ABSTRACT

When a vehicle is subjected to a frontal crash test into a rigid barrier at a high speed, its front surface becomes crushed into a more or less planar surface. By no means does this suggest that the force is distributed uniformly across the surface. Variations in vehicle structure stiffness across the front will result in variations in the forces exerted on various sectors of the barrier face. These variations may be important factors in making a vehicle more or less aggressive when striking other vehicles or objects, or may influence its response when the whole structure is not engaged uniformly, as in offset or override/underride impacts.

Accordingly, it has been the practice of the National Highway Traffic Safety Administration (NHTSA) to use an array of load cells (force measurement transducers) across that part of the barrier face that is expected to be contacted. Chapter 14 describes some of the arrays used by various test agencies. In its frontal New Car Assessment Program (NCAP) tests, the NHTSA uses a standard 4 × 6 array of load cells. In the instrumentation lists for such tests, one will find 36 channels of load cell data. These data may be very useful to a reconstructionist dealing with an offset or override/underride collision. Chapter 14 describes how to locate, identify, and download load cell barrier data. It also discusses how some of the channels may be grouped together for analytical purposes.

There may be over 150,000 data points to be processed. Chapter 14 discusses the computational burden imposed by processing so much data. That burden may be lightened by periodic sampling of the data, but such a procedure presents the risk of aliasing. Chapter 14 describes what aliasing is, and how it can lead to misinterpretations of the data. It also discusses the use of the NHTSSA’s PlotBrowser software, not only for filtering, but for grouping the load cells. An example is presented of grouping, and how force–deflection and force–time curves can be derived from the data.