The Research On The Modeling Method Of Finite Element Model And Injury Mechanisms Of Older And Obese Occupant

Motor vehicle crashes (MVCs) are one of the leading causes of injuries and deaths among population. There are approximately1,200,000deaths and20,000,000injured in traffic accidents worldwide every year. Along with the development of vehicle safety technology and the increasing attention on the issue of occupant safety in cars, occupant safety research on the injury prevention of older and obese occupant has been significantly improved over the past century, especially for the mid-size, yong male occupants and child safety reaearch. However, older and obese populations are often at increased risk of death and serious injury compared with mid-size young male, which is especially well documented in motor-vehicle crashes (MVCs). Unfortunately, Injury assessment tools considering aging and obesity effects and capable of simulating the geometrical and biomechanical variations among the population are not currently available. As a result, older and obese populations are generally not considered in current safety design process. Due to longer life expectancy and increasing life level, the projected increase of aging and obese population in the world further necessitate future efforts to develop more advanced injury assessment tools to evaluate safety designs for mitigating injuries that these aging and obese populations may be susceptible to. Based on the literature review, this paper focused on the study of parametric humen finite element model and injury epidemiology and injury prevention of older and obesity population through using human anthropometry, statistic analysis, mesh morphing, computer simulation and optimization.1. A parametric statistical skelekon model was developed. In this study, data from clinical thorax CT scans from89subjects were obtained. Rib cage geometries were extracted from CT images through image segmentation. Landmarks were manually identified on each rib using Hypermesh11.0(Altair, U.S.). After landmarks were collected for all subjects, the whole dataset was processed by a series of numerical analyses, including Procrustes analysis, principal component analysis (PCA) and multivariate regression analysis. The purpose of Procrustes analysis is to align the rib cage landmarks into the same center and orientation. After that, a statistical human body geometry model was developed. Using this model, detailed3D skeleton geometries of human body can be predicted by stature, gender, age, BMI, and some other human parameters. The results show that all of these parameters showed strong effects on rib cage geometry. Also, a linear mixed model was built to test whether age, gender, stature, BMI, rib number, and cross-section location along each rib are significant predictors for rib cross-sectional area. Except for BMI, all parameters also showed significant effects on rib cross-sectional area using a linear mixed model. Statistical results also indicated that the age and sex effects on rib cross-sectional areas varied significantly by the number and location of the ribs. This statistical rib cage geometry model can serve as a geometric basis for developing a parametric human FE model for quantifying effects from different human attributes on thoracic injury risks.2. Development of an automatic mesh morphing method based on radial basis function (RBF). In mesh morphing, RBF will be used as a3D interpolation and smoothing method, in which an interpolation function is calculated based on the data from the corresponding landmarks on the geometry model and the baseline FE model. Based on the landmark locations, a transformation field was calculated by RBF, which was used to transform the baseline mesh into the geometry described by the landmarks predicted by the statistical geometry models. Comparison showed that the morphed rib cage model can accurately represent the target geometry as well as maintain a comparable mesh quality of the baseline model. This algorithm can be applied programmatically, making them an efficient tool for generating a parametric human FE model.3. Development of a procedure for building a parametric human FE model and validation of this model. Using THUMS4as the baseline model, a combined model including the outer body shape model and inner skeleton model was built. Based on the combined model and mesh morphing method, a procedure for building a parametric human FE model was developed and used to build several appointed humen FE model. After that, the morphed human FE models were validated against cadaver tests under belt loading on the abdomen and whole-body frontal crash tests. This study demonstrated the feasibility of using this procedure to build a parametric human FE model. This validated parametric human FE model provides a useful tool to investigate the vehicle inner environment effects and to develop restraint system design guidelines for aging and obese occupants.4. The injury epidemiology of older population and the effect of age on rib fracture were studied and analyzed in this paper. Even though the literature has shown that the thorax injury tolerance reduced with aging, the exact mechanisms of the reduction (material or structural) are not well described. Furthermore, a comprehensive description of the age-related factors that influence thoracic stiffness is unavailable, yet this issue is of critical importance for designing "age-friendly" restraints. Therefore, in this study the effects from age-related thoracic geometric changes and bone material property changes on thorax stiffness and tolerance will be quantified in a parametric study using the newly-developed parametric thorax FE model. A Design of Experiment (DoE) will be conducted with varying thorax geometries and material properties according to different ages under hub loading condition. Results showed that age-related thoracic geometric changes, rib material property and cortical bone thickness changes make some different vary trend on thorax stiffness, rib cortical bone Von Misese stress and first component strain, expecially for the last two index, they will be at lower value as age increased. It means that eldly occupants will have much higher rib fracture injury risk in motor vehicle crashes.5. The injury epidemiology and injury prevention of obese population were studied and analyzed in this paper. Based on mesh morphing method and paremetric human FE model, the THUMS4model was morphed into human models with different BMIs. A parametric study was conducted using these morphed models to investigate the obesity effects on the occupant responses in MVCs. Results showed that obese occupants sustained higher risks of thorax and lower extremity injuries than non-obese occupants due to a combination of increased mass and poor belt fit for obese occupants. The conclusions from this research provide valuable information for future designs of obese occupant restraint systems.