It combines proven technology with the latest sensing and control systems to provide fast, cost-efficient deceleration testing of a wide range of transport safety systems. The sled delivers a speed accuracy of ±0.5% with a maximum speed of 25 m/s and rapid turnaround. 

The design of the sled allows for an increased number of tests to be conducted more quickly yet without compromising accuracy or consistency. It incorporates updated bungee sled technology integrated with the latest electronic control and data collection systems.

Traditional bungee sleds use lengths of synthetic rubber (the bungees) that are tensioned as the sled is pulled along the rig to the propulsion end of the rails. The system then fires like a catapault, propelling the sled down the rails to the impact face at the far end. Although low-cost and convenient, the energy released by the bungees is dependent on many factors, including temperature, humidity, the age of the bungee and how recently it was used. Combined, these factors could lead to variations in impact speeds in excess of ±1%, which was way outside the research-quality accuracy needed by TRL’s engineers.

The TRL sled uses similar bungee material but in an innovative tensioning system, designed and patented by TRL, which ensures low start accelerations, avoiding the very rapid initial acceleration that can dislodge test pieces on traditional bungee sleds. The number of bungees tensioned can be selected (from one to 12) to optimise the acceleration of the test piece.

Consistency is achieved through a closed-loop control system that uses load cells in the tensioning mechanism to calibrate the system during every pull-back. A laser positioning system tracks the position of the sled during pull-back and during the impact, recording any elastic deformation of the test piece - a task traditionally conducted by a piece of modelling clay, a spike and a ruler.

A range of deceleration mechanisms can be applied, including metal crumple tubes and polymer energy absorbers. The face and bedplate of the sled are designed

to accommodate bespoke deceleration mechanisms. 

To solve the problem of synchronising data-gathering on and off the sled, TRL developed a unique optical coupling system to replace traditional electro-mechanical systems. There are five programmable trigger pulse outputs allowing numerous recording devices or ancillaries to be controlled through a single trigger. Up to 94 channels of on-board data can be collected at 20 kHz.

TRL engineers also considered how to improve the usability of the system, developing a range of techniques that allow them to offer fast turnaround and highly integrated data packages. A computerised control system manages the entire test procedure, including calculation of pull-back to minimise pre-test calibration runs. Other innovations include speed timers in the track and in-situ weighing via load cells in the rails.

The Impact Sled Facility can be used across a wide range of TRL’s safety research programmes as well as for commercial test programmes for TRL’s customers. 

Bungee Facts

Maximum speed (at 400 kg sled mass) = 25.5 m/s = 57.5 mph
Maximum sled mass = 2200 kg (to 11.9 m/s = 26.9 mph)
Maximum speed at A < 1 g = 13.8 m/s = 31 mph (any sled mass)