Evaluation of a new visco-elastic foam for automotive applications

The geometry and mechanical characteristics of the automotive seat greatly influences the occupant kinematics in rear-end collisions. The head restraint is important particularly with respect to soft tissue neck injuries. While several studies analysed the effect of geometrical properties of head restraints, little is reported on the potential to reduce such injury by changing the material of the head restraint padding, i.e. the underlying foam. This study investigates whether the head restraint foam alone can be tailored to reduce whiplash injury. A newly developed visco-elastic (VE) foam was chosen, because advanced energy absorption properties are expected to produce beneficial effects on the occupant motion. The behaviour of the visco-elastic foam was evaluated by performing impact pendulum tests. The most important novel property of the foam thereby consists of its broad temperature range over which it keeps its advantageous visco-elastic deformation properties, while sustaining the ability to dissipate energy. The tests indicated in particular a broad glass transition temperature resulting in a stable impact behaviour over a temperature range of 5degreesC to 35degreesC. Applying this foam as a head restraint padding material, several sled tests using a standard car seat were performed. The tests were conducted to mimic rear-end collisions with a delta-v of 16 km/h. A BioRID dummy was used as a human surrogate. For the seat tested, the change of the foam resulted only in minor changes at room temperature, while the standard foam exhibited adequate performance. Additional changes of the head restraint geometry were shown to have a larger beneficial influence on the occupant kinematics.