Crash behavior of parts used in exterior automotive applications.

For many applications, the behavior of the material and the finished part under impact load is of major importance. To prevent minor damage, automotive bumpers, for example, must be able to withstand an impact of 4 kmh (ECE R 42, EU) or 8 kmh (CMVSS 215, Canada) without damage. In future, these parts will also have to comply with the more stringent specifications of the EU initiative on pedestrian protection (leg, hip and head impact at up to 40 kmh).
For the simulation of such dynamic loads under conditions normally encountered in practice, the Physical Testing department of the Polyurethanes Business Unit uses various dropping devices equipped with the relevant impact bodies and the collision test stand shown in the picture. All the testing equipment is fitted with state-of-the-art measuring technology so that deceleration and energy balances can be determined with a high level of temporal resolution.

The measured test results (e.g. on energy-absorbing Bayfill® EA foams) form the basis for the optimization of product formulations. Apart from that, they also constitute the input data for CAE material models and FEM calculations when performing a CAE optimization of the part. The experimental validation of the part simulation is then carried out in crash tests on corresponding prototype parts.

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The part shown in the picture consists of a lightweight bumper cover of Bayflex®180/190, ack-foamed with Bayfill® EA. The bumper is in a heat-conditioning chamber (-30 to +80°C), and the cradle can be operated at speeds of up to 20 kmh and with a total mass of up to 2,000 kg. The moment of impact can be documented by high-speed imaging.

Use of the impact test stand and drop apparatus is not limited to the testing of parts for exterior automotive applications. They have been deployed in the past, for example, for testing rigid polyurethane foam for pipe insulation (simulating an offshore oil pipeline being hit by the drag anchor of a fishing net) and polyurethane elastomers (stop buffer for a crane).