| As vulnerable road users,pedestrians are injuried or even killed frequently in pedestrian-vehicle collisions due to lack of protective equipments.According to the investigation of traffic accident data,it can be found that lower extremity injuries are very common injury paterns,accounting for 32.8% of all reported pedestrian injuries.Although rarely fatal,lower extremity injuries will cause long-term imparement and even disability,resulting huge social and economical cost.Therfore,it is necessary to clearly understand the injury biomechanics characteristics of lower extremity for reducing the lower extremity injury risk in pedestrian traffic accident.The objective of this study is to carry out an epidemiology investigation of lower extremity injury by using selected data from traffic accident databse.Furthmore,the significant factors for lower extremity serious injuries can be found through statistical methods.And,long bone fractures can be predicted after revising and validating a human lower extremity Finte Elemnt(FE)model.Injury mechanism of long bone fractures is to be analyzed through simulations of the lower extremity dynamic process in vehicle front impacts.Injury tolerance limit is to be determined by the output injury parameters.At last,the influence of leg bone(tibia/fibula)fracture on knee joint dynamic response and injury was studied through the FE method.In order to indentify the correlations of pedestrian AIS2+ injury risks of the lower extremity with the pedestrian kinematics variables and vehicle design variables by using real-world accident data.A sub-sample of 404 pedestrian accident cases with lower extremity injuries was selected from GIDAS(German in-Depth Accident Study)databse to conduct variance test and logistic regression analyses.The main variables related to the severity of lower extremity injuries were used for the present study,including vehicle impact speed,age,height and weight of the pedestrian as well as vehicle design variables: lower bumper height(LBH),upper bumper height(UBH),bumper leading(BL)and bonnet leading edge height(BLEH).The results revealed that the predicted variables of the impact speed,pedestrian age and weight,the LBH and BLEH were statistically significant for AIS2+ lower extremity injuries.Impact speed,pedestrian age and LBH were statistically significant predictors for tibia/fibula fractures.While,age and weight of pedestrian,the BLEH was statistically significant factors for AIS2+ knee joint injuries.The findings suggest for a speed-limitation setup in the urban area and provide background knowledge for improvement o f pedestrian protective strategies in passenger car design.A lower extremity FE model with standing postion was revised baed on the anatomy of a European 50 th percentile male adult employing Hypermesh 10.0 code.This FE model can represent the reasonable physiological characteristics of pedestrian lower extremity after revising.The revised model consisted of skeleton system(pelvis,femur,tibia,fibula,patella and foot bones)and soft tissues system(flesh,skin,joint capsule,articular cartilage,knee ligaments and the main muscle).Furthmore,the biofidelity of this model was validated against published PMHS tests.The employed PMHS tests consisted of quasi-static and dynamic 3-point bending tests of long bones(femur?tibia and fibula);dynamic 3-point bending tests of leg and thigh;4-point bending and 3-point combined tests of knee joint;lower extremity bending and shearing tests at impact speed of 40km/h.The results demonstrated that the simulation results from the revised lower extremity FE model can well match the corresponding experimental data well.Therefore,this FE model can be used for investigating the injury biomechanics and predicting injury risk of lower extremity in vehicle front impacts.Two pedestrian accident cases with long bone fractures X-ray film from GIDAS database were selected to investigate the capability of this lower extremity FE mdoel for injury prediction in real traffic injury.The injury biomechanics of long bones can be determined as well in this study.In this study,the two selected cases were constructed using multi-body system to get lower extremity impact boundar y conditions,such as impact velocities,locations and oritentions of pedestrians and cars.Then,the revised lower extremity FE mdole was used to predict long bone fractures by calculating injury related parameters.At last,the comparsions of simulated injur y results and recorded injury data in hospital were conducted to demonstrate the injur y prediction capability of this lower extremity FE model.The simulation results of long bone fractures were consistent with injury pattern and postions from hospital X-ray flim.The calculated fracture moments of tibia and fibula shaft as well as femur intertrochanteric region were 304,19.8 and 318.8N.m.At last,the effect of leg bone fractures on knee joint dynamic response was analyzed by comparing the dynamic process with and without leg bone fractures.The influence of the leg bone fractures on knee injury severity was analyzed by comparing the outputed knee injury related parameters,such as knee shear displacement,knee bending angle and the forces of the major knee ligaments.The results indicated that the knee joint dynamic response was dependent on whether or not the leg bone was fractured.Moreover,the knee shear displacement and bending angle were decreased when fractures occurred.In current simulations,calculated ligament force of MCL in the case of no leg bone fractures was about 20% higher than that in the case of leg bone fractures.The simulation results demonstrated that the occurrence of leg bone fractures reduced the knee injury risk during the pedestrian-vehicle crashes.In conclusion,the statistically significant predictors for lower extremity injur y can be determined by conducting statistical analyses.The results can provide reliable data support for the design of vehicle front structure parameters.Furthmore,the revised lower extremity FE model is desmonstrated with reasonable high biofidelity,which can be used to conduct long bone fracture prediction and injury mechanics investigation.Finally,the occurrence of leg bone fractures will significantly influence the dynamic response and injury severity of knee joint in the pedestrian traffic accident.The results suggested that leg fractures should be setted when we ues the legfrom impactor to assess the veihicle proctection performance. |
PDF Full Text Request