Our recent rear seat safety research found that more-forward and higher lap belt anchorage locations and much shorter and stiffer seat cushions can improve the protection of older children from 6 to 12 years old who are using the vehicle belt without a booster. The objective of this study was to investigate whether the optimal rear seat restraint systems for adults and infants are consistent with those for older children.We conducted sensitivity analyses and design optimizations for adults and for infants in a rear-facing child restraint system (CRS) using a set of MADYMO models, an automated simulation framework, and occupant belt-fit and posture prediction models from our previous studies. A series of 12 sled tests was also used to validate the computational models.The optimal belt anchorage locations and the seat cushion length for older children, adults, and rear-facing CRS-seated infants conflict with each other. In particular, more-forward lap belt anchorage locations that prevent submarining for older children would reduce the protection to both adults and CRS-seated infants, although the protection is still acceptable based on regulated injury criteria. A shorter seat cushion could provide optimal protection to older children and adults but would significantly increase the CRS rotation.The findings of this study suggested that adaptive/adjustable restraint systems are necessary to simultaneously improve the rear seat occupant protection for all age groups. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.
Injuries to the lower extremity (LE) continue to occur in frontal crashes despite increased attention on the vehicle structure and restraint design. This study focuses on thigh, leg, foot, and ankle injuries as well as occupant factors and intrusion levels. Sixteen vehicles, including three same types, with same moving deformable barriers of the same mass, velocity, and barrier face properties, and the same occupant Test Device for Human Occupant Restraint (THOR) 50th percentile adult male in the driver's seat were used to conduct oblique impact test. Data from the left (driver side) oblique crash tests conducted by National Highway Traffic Safety Administration (NHTSA) were used in this paper to analyse the detailed intrusion characteristics and the driver side THOR injuries from head to foot in these 16 tests. Different regions of the THOR dummy were analysed. Maximum values of all lower extremity injury criteria were obtained and analysed. Intrusion and lower extremity injuries correlation was found, knee airbag and lower extremity injury correlation was also analysed. The foot-well X and Y intrusions in the 16 tests rank from minimum 14 to maximum 309 mm and from −7 to 184 mm, independently. Sixty-nine per cent right knee displacement is greater than the left knee displacement. Thirty-one per cent knee displacement and 44% left upper tibia force of the 16 tests have values that exceed injury assessment reference values. Left upper tibia force was generally greater than other tibia forces. Half of the left upper tibia index (TI) and 37.5% of the right lower TI do not meet the standard value. The foot/ankle complex is generally at a higher risk than the other parts of the leg. Same vehicle reproducibility and injury were also analysed. Right knee displacement, left femur force, left upper tibia force, left upper TI, and left ankle rotation are the most critical injuries in the respective regions of the lower extremity. Intrusion may be more prominent in some frontal damage types than in others, but not the only reason for lower extremity injuries. Other factors that influence LE injuries are the position of driver foot, the geometry of the foot-well area, the direction of intrusion, the impact energy, and acceleration of the floor. Lower extremity is the most frequently injured body region with respect to more serious injuries in the analysed test data.
Objective Field data analyses have shown that obesity significantly increases the occupant injury risks in motor vehicle crashes, but the injury assessment tools for people with obesity are largely lacking. The objectives of this study were to use a mesh morphing method to rapidly generate parametric finite element models with a wide range of obesity levels and to evaluate their biofidelity against impact tests using postmortem human subjects (PMHS). Methods Frontal crash tests using three PMHS seated in a vehicle rear seat compartment with body mass index (BMI) from 24 to 40 kg/m 2 were selected. To develop the human models matching the PMHS geometry, statistical models of external body shape, rib cage, pelvis, and femur were applied to predict the target geometry using age, sex, stature, and BMI. A mesh morphing method based on radial basis functions was used to rapidly morph a baseline human model into the target geometry. The model‐predicted body excursions and injury measures were compared to the PMHS tests. Results Comparisons of occupant kinematics and injury measures between the tests and simulations showed reasonable correlations across the wide range of BMI levels. Conclusions The parametric human models have the capability to account for the obesity effects on the occupant impact responses and injury risks.
Skull fracture characteristics are associated with loading conditions (such as the impact point and impact velocity) and could provide indication of abuse or accident-induced head injuries. However, correlations between fracture characteristics and loading conditions in infant and toddler are ill-understood. A simplified computational model representing an infant head was built to simulate skull responses to blunt impacts. The fractures were decided through a first principal strain-based element elimination strategy. Simulation results were qualitatively compared with test data from porcine heads. This simplified model well captured the fracture pattern, initial fracture position, and direction of fracture propagation. The model also very well described fracture characteristics found in studies with human infant cadaveric specimens. A series of parametric studies was conducted, and results indicated that the parameters studied had substantial effects on fracture patterns. Additionally, the jagged shapes of sutures were associated with strain concentrations in the skull.
Because of the lack of pediatric biomechanical data, the Hybrid-III (HIII) child anthropomorphic test devices (ATDs) are essentially scaled from the mid-size male ATD, and are often criticized for its rigid spine comparing to those from children. In this study, possible design modifications for improving the spine biofidelity of the HIII 6-year-old ATD were explored by child cadaver/volunteer test reconstructions and accident reconstructions using computational modeling and optimization techniques. It was found that the translational characteristics of the cervical and lumbar spine in the current child ATD need to be reduced to achieve realistic spine flexibility. It was also found that adding an additional joint at the thoracic spine region with degree of freedom in both flexion/extension and tension can significantly improve the ATD biofidelity in terms of predicting the overall spine curvature and head excursion in frontal crashes.
The effects of formalin fixation on bone material properties remain debatable. In this study, we collected 36 fresh-frozen cuboid-shaped cortical specimens from five male bovine femurs and immersed half of the specimens into 4% formalin fixation liquid for 30 days. We then conducted three-point bending tests and used both beam theory method and an optimization method combined with specimen-specific finite element (FE) models to identify material parameters. Through the optimization FE method, the formalin-fixed bones showed a significantly lower Young's modulus (-12%) compared to the fresh-frozen specimens, while no difference was observed using the beam theory method. Meanwhile, both the optimization FE and beam theory methods revealed higher effective failure strains for formalin-fixed bones compared to fresh-frozen ones (52% higher through the optimization FE method and 84% higher through the beam theory method). Hence, we conclude that the formalin fixation has a significant effect on bovine cortical bones at small, elastic, as well as large, plastic deformations.
The objective of this research was to develop a new technique for categorising the contributing factors leading to automobile crashes at intersections. Fault tree analysis was used to identify the individual roles played by the driver, vehicle and the road and roadside environment, as well as their interactions in intersection crashes. The application of a fault tree model to an Australian real-world crash data set identified the most common factors contributing to intersection crashes. The most common combination of contributing factors (minimal cut set) was ‘Misjudged speed/gap, No evasive action’, with a probability of occurrence of 0.15. More than one-third (37%) of the serious injury crashes examined were found to be the result of intentional behaviours. Some potential preventative measures were proposed to address these contributing factors.
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