Application of additively manufactured conformal negative stiffness honeycombs for impact isolation in protective headgear

The primary goal of this research is to study the implementation of conformal negatives stiffness elements for impact isolation in baseball helmets. These conformal elements utilize pre-curved beams designed to a specific geometric profile that have been exhibited to have better impact absorption due to their snap-through behavior. A preliminary study is carried out to develop a thorough understanding of pre-curved beams and the negative stiffness elements that utilize this concept. The basic principles and equations of such structures are discussed. Subsequently, the application of the above principles in the context of conformal negative stiffness design is studied. A conformal negative stiffness element is designed and manufactured by SLS using nylon 11. Preliminary tests done on these elements indicated a requirement to improve the effectiveness of the elements so that they are able to absorb impacts of low as well as high magnitude. A novel method to increase the effectiveness by introducing variable force thresholds in these elements is introduced and discussed. The methodology for designing and optimizing an improved element is discussed. The elements are manufactured by SLS using nylon 11. FEA analysis of these elements are carried out in ABAQUS under quasi-static conditions and dynamic conditions. The elements are subjected to physical quasi-static and impact testing as well. Finally, the performance of these elements is compared to a conventional padding used in baseball helmets under one-dimensional impacts using a drop test rig. The results obtained from physical tests are also compared with those obtained from FEA analysis.Mechanical Engineerin