New composite liners for energy absorption purposes

This work studies the capacity of cork to act as material for the absorption of impact energy. Focus is given on the viability of hybrid paddings consisting of micro-agglomerate cork (MAC) and expanded polystyrene (EPS) through simulations of multi-impacts. EPS is a widely used material for energy absorption applications. However, once deformed, it shows no springback, which means that its capacity for energy absorption is greatly reduced after the first impact. On the other hand, cork is a viscoelastic material that has a good level of energy absorption capacity with almost total springback. An example in which EPS is commonly used is motorcycle helmet liners. In the first part of this work, a compression test is used to assess the effectiveness of the material laws chosen to model the cellular materials under study. Results show that the constitutive laws employed for EPS and micro-agglomerate cork adequately model the actual behaviour in springback absence. In the second part of this work, it was developed a simplified model of a road helmet energy absorption liner. This representative padding was subjected to double impacts as specified in an international helmet standard. The work also studies the use of MAC and EPS arrangements on the energy absorption linear through various configurations. Results were obtained with regard to the head centre of gravity acceleration, final padding thickness and the final weight of a helmet. Conclusions are drawn about the best configuration for the application under study.