Research Of Human Thorax FEM For Analysis Of Explosion Protection

The main threat to military personnel on the battlefield is ballistic injury. The use of body armors efficiently reduce the penetrate injury. While the bullet is stopped and the effects of the projectile penetrating the biological tissues are prevented, a considerable amount of energy is still transmitted through the protective layers of the armor to the human body and damaged the tissues behind. This phenomenon is referred to as "rear effect" or "behind armor blunt trauma(BABT)" presenting as lung and heart contusions as well as rib fractures. If the blast wave from an explosion is transmitted to the torso of an individual, it can induce an acceleration of violent levels which exists as a potential thread, particularly to the gas containing organs. Finite element model can be used to calculate the biomechanical response of human thorax against different loads and impact conditions by simulating various experiment methods and provide stress-strain result, displacement-time, velocity-time and acceleration-time result between tissues. It willl be helpful in researching the mechanism of BABT, the relationship of the mechanical response against blast wave and tissue injury of thorax. It can also be used in design and amelioration of body armor.A 3D human thorax finite element model is built on the basis of "Chinese Visible Human" slice images and computed tomography images in Mimics and validated by human cadaver test and animal test. The main studies were as follows: The computed tomography images and "Chinese Visible Human" slice images were selected as source images to rebuild the 3D model. The images were processed and segmented in MIMICS. The regions of interesting were get and the 3D objects were calculated in the system. The 3D human thorax model with inner organs and bone tissues was reconstruct. The 3D model was meshed with tetrahedral elements which will be replaced by hexahedral elements later in ANSYS ICEM CFD software. The final human thorax FEM was finished in ANSYS LS-DYNA code. To validate the FEM under blunt ballistic impact, the data from the experimental tests on human cadavers done by Bir were used. The test conditions were 140g at 20m/s, 140g at 40m/s and 30g at 60m/s respectively. The force applied by the projectile versus time and the deflection of the torso versus time were computed and compared with the experimental data. The material properties were verified by animal test data. The dog was impacted by biomechanical machine, the mass of the impactor is 360g and the impact velocity is from 7.5m/s to 12.7m/s. A simple dog chest FEM was build. The animal test conditions were reproduced numerically, and the computed results were compared to the test results.Followings are the main results and conclusions:1. A 3D human thorax model with approximate anatomical structure was reconstruct by CVH slice images and CT images.2. A human thorax FEM that include muscle, skeleton and organs was developed in ANSYS LS-DYNA code. All parts of the model consisted of 475560 SOLID164 elements and 530949 nodes. The bone tissues such as sternum and ribs were assumed to be linear-elastic while all internal organs and muscle tissue were modeled as viscoelastic. The material properties of organs and tissues were defined by previous literature.3. It's difficult to mesh a model which had complex shape in hexahedral elements directly. The used hexahedral element was transformed by tetrahedral element. it's quality and precision was a little worse than regulation one, but was better than degenerate element. The hexahedral mesh was easily achieved and could reduce the modeling time. and also feasible in building complex finite element model.4. When the mass of the impactor was 140g and the impact velocity, 20m/s and 40m/s, the computed results were consistent with the cadaver test results. The FEM was validated under these impact condition. When the mass of the impactor was 30g and the impact velocity, 60m/s, the computed results were different with the cadaver test results. The material properties of the FEM under such test condition need further study.5. A simple dog chest FEM was build with the same material properties of the human model, and computed under animal test conditions. The calculated results were accorded with the test results. The load and deflection of the animal thorax could be reflected by the animal model. The applied material properties should be credible.