Bumper model improves testing

Opel and BASF have used a new mathematical model to create a plastic car part which will reduce the risk of injury during collision with a pedestrian.

The lower bumper stiffener (LBS) is made of BASF’s Ultramid B3WG6 CR, a reinforced polyamide 6 developed for crash applications. The LBS weighs about one kilogram, is one metre long and is installed behind the front bumper so as to reduce the risk of serious knee injury in the event of a collision with a pedestrian.

BASF used a new method of integrative simulation to develop LBS. The numerical material model takes into consideration the directionally dependent behaviour of glass fibre-reinforced thermoplastics. Along with the material parameters of the pure plastic, the content, geometry and orientation and distribution density of the fibres in the finished part all form part of the calculation.

The simulation is fed with the findings from a classic mould-fill simulation and the experimental data obtained from a high-speed measuring device made by BASF. This gives the part shape that best complies with the requirements as well as the optimum mould design.

“Once the BASF method had been seamlessly integrated into the development process and into the simulation software at Opel, it became possible to model the LBS in detail and to describe its crash behaviour with an unprecedented degree of precision”, said Dr. Steffen Frik, group leader for Simulation Passive Safety at Opel in Rüsselheim.

Without having to perform all too many costly tests, the refined simulation method succeeded in designing the LBS in such a way that it fulfils the requirements set by Germany’s pedestrian protection directive.

At the same time, if the vehicle crashes against a stationary obstacle where the load is much higher than impact against a leg, damage to other parts in the front end of the vehicle is prevented by LBS systematically failing. This lowers repair costs and could translate into more favourable insurance ratings.