Cars need to lose some weight, but in so doing the safety of the vehicle’s occupants must not be jeopardised. At the department for lightweight structures at the Fraunhofer Institute for Structural Durability and System Reliability LBF in Darmstadt, Germany, components and systems in fibre reinforced as well as non reinforced plastics are investigated to reflect a holistic approach in relation to material, design, production and operation; prototypes are built and evaluated in terms of their system reliability. Plastics met Prof. Dr-Ing. Andreas Büter and talked with him about the challenges presented by electro-mobility.
Plastics: Looking at the plastics side of things, what are the challenges that concern you at the moment at the Fraunhofer Institute LBF?
Büter: At the moment we are working with the broad spectrum of continuous fibre reinforced thermosets and thermoplastics as well as with classics such as chopped strand reinforced thermoplastics and SMC. In addition, we are also increasingly turning our attention to the natural fibres sector. Currently, in one project, we are concerning ourselves with the use of paper fibres in plastics. The aim of our material analyses is to enable reliable operation for parts made of this new material. For this, tests on specimen as well as components are necessary.
Plastics: In response to e-mobility and the efforts being made in the field of lightweight design, the proportion of plastics in the automobile is set to increase to 25% by weight or more, according to various market research companies. Do you agree with this?
Büter: As a result of e-mobility, lightweight design activities have acquired a new level of quality. It is true to say that chopped strand reinforced thermoplastics have been established in automotive design for many years and will doubtless also continue to be used in specific applications. SMC and LFT, for instance, have tended to be employed in secondary components. The high strength and rigidity of these types of plastic will certainly be exploited even better. Additional innovation can be expected from the use of continuous fibre reinforced material as in BMW’s i3.
Weight can, however, be influenced not only by the choice of material but also by the design. We have observed that safety-relevant components of the first generation are often designed very conservatively. With the acquisition of experience through test results, they become lighter – without compromising on safety – as development continues.
Plastics: Naturally, we in our sector often equate lightweight design with metal substitution by plastics. But, in the steel and aluminium sectors, there are also on-going developments that encourage lightweight design. Are there some components which we will never see in plastic?
Büter: I don’t think we will ever see a volume production vehicle completely made from plastic, in the end it will invariably boil down to hybrid constructions. Metal is unassailable where a component is required to display rigidity in all orientations. Fibre composites, on the other hand, allow tailoring stiffness through fibre-orientations and enable specific adaptation to the characteristics profile targeted or the integration of functionalities. The selection of materials will always be an optimisation process. Nor do I think that “black metal” would, in the final analysis, be any lighter than a hybrid construction.
Plastics: What are the new developments in plastic which would be useful from your point of view?
Büter: Safety components such as wheels or chassis components. But this still represents an enormous step. Initially it is automated, reasonably priced production processes that are the focus of interest. Nevertheless, all safety aspects must be examined without exception.
Take, for example, the CFRP wheel that we designed (polymotive reported on this, issue 3/2012). Initially, it was our aim to show that even components that are subject to large stresses and safety relevant components can be realised in plastic. By way of a finishing touch, we subsequently employed electric motors with a view to using them as wheel hub drives in e-cars. But the design and testing of the prototype was only the first step. You also need to look at cost-effective manufacturing which will make economic production a possibility; you need to determine structural durability by carrying out tests on components and to apply for permits and certifications. Plus, repair or recycling concepts also need to be taken into account.
Plastics: In the case of the BMW i3, we see a change in vehicle design, for instance you can’t help noticing the B-column is missing. As far as you are concerned, does the i3 represent a successful scion of BMW?
Büter: From the plastics point of view, the i3 undoubtedly represents a step in the right direction and is a courageous undertaking on the part of BMW. Where electric cars are concerned, BMW is forging ahead. Something’s got to happen if we want to make up for the additional weight of the battery.
Plastics: According to a report by “Automobilwoche” (Automobile Weekly), in 2012 eight times as many show horses were registered than electric cars in Germany. What needs to happen to enable the electric cars to move out of the niche and into the mainstream markets?
Büter: First of all it is a question of price. As long as the price of fuel is still affordable and electric cars are expensive, only a minority of consumers will be interested in changing. One factor that should not be underestimated however is the image of the cars. Fraunhofer LBF is currently undertaking tests using our own fleet of electric vehicles and encouraging our employees to also use them also for trips with their families and friends. Their experience in real-life electro-mobility is being investigated as part of on-going research.
Plastics: Many thanks!