## 3 Results  
Figure 6 shows the experimental results obtained for the variation of the peak headform acceleration over time, in the impact test conducted using the full-face helmet. The acceleration increases rapidly to a maximum value of 204 G at 3 ms, falls to around 190 G at 4 ms, and then increases once again to a local maximum value of 196 G at 5 ms. The acceleration then reduces to zero, after approximately 12 ms. A small local acceleration peak is observed at approximately 11 ms.  
Figure 7 compares the simulation results for the headform acceleration in the full-face helmet impact test with the experimental results. It is observed that the simulated value of the global maximum acceleration (197 G) is slightly lower than the experimental value (204 G). Similarly, the simulated value of the local acceleration peak (186 G) is also slightly lower than the experimental value (196 G). The tendency of the simulation model to understate the acceleration is most likely due to the model error value. However, in general, the simulated acceleration profile is in good qualitative agreement with the experimental results, thus confirming the general validity of the modeling method.  
Figure 5: Finite element models of: (**a**) full-face; (**b**) open-face; (**c**) half-face; (**d**) prototype open-face helmet 8 mm design; (**e**) prototype open-face helmet 14 mm design; and (**f**) prototype open-face helmet 18 mm design helmets used in simulated impact tests.  
Figure 8 presents the simulated headform acceleration profiles for the full-face, open-face, and half-face helmets, given an impact speed of 6 m/s. A good general agreement exists between all three profiles. However, a close inspection reveals some subtle differences between them. For example, the half and open-face helmets have peak accelerations of 303 G and 235 G, respectively, whereas the full-face helmet has a much lower peak acceleration of 197 G.  
Figure 9 compares the simulated acceleration profile of the original open-face helmet, with the profiles obtained for the prototype helmet design with ventilation slot widths of 8 mm, 14 mm, and 18 mm, respectively. As discussed above, the original open-face helmet has a maximum acceleration value of approximately 235 G. In contrast, the peak acceleration value of the prototype helmet is 160 G for a slot width of 8 mm, 175 G for a slot width of 14 mm, and 150 G for a slot width of 18 mm. In other words, for all values of the ventilation slot width, the peak acceleration experienced by the headform during impact is lower than that produced by the original open-face helmet design.  
Figure 6: Experimental results for impact energy dissipation in the full-face helmet impact test.  
Figure 7: Comparison of simulated and experimental acceleration profiles for a full-face helmet.  
Figure 10 shows the magnitude of the stress and displacement contours of the full, open-face, and 8-mm ventilation slot helmets. The level of stress recorded for the 8-mm ventilation slot helmet is 2 Mpa, whereas the displacement value is 21 mm. However, in the case of a full helmet, the level of stress is 1.3 Mpa, whereas the displacement value is 15 mm; however, for an open-face helmet, the level of stress is 1.5 MPa and the displacement value is approximately 16 mm. Thus, the 8-mm ventilation slot helmet possesses the ability to achieve buffer distances that absorb energy.  
Figure 8: Simulated headform acceleration profiles for full-face, open-face, and half-face helmets.  
Figure 9: Simulated headform acceleration profiles for the open-face helmet and prototype open-face helmet with three different ventilation slot widths.