Simulation and Analysis of Child Kinematics during Pre-Crash Maneuvers

Road traffic injuries are the most common cause of fatal injuries among children in the European Region (Sethi et al., 2008). Impacting the front passenger seat back is one of the main injury mechanism of AIS2+ head injuries for children aged 3-13 (Bohman et al., 2011a). Occupant and vehicle kinematics prior to and during a crash play an important role in the probability of the head impacting either the front seat or side door interior while seated in the rear seat. Studies also show that children who are placed on a belt positioning booster are less likely to sustain injuries than if only using a seat belt (Durbin et al., 2003). In a majority of cases with head contacts in frontal impacts, a steering or braking maneuver has preceeded the crash event in an attempt to avoid impact with the other vehicle or object (Bohman et al., 2011a). In order to understand the principals behind vehicle occupant injuries different anthropomorphic test devices (ATD) are available. The Q6 is an ATD representation of a six year old child available as both a physical dummy and as a finite element (FE) model. Little is known on its kinematics when in uenced by low longitudinal and lateral accelerations as are present during a pre-crash maneuver. The purpose of this thesis was to investigate and compare the kinematics of the physical Q6 ATD (Q6 ATD) and the Q6 FE-model (Q6 model) placed on a booster in such maneuvers. Physical tests were carried out comprising two turning maneuver tests (50km/h, 14m radius) and six emergency braking maneuver tests from 70km/h. During the braking maneuver test the Q6 ATD was positioned in three different positions; upright (T0), tilted 1 (T1) and tilted 2 (T2). Video images and vehicle data was used to analyze the head trajectories during the different maneuver tests. The FE-simulations were carried out using FE models of a Volvo V60 vehicle body, rear seat, front seat and a model of a booster. The upright positioned Q6 model was simulated during a turning maneuver pulse similar to the physical turning maneuver test. It was also subjected to a braking maneuver pulse corresponding to the physical braking test. The same brake pulse was then used to carry out tests with the Q6 model seated in two different tilted positions, T1 and T2. In addition, two methods of pre-tensioning the belt was used for the FE-simulations. The physical tests resulted in the turning maneuver causing the Q6 ATD to tilt sideways to a 14 angle. The braking maneuvers caused the Q6 ATD to have a forward forehead displacement of 115mm (T0), 130mm (T1) and 165mm (T2) respectively. The FE turning maneuver caused the Q6 model to tilt sideways to a 15 angle. The FE braking maneuver caused the Q6 model with a manual pretensioner to have a forward forehead displacement of 210mm (T0), 220mm (T1) and 220mm (T2). The FE braking maneuver using the automatic pretensioner caused the Q6 model's forehead to have a forward displacement of 230mm (T0), 185mm (T1) and 220mm (T2). During both the physical tests and the FE-simulations; the forward displacement increased with a larger tilting angle prior to braking. The Q6 ATD and Q6 model showed similar behavior, as the tilting angle prior to braking had similar effects on the Q6 ATD and Q6 model. In pre-crash scenarios when turning occurs before braking, it is concluded that both the Q6 ATD's and the Q6 model's head has a greater longitudinal displacement with increasing tilting angle. This indicates that a combination of pre-crash maneuvers, may increase the risk of impacting the head. While using the Q6 model for low pulse maneuvers has proven to be possible, it is important to keep in mind that both the Q6 ATD and Q6 model are designed for crash scenarios and are not validated for low pulse simulations. In order to use the Q6 ATD and Q6 model as a tool for evaluating child kinematics during pre-crash maneuvers comparisons with data from driving studies with real children need to be carried out