# Accident Reconstruction of Damaged Human Body Using MDCT and Computer Numerical Analysis
## 4 Analysis of Damage Mechanism Using ADINA
### Pre-Processing of Computational Numerical Analysis  
The digital human bone model of this study is composed of ribs, sternum, spine, and rib cartilage; Table 1 shows the mechanical properties of these components. There are discs between vertebrae and Table 2 shows their elastic modulus. In the case of costal cartilage, it is impossible to obtain  
Figure 5: Reconstruction of the digital bone model’s damaged parts. its mechanical properties by conventional test methods such as tensile tests due to difficulties in using test specimens as costal cartilage is limited in size. Therefore, an instrumented indentation technique that uses AIS3000 and a specific jig for this study was applied to obtain the mechanical properties of costal cartilage [5; 6]. Using the specimens collected from the body, the elastic modulus, yield strength, and tensile strength were obtained and their average values calculated from the results of 15 tests were used and are shown in Table 1. Figure 6 shows a photograph of the specimen of costal cartilage and the results of the tests. The conversion of human bone to a finite element model is necessary before performing a finite element analysis of the reconstructed digital human bone model. Figures 7 and 8 show a finite element model of the digital bone model. Generating a finite element model, the connection of nodes between the ribs and cartilage was constructed using a rigid link element and the connection of nodes between the spines was constructed using a spring element. The mechanical properties of the connections are designated as those of the disc. Finite element analysis was performed by applying the appropriate mechanical property to each model of the converted digital human bone model. To obtain compatibility and reliability between 2-D CT images and a 3-D human bone model, skin and lung tissue are excluded and analysis was performed only for the pure human bone. The 3-D model of the human bone and the number of elements was 398,174. To obtain the value of impact force, a mechanical environment is assumed and estimated using three-dimensional images obtained from MDCT for personal injury and CCTV image analysis based on the results of the investigation of the forensic point of view. Potential energy from 21.3 m high is fully converted to kinetic energy by the principle of the conservation of energy. The speed of the falling body at the ground is calculated as Equation (1). \[\mathrm{v}_{\mathrm{final}}=\sqrt{2\mathrm{gh}_{\mathrm{initial}}} \tag{1}\]  
Here, \(\mathrm{v}_{\mathrm{final}}\) is the speed of the falling body at the ground, g is acceleration of gravity and \(\mathrm{h}_{\mathrm{initial}}\) is height of the falling. From the image analysis of the CCTV information of the event, delay time was measured as 3.56 ms and finally, impact force is calculated by Equation (2). \[\mathrm{Impact\ Force}=\frac{\mathrm{mv}_{\mathrm{final}}}{\Delta\mathrm{t}} \tag{2}\]  
Here, m is the weight of the body and \(\Delta\mathrm{t}\) is the delay time. Boundary conditions and load conditions are shown in Figure 9 considering the calculated impact force, 5750 N. Each 50 N was applied to 115 nodes which are estimated to contact the ground as shown in Figure 9. In the case that the body falls freely from 21.3 m high, finite element analysis is performed. The analysis starts at 2 mm away from the rigid wall and the initial speed is calculated as 20.4417 m/s by Equation (1). Figure 10 shows the finite element model and the boundary condition for the analysis of the falling body. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Young’s** & **Density** & **Poisson’s** & **Yield Strength** & **Tension Strength** \\  & **Modulus** & **(kg/m\({}^{3}\))** & **Ratio** & **(MPa)** & **(MPa)** \\ \hline Rib & 13.9 GPa & 1561 & 0.3 & 93.9 & 124.2 \\ Sternum & 3.51 GPa & 1354 & 0.387 & 34.48 & 48.27 \\ Vertebra & 4.67 GPa & 1500 & 0.3 & 52.62 & 69.06 \\ Costal Cartilage & 19.92 MPa & 1203 & 0.4 & 141.32 & 285.94 \\ \hline \hline \end{tabular}
\end{table}