High speed measurement of contact pressure and area during knee-to-instrument panel impact events suffered from frontal crashes

Numerous human cadaver impact studies have shown that acute injury to the knee, femoral shaft, and hip may be significantly reduced by increasing the contact area over the anterior surface of the knee. Such impact events are common in frontal crashes when the knee strikes the instrument panel (IP). The cadaveric studies show that the injury threshold of the knee-thigh-hip complex increases as the contact area over the knee is likewise increased. Unfortunately, no prior methodology exists to record the spatial and temporal contact pressure distributions in dummy (or cadaver) experiments. Previous efforts have been limited to the use of pressure sensitive film, which only yields a cumulative record of contact. These studies assumed that the cumulative pressure sensitive film image correlated with the peak load, although this has never been validated. A temporal record of the varying contact pressures would thus be helpful in validating models studying high-speed contact events (i.e. knee impact) incurred during automotive crashes. Thus, the aim of the current study was to present a new methodology to study the contact mechanics of the knee-IP impact event. This was achieved by using specially designed electronic pressure mats capable of transducing the corresponding contact area and pressure magnitudes at a sampling frequency of 1,340 Hz. Sled tests were performed at different delta-V’s using a Hybrid III, 5th percentile female dummy. The instrument panels were simulated with blocks of different padding materials of varying stiffness. This produced a variety of contact pressures, areas, and femur loads. The impact load values as recorded by the load cell in the femoral shaft of the dummy, were correlated with the corresponding contact area and contact pressure values to investigate if the peak load at the knee also corresponds with the cumulative pressure distribution. The current study showed that the center of pressure migrated approximately 13 mm suggesting that the temporal pressure distribution is a better measurement than a cumulative image if the true contact area is needed.