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K 2007Trade press conference

July 3 and 4, 2007 inFrankenthal, Germany

Material – simulation – crash

The new “crash” grades in BASF’s polyamide range: UltramidCR

Presentation byDr. Anka Bernnat,

Technical Marketing Ultramid,

BASF Aktiengesellschaft, Ludwigshafen, Germany

Two of the most important characteristics of modern components in motor vehicles today are low weight coupled with high functionality. If motor cars are becoming steadily heavier, e.g. due to numerous fittings for the safety of occupants and pedestrians, although fuel consumption is supposed to fall dramatically in future, the solution to these contradictory requirements is lightweight construction using plastics. A known example of this from BASF’s own activities is the lower bumper stiffener (LBS) developed in collaboration with Opel, which meets in full the high requirements for pedestrian safety and at the same time those for favourable insurance premiums. The LBS was the first series-built polyamide component meeting crash requirements that was developed completely from start to finish with the aid of BASF’s method of Integrative Simulation.

Plastic + computer-aided design for the customer

The LBS was the proof that today plastic parts likely to be subjected to stress in a crash can only be designed efficiently when, on the one hand, the material is sufficiently rigid and nevertheless absorbs a lot of energy and, on the other hand, its behaviour in a crash can be precisely described by means of sophisticated CAE software. BASF is now able to offer its customers under the brand name Ultramid® CR a group of polyamides which, with the aid of its method of Integrative Simulation developed in-house, are exactly matched to the demands imposed on components in the event of a crash. Apart from materials with optimized composition and the materials data available for the simulation – at high strain rates, among other things – the package also contains particularly narrow material specifications and intensive quality controls.

Four CR grades for high energy absorption

The Ultramid® CR range consists at present of four Ultramid grades especially for high energy absorption and two grades that are optimised for dynamic loads. The materials for high energy absorption include three Ultramid B grades (PA 6) having different levels of rigidity. The three black coloured products Ultramid B3WG6 CR, B3WG7 CR and B3WG8 CR are reinforced with 30, 35 and 40 per cent of glass fibres respectively. High-speed tensile tests show that these CR grades exhibit distinctly more advantageous behaviour for crash applications than the conventional variants. The material Ultramid A3WG7 CR1 also exhibits high energy absorption and combines very good impact resistance with the resistance to heat and chemicals typical of PA66. Accordingly, the material has a relatively high temperature reserve for short-term thermal loads (greater than 200°C) as can occur, for example, in a CDP oven (CDP = cataphoretic dip painting).This is particularly important for structural components that are installed in the vehicle at an early stage of production and pass through the complete CDP process. Such structural inserts stiffen the bodywork of the vehicle and affect failure in a crash.

Two CR grades for high dynamic loads

In addition, the two PA 66 grades Ultramid® A3WG7 CR and Ultramid A3WG10 CR, reinforced with 35 and 50 per cent of glass fibres respectively, encompass the same package of material characteristics provided especially for crash simulation. These two plastics reinforced with high levels of glass fibre are particularly suitable for high dynamic loads and, accordingly, are generally an alternative to metal. They possess high strength and rigidity and can be used at high temperatures. Initial implementations on the chassis have taken place and initial work on top mounts using Ultramid A3WG10 CR is in progress. The service support provided to customers by BASF for these products includes the complete description of the material for crash simulations. Apart from the dependence on strain rates this includes consideration of the orientation of the glass fibres and of fracture behaviour. The material models can be implemented in all crash simulation programs commonly available on the market such as LS-Dyna, PamCrash and Radioss.On this basis wide-ranging project partnerships can arise in which entire components are simulated and optimised.

Photo: Opel/BASF, 2006

The lower bumper stiffener (LBS), developed by Opel together with BASF, is an important contribution to pedestrian protection. It makes the lower bumper of the Opel Corsa more rigid and was produced for the most part on the basis of computer models and BASF’s method of Integrative Simulation. BASF now supplies six Ultramid® grades (PA 6 and PA 66) specially optimised for crash applications together with the associated high-speed material data. On the photo at the top, the simulated crash behaviour of the LBS for an insurance test can be seen. In the centre the crash test on the real component is shown. BASF’s Integrative Simulation predicted the location of fracture exactly. In the Opel Corsa the component is installed as standard beneath the front bumper (bottom).