Research On Fluid-structure Coupling Model And Injury Mechanism Of Human Head During Car Crash

Head injury is one of the most common types of injuries in traffic accidents，and oftenresults in serious injury or even death. Crash test dummies are currently used to design andevaluate collision safety, improving vehicle safety greatly. However, compared with the realanatomy of human head, the dummy’s head structure and function are very simple. There aresome limitations for studying head injuries. In terms of structures, the dummy’s headstructure consists of a cast aluminum skull and a skull cover with vinyl skin, while humanhead is composed of skin, skull and brain tissues. In terms of injuries, the dummy can onlyshow the HIC value at the centroid of head, which is different from the real physiologicalphenomena of skull fracture, tissue damage and bleeding. In fact, vehicle safety designsshould be based on a real person for protecting passengers better.Head injury problems have attracted great attention of researchers for a long time. Thestudies for head injuries began in the1940s. The methods include the use of volunteers,cadavers, animals, anthropomorphic test devices and mathematical and computer models.The mathematical model using the finite element (FE) method has been a main tool forstudying head injuries. This paper relies on the National Natural Science Foundation project"Fluid-structure Coupling Model and Injury Evaluation Techniques of Human Head duringAutomotive Passive Safety Design". According to the fact that none of existing head modelsconsiders the intracranial fluid-structure coupling, a fluid-structure coupling human headmodel for collision analysis is established, based on a Chinese50thpercentile male. Theresearch on modeling and injury mechanism of human head during car crash is carried out.Arbitrary Lagrangian-Eulerian (ALE) method is used to simulate the interface between skull,cerebrospinal fluid (CSF) and brain. This main contents can be summarized as follows:(1) Fluid-structure coupling theory and alternative model of headALE fluid-structure coupling theory is carried out. Based on Corina’s experimental datawhich is about physical alternative head model, the simulation method is studied. The results confirm the necessary and effectiveness of the fluid-structure coupling modeling in headmodel.(2) Human head geometry model and FE model based on the50thpercentile ChinesemaleA three-dimensional geometric model of human head is established, based on the CTand MRI scan data from a50thpercentile adult male volunteer. According to the geometrymodel, a detailed FE model is established. The model contains brain, cerebellum, brainstem,ventricles, CSF, corpus callosum, dura, pia mater, falx, tentorium, skull, facial bones andskin. The fluid-structure coupling interaction between skull, CSF and brain tissue issimulated by ALE method with overlapping grids. According to published literature, thematerial parameters of the head model are defined.(3) Validation of head model for collision analysisThe biomechanical responses of the fluid-structure coupling human head model arevalidated, based on classic cadaver experimental data internationally recognized. Theintracranial pressures by Nahum, intracranial dynamic responses by Trosseille and brainrelative displacements with respect to skull by Hardy are simulated. The model is adjustedand amended to ensure its effectiveness.(4) Different simulation methods for skull-brain contact interfaceThe influence on intracranial responses between the fluid-structure coupling model andshare-nodes models with different CSF material parameters is compared and analyzed. Theresults showed that the skull-brain displacements predicted by the Lagrange models aresmaller than experimental data. However, those predicted by the coupling model are closerto experimental trends and values, compensating for the deficiency.(5) Application of the fluid-structure coupling human head modelThe frontal and rear-end crash models are established, using multi-body models. Sixaccelerations of dummy head are extracted from the processes. The accelerations are used asinputs on the rigid skull. Brain responses are simulated during impact. Through comparingintracranial biomechanical parameters with injury limits, brain injury risks are predicted. Theresults show that the passenger may suffer brain contusion, severe nerve damage and diffuse axonal injury risk although an airbag reduces HIC values greatly in a front collision. Andmoderate nerve damage and diffuse axonal injury may occur, even if the HIC is small whenthe head impact headrest under rear-end collision. The fluid-structure coupling model cangive more comprehensive and effective injury evaluations than dummy.The following deficiencies exist, which need to further improvement and exploration.(1) This paper aims to explore the fluid-structure coupling relationship between skull,CSF and brain. The arachnoid trabecular and sulcus on brain surface are simplified orignored, which may affect the simulation results.(2) The paper focuses on intracranial biomechanical responses, which includeintracranial pressures and skull-brain relative displacements. If involving skull injuries, thefracture characteristics of skull and facial bones need to be verified.(3) Blood vessels are not considered in the establishment and injury prediction of themodel. Blood vessel tear, hematoma and other phenomena in collision can not be examined.The model needs to be refined further.Aiming to no consideration of intracranial fluid-structure coupling in current models, anew detailed FE human head model is established. The model is based on the medicalimaging from a Chinese50thpercentile adult male. The fluid-structure relationships between“skull-CSF-brain” are simulated. This model is able to compensate for small skull-brainrelative displacement amounts of the conventional models, and more accurately predict braindamages. Also, it can make up the insufficiency that only HIC predicts the head injury ofcrash dummy, and achieve a more comprehensive prediction of brain injuries, helpingautomobile safety design.