Performance Analysis of a Single-Layer Helmet with Varying Foam Densities under Low- (۳ m/s) and Mild-Speed (۶ m/s) Impacts

Helmets play a critical role in protecting the head during impacts in sports, motorcycle, and car rally events. The energy-absorbing liner, commonly manufactured from expanded polystyrene (EPS) foam with varying densities, is primarily responsible for absorbing impact energy. The performance of the EPS liner is highly dependent on foam density and the impact severity. This study aims to evaluate the response of helmets with different foam densities under two impact speeds of low-speed (۳ m/s) and mild-speed (۶ m/s) using the finite element (FE) method. A commercially available full-face helmet was prepared and geometrically modeled in CATIA, and the geometry was transferred to HyperMesh for meshing and LS-DYNA for FE simulations. The constitutive behavior of EPS foam was defined using Ashby's material model. Foam densities ranging from ۱۰ to ۱۰۰ kg/m³ were examined. The model was validated against experimental data from the literature, and helmet performance was assessed based on peak head acceleration and the Head Injury Criterion (HIC). The results show that there is a clear trade-off between foam density and impact velocity. Lower-density foams show better energy absorption behavior at low impact speeds but reach densification at higher velocities, resulting in increased head accelerations. Conversely, higher-density foams perform better under mild-speed impacts but generate higher accelerations at low speeds. Among the investigated EPS foams, a foam density of ۴۰ kg/m³ provided the most balanced performance across both impact conditions. These findings emphasized the inherent limitations of single-layer helmet liners and support the need for hybrid or multilayer liner concepts to achieve effective protection over a broader range of impact severities.

کلیدواژه ها:

Helmet safety ، Expanded polystyrene foam ، Impact analysis ، Head injury criterion ، Finite element modeling