Research On Child Occupant Safety In Frontal And Side Impact Based On Tests And FE Simulations

Child occupant safety is one of the important research subject in the field of vehicle crash safety. Child occupant safety research started from 1960s in the world. The US and European countries established regulations for child occupants in 1970s and 1980s. With the number of vehicles increasing every year in China, child occupant safety problem becomes more and more important. As child restraint system (CRS) is shown to be effective on child occupant protection in vehicle crash, the research work in this field has an important social significance, regarding that the policy of one-child in one-family performed in China.In this research, by using a Hybrid III 3YO dummy FE model and a child human FE model, FE simulation of frontal sled tests for four typical types of CRSs (wearable type, impact-shield type, 5-point harness conventional type, ISOFIX CRS) were conducted. Results of the dummy's kinematics and accelerations in the tests and FE simulations were correlated. A 3-year-old child human FE model was also used in this research. Injury criteria (the head forward excursion, HIC 15, chest 3 ms acceleration and chest deflection) were compared between the four types of CRSs. Stress distribution was analyzed for the child human FE model. Misuse case of seatbelt having 100 mm slack for the impact-shield type and 5-point harness conventional type CRS were analyzed by FE simulation. And misuse case of harness having 100 mm slack for the 5-point harness conventional type and ISOFIX CRS was also analyzed by FE simulations. Results showed that the frontal safety performance of ISOFIX CRS was the best.ISOFIX CRS implements a simple, rigid and standardized connection with vehicle. In this research the child occupant protection in ISOFIX CRS were analyzed in detail. Regarding that it is very important of the neck protection of a child under 4 years old and restrained by a forward-facing CRS, the upper neck response were analyzed in detail. The upper neck force and moment were calculated based on the motion of the head. The torso pose and the contact behavior of the chin and chest were different between the dummy and child human FE model. Different contact behavior caused different contact force. And the upper neck force was affected by the contact force and the head inertial force. For the Hybrid III dummy model, the upper neck shear and tension force were large while for the child human FE model the upper neck shear force was small and the tension force was large.A top-tether force limiter was proposed to reduce the loadings to the head, neck and chest of the child positioned in the ISOFIX CRS. For evaluating the effectiveness of the top-tether force limiter, FE simulations for two conditions, CRS in proper use and CRS harness having slack, were performed. Results showed that the head and chest accelerations and upper neck force and moment were reduced. Ridedown and restraint energy density and the restraint energy density related with the CRS harness and CRS installation system were calculated and analyzed of the relation with the chest acceleration. It was concluded that the chest acceleration was not dependent on the ridedown energy efficiency but dependent on the energy efficiency absorbed by the CRS harness (i.e., the chest acceleration will increase when the energy efficiency absorbed by the CRS harness increases).As there is not an international standard for side impact sled test, in this research full car side impact tests were analyzed. Results of three full car side impact tests of Q3s and CRABI 6MO dummies restrained by three types of CRSs (forward-facing, rear-facing and car-bed type) were analyzed and compared. Except the chest deflection (23.3 mm) of the Q3s restrained by a forward-facing CRS exceeding slightly the threshold (23 mm), all injury criteria were lower than thresholds. Although the door beltline impact the dummy's head through the CRS side shell indirectly, the HIC 15 was very low. This was because the CRS side shell absorbed lots of impact energy, and the dummy's head was contained in the CRS shell all along. A simple FE model of side impact was established by using the Hybrid III dummy and child human FE model. The head, chest and pelvis resultant acceleration peaks were comparable between the test and simulations.In this research, based on tests and FE simulations, the behavior, reponses and injury parameters of the child occupant restrained by differet types of CRSs were analyzed. By using a Hybrid III 3YO dummy FE model and a child human FE model, FE simulation of frontal sled tests for four typical types of CRSs were conducted. A top-tether force limiter was proposed to reduce the loads to the child head, neck and chest. By applying the theory of ridedown and restraint energy efficiencies, the relation of the energy efficiencies anad the chest acceleration was proposed. It was found that the torso pose and the contact behavior of the chin and chest were different between the dummy and child human FE model. Results of three full car side impact tests of Q3s and CRABI 6MO dummies restrained by three types of CRSs were analyzed and compared. A simple FE model of side impact was established by using the Hybrid III dummy and child human FE model. Hope that this research can be a good reference for the child occupant safety research work and the establishment and execution of the child occupant safety regulation in our country.