# Optimization Study of Driver Crash Injuries Considering the Body NWH Performance
## 3 Vehicle Crash Simulation Analysis
### Analysis of Crash Results
Head injury constitutes a primary form of harm in traffic accidents, and injuries of varying severity can lead to serious harm or fatality for the vehicle occupants. This study specifically focuses on head injuries sustained by individuals involved in traffic accidents. Such injuries can be categorized into two scenarios: the direct effects of the head colliding  
Figure 4: Vehicle 25% overlap frontal crash front deformation and overall vehicle attitude. with the vehicle's interior and brain tissue injuries resulting from the inertial forces acting on the head. The head injury criterion (\(HIC\)) currently serves as the predominant metric for assessing human head injuries in trials [38]. The calculation is presented as follows:  
\[HIC=\text{max}_{t_{1},t_{2}}\bigg{[}(t_{2}-t_{1})\bigg{(}\frac{1}{(t_{2}-t_{1})} \int_{t_{1}}^{t_{2}}a(t)\text{d}t\bigg{)}^{2.5}\bigg{]} \tag{1}\]  
In Equation (1), \(t_{1}\) and \(t_{2}\) represent the starting and ending moments of the selected period within the entire simulation, respectively, while \(a(t)\) signifies the synthesized acceleration of the human head's center of gravity. The most commonly used head injury measures in vehicle crash testing are \(HIC_{15}\) and \(HIC_{36}\). \(HIC_{15}\) reflects the maximum head injury for crash durations up to 15 ms, whereas \(HIC_{36}\) includes the maximum head injury for crash durations up to 36 ms. \(HIC_{36}\) provides a more comprehensive evaluation of the effects on the head in accidents due to the longer time frame considered. This extended duration allows for the detection of sustained effects and scenarios that could lead to severe consequences. Furthermore, \(HIC_{36}\) better captures the biomechanical characteristics of the human head, as it is more sensitive to longer-duration effects. Consequently, \(HIC_{36}\) provides a more precise quantification of head injuries sustained in real accidents. Table 1 below outlines the relationship between abbreviated injury scale (AIS) levels and the human head injury index \(HIC_{36}\). Figure 5: Frontal crash with 25% overlap energy change and mass gain curves. The results of accelerometer measurements in the X, Y, and Z directions at the dummy head measurement point were obtained. The acceleration variations in these three head movement directions during the crash are presented in Figure 6. X-direction acceleration represents the forward and backward movement of the head. The X-direction acceleration curve reaches its peak value between 70 ms and 80 ms and then gradually decreases. Y-direction acceleration corresponds to the left and right movement of the head. The curve fluctuates within the range of approximately \(\pm\)30 m/s\({}^{2}\). However, there is a notable peak in the Y-direction acceleration, reaching 69.3 m/s\({}^{2}\) at approximately 148 ms. This peak is attributed to the substantial lateral movement of the body during the crash. Z-direction acceleration illustrates the head's pitching motion. The acceleration curve reaches a negative peak of \(-\)62.42 m/s\({}^{2}\) at 61.5 ms and then gradually declines due to the reaction forces. It subsequently reaches a positive peak of 64.56 m/s\({}^{2}\) at 85.1 ms. The three-axis accelerations were synthesized to create a composite acceleration curve by taking the square root of the sum of squares of the three-axis acceleration curves. This composite curve is displayed in Figure 7.  
Using Equation (1), the composite acceleration curve was utilized to calculate the \(HIC_{36}\) value for the driver during the crash process. The \(HIC_{36}\) value peaks at 845.96 between 59.30 ms and 95.30 ms. Referring to the relationship table between the abbreviated injury scale levels and the human head injury index \(HIC_{36}\), it was concluded that the corresponding level of head injury sustained is moderate. Specifically, the injury can be described as a temporary loss of consciousness and a linear fracture.