Mechanical Characterization of Expanded Polystyrene (EPS) as a Liner Foam in Motorcycle Helmets

Helmet is the most effective personal protective equipment for motorcyclists that can significantly reduce the risk of skull fracture and traumatic brain injuries. The performance of the helmets is evaluated using a drop-weight impact tower test. Due to restrictions to access the drop tower test assembly in many low-income countries, evaluation of helmet performance is a major challenge. The current study aimed to develop a simple biomechanical method to help the assessment of motorcycle helmets without employing sophisticated test setups. Since liner foam is the main component of the helmets that can absorb the impact energy, the viscoelastic properties of expanded polystyrene (EPS), as a most commonly used foam in the helmets, were characterized. A simple lumped model of the head and the helmet was developed to characterize the head linear acceleration under impact condition. The results of the current study showed that the value of head injury criteria (HIC) was less than the maximum acceptable value for the standard. Also, the results of scanning electron microscopy (SEM) showed that EPS foam which has experienced 10% compressive strain could recover after loading; indicating that the motorcycle helmet contained EPS as a liner foam could pass the safety standards.