Parametric Study on Multi-Layer Dome-Shape Structures for Use in Protective Pads

Abstract

This study seeks to develop novel multi-material and multi-layer pads that are comfortable to wear and effective in protecting body parts that are subject to blunt impact. The proposed body protection pad will address a safety issue prominent in elderly people, industry workers, law enforcement/military personnel, and sport players. Among the population of those people, blunt impact due to various causes such as falls, bullets, and blast waves reduce quality of life, increase the possibility of early death, and cause extremely high medical costs to incur. Protector pads represent a promising strategy for reducing impact force and preventing injuries in high-risk individuals. However, clinical efficacy has been limited by poor user compliance. Currently available protectors are made of either hard shells or soft thick pads. Some of them are made of Non-Newtonian materials that are believed to be very efficient but their effectiveness hasn’t been proved yet. Even though some available protectors can be effective if worn, most people who need protection are reluctant to wear bulky and heavy garments or rigid shells. 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 authors brought up many different design ideas and the most promising ones were selected and their effectiveness is investigated in detail. One of those pads utilizes dome shape top layer and thin fabric membrane component, such as Kevlar, that is very strong in tension but flexible in bending. Such design will make the pads excellent in dissipating shock energy and converting normal shock force to lateral direction to minimize the shock force transmitted to the body parts. Through computational simulations, these pads were proved to be very flexible in bending and torsion while strong and rigid in compression. In addition, suitable materials were identified, and it has been verified that such materials can be used to design a viable product(s) that is thin, light, and flexible for wearing comfort but strong in normal impact direction to protect the body. This paper reports a parametric study using computational analyses (finite element analyses) conducted for dome-shaped structures with various materials such as thermoplastic polyurethane (Ninjaflex® and Semiflex®), polyethylene, resin polyester, polylactic acid (PLA), resin epoxy, epoxy S-glass, and epoxy E-glass. Parametric 3D CAD models of the dome-shape structures were created with various combinations of layers such as dome shell only, dome with fabric (such as Kevlar) membrane, dome with fabric membrane and solid filler, and dome with fillers of auxetic structure. Then, key structural characteristics of protectors such as normal (compression), bending, and torsional stiffness were evaluated through static analyses of FEA models. Then, impact/shock analyses were conducted using multiphysics finite-element-analysis models to validate the results obtained from the static analyses. Advanced additive manufacturing techniques (3D printers) were used to build prototypes of the pads for tests. Dimensions and materials of the multi-layer pads are optimized for light weight and flexibility while keeping excellent shock absorption capability. The mechanism for ideal input force distribution or shunting are explained and suggested for designing protectors using various combinations of materials and layers to reduce the risk of injury. The results show that the dome-shape structure can be an effective component of optimized body protection pads using a combination of various materials.