**3. Result and discussion**

As shown in **Figure 4**, in all head form models, the head peak accelerations were delayed when the pole was laminated with various padding thicknesses as compared with the head when it impacted against the steel pole (SB\_0, SCB\_0, SCCB\_0). For the simplified head form model, SB, increasing of the padding thickness exhibited an insignificant peak acceleration reduction, however, the rate of acceleration reduced as the padding thickness increased From a point of vehicle crashworthiness, delaying the peak acceleration can significantly reduce the head/brain injury. Recent studies have indicated that a high rate of onset acceleration, i.e. high jerk, during a low-speed vehicle collision increases the risk of whiplash injury by triggering inappropriate muscle responses [20, 21].

It is also worth mentioning that the development of a representative head form model plays a crucial role to obtain the actual acceleration/deceleration and predict the injury level resulting from the vehicle crash. As shown in **Figure 4(c)**, the head form, SCCB, that consisted of the scalp, composite skull, CSF, neck, and muscle exhibited the highest acceleration and became more responsive to padding thickness and (a reduction of acceleration) when it impacted the steel pole: at 25 mm padding thickness, the lowest acceleration was obtained by the SCCB. On the other hand, the more rigid and simplified model, SB, exhibited the lowest acceleration at zero padding thickness and was less responsive to the change in padding thickness;

**Figure 4.** *Comparison of acceleration-time graph: (a) SB, (b) SCB, (c) SCCB, (d) 25 mm padding thickness.*

**147**

**Figure 5.**

*padding thickness.*

*Head Impact Injury Mitigation to Vehicle Occupants: An Investigation of Interior Padding…*

at 25 mm padding thickness, the highest acceleration was obtained by the SB, as shown **Figure 5(d)**. This phenomenon can be explained by the fact that in the SB model, the skull, CSF, neck, and muscle were represented by a single material type, the bone, that increased the stiffness of the model and reduced the energy absorption resulting from the interactions among the head form parts and the pole. Generally, padding of the interior part of a vehicle structure with energy absorbing materials, regardless of the type of head model (simplified or detailed model),

**Figures 5** and **6** show the results for the strain time-histories in three regions of the brain (coup (back), contrecoup (front), and middle (reference point (RP), **Figure 3**)). **Figure 5** displays the strain versus time-history of the coup for a duration of 20 milliseconds for various padding thicknesses for each head model. **Figure 6** shows the strain for the contrecoup and middle regions of the brain as well, for a similar time history for the three head models at a padding thickness of 25 mm. As expected, the simulation results for each case concluded with a general decrease in the peak strain present within all regions of the brain as the thickness of the padding increased. By analyzing the various models, it was concluded that the presence of the CSF resulted in a quicker strain response, as well as a damping effect on the peak strain present within the brain. The most simplified model, SB, resulted in a delay of the peak strain on the contrecoup compared to the more detailed models, SCB and SCCB, due to the rigidity of the system corresponding with the absence of the CSF, shown in **Figure 6(b)**. The stress delay on the contrecoup also corresponds with the absence of materials, including the skull and the CSF within the system, resulting in a larger time duration before the strain from the impact transfers to the contrecoup. Due to the fluid material properties of the CSF, a damping effect of the strain present within the brain upon impact was also applied to the models where CSF was implemented, SCB and SCCB, resulting in a

*Comparison of strain-time graphs for three head form models: (a) SB, (b) SCB, (c) SCCB, (d) at 25 mm* 

*DOI: http://dx.doi.org/10.5772/intechopen.95250*

significantly reduced the peak and the rate of acceleration.

#### *Head Impact Injury Mitigation to Vehicle Occupants: An Investigation of Interior Padding… DOI: http://dx.doi.org/10.5772/intechopen.95250*

at 25 mm padding thickness, the highest acceleration was obtained by the SB, as shown **Figure 5(d)**. This phenomenon can be explained by the fact that in the SB model, the skull, CSF, neck, and muscle were represented by a single material type, the bone, that increased the stiffness of the model and reduced the energy absorption resulting from the interactions among the head form parts and the pole. Generally, padding of the interior part of a vehicle structure with energy absorbing materials, regardless of the type of head model (simplified or detailed model), significantly reduced the peak and the rate of acceleration.

**Figures 5** and **6** show the results for the strain time-histories in three regions of the brain (coup (back), contrecoup (front), and middle (reference point (RP), **Figure 3**)). **Figure 5** displays the strain versus time-history of the coup for a duration of 20 milliseconds for various padding thicknesses for each head model. **Figure 6** shows the strain for the contrecoup and middle regions of the brain as well, for a similar time history for the three head models at a padding thickness of 25 mm. As expected, the simulation results for each case concluded with a general decrease in the peak strain present within all regions of the brain as the thickness of the padding increased. By analyzing the various models, it was concluded that the presence of the CSF resulted in a quicker strain response, as well as a damping effect on the peak strain present within the brain. The most simplified model, SB, resulted in a delay of the peak strain on the contrecoup compared to the more detailed models, SCB and SCCB, due to the rigidity of the system corresponding with the absence of the CSF, shown in **Figure 6(b)**. The stress delay on the contrecoup also corresponds with the absence of materials, including the skull and the CSF within the system, resulting in a larger time duration before the strain from the impact transfers to the contrecoup. Due to the fluid material properties of the CSF, a damping effect of the strain present within the brain upon impact was also applied to the models where CSF was implemented, SCB and SCCB, resulting in a

**Figure 5.**

*Comparison of strain-time graphs for three head form models: (a) SB, (b) SCB, (c) SCCB, (d) at 25 mm padding thickness.*

*Advancement and New Understanding in Brain Injury*

**3. Result and discussion**

with a predefined velocity of 4 km/hr. towards the pole.

triggering inappropriate muscle responses [20, 21].

"Tie option" interaction available in ABAQUS®. Similarly, at the interface between the skull and the CSF, the CSF and the brain, as well as the skull and the scalp, a tie option was also implemented. In this work the pole was constrained with a fixed boundary condition at the two ends. The initial condition was imposed on the head

As shown in **Figure 4**, in all head form models, the head peak accelerations were delayed when the pole was laminated with various padding thicknesses as compared with the head when it impacted against the steel pole (SB\_0, SCB\_0, SCCB\_0). For the simplified head form model, SB, increasing of the padding thickness exhibited an insignificant peak acceleration reduction, however, the rate of acceleration reduced as the padding thickness increased From a point of vehicle crashworthiness, delaying the peak acceleration can significantly reduce the head/brain injury. Recent studies have indicated that a high rate of onset acceleration, i.e. high jerk, during a low-speed vehicle collision increases the risk of whiplash injury by

It is also worth mentioning that the development of a representative head form model plays a crucial role to obtain the actual acceleration/deceleration and predict the injury level resulting from the vehicle crash. As shown in **Figure 4(c)**, the head form, SCCB, that consisted of the scalp, composite skull, CSF, neck, and muscle exhibited the highest acceleration and became more responsive to padding thickness and (a reduction of acceleration) when it impacted the steel pole: at 25 mm padding thickness, the lowest acceleration was obtained by the SCCB. On the other hand, the more rigid and simplified model, SB, exhibited the lowest acceleration at zero padding thickness and was less responsive to the change in padding thickness;

*Comparison of acceleration-time graph: (a) SB, (b) SCB, (c) SCCB, (d) 25 mm padding thickness.*

**146**

**Figure 4.**

**Figure 6.** *Strain-time graph: (a) middle, (b) front.*

significant decrease of the peak strain values. However, when analyzing the middle region of the brain, the peak stresses resulted in a much lower value, overall. The stress wave fluctuations in this region, shown in **Figure 6(a)**, also resulted in a decrease of peak strain values with the presence of the CSF. However, for the most simplified model, SB, the drastic change in strain value due to the stiffness of the system, as well as the stress fluctuations between the coup and contrecoup could potentially cause a significant shear tear-out behavior of the brain tissue. Such behavior could lead to a diffuse injury, or shear injury, which is an important aspect involved in the causes of long-term TBI [22].

**Figure 7** illustrates the pressure being transmitted through the brain due to the impact with a padding thickness of 25 mm at various time histories. The pressure

**149**

**4. Conclusion**

**Figure 8.**

elasticity in the most detailed model.

*Head Impact Injury Mitigation to Vehicle Occupants: An Investigation of Interior Padding…*

in the brain for each head model, SB, SCB, and SCCB, is illustrated for t = 3 ms, t = 5 ms, and t = 10 ms. **Figure 7** displays specific parameters, including the pressure versus time-history for the coup, middle, and contrecoup of the brain in order to visualize the quantitative tensile and compressive behaviors of the brain upon impact. Comparable to the strain versus time-history results in **Figures 5** and **6**, the initial peak pressure values of the more detailed models, including the CSF, significantly decreased compared to the simplified model, SB, shown in **Figure 7**, along with the corresponding graphical results in **Figure 8(a)**-**(c)**. These outcomes similarly correspond with the results provided from previous studies [23] that displayed the reduction of pressure oscillation due to the damping factor provided by elastic materials, such as CSF. The buoyancy of the CSF, as well as the effect of mass due to the presence of the skull and CSF layers, results in a reduction in the peak pressure values for the coup, middle, and contrecoup, corresponding with the reduction in the peak strain values as well. However, when analyzing the simplified model, the decreased acceleration, illustrated in **Figure 4(d)**, corresponds with an increase in pressure, **Figure 8(c)**, within the brain due to the inflexibility of the model. On the other hand, when comparing the similar pressure behaviors of SCB and SCCB, it is seen from **Figure 8(a)** that the peak pressure of the contrecoup increases for SCCB while the acceleration increases as well, shown in **Figure 4(d)**, due to the flexibility of the neck from the alteration of the modulus of

This current work has studied the effect of vehicle interior padding thickness on the response of three head form FEM models subjected to an impact loading. The

*DOI: http://dx.doi.org/10.5772/intechopen.95250*

*Pressure–time graph: (a) front, (b) middle, (c) Back.*

**Figure 7.** *Pressure response: (a) SB, (b) SCB, (c) SCCB.*

*Head Impact Injury Mitigation to Vehicle Occupants: An Investigation of Interior Padding… DOI: http://dx.doi.org/10.5772/intechopen.95250*

**Figure 8.** *Pressure–time graph: (a) front, (b) middle, (c) Back.*

in the brain for each head model, SB, SCB, and SCCB, is illustrated for t = 3 ms, t = 5 ms, and t = 10 ms. **Figure 7** displays specific parameters, including the pressure versus time-history for the coup, middle, and contrecoup of the brain in order to visualize the quantitative tensile and compressive behaviors of the brain upon impact. Comparable to the strain versus time-history results in **Figures 5** and **6**, the initial peak pressure values of the more detailed models, including the CSF, significantly decreased compared to the simplified model, SB, shown in **Figure 7**, along with the corresponding graphical results in **Figure 8(a)**-**(c)**. These outcomes similarly correspond with the results provided from previous studies [23] that displayed the reduction of pressure oscillation due to the damping factor provided by elastic materials, such as CSF. The buoyancy of the CSF, as well as the effect of mass due to the presence of the skull and CSF layers, results in a reduction in the peak pressure values for the coup, middle, and contrecoup, corresponding with the reduction in the peak strain values as well. However, when analyzing the simplified model, the decreased acceleration, illustrated in **Figure 4(d)**, corresponds with an increase in pressure, **Figure 8(c)**, within the brain due to the inflexibility of the model. On the other hand, when comparing the similar pressure behaviors of SCB and SCCB, it is seen from **Figure 8(a)** that the peak pressure of the contrecoup increases for SCCB while the acceleration increases as well, shown in **Figure 4(d)**, due to the flexibility of the neck from the alteration of the modulus of elasticity in the most detailed model.
