# Evaluation of Combat Helmet Behavior under Blunt Impact
## 3 Results
### Influence of Impact Velocity  
The influence of impact velocity is analyzed in this section using the flat anvil. The impact velocity is reduced to 3, 3.5, and 3.9 m/s, since it is assumed that with higher velocities, more severe injuries are induced than in the previous sections.  
Peak Linear Acceleration (PLA)  
The main consequence of reducing the impact velocity is the decrease in the risk of suffering serious injuries. Table 10 shows the injuries according to the AIS scale. All the cases are below the AIS 1 and 2 levels. As described above, the probabilities of obtaining AIS \(\geq\) 3 are greater than 50% for impact velocities of 4.4 m/s for all configurations, as shown in Table 6. Therefore, impact velocity is a critical factor in traumatic brain injuries by blunt impact at low impact velocities  
Analysis of traumatic brain injury, according to AIS, is shown in Table 11 for the different impact velocities. As mentioned above, a reduction in the impact velocity leads to a decrease in the parameter  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Head Model**} & \multirow{2}{*}{\
\begin{tabular}{c} **Impact Velocity** \\ **(m/s)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **AIS Head** \\ **(Equation (6))** \\ \end{tabular} } & \multirow{2}{*}{**AIS Level**} \\ \hline \multirow{8}{*}{**Head surrogate**} & 3 & 147 & 1.97 & 2 \\  & 3.5 & 195 & 2.5 & 2 with a 50\% of probability to \\  & 3.9 & 217 & 2.65 & 2 with a 65\% of probability to \\  & 4.4 & 270 & 3.03 & 3 \\ \hline \multirow{8}{*}{**Human head**} & 3 & 166 & 2.1 & 2 \\  & 3.5 & 203 & 2.5 & 2 with a 50\% of probability to \\ \cline{1-1}  & 3.9 & 234 & 2.8 & 2 with high probability to \\ \cline{1-1}  & 4.4 & 258 & 2.95 & 3 \\ \hline \hline \end{tabular}
\end{table}
Table 10: PLA and AIS for impact velocity v\({}_{0}\) = 3 m/s.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Head Model**} & \multirow{2}{*}{**Location**} & \multirow{2}{*}{**HIC**} & **AIS 1** & **AIS 2** & **AIS 3** & **AIS 4** & **AIS 5** & **AIS 6** \\  & & & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** \\ \hline \multirow{4}{*}{\
\begin{tabular}{c} **Head** \\ **surrogate** \\ \end{tabular} } & Top & 818 & 97 & 77 & 36 & 10 & 0 & 0 \\  & Frontal & 1066 & 100 & 90 & 55 & 18 & 2 & 0 \\  & Rear & 502 & 80 & 40 & 12 & 3 & 0 & 0 \\  & Lateral & 620 & 90 & 55 & 20 & 5 & 0 & 0 \\ \hline \multirow{4}{*}{
\begin{tabular}{c} **Human** \\ **head** \\ \end{tabular} } & Top & 1695 & 100 & 100 & 95 & 72 & 33 & 7 \\  & Frontal & 2025 & 100 & 100 & 98 & 90 & 70 & 30 \\ \cline{1-1}  & Rear & 1584 & 100 & 100 & 91 & 62 & 22 & 4 \\ \cline{1-1}  & Lateral & 1038 & 100 & 91 & 57 & 19 & 2 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 9: HIC and AIS (%) for curbstone anvil case.  
values. For impact velocities below 3.5 m/s, the values are well within safe limits and, consequently, involve a reduction in the risk of suffering serious injuries according to standards ECE R22/05 [19] and NHTSA [43]. Thus, the probability of causing traumatic brain injuries according to AIS 3 is considerably low.