Abstract: With the increasing popularity of automotive active safety systems, the probability of collisions between vehicles and pedestrians has gradually decreased. Among them, the AEB system, as an important part of active safety systems, can actively intervene to avoid collisions in advance. However, in actual road traffic conditions, there are still situations where the AEB system cannot completely avoid collision accidents, and the impact speed between pedestrians and vehicles may drop to below 40 kph. However, the aPLI legform impactor, which is widely used in pedestrian protection evaluations in various regions, has a standard impact speed of 40 kph in the test procedure. The response of the aPLI to low-speed collisions and the resulting pedestrian leg injuries is still unclear. Based on finite element simulation, this study compared the kinematic responses and injury responses of the aPLI impactor with human body models (THUMS and GHBMC) under 5 different speeds (20kph, 25kph, 30kph, 35kph, and 40kph) and 3 collision angles (-40°, 0°, and 40°). Firstly, with reference to the simplified vehicle model specified in the ISO/TS 20458 technical document, 3 sets of dimensional parameters representing sedans and 3 sets representing SUVs were selected to establish the finite element model. Secondly, finite element simulations were conducted in accordance with the pre-designed simulation matrix, and relevant data were extracted. Finally, a systematic comparison was made on the kinematic responses and injury responses (including ligament elongation and bone bending moment) between the aPLI impactor and the THUMS, GHBMC models under different conditions.
The results show that in terms of kinematic responses, the HBMs exhibit a closer kinematic response to the aPLI under low-speed collisions; moreover, compared with GHBMC, THUMS is more similar to aPLI in terms of lower leg rebound and ankle inversion. In terms of injury responses, there are differences in the peak values of femur and tibia BM between the HBMs and the aPLI, while their performances in terms of ligament elongation are relatively close. After normalizing the injury peak values of each model under the 5 speeds, it was found that the normalization curves of the three models show similar variation trends in most cases. However, the MCL elongation of aPLI is more sensitive to speed changes, the reduction amplitude of its injury value is greater than that of the HBMs. In addition, scatter plot fitting diagrams of HBMs and the aPLI were drawn. It was observed that the slope of the fitting line for MCL tends to increase as the speed decreases; in contrast, the fitting lines for the femur and tibia basically overlap, with the R² value greater than 0.95. Overall, when the collision speed decreases, the aPLI still maintains a high degree of similarity to HBMs in terms of kinematic responses, but its injury response is more sensitive to speed changes.