| Objective: Head injury queues up in the first place in the study of trauma in clinics and forensics. The biomechanical mechanism of head injury concerning forensics is, to some extent, unknown. As the head injury mechanism is approached further, it is likely to solve some problem hard to understand in forensic medicine. On one hand, this subject including tests which aim at studying the biomechanical mechanism when human head impacted with blunt. At the same time, all the outcome from the test will act as necessary preparations for the finite element model of human head. On the other hand, through reconstruction and validation of a three-dimensional finite element model of human head, will CAE (compute aided engineering) Technology be introduced into forensic practice. Methods:1. The hammer equipped with a force sensor in its anterior part is often used to demonstrate the dynamical characteristic of subjects. In this study, this mechanical tool is utilized to detect the contact force response when it hits on the human head. The response curve is recorded on the screen of a storable oscillometer in different cases such as different impact speed, different mass or/and size of hammer, etc. The laceration of scalp and the fracture of skull are documented.2, The fresh CT scans of human head were performed and transformed into tiff image format. Bone contours were extracted slice per slice from the stack of 216 tomograms with a slice increment of 1 mm. The volume of skull reconstructed with the MIMICS software and then its surface was smoothed with another software. Then, the volume was introduced into ANSYS LS-DYNA and anothervolume was generated in skull cavity as brain model. Through meshing the two volumes, the 3-D finite element model was gotten. After that, the simulation in which human head was impacted with a hammer was carried out and the stress and deformation were animated. Results:1.Trough the impact test on the human head, the typical contact force-time curve was obtained from which the important information-contact time can be acquired which characterizes a certain time of impact. The buffer effect of scalp and the approximate value of endurable maximum force in each part of human head were determined. The system which consists of the hammer and human head during contact time was hypothesized as a damped oscillator and this thought proved to be correct. The mechanical behavior of the skull preserved for years is deferent from that of fresh specimen .2. A finite element model of human head was reconstructed and was validated. The event was simulated in which a rigid hammer impacted the head in the mid-sagital plane in an anterior-posterior direction. The results of the finite element analysis were compared with the test data. Good correspondence was found for the duration of contact force. The contrecoup took place in the finite model and the time and the site that contre-coup emerged agreed with the test. Besides, the distribution of the Von-Mises stresses showed in the finite element model had good agreement with the observed skull fracture. The above-mentioned demonstrates that the finite element model is at least "partially validated". Conclusion:The contact force-time curve is similar to sine wave pulse. Its start part and end part have "fillet-like" changes. Scalp decreases the maximum contactforce by about 20~30% when the impactors are rigid and by 10-15% when the impactors are woody. To study the mechanical behavior of human head, it is suitable to consider the system which consists of human head and impactor as a damped oscillator.The finite element model was reconstructed and was partially validated. At the same time, the simulation in which a hammer impacted the human head has created good background for further study of biomechanical mechanism of head injury in the future. This kind of simulation through FE analysis promises sound prospects in future forensic practice and enrich the content of "digital physical human" . |
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