Assessment of injuries to the lower leg and head of pedestrians in vehicle-to-pedestrian collisions through FE simulations
Examensarbete för masterexamen
Automotive engineering (MPAUT), MSc
In this thesis an analysis of predicted injuries to the lower leg and head of pedestrians in vehicle-to-pedestrian collisions through finite element (FE) simulations were analyzed. Today, pedestrian regulatory tests consist of subsystem tests using impactors that are made to hit the vehicle; there is no use of any pedestrian crash test dummy. Hence, the kinematics of the impactors used in the testing procedure can be questioned. An alternative way to assess vehicle-to-pedestrian interaction and injury risks is through the use of a FE-Human Body Model (HBM). This thesis presents a comparison of injuries predicted by simulated regulatory tests and injuries predicted by a modified Total Human Body Model for Safety (THUMS), with KTH head and neck model, when impacting an advanced FE-model of a sedan passenger car. The injuries in focus are those sustained to the lower extremities, mainly to the knee ligaments and tibia bone fracture, and the head. Further, real-life vehicle-to-pedestrian accidents were reconstructed with the modified THUMS to indicate the power of accident reconstructions using FE simulations. The modified THUMS and the leg impactor did not predict similar risk of leg injuries. THUMS predicted lower ligament elongation and higher tibia bending moments than the impactor. The ligament elongation difference between THUMS and impactor is not comparable. For tibia bending moments, THUMS predicted 18% higher bending moments than impactor for impact point P3 and tibia-2 cross-section for small passenger vehicle-to-pedestrian collision, on average it was 60% higher for Flex-PLI positioning 75mm above ground and 42% higher when Flex-PLI is positioned according to THUMS walking stance. For tibia injury risk as predicted with modified THUMS, vehicle velocity and pedestrian impact location along the width of the energy absorber were significant. Moreover, presence of a femur fracture influenced the tibia bending moment; femure fracture varied as a function of impact location and vehicle velocity. The injuries to the head as predicted by the modified THUMS, with Rigid KTH head and neck model, and headform impactor were found to have similar head impact kinematics with similar head impact duration and behavior of acceleration curve. Predicted head injuries, using the injury measures HIC15 and BRIC, were influenced by the head impact location on the vehicle, vehicle height in relation to THUMS and vehicle velocity. In the accident reconstructions modified THUMS model predicted high HIC15 values, representing high risk of head injuries as compared to the head injury reported in the two cases that were reconstructed. The difference is qualitative only, no quantitative difference conclusion can be drawn from the results. This deviation in results could be explained due to the fact of non-availability of head impact locations in the database cases, not including the vehicle deceleration which may be present during actual accident and non-inclusion of road and weather conditions. Keywords: THUMS, KTH head, Flex-PLI, vehicle-to-pedestrian simulations, impactor-to-vehicle simulations, positioning, legform, headform, accident reconstruction.
Teknisk mekanik , Farkostteknik , Transport , Applied Mechanics , Vehicle Engineering , Transport