The Effect of Crash Severity and Structural Intrusion on ATD Responses in Rear-End Crashes 2020-01-1224

This study assesses vehicle and occupant responses in six vehicle-to-vehicle high-speed rear impact crash tests conducted at the Exponent Test and Engineering Center. The struck vehicle delta Vs ranged from 32 to 76 km/h and the vehicle centerline offsets varied from 5.7 to 114 cm.

Five of the six tests were conducted with Hybrid III ATDs (Anthropometric Test Device) with two tests using the 50^th male belted in the driver seat, one test with an unbelted 50^th male in the driver seat, one test with a 95^th male belted in the driver seat, and one with the 5^th female lap belted in the left rear seat. All tests included vehicle instrumentation and three tests included ATD instrumentation. The ATD responses were analyzed and compared to corresponding IARVs (injury assessment reference values). Ground-based and onboard vehicle videos were synchronized with the vehicle kinematic data and biomechanical responses.

The timing of the vehicle crush, occupant compartment intrusion, seatback motion, and ATD kinematics were assessed. The results indicated that the rear structures of the struck vehicle were significantly crushed by the striking vehicle with override contributing to the overall level of crush. In the three crashes with the front seat ATD, the intrusion of the second-row seat structure first supported and then displaced the driver seat back forward, affecting the ATD dynamics. The driver ATD neck forces exceeded the IARVs in the two tests with ATD instrumentation. In one test, the maximum neck loading occurred around 200 ms, which coincided with the ATD response from the second-row being displaced forward into the driver seatback.

In the test with the unbelted ATD, a rigid support structure was used to limit the driver seatback rearward rotation to 45 degrees from vertical. The ATD initially moved rearward and loaded the seatback, which yielded and rotated until it contacted the rigid support structure. The ATD then ramped upward into the roof structure, resulting in a compressive neck force that exceeded the IARV.

The test with the left second-row ATD involved a full-size pickup striking the rear of a stationary passenger car that resulted in a 32 km/h delta-V. The second-row intrusion occurred early and displaced the ATD torso forward. The measured ATD responses were all below the IARVs.

The test with the belted and instrumented ATD in the driver seat impacted by the tractor showed that second-row intrusion displaced the driver seatback and ATD forward at approximately 40% into the crash pulse duration, where the duration was defined as the time segment from impact to maximum delta-V. The chest data showed the attenuation of the ATD loading into a non-rigid seatback frame and was immediately followed by an increase in ATD loading by the intrusion of the striking vehicle that rapidly increased the ATD velocity so that it approached the striking vehicle center of gravity (CG) velocity.

The results from the study highlight the effect of forward and vertical occupant compartment intrusion on vehicle structure and ATD responses in high-speed rear impacts. The results also show that limiting front-seatback rearward rotation from intrusion would increase the acceleration loading on the ATD and that intentionally bracing the seatback would redirect the ATD kinematics.