The Research On The Injury Prevention Of Child Occupant Seated On The Rear Seat

Motor vehicle crashes (MVCs) are one of the leading causes of injuries and deathsamong children. There are approximately260,000child fatalities and10,000,000injured in traffic accidents worldwide every year. Due to the one child policy in China,the safety of children in cars has become the spotlight in China. Along with thedevelopment of vehicle-safety-technology and the increasing attention on the issue ofchild safety in cars, child occupant safety has become an important research subject inthe filed of vehicle crash safety. Based on the literature review, this paper focused onthe study of injury epidemiology and injury prevention of child occupant seated in therear seat, injury prevention for the other occupants (adults and infants) seated in therear seat and improvement of spine biofidelity of child dummy through using statisticanalysis, computer simulation and optimization.1. Investigation of injury epidemiology of rear-seated child occupants. In thisstudy, NASS-CDS database was used to calculate the restraint types and injury risksfor rear-seated children/youth aged4-18and evaluate specific cutoff points for age aseffect modifiers of the association between the using of vehicle seat belts andsignificant injury, through applying the method of descriptive statistics andmultivariate logistic regression. The results showed that vehicle seatbelt was theprimary form of restraint for children older than3years-old. Among Children/youthaged4to18, children aged8to12had the highest injury risk. Head injury was themost common injury for children/youth aged4-15. Face injury rarely happened inyounger children (4-7years old), but had a high risk of injury for children/youth aged8-18. Chest injury risk was the highest for youth aged16to18(0.54%), but the risk ofspinal injury was the lowest (0.03%). Abdomen injury risk decreased when ageincreased, except for children aged4to7. Children in4to8seemed to be at aincreasing risk of significant injury when using seat belts (OR:2.51;95%CI:1.55-4.04). Among children/youth in9to18, there was a protective effect on significantinjury from using seat belt (OR:0.93;95%CI:0.81-1.07). This research can providea realistic basis for future studies on injury prevention for child occupants.2. Development and validation of the parametric child ATD model. In this study, aparametric ATD model capable of representing6–12YO children was developedbased on Hybrid-III6year old child ATD model provided by MADYMO. A more realistic representation of pelvis and abdomen geometry, modified joint stiffness andimproved contact characteristics were added to the baseline model. The newparametric ATD model was validated against results from12sled tests using realsecond-row vehicle seats with Hybrid III6YO and10YO ATDs under differentrestraint configurations, using a multi-objective optimization method. The modelvalidity was evaluated by statistical assessments of output measurements between thetests and simulations. Results showed that the model-predicted ATD head, chest andpelvis accelerations as well as the seatbelt forces were in good agreement with thosefrom the tests. This validated parametric child ATD model provides a useful tool toinvestigate the body size effects and to develop restraint system design guidelines for6–12YO child occupants.3. Parametric analysis and optimization of restraint system for rear seated childoccupant. In this study, a parametric analysis was conducted to investigate the effectsof body size, seat belt anchorage locations, and rear seat design parameters on theinjury risks in frontal crashes of children aged6to12by using the parametric childATD model developed above. An automated program was developed to integrate thedummy positioning procedure, belt fitting and varying seat and seat belt systems intocrash simulations by means of MADYMO, Modefrontier and Scilab software. Theresults of parametric analysis showed that child body size was the dominant factoraffecting outcome measures. In order to improve restraint system design, optimizationapproach was adopted to reduce head and knee excursions and prevent submarining.In general, lower and more rearward D-rings (upper belt anchorages), higher and moreforward lap belt anchorages, and shorter, stiffer, and thinner seat cushions wereassociated with improved restraint performance. In these simulations, children withsmaller body sizes require more-forward D-ring, inboard anchor, and outboard anchorlocations to avoid submarining. The range of optimum restraint system configurationobtained from this study can guide the future design of restraint system for older childoccupant.4. Investigation of injury prevention for other rear-seated occupants (adult andinfant in the rear-facing child restraint system（RF-CRS）). In order to investigate howthe optimum restraint system configuration for older children affects the injuries ofother occupants, rear-seated adult and infant in RF-CRS models were developed inthis study. A series of12sled tests were used to validate the computational models.The validity of two models were evaluated by statistical assessments, and the resultsshowed good agreement between tests and simulations. The optimum seat and seat belt configurations were obtained by optimization techniques and were compared withthose of the6year old child. Results showed that the optimal belt anchorage locationsand the seat cushion length for older children, adults, and infants in RF-CRS areconflicting to each other. In particular, more forward lap belt anchorage locationsthat prevent submarining for older children would reduce the protection to both adultsand CRS-seated infants. Shorter seat cushion could provide optimal protection toolder children and adults, but would significantly increase the CRS rotation. Thefindings of this study suggested that adaptive or adjustable restraint systems arenecessary to improve the rear seat occupant protection for different age groups.5. Improve spine biofidelity of Hybrid-III6year old ATD. Because Hybrid-IIIchild ATDs inherit a rigid thoracic spine from the adult HIII ATDs, so they can notcorrectly reflect child responses in MVCs. A previously developed and validated HIII6-year-old MADYMO ATD model was used as the baseline model to investigate thepossible design modifications on the spine biofidelity of current ATD. Several sets ofchild volunteer, cadaver test and motor vehicle crash data were considered as thedesign targets. Optimization techniques were used to match simulation results to eachset of test results. ATD design modifications include adding an additional joint to thethoracic spine region and changing the joint characteristics at the cervical and lumbarspine regions. The results indicated that, to achieve a realistic spine flexibility, thetranslational characteristics of the cervical and lumbar spine in the current child ATDneed to be reduced, and an additional joint at the thoracic spine region with degree offreedom in both flexion/extension and tension should be added. The child ATD modeldeveloped in this study can be used as an important tool to improve child ATDbiofidelity and child restraint system design in motor-vehicle crashes.