Head injuries are a major concern in sports. In the case of a bicycle accident, a hard enough impact to the head can lead to serious injury and even death. The objective of a helmet is to protect the rider from a head injury during an impact event. In this project, Finite Element models were developed to analyze the role that a helmet plays during a bicycle crash. The first FE model consists of a skull, while the second consists of a skull and a helmet. The impact cases were studied using SimScale - Nonlinear Dynamic Analysis.
- Simulate the impact of a human skull with and without a helmet with a Nonlinear Dynamic Analysis
- Analyze the von Mises stress, nonlinear strain, and acceleration in the skull at the maximum impact point
- Compare the results of the two cases and comment on the role wearing a helmet plays in an impact event such as a bicycle crash
The 3D geometry of the skull  was edited and cleaned before being uploaded to the SimScale platform. Due to symmetry, only one half of the skull was considered for the analysis. The geometries of the skull with and without helmet are shown in Figures 1 and 2, respectively.
Figure 1: Geometry of the skull without helmet
Figure 2: Geometry of the skull with helmet
Both geometries were meshed on SimScale using the tet-dominant meshing algorithm. Mesh refinements were added to the wall and inner and outer surfaces of the skull. The generated meshes are shown in Figure 3.
Figure 3: Tetrahedral mesh with refinements
A Nonlinear Dynamic Analysis was performed to simulate the skull impact during a crash event. The skull with and without a helmet was given an initial velocity of 6.944 m/s (25 km/h). The wall, (ie the object that the skull/helmet comes into contact with) was considered to be rigid by constraining it in all directions. The symmetry boundary condition was applied to the symmetric side of the skull and helmet.
For the case of skull with the helmet, the helmet strap was considered to be bonded to the helmet outer shell and skull by using remote force boundary condition. Augmented Lagrange contacts were defined between the wall, skull, and helmet. The impact was simulated over a long enough time span to capture the full extent of the impact.
Results and Conclusions
The Figures below show the von Mises stress (Figures 4, 5, and 6) in the skull at the highest impact point for both cases. It can be seen that there are higher stresses in the skull without the helmet. Figure 6, clearly shows that the damage to the brain would be more in case of no helmet.
Figure 4: Front view of vonMises Stress on the skull with helmet (left) and without helmet (right)
Figure 5: Side view of vonMises Stress on the skull with helmet (left) and without helmet (right)
Figure 6: Internal view of vonMises Stress on the skull with helmet (left) and without helmet (right)
Comparing, the von Mises stress (MPa), the stresses in the skull are much higher during an impact when a helmet is not worn.
Figure 7: Comparison of von Mises stress in skull with and without helmet
The graph in Figures 8 shows the acceleration (G) in the skull with and without the helmet. A decrease of nearly 35% of acceleration was achieved by the introducing the helmet to absorb part of the impact.
Figure 8: Comparison of skull acceleration with and without helmet
Figure 9: Side view of the acceleration in the skull with and without helmet
Based on the analysis, a decrease of nearly 35% of acceleration and and 60% of stress in the skull was achieved by the introduction of the helmet to absorb part of the impact. Thus, while riding a bicycle it is essential to wear a helmet to decrease the chances of severe head injury in the case of a crash.
 Skull Geometry, https://grabcad.com/bro1977-1/projects