F02 Chainmail inspired metamaterials for use in protective sports equipment

Abstract

Contact sports and action sports require intense performance yet also include a high risk of injury. Subsequently, protective equipment for those sports usually must trade flexibility for protection and vice versa. Chainmail inspired mechanical metamaterials could be a solution to this dilemma. Chainmail is a type of body armour, consisting of a structured fabric made up of thousands of interlocking metallic rings. Chainmail inspired materials have recently been made from connected 3D shapes, rather than the typical 2D (flat) rings. This chainmail inspired material is flexible when relaxed but stiff when the chains are compressed together. This ability to control the material’s stiffness means chainmail is a type of mechanical metamaterial. Mechanical metamaterials are engineered structures which derive their properties from the structure of the material, not the material itself. In relation to protective equipment, this means that these chainmail materials or fabrics, can be flexible during normal use but stiffen when indented or impacted. The flexibility of these materials can be influenced by changing the size and shape of the connecting chains but to what extent and the effect this has on their stiffness is unknown. This type of structure could improve sporting protective equipment, where (as stated before) there are various trade-offs. The aim of this project was to develop a chainmail inspired material and test the effect of varying cell sizes has on the flexibility and indentation resistance of the material. Additive manufacturing was used to create the chainmail materials and a range of indenters were used to test them, the results of which indicate that as cell size decreases and number of cells increase; their flexibility and formability increases while also maintaining a good degree of indentation resistance, when compared to larger cell sizes. Based on this work, these structures could be tailored to different sporting protective equipment where flexibility, support, and stiffness requirements may vary between normal use and collisions or falls. These chainmail inspired materials could have various applications in contact sports such as rugby, American football and ice hockey where protection for players is key to reduce the severity of injuries. Similarly, action sports such as mountain biking, skateboarding, skiing and snowboarding also necessitate a high degree of protection. An Alternative application for these materials could be as a first aid device, where the material would be formed around the injury site as a brace and stiffened with compression, such as a vacuum pack.