Study On Biomechanical Response And Injury Assessment Of Ribcage And Liver In Impacts To The Occupant

For AIS 2+traffic injuries,thorax-abdominal injury ranked 3^rdbehind head and extremities.While thorax-abdominal injury ranked 2^nd only behind head when evaluating AIS 3+injuries.as the largest organ in abdomen,the liver partly covered by the ribcage and facing the low rim of streering wheel behaved the characteristic mechanical response and injury pattern under impact,comparing to the heart-lung injury with widely research.It was meaningful and vital for improvement of driver protection to study the biomechanical respones of driver rib-covering-liver part in vehicle collisions.unlike the occupant side arrangement,the loading from streeing wheel,airbag and seatbelt was the main cause of injuries of the driver rib-covering-liver part.It was necessary for deep research of the injury mechanism.The object of this thesis is to study the biomechanical responses and injury mechanism of human ribcage-covering liver part in static blunt impacts,as well as the vehicle frontal collisions in order to discuss the adjustable factor influence of the seatbelt,airbag and the steering wheel.The newly developed liver model with detailed anatomic features and test data-based material constitutive model was integrated into the CHUBM-M50,which was used for the whole research.Finally,the evaluation method for the occupent protection based on the biomechanical FEM was explored and compared to the traditional assessment from C-NCAP?China-New Car Assessment Program?regulation,which utilized the ATD.The development of accurate liver finite element model was accomplished for improving the biofidelity and validity in crash simulations.12 human liver finite element models in the current research were constructed from high resolution CT data of a Chinese male 50^thh percentile human subject,including the main structures like left lobe,right lobe,capsule and falciform ligament.The uniaxial static tensile test was contucted for the material properties of liver parenchyma ans capsule.the thorax-abdominal model of CHUBM-M50 was validated according to the EEVC FID by comparing predicted responses with normalized experimental results.It demonstrated that the CHUBM-M50 could be useful in various cadaveric impacts reported in literature.This paper integrated the features and conditions into numerical FE analysis on thorax-abdominal mechanical responses with CHUBM-M50,to realize peak force,maximum compression,viscous criterion(VC_max),effective stiffness?EF?,and rib fractures of the thorax,under various blunt loadings of impact speeds,locations and directions.The model was validated by test simulations via the cadaver pendulum tests.A total of 45 cases designed by 3vertical alignments×5 directions×3 speeds,were carried out.It indicated that the thoracic characteristics had significant correlation with impact location,and the mechanical responses at midsternal level were much stiffer than those at xiphoid process.It also demonstrated that the impact at xiphoid process causes more severe injuries even at low speed.The thoracic response pattern was similar between left and right side impact,which showed that the symmetrical characteristic in spite of asymmetric anatomical features of viscera.Frontal sled test is simulated by using the belted driver FEM with steering wheel and airbag.The causation of ribcage-covering-liver part injury was studies based on the variation of the limit force and upper slip ring of the seatbelt,the height and horizontal distance from the steering wheel to the diver,and the relative distance and angle between the airbag and driver.The effect of the adjustable factors on the ribcage and liver injuries was summerized by analyzing the mechanical response and injury characteristics.It illustrated that the seatbelt without force limitor was better able to restraint the driver torso from moving forward with a larger restraint force against the thorax-abdominal part,causing a fierce compression and multiplied fractures.The deployment of airbag resulted in a serious hepatic trauma without rib fractures.Finally,the assessment of a SUV's safety performance in full-frontal impact and 40%offset frontal impactwas carried outultalizing the occupant biomechanical model according to C-NCAP.Moreover,the assessment results of theoccupant biomechanical model were compared with those of the Hybrid III dummy in 40%offset frontal impact test of the sample car.The reaults indicated that the assessment metod of vehicle crashsafety on the basis of the occupant biomechanical model in this tudy was feasible on the theoryand technology.The injuries of ribcage-covering-liver part induced by the40%offset frontal impact were more serious than those by full frontal impact.The assessment results of the occupant biomechanical model were much moredetailed and clear than those of the mechanical dummy,and were more targetd to theimprovement of automobile structure safety.Therefore,the design and assessment of vehiclecrash safety based on the occupant biomechanical model had a unique advantage andadvancement comparering to the traditional methods.In conclusion,the study in this paperwill provide important significance and practical value to the improvement of vehicle safetydesign,occupants'injury protection and automobile safety regulations.