Papers by Author: Gundolf Kopp

Abstract: In this paper, the influence of corrosive conditions on the mechanical performance of Flow Drill Screw (FDS) joints is investigated in greater detail. Different combinations of light metals such as aluminium or magnesium alloys and high strength/stainless steel served as the test material. The joint strength of FDS joints, under quasi-static and cyclic loading, was measured before and after six weeks’ of corrosion climate change testing. Furthermore metallographic sections of the samples were compared in order to evaluate the stage of surface, galvanic and crevice corrosion. To classify the effect of progressing corrosion on the mechanical properties of FDS joints, the following factors are taken into account: corrosion resistance of the materials, joining parameters and the geometry of the joint. For all material combinations there is an apparent change in both the fatigue strength and the failure behaviour after corrosion testing.

Abstract: On modern vehicles, the demand is made to be in every respect as efficient as possible. A technical method to increase energetic efficiency is to reduce the vehicle mass through the implementation of lightweight construction measures. The energy consumption decreases by that and the vehicle dynamics behavior of conventionally and alternatively respectively electrically powered vehicles increases. In the department Lightweight and Hybrid Design Methods of the Institute of Vehicle Concepts in Stuttgart in collaboration with 3A Composite Core Materials, a method which allows to realize sandwich structures for automotive structural applications analytically and conceptually, is developed. The development method based on material and component testing and material values would be determined at different loads, for example in pressure and in-plane tests. These values are transmitted into the analytical determination of so called failure mode maps to derive appropriate sandwich structures. With novel sandwich structures the objectives of high structural stiffness and strength are tracked, as well as a high level of energy absorption potential. By function integrating the potential of lightweight construction, depending on the energy absorption per structural weight, can be further increased. Accompanying tests on generic structures are made to validate the failure behavior. Also the influence of core material on the deformation behavior is examined. The results from the tests are transferred to a vehicle front structure of a planned lightweight vehicle of class L7E called "Safe Light Regional Vehicle" (SLRV). The behavior of the structure is examined in static and dynamic tests. The energy absorbing capacity can be further increased by geometric optimization and the use of different core materials. The research on sandwich materials is part of the research project Next Generation Car (NGC) of the DLR and represents in terms of the new vehicle concept SLRV in sandwich design a novel vehicle concept of this joint project.

Abstract: State of the Art

Abstract: 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.

Abstract: The technical requirements to produce parts as light as possible with more complex geometries are ever increasing in recent years in automotive industries, rail vehicle and aerospace. Manufacturing technologies such as super-plastic metal forming, which had been considered as a niche technology earlier, is now gaining greater technical relevance for industrial size production. The parts that have been generated through super-plastic forming in innovative vehicle for example Mercedes SLS AMG reflect the industrial activity in this area. Manufacturability of thin-walled structures enables lightweight design. Also the tool and manufacturing costs are lower in comparison. However, the main challenge could be found in maintaining exact process parameters. There is a large research potential in super-plastic forming; from the determination of optimal material data through process simulation to manufacturing of real parts and their characterization. In the framework of the project international Bureau of the Federal Ministry of Education and Research UKR005/08 “Manufacture of parts with special properties” a preliminary research work has been carried out.

Abstract: A major motivation for the development of new vehicle structures is, apart from the reduction of fuel consumption, is to decrease emissions which affect the climate. Therefore we also have to look at the reduction of vehicle weight and consequently at various strategies for lightweight construction. In the future steel structure concepts still show lightweight potential. But even more attractive potential for lightweight body in white structures could be realised by new multi-material design concepts and highly integrated light metal applications. Today’s research activities are focussed on the area of multi-material design, with the objective of placing the material with the best properties for the given requirements in the right position. Based on various methods of lightweight construction, techniques and tools, it is possible to find an optimum between lightweight design and costs. These activities will be illustrated by several research examples. One example will be the lightweight concept of the front module developed by the Institute of Vehicle Concepts (DLR) in the European research project -‘Super Light Car’ (SLC). By using aluminium in the front structure and the high pressure die casting strut tower the concept has a weight benefit of 32% compared to a steel reference structure. The methodology for reaching targets and requirements like weight reduction, crash performance and cost targets will be explained. Another example is a concept which is developed in the DLR project ‘Novel Vehicle Structures’. This concept shows the combination of different materials and a new construction method to increase front impact crash performance.

Abstract: Besides reducing fuel consumption, the chief motivating factor behind the development of new vehicle structures is the desire to decrease climate-affecting emissions. One approach to addressing this involves reducing the vehicle mass and, as such, the various strategies relating to lightweight construction. Various methods of lightweight construction are used as a basis for deriving the technically relevant criteria for designs and material concepts. The work conducted in this field today centres around the synthesis of construction method and material development with the objective of devising a multi-material-design [1, 2]. Modularisation is an economic approach aimed at shaping the diversification of the vehicle concepts and implementing this effectively [3]. As a result of hybrid and later fuel cell drives, the requirements on the vehicle concepts will continue to grow in future. Modularisation also sometimes opposes the striving for a high level of integration. The modular lightweight concept of the DLR aims at designing powertrain evolutions in a scalable and cost-efficient manner and in a way that retains the concept flexibility or, in some cases, even increases this. These approaches lead to the strategy known as “hybrid3”. This strategy not only involves matching different materials and various construction methods with each other, but also taking account of the integration of functional effects. This entails, for example, optimising the design of thin-walled structural components in terms of their vibratory or acoustic properties with structure- integrated, active materials. Further examples of the approach with “hybrid3” effects could be selectable surfaces or integrated energy conversion. The various development directions are depicted in the form of a roadmap and discussed on the basis of forward-looking examples from the field of vehicle construction.