Urethane Energy Absorbers for Automobile Bumpers

Abstract

Abstract It is believed that the concepts and data presented here are not only useful for the design and application of urethane foam for bumpers, but demonstrate the inherent fitness of the material for this purpose. To review quickly the factors listed in the beginning of the paper: 1. Urethane-faced bumpers will not only prevent damage to the bumper or vehicle, but will eliminate or minimize damage to the object impacted. 2. Repeated tests at severe overloads have demonstrated the recoverability of the foam after repeated impacts. 3. High hysteresis of urethane results in minimum rebound. 4. The material is velocity responsive within the specification range. 5. A wide variety of usable arrangements plus ready moldability provide considerable styling freedom. 6. Temperature compensation features assure designable performance consistency. 7. High efficiency or form factor is achievable, resulting in minimum force and stroke. 8. No maintenance is required. 9. Urethane microcellular foam is among the lower cost plastic materials on a per pound basis. Low densities and discreet placement can result in very competitive systems. Steel stroking bumpers are designed to ward off blows with emphasis on protection of the vehicle on which they are mounted. As a result, they present a far more hostile motoring environment than ever before for anything or anyone except another similar bumper. Urethane bumpers have a great potential for creating a far less hostile environment for everyone and everything, including fronts and rears of current vehicles, sides of all vehicles, other objects, pedestrians, and occupants. The current specification severely inhibits the realization of that potential. Doing anything about it is no easy matter since it could easily lead into a specification of horrendous complexity. However, following is one suggested approach. In testing for occupant protection, a manikin or dummy is selected as a representative test device. It is by no means truly interchangeable with the real thing or all situations, but does provide a firm and representative means for reasonable evaluation and standardization. In like manner, it would be possible to select a reasonably typical front or rear current-model configuration to serve as a representative test device on the face of the pendulum, and simply specify “no damage to the test device” rather than “no contact to specified planes”. A manufacturer could be contracted with by the government to produce identical test devices for all who wished to run such tests. Such a specification could be amended to the current specification as an alternate, rather than attempting to revise what is already an excellent document for the steel stroking bumper.