Nature-inspired bamboo-spiderweb hybrid cellular structures for impact applications

Abstract

Rapid increase in the operating speeds of aerospace/automobile vehicles has demanded for the design of light weight structures resisting high velocity impact loads. Cellular structures have shown significant potential for mitigating the effects of extreme loading. Due to its geometry, honeycomb structure is observed to possess the highest load carrying capacity as compared to other regular shapes. In this study, three different hybrid cellular structures, namely: design 2, design 3 and design 4, are designed and developed for impact applications, through a systematic study considering the hexagonal basic unit cell, and combining order and levels by mimicking bamboo-spiderweb structures. Parametric studies are performed and the proposed unit cell in design 4 is observed to demonstrate the best performance in terms of specific energy absorption and crush force efficiency. Analytical models are developed to estimate the energy absorption of unit cells in designs 2–4 during the impact. Numerical studies are performed considering the proposed unit cells to estimate the energy absorption characteristics. Results from analytical and numerical investigations are compared to notice a close agreement, with a maximum error of 9.97%. The resistance to local impact is tested by developing sandwich structures with cores developed from the proposed unit cells. Bullet impact studies are performed on the sandwich structures at three different identified locations with an impact velocity of 115 m/s. Design modifications are carried out by combining the multi-staging and strategically offsetting the unit cells in each core of a two core sandwich structure, such that it can withstand the impacts at arbitrary locations for bullet speeds up to 115 m/s. The proposed novel fourth order and third level hybrid unit cell in design 4 is found to efficiently resist the impact loads. Hence, it is recommended for applications involving energy absorption under extreme loads.