Development Of 6-year-old Pediatric Biomechanical Thorax Model And Injury Analysis

Pediatic occupant, as one of the most endangered subject in traffic accident, has different body structure and injury mechanism from adults. Restrain system targeted adults could not provide children effective protection. According to road traffic accident statistics, pediatric thorax injury in accidents often results in high morality rate,occuring secondly frequent than head injury. Reasearch on pediatric thorax injury,however, has not been fully conducted. Injury criterion in different safety standards for child are far from perfect, and injury thershold for children demands more research and establishment. Meanwhile, the existing thorax of dummy model is simple in structure,which can not indicate child bone and soft tissue injury directly and precisely. Thus,study on domestic child based thorax injury biomechanics has much urgent practical significance. According to problems above, relevant work has been done in this article on basis of a large number of literature research, including the development of a 6-year-old biomechanical thorax and corresponding human model, injury mechanism study of pediatric thocic bones using schoolbus frontal crash simulation. Main content of this article is as follows:1) Based on domestic child stature statistics, a fresh 6-year-old child corpse, is chosen to conduct CT scan. Head, neck and thorax geometric models are built on the DICOM images via reverse modeling. Volumn mesh is done on the thorax part,including sternum, rib cartilage, ribs, heart and lungs, muscle and skin, ensuring mesh quality and quantity, and a finite element biomechanical thorax model is established.Material parameters are defined in each parts, combining adult material parameters study, scaling methods, and reverse calculating in modeling and verifying. Based on this, the reconstruction of human model is carried out, and a 6-year-old PEdiatric BIomechanical Thorax Human Model (PEBIT human model) is completed.2) The dynamic response validation of the 6-year-old biomechanical thorax model is conducted, based on adult PHMS (Post Human Mortal Subject) thorax impact experiment with scaling method and pediatric PHMS thorax impact experiment.According to test data and simulation results, a good match of thorax force, deflection,and force-deflection curve between simulation and test data is found. The biological resemblance of thorax model is improved.3) School bus frontal crash is selected as simulation condition for its dangerousness. The overall motion posture, motion trajectory of each parts and motion morphology of the spine during the crash is compared among multi-body dummy,MADYMO human model and PEBIT human model. Calculation methods of motion displacement error and motion trend error are proposed to analyze the trajectory similarity between MADYMO human model spine and PEBIT human model spine.The result of 11% error indicates a sufficient similarity of motion result and motion process between the two human models, completing the system-level verification of the PEBIT model, allowing it to be used in full loading condition. In 3 point safety belt restrain, the better thocic resilience stops the head movement, which is more aligned with real biomechanical response.4) The verified PEBIT human model is used in school bus frontal crash simulation for thocic bones injury mechanism analysis. Crash conditions with different loading accelerations are built by simplifying crash waveform and extracting its characteristic parameter. Simulation of PEBIT thorax model dynamic response during frontal crash is conducted using 3 point safety belt. From local to the overall, reference points from medial and lateral of sternum - rib cartilage - ribs of the fourth rib are selected to perform stress and strain anaysis, initialy comfirming dangerous areas of the ribcage under frontal loading. Combined with cloud image, injury postion and situation are further determined, and global reference points that are able to reflect overall bone injury are selected.According to reference point strain, a thoracic bone damage risk function based on failure strain is proposed, containing three stages: potential injury, injury transition and injury prediction. Potential injury stage indicate the possible criticality of bone injury when it has not occurred. Injury transition stage means the process potential injury transforms into actual injury. And the injury prediction stage is when the evaluation fuction is able to show the actual bone injury situation. The accuracy of the function is verified under different failure strain. The injury coefficient from potential injury to injury transition is calculated to be 23.9%, while the value is 27.2% when the function starts in injury prediction stage.5) The relation between thoracic bone damage risk function and thorax injury evaluation criterion is established. Thorax acceleration, deflection, safety belt force,VC, bone and lung dissipative energy under different loading acceleration is analyzed,and fitted relation between each criteria and acceleration is built, and further the relationship between bone damage risk function and each evaluation criterion. The risk function has a most distinctive linear relation with thorax cdeflection, and a high level linear relationship between heart and lung principal strain and its dissipative energy.Bones and lungs injury mechanism is summarized. Initial injury threshold is determined:when thorax deflection ratio reachs 25.76%, heart and lungs begin to suffer injury, and bone injury appears when thorax deflection ratio reachs 29.23%.6-year-old PEBIT human model developed in this article, has a high biological resemblance in thorax part. The model can be used in overall crash loading condition,and is an efficient tool for evaluating 6-year-old pediatric thorax injury during vehicle frontal crash. PEBIT human model is significant in pediatric thoracic bone injury mechanism study and development restrain system protection.