A Numerical Study On Chest Injury Mechanisms And Risks Based On The Sled Biomechanical Experiment In The Belted Occupant FE Modeling

Road traffic accident has become a big threaten to people's lives.Chest injury is the second largest injury type in frontal crash which is only inferior to head injury.The most comme type of chest injury is rib fractures.Compared with driver's injury in frontal crashes,the occupant has the different kinematics and injury characters due to the large space between seat and instrument panel.Thus,the study of injury biomechanics in frontal impact to improve the occupant protection efficiency is one of the focus on the vehicle crash safety.The chest injuries commonly come from the occupant restraint system especially seatbelts.Thus,chest injury mechanism resulted from the seatbelt load needs to be investegated deeply.Additionally,under the condition of whole body test,the mechanical dummy is mostly used to evaluate the chest injury though the difference between this dummy and cadaver test is not fully studied.And the relationship between chest deflections and rib fractures from the seatbelt load has not been sufficiently studied using the model of human anatomy.This study aims at development and validation of a belted occupant FE model and the model is used to study the dynamic response of the belted occupant,chest injury mechanism and the causation of chest injury due to seatbelt load in frontal impact.Then,the influence of seatbelt position parameters is analyzed on the chest injury and the change of chest injury due to the various impact speeds.At last,analysis of the difference of the chest injury parameters between the mechanical dummy model and human body model under seatbelt restraint.For the aims mentioned,the finite element method is used in combination with analysis of experimental test data in present study.The 8 PMHS sled tests are selected and analyzed based on the test data.A belted occupant FE model(BOM)is built using the Global Human Body Models Consortium(GHBMC).Parameter sensitivity study is conducted in terms of the position parameters and contact between seatbelt and chest.According to the test configuration,a sled frontal impact is simulated with the model.The outcomes of injury parameters are obtained under different impact speeds and seatbelts with verified model.The parameter study is conducted with design of experiment and analysis of variance(ANOVA).The rib fracture mechanism is investigated via analysis of strain/stress distributions.Frontal sled test is simulated by using the belted occupant FE model.A comparative analysis was conducted for the validation of the biofidelity in terms of the kinematics,belt forces and chest deflections between simulations and experments.An analysis of the injury risk is also conducted via strain/stress distribution on each rib.The strain/stress and fracture results from simulations can match results observed in sled tests,especially the injuries of left rib 5 to rib 9 and right rib 2 to rib 6.Additionally,the prediction of rib fracture based on the strain/stress response can well match the tests,especially for the serious fractures from rib 6 to rib 10.The causation of chest injury is studied based on the variation of seatbelt height and seatbelt angle using BOM.Then the sensitivity study is conducted with the ANOVA.The influence of seatbelt height on chest injuries in terms of strain/stress distribution and chest deflection is more significant and the responses of the seatbelt height are in the reasonable deviation.The results of ANOVA show that the p-value of the seatbelt height on the chest deflection is less than 0.05.And with the increase of the number of fractured ribs,the influence of seatbelt height will increase.In which the p-values will be less than 0.01 when the number of fractured ribs over 4,while p-values of seatbelt angle are always beyond 0.3.Meanwhile,the changing of the input parameters on chest deflection and strain/stress are the same.The kinematics of the belted occupant under sled frontal impact condition is simulated using the human body model.The injury risk function is built according to the statistical analysis.There is a strong linear correlation between impact speed andfracture risks.And p-values of chest deflections and injury risks are both less than 0.01 which means the influence is signifcant.There is an obvious nonlinear correlation between seatbelt position parameters and rib fracture risks.In most cases,the p-values of the seatbelt angle are greater than 0.082.The calculated chest injury parameters are compared via seatbelt restraint parameters between GHBMC and THOR dummy models under the same condition.The difference of the injury parameters between these two models is analyzed under frontal impact and reasons for the difference are discussed.It is sure that THOR FE model has good biofidelity in kinematics.It is coupling of the THOR model in chest deflection,especially for the LR with 30 mm.But the deflection in left chest is 15 mm-20 mm greater than the reality.The chest deflection of the THOR dummy can well represent the deflection,but it must be modified if studied in detail.Overall,the following conclusions are drown.The validated belted occupant FE model has demonstrated a good biofidelity.The model can be used to investigate the chest injury mechanism under frontal dynamic loads.The influence of the seatbelt height on the injury output is more significant than the influence of seatbelt angle.The changes of the chest injury severities associate with the inertia from impact load and torso twist due to seatbelt constrant.The correlation between impact speed and chest injury are of linear feature and the correlation between seatbelt position parameters and chest injury is of nonlinear feature.The injury risk curves can illustrate the chest injury severity quantitatively.However,there is an obvious difference between THOR dummy tests and cadaver tests because of the coupling in THOR.The results from sensitivity study and injury risk analysis can provide a reference for improvement of the protection efficiency of the seatbelt system.