Application of Auxetic Polymeric Structures for Body Protection

Abstract

Negative Poisson’s ratio (NPR) materials, also known as auxetic materials, have many promising application areas. In recent years, various auxetic material structures have been designed and fabricated for diverse applications that utilized normal materials which follow Hooke’s law but still show the properties of negative Poisson’s ratios. In light of this, efforts are made to apply auxetic material structures to body protection pads that are comfortable to wear and effective in protecting body parts by reducing impact force and preventing injuries in high-risk individuals such as elderly people, industry workers, law enforcement and military personnel, and sport players. For those people, blunt impacts such as falls, bullets, and blast wave may reduce quality of life, increase the possibility of early death and generate an extremely high medical costs. Therefore, it is important to develop new body protectors that best combine each individual’s requirements of wearing comfort (flexible, light weight), ease of fitting (customized), ensured protection, and cost-effectiveness. The developed protection pad would be made from multilayer materials with an adaptive structure to achieve a unique multifunctional properties such as high hardness, impact toughness, light weight, excellent shock absorption, self-assembly suitable for the needs. Particularly, an integrated computational (finite element analysis) approach is used to investigate the effect of three material structures (honeycomb or flexin structure, re-entrant hexagonal cells or reflexin structure, and arrowhead structure) in combination with three polymeric materials (Polylactic acid (PLA) and two thermoplastic polyurethane (TPU) materials). Efforts are made to relate the individual and/or combined effect of auxetic structure and materials to the overall stiffness and shock-absorption performance of the body protection pads. Initially, parametric 3D CAD models of auxetic polymeric structures are developed. Later, key structural characteristics of protectors are evaluated through static analyses of FEA models. Impact/shock analyses are conducted to validate the results obtained from the static analyses. The mechanism for ideal input force distribution or shunting is suggested for designing protectors using various shapes, thicknesses, and materials of auxetic materials to reduce the risk of injury. The results show that the auxetic material can be considered as an effective material structure for body protection pads.