Measurement Error in Lateral Thoracic Deflection and Deflection Rate Due to Oblique Loading

Anthropometric test devices (ATDs) instrumented with potentiometers and accelerometers are used regularly to assess thoracic injury risk in side impact crash tests. Measurements from these sensors are compared with injury assessment reference values (IARVs) for lateral loading to establish the risk of injury for humans subjected to similar impacts. In crash tests, the deflections and deflection rates derived from these two types of sensors (potentiometers vs. accelerometers) have varying degrees of agreement. In some cases, differences can be relatively large. In the past, it was unclear whether the reason for the differences was off-axis loading that misaligned the accelerometers used in the calculation, an inherent inability of the potentiometer to capture high deflection rates under certain conditions, or some other phenomenon. Lateral pendulum impacts were conducted using a SID-IIs ATD with varying degrees of off-axis loading and were filmed from above with a high-speed digital imager. Under oblique loading conditions, the potentiometer's rotation caused the sensor to underreport the full lateral component of deflection rate by 3-5 percent and deflection by 12-22 percent. Rotation of the rib accelerometer under similar loading conditions produced readings 2 percent higher than the lateral peak deflection rate and 5-9 percent higher than the lateral peak deflection. These results suggest that improvements to ATD designs or new sensor technologies are needed.