Assessing The Temporal Characteristics of Strain Energy in Shell and Foam and Their Effects on Brain Strain During Helmeted Head Impacts

Helmet structural design, particularly the combination of helmet shell and foam, plays a critical role in reducing head kinematics and brain strains, mitigating the risk of Traumatic Brain Injury (TBI). However, the individual and combined contributions of shell and foam to brain responses remain insufficiently clarified. This study used factorial analysis and factorial and ANOVA main effect analysis to quantify the effects of foam and shell under representative football impact conditions. We found that helmet outer shell absorbed the highest amount of energy, around 50%, followed by foams close to impact sites. As important components beneath the outer shell that absorb energy through deformation, the role of foam cannot be ignored. Factorial analysis showed that foam played the most important role in brain strain responses. These results indicate that both shell and foam significantly influenced brain injury metrics, providing strategy to optimize shell and foam to mitigate the risk of TBI. Using ANOVA main effect analysis, we found that high shell and foam stiffness reduced strain responses by up to 14.9% compared to the baseline model, while low shell and foam stiffness reduced peak linear acceleration by up to 11.8%.