendungen einer geeigneten Leichtbaustrategie, durch Nutzung der Topologieoptimierung und durch eine neue kostenattraktive Bauweise erhebliche Gewichtseinsparungen erzielt werden konnen.

Dynamic bending behaviour of magnesium alloy rectangular thin-wall beams filled with polyurethane foam

ABSTRACT This study proposes a hybrid structural design concept of polyurethane foam-filled magnesium alloy AZ31B rectangular thin-walled beams which serve as energy absorbing components in automotive applications. Uniaxial tensile and compressive tests, and fracture tests were performed to investigate the material mechanical properties. Dynamic three-point bending tests were performed to study the deformation/fracture modes and energy absorption capacity for the foam-filled AZ31B beams, and to compare these mechanical properties with those for mild steel DC04 beams. Different AZ31B beams were filled with a variation of foam density (0.05, 0.20 and 0.30 g/cm3). It was found that the AZ31B beam filled with 0.20 g/cm3 foam reached the highest specific energy absorption; moreover, it absorbed more energy and reached much higher specific energy absorption than the foam-filled DC04 beam filled with the same foam, although the former one was nearly 54% lighter. The potential advantage of the foam-filled AZ31B beams is possibly associated with the high work hardening rate of AZ31B sheet in compression, which may involve more material in plastic deformation compared with the foam-filled DC04 beams. It has therefore been demonstrated that the hybrid structural design concept of the polyurethane foam-filled AZ31B beam has potential applications in auto-body structures.

Entwicklung einer leichten, funktionsintegrierten Karosserie

Am Institut fur Fahrzeugkonzepte des Deutschen Zentrums fur Luft- und Raumfahrt (DLR), wird ein sehr leich-tes Fahrzeugkonzept der L7e-Klasse, als Forschungsdemonstrator, mit einem Karosseriegewicht von nur 90 kg entwickelt, das gleichzeitig sehr gute Crasheigenschaften aufweist. Das Strukturkonzept beinhaltet die konse-quente Anwendung von Hybrid-Werkstoffen in einer Sandwichbauweise, so dass sich eine leichte Struktur ergibt, die aus vergleichsweise wenigen, einfach geformten Bauteilen besteht. Diese Struktur wird durch FE-Simulationen sowie Versuche auf Bauteilebene, fur verschiedene Crashlastfalle untersucht. Die hohen Anforderungen an Gewicht und Crashsicherheit erfordern auserdem ein leichtes, auf die Crashszena-rien abgestimmtes Fahrwerkskonzept, das ebenfalls durch Crashsimulationen untersucht wird. Die Ergebnisse dieser Untersuchungen, die zum Verbundforschungsprojekt Next Generation Car (NGC) des DLR zahlen, wer-den hier vorgestellt.

ENTWICKLUNG UND UNTERSUCHUNG EINER LEICHTEN, FUNKTIONSINTEGRIERTEN KAROSSERIE IN METALL-SANDWICH-BAUWEISE

Am Institut fur Fahrzeugkonzepte des Deutschen Zentrums fur Luft- und Raumfahrt (DLR) wird im Rahmen des Verbundforschungsprojektes Next Generation Car (NGC) ein sehr leichtes Fahrzeugkonzept der L7e-Klasse als Forschungsdemonstrator mit einem Karosseriegewicht von nur 90 kg entwickelt, das gleichzeitig sehr gute Crasheigenschaften aufweist. Das Strukturkonzept beinhaltet die konsequente Anwendung von Hybrid-Werkstoffen in einer Sandwichbauweise, so dass sich eine leichte Struktur ergibt, die aus vergleichsweise wenigen, einfach geformten Bauteilen besteht. Diese Struktur wird durch FE-Simulationen sowie durch statische und dynamische Versuche fur verschiedene Crashlastfalle untersucht.

Next Generation Car – Lightweight Design Through Function Integration In Vehicle Structures

The „Next Generation Car” (NGC) project combines the research activities of the German Aerospace Center (DLR) in the area of road vehicles. The aim is the development of vehicle concepts and structures, with a high energy efficiency. Under the roof of NGC the DLR develops different vehicle concepts. The concepts have different aims and requirements, e.g. driving distance, number of passengers or maximum speed and should give answers for future vehicle structures. The challenge is to fulfill opposed requirements, e.g. mechanical performance (e.g. crash) and economical values (e.g. costs). At the example of the concept of the „Safe Light Regional Vehicle“ (SLRV) we will show the development of a light and safe body in white (BIW) structure. The BIW realizes special requirements, e.g. packaging, fatigue strength, stiffness and crash performance within a 2 passenger vehicle concept with a mass lower than 500 kg. The BIW design is a sandwich structure with a resulting structural mass of only 90 kg. Simulations indicate that the crash performance is very good, even if the mass of the BIW is so light. The simulations are validated by component crash tests. The result will be shown in this paper.

Next Generation Car — Example of Function Integration at the Light Urban Vehicle (LUV) Vehicle Concept

In times of climate change vehicle emissions have to be reduced clearly. One possibility is to reduce the mass of the body in white using lightweight sandwich structures. The department ‘Lightweight and Hybrid Design Methods’ of the Institute of Vehicle Concepts develops a vehicle body structure by using sandwiches with aluminum top layers and polyurethane foam as core material. For that the foam and the sandwiches were investigated under different load cases, e.g. pressure loading and in-plane tests. In tests with components the high potential of the sandwich materials were shown. On the dynamic component test facility of the institute, vehicle front structures were tested successfully. The results of all investigations regarding sandwich materials, integration of functions (e.g. crash, thermal) in vehicle structures and the concept LUV are developed under the research program of Next Generation Car of the DLR. We will show the development and results of the LUV.

Peeling of Aluminium Tubes as an Efficient Method for Energy Absorption in Vehicle Front Structures

Current crash structures in cars are still using the buckling of metallic structures to absorb the kinetic energy in case of an impact. The disadvantage of this technology is that changes within the static structural behaviour, like e.g. the stiffness or eigenfrequencies, will cause changes in the crash behaviour, even if this is not desired. This correlation between static and dynamic behaviour causes many development loops to adjust the crash behaviour, e.g. through optimizing trigger geometries which lower the initial crash forces. The German Aerospace Center (DLR) - Institute of Vehicle Concepts has developed a novel method to offer an efficient way of absorbing energy by peeling the outer skin of load bearing structures, like the crash boxes and the longitudinal rails. This technology provides an adjustable force level without changing the static behaviour of the front structure itself. This property offers the opportunity to create adaptable crash behaviour with only smallest changes within the peeling depth. Furthermore, it is possible to generate close to ideal force-deflection curves, which offers the potential to achieve high specific energy absorption. The DLR will show results of static and dynamic testing of crash tubes and of a vehicle front structure equipped with this mechanism. In addition the implementation of the methodology into the dynamic simulation with LS-Dyna will be shown. Benefits and limitations of this novel energy absorption method will be discussed.

Cost-Efficient lightweight design in the front-end structure

Decreasing the mass of a vehicle plays an important role in reducing CO2 emissions. Using the example of a magnesium casting component for the front-end structure, this project from the DLR shows how considerable weight savings can be achieved through the application of appropriate lightweight design strategies, the use of topology optimisation and a new type of cost-efficient construction.