Dynamic crushing of tailored honeycombs realized via additive manufacturing

Enhancing the energy absorption characteristics of a material/structure without compromising its strength and stiffness has been a longstanding challenge in the pursuit of lightweight engineering. Here, we introduce a novel tailoring strategy where the wall thickness of the honeycombs is bi-linearly graded along the out-of-plane direction to tune their energy absorption and impact resistance by varying two design parameters, the gradation parameter α and the normalized taper length η'. Based on the proposed scheme, hexagonal honeycombs of the same mass and varying parameters [α, η'] were designed and realized via Digital Light Processing (DLP) additive manufacturing. Low-velocity out-of-plane impact tests and dynamic FE calculations were performed to examine the collapse response of geometrically tailored honeycombs and assess their energy absorption characteristics and collapse mechanisms in relation to those observed in conventional (non-tailored) honeycombs of the same mass. The measurements and predictions revealed that the bi-linearly wall-thickness tailored honeycombs consistently outperform their non-tailored counterparts when the impact energy is high, reporting an increase in energy absorption as high as 250%. Such remarkable enhancement in energy absorption is attributed to a transition in the underlying collapse mechanism from global buckling mode to progressive crushing of the cell-walls. We also examined the impact response of honeycombs with periodic variations in cell-wall thickness and found that the latter structures collapse rapidly in an unstable manner, similar to what observed in conventional honeycombs, leading to limited capacity to dissipate the impact energy. With careful selection of the design parameters [α,η′], we experimentally demonstrate that bilinearly wall-thickness tailored honeycombs can exhibit simultaneous improvements in energy absorption and impact resistance, providing new opportunities for expanding the property space of honeycombs and opening the door for a wide range of applications.