# Numerical Analysis of EOD Helmet under Blast Load Events Using Human Head Model
## 2 Numerical Model
### Blast Load Modelling  
To simulate load blast, a hybrid technique that mixes the principal advantages of CONWEP (Conventional Weapons) and ALE (Arbitrary Lagrangian-Eulerian) method has been used through the implemented function in LS-Dyna, \"LOAD_BLAS_ENHANCED. In this card, it is necessary to define coordinates where the explosion occurs, the time instant when it is produced, the type of the explosion (spherical or hemispherical expansion, reflected shock wave, etc.), and the amount of explosive load of trinitrotoluene (or the equivalent mass of TNT if a different explosive is used).  
Table 4 shows a summary of the amount of explosive load and target distance used by various researchers.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Authors** & **Load [kg TNT]** & **Target Distance [m]** & **Comments** \\ \hline  & 0.85 kg de TNT & 1.06 m & \\ [PERSON] et al. [9] & 1.50 kg de TNT & 1.45 m & Based on [PERSON]’s lung \\  & 1.70 kg de TNT & 1.85 m & damage threshold curves \\  & 5.40 kg de TNT & 2.80 m & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Literature review about different works about blast load effect on the protective helmet.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Head Part** & **Material Model** & & \\ **LS-Dyna** & **Material Properties** & **Source** \\ \hline Scalp and Neck Flesh & Fu Chang Foam & Stress–Strain curves at 3 & Human cadaver Scalp in Compression, \\  & & Strain rates & McElhaney [36] \\ Skull Tables & Piece-Wise Linear & E = 6.48 GPa & Human Skull Tables in Shear, McElhaney [36] \\ Skull Diploe & Isotropic Elastic Plastic & E = 40 MPa & [PERSON] [36] \\ Dura Mater & Elastic & E = 40 MPa & Human Dura in Tension \\ Pia Mater & Elastic & E = 12.5 MPa & [PERSON] [37] \\ Cerebrospinal Fluid & Elastic Fluid & K = 2.1 GPa & Bovine Pia-Arachnoid in Shear [38] \\ (CSF) & Elastic Fluid & \(\upsilon\) = 0.4999 & [PERSON] [36] \\ Brain & Brain Linear & G0 = 1.6 kPa & Porcine Brain Tissue in Shear Arbogast \& \\  & Viscoelastic & G1 = 0.9 kPa & [PERSON] [39] \\ Falx and Tentorium & Elastic & E = 12.5 MPa & [PERSON] et al. [38] \\ Vertebrae & Rigid & - & - \\ Intervertebral Discs & Elastic & E = 10 MPa & [PERSON] et al. [40] \\ and Facet Joints & Elastic & E = 43.8 MPa & [PERSON] [41] \\ Neck Ligaments & Elastic & E = 10 MPa & [PERSON] [41] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Mechanical properties of different parts of the human head.  
On the other side, NIJ0117 standard [49], concerning to test of protective equipment subjected to explosive loads, states that the experimental test must be carried out using a complete body Hybrid III Dummy, placed in a particular position (similar to deactivation-task position) and worn with complete protector equipment. The load is positioned at 0.77 m from the ground and 0.6 m from the target at 20 degrees under the horizontal from dummy eye-line [17]. However, this work focuses on the protective performance of the helmet only; the load is, therefore, placed at the same distance, but in the same horizontal plane, as is shown in Figure 4.  
Furthermore, three different load cases have been analyzed: 0.050 kg, 0.075 kg, and 0.100 kg of TNT, for blast situations with/without a protective helmet, keeping the same load-target distance. The simulation time was 10 ms, similar to other studies [9; 10; 50] where it is considered sufficient to analyze the effects of the explosive.