This article described a lorry front underrun guard developed by the Transport and Road Research Laboratory and TI Tube products. This guard consists of a cross beam welded to two vertical drop-arms. These are pivoted from brackets attached to the truck's chassis. The cross beam is a rectangular hollow steel section and is positioned to have a ground clearance of about 300 mm. Energy absorption in this device is based upon plastic deformation of mild steel in the form of invertubes. In each cartridge impact energy is absorbed by turning a steel tube inside out. The maximum stroke of the invertubes is 200 mm but the geometry of the mounting gives about 300 mm horizontal movement of the underrun guard. This can be accommodated within the space available under the front of the lorry. Results of impact tests indicate that this guard is able to offer protection to car occupants wearing seat belts in frontal impacts with heavy trucks at closing speeds of 64 km/hour. Recent research has investigated the question of ground clearance for these devices. From results so far it appears that for optimum energy absorption it seems that the main load bearing parts of the car's front structure should interact directly with the underrun guard.
Abstract