Study On The Development Of Parametric Lower Extremity Models Representing Chinese Population And Occupant Injuries Under Impact Conditions

Injuries and casualties caused by traffic accidents and the convenience provided by vehicles are just two sides of the same coin.In frontal motor vehicle crashes,lowerextremity is still the most injured body part.Finite element analyses have been widely used in the study on occupant protection,but current human body finite element models do not account for the diversity of sex,age,stature and BMI among people.In addition,the geometry target of the lower-extremity model is from American people,and the differences between lower-extremities of Chinese and American population have not been fully studied.In this study,a systematic procedure of developing parametric lowerextremity models was proposed to build a parametric lower-extremity finite element model representing Chinese population using CT scans and study the effects of subject characteristics on the geoemtry and injury responeses of the lower-extremity during impacts.Another lower-extremity model representing American population was built at the same time to explore possible differences between lower-extremities of Chinese and American population in terms of geometry and injury responses during imapcts.In this study,a surface projection method adapted for parametric lower-extremity modeling and a method to estimate cortical bone thickness for lower-extremity using clinical CT scans were proposed,and a cadaver test was performed to calibrate and validate the key parameter in the proposed method.Using lower-extremity CT scans of Chinese and American subjects,through a modeling process including landmark identification,mesh morphing and surface projection,cortical bone thickness estimation,principal component analysis and multivariable regression,a statistical lower-extremity model was built to predict bone geometry and cortical bone thickness distribution using subject characteristics as inputs.Studies were performed to address the effects of subject characteristics on the aforementioned bone geometry.Results indicated that subject characteristis had significant effects on bone size and shape,and that such effects were different between Chinese and American populations.Subject characteristics also showed significant effects on the distribution of cortical bone thickness.It was also revealed that there was a significant difference between Chinese and American population in terms of the size,shape and cortical bone thickness distribution of the bone in the lower-extremity.Based on the statistical lower-extremity model,a thickness adjustment method and an automatic mesh quality checking and fixing technique were proposed to build parametric lower-extremity finite element models,which were validated against femur cadaver tests in literature.By integrating the lower-extremity models developed in this study with other models of different body parts,a set of whole human body finite element models of various subject characteristics representing Chinese and American population were built.In addition,the knee-thigh-hip part was validated against cadaver tests in literature.In the end,a crash simulation procedure targeting parametric human body models was established.Frontal oblique crash simulations were performed using the human body models representing various subject characteristics and the occupant lower-extremity injuries were carefully studied.The results indicated that aged,obese and female occupants suffered a higher lower-extremity injury risk.Under the same impact condition,there was no significant difference between the impact loads sustained by Chinese and American lower-extremities,but Chinese femurs had a larger area of high stress values.Taking the variation of the distribution of subject characteristics in both populations into consideration,the lower-extremity injury risk of Chinese population was 12% lower than that of American population.The parametric models developed in this study can offer meaningful reference and help in the study of occupant injury responses under various impact conditions and the protection of vulnerable occupants,and the optimization of occupant restraint systems.The parametric lower-extremity model can also lay a foundation for establishing new injury criteria suitable for Chinese population.