Design of an energy absorbing, underride resisting, truck-front bumper bar.

Abstract

An experimental investigation was conducted aimed at reducing fatalities and injury associated with head-on collisions between passenger vehicles and trucks, or other heavy vehicles. Such collisions create extensive and hazardous damage to the car and relatively little to the truck. This disparity is brought about in part by the difference in heights between the truck's and car's bumper, which permits the truck to override the front structure of the car leading to extreme occupant compartment intrusion, and in part by the much greater strength of the truck's structure. This work focuses on the design, testing and development of a mechanism, mounted to the front of a truck, to prevent underride and to absorb a significant portion of the crash energy. It is important to note that not all the objectives were required to be met in any one test. Each experiment was an integral contribution to a final practical solution. Seven full-scale car-to-truck crash tests were performed using a prototype bumper bar system at impact speeds ranging from 56 to 100 km/h. This bumper bar system consists of a rigid barrier supported in front of the truck by four telescopic struts incorporating ball joints at each end, making the assembly a ball jointed spatial mechanism. The use of a mechanism largely eliminates bending moments within the supporting struts, which if resisted, would require very large and heavy components. Energy absorption is via the plastic deformation of thin wall seamless steel tubing undergoing the inversion mode of collapse. The properties of the steel tubes were determined from quasi-static conditions, low speed dynamic tests ranging up to 30 km/h and one high speed test at 80 km/h. No strain rate sensitivity was detected in these tests. The results were therefore used to estimate the energy absorbed by the truck bumper bar system in the crash test collisions. From these initial car-to-truck collisions it was concluded that it is possible to significantly reduce the severity of head-on collisions between cars and trucks at very hazardous closing speeds with suitable energy absorbing, underride resisting truck bumper bars. Further work is needed to examine a wider range of collision modes and to develop means of reducing the bulk of the truck bumper bar components.