Abstract
Small cars pose various challenges when designing for safety. Due to the size, the deceleration pulse required to absorb energy in crash is generally more severe than that in larger cars. In addition, smaller cars usually target a low-cost market, which means that expensive solutions to improve safety are normally not considered. Low fuel consumption in small cars is usually a top priority, making achieving vehicle weight targets a priority. In this paper we look at the use of polymer-based solutions to help improve occupant and pedestrian safety in small cars, while providing cost effective lightweight solutions.
Our first consideration of polymer-based solutions in this paper relates to the body-in-white (BIW). Two main solutions will be discussed:
- foam reinforcement of the BIW cavities to stabilize the structure and prevent undesired buckling of body pillar sections, thus increasing the load-bearing capacity
- crash-durable adhesives to bond the BIW structure together, minimizing and in some cases replacing spot welds. This approach improves body stiffness and allows use of dissimilar materials while lowering the BIW mass.
The use of foam and adhesive in the BIW allow tuning of sheet metal thickness distributions and use of the most appropriate material exactly where it is needed. In this way it is possible to use high-strength steel in specific locations or to down-gauge the metal at less critical areas in the structure thus such technologies are particularly suitable for small cars.
Once the BIW has been optimized, the next step is to consider the occupant compartment. For many years now, plastics, foams and adhesives have been used to form a large part of the interior of the car. The use of these materials to provide passive safety for occupants continues to develop. We will present current developments and the extension of the use of polymer-based solutions to improve safety, cost effectively and with significant mass reductions. Important factors in designing for passive safety in small cars are cost, space and weight. Examples of instrument panel design, seats and doors will be reviewed.
On the car exterior, safety of pedestrians is becoming a critical requirement. This is particularly challenging with small cars, since the available packaging space is limited and wrap around distances are low. During impact, the pedestrian very quickly comes in contact with hard structures, due to the limited space to absorb energy. A very efficient energy absorption solution is required to build loads up to acceptable levels and maintain that load level throughout the impact event. In this way a maximum energy can be dissipated while limiting the injury to the pedestrian. Polymer body panels, foams and adhesives offer various options to optimize the performance and protect the vulnerable road user.
Keywords: polymer, adhesive, foam, composite, weight