# FE Analysis of Motorcycle Helmet Performance under Severe Accidents
## 4 Model Validation  
An impact test with a flat anvil according to the TIS 369-2557 standard was performed for the validation procedure to compare with the simulation results. All components of the helmet structure were combined and set up as shown in Figure 5, in which the anvil was assigned as the fixed support. An initial velocity of 27 kph (7.5 m/s) was then applied downward for the other components. Since this paper needs to clarify the ability of comfort padding to reduce head injury during impact accidents, the model was divided into two cases: without comfort padding (Figure 5a) and with comfort padding (Figure 5b). Deformation behavior of a helmet can occur naturally when contact between the shell component and anvil is defined by AUTOMATIC_SURFACE_TO_SURFACE, which has a friction coefficient of 0.2. The analysis procedure was performed for 10 ms and the acceleration and HIC results were compared with the test and criteria of the standard. Acceleration, which was recorded from the CG of the headform for all three cases (impact test according to TIS 369-2557 (Section 2.2), FE model with comfort padding, and FE model without comfort padding), is illustrated in Figure 6. The results from the test and FE models were recorded and compared based on the TIS 396-2557 criteria. The results were significantly different when the helmet caused the first impact with the anvil at 1 ms because the chin strap was neglected in the finite element model. The headform could fall and freely impact with the flat anvil under the assigned initial velocity more than the test and affect the CG of the headform to obtain the acceleration results. Peak acceleration  
Figure 4: CAD model of the headform. Figure 5: Model configurations for impact simulation according to TIS 369-2557. (**a**) Without comfort padding; (**b**) with comfort padding. occurred when the acceleration of the headform was transferred to the helmet's structure until it caused the highest deformation. The results in Figure 6 display characteristics of finite element analysis that were similar to those of the test according to TIS 369-2557. Furthermore, the acceleration during the impact simulations clearly showed the same tendency as the test, which can confirm that the simulations had sufficiently accurate results to represent the test. The related results from the simulation (peak acceleration and HIC) in Figure 6 can be compared with the testing results in Table 3. The model without comfort padding achieved the highest performance to represent the helmet structure under impact conditions, which showed a maximum error of only 5.5% for HIC. However, the model with comfort padding achieved an unacceptable error of 17.1% for HIC, even when the peak acceleration was close to that of the test. Therefore, the finite element model without comfort padding could be employed to analyze other impact scenarios and investigate the damage to motorcyclists due to head injury. However, this commercial helmet in Thailand did not pass the TIS 369-2557 standard due to the testing and simulation results, with the HIC values being higher than the limit for this regulation, even though it has been sold commercially in stores. Both helmet models, with and without comfort padding, were then analyzed to investigate the effect of comfort padding and head protective ability by impacting with a flat surface at four different positions (refer to Figure 1). The energy absorption, which was obtained from simulation, for all cases is compared in Figure 7, in which the comfort padding did not influence the reduction in head injury. The comfort padding component is primarily responsible for enhancing the wearer's comfort, rather than protecting against a head injury. The overall energy absorption was increased slightly from that of the helmet structural model with comfort padding. Therefore, these results emphasize that the helmet model without comfort padding was the most effective for further investigations concerning different kinds of impact accident cases.