The use of force measuring crash test walls using specialist sensors is now an essent ial part of the process of bringing a new car to market and contributes towards raising safety standards in vehicles. During crash testing it is necessary to measure accurately the forces exerted during an impact on vehicles, their occupants and pedestrians. With future growth of the crash safety industry and the increase in legislation, the need for a flexible force sensing crash wall will become increasingly important.
The latest version has data acquisition system (DAS) modules integrated within the sensor mounting plates. The wall allows vehicle designers to analyze load patterns and optimise vehicle force and crush profiles. All the crash wall sensors are manufactured out of one solid block of material as multi column sensors; they are very stiff, which has enabled them to be matched to the sensor mounting plate and other critical components resulting in a system with a very high speed response performance. The high stiffness and high natural frequency of the crash wall sensors make them ideal for measuring impact forces. The wall is made up of an array of sensors; typically each sensor face is 125mm x 125mm, which enables a 128 sensors to make up a wall of 2m x 1m for full width rigid frontal testing. The sensor elements are manufactured in a high strength stainless steel or the lightweight version, which is made from a high strength aluminium alloy.
The strain gauges on the crash wall sensor element measure the force or moment applied as the change in electrical resistance of the gauges. This being a linear effect enables the sensors to have a <+/- 0.2% non-linearity in the axial direction and maintain that +/- 0.2% linearity when loaded in any 62.5mm diameter area over the 125mm x 125mm face. Tri-axial sensors maintain a non-linearity of < +/- 2% across all three axes (Cross Talk). This allows the crash test engineers to look at all different axis of impact and still be confident in the results obtained. All crash wall sensors undergo rigorous proving tests during manufacture where they are calibrated to 250% of capacity. This enables the sensors to be capable of confidently withstanding 150% of overload capacity in impact conditions.