Design and testing of novel three-dimensional modular negative stiffness honeycomb structures as reusable crash absorbers

Abstract

Conventional crash absorbers dissipate kinetic energy of impacts into plastic irreversible deformation, needing an immediate replacement to restore safety of the structure, highly increasing cost and inconvenience of the system. Aim of the present work was to develop innovative prototypes of reusable crash absorbers, able to withstand multiple collisions. A novel design was proposed, based on a modified Negative Stiffness Honeycomb (NSH) approach, using a three-dimensional modular layout with the objective of improving performance, reliability, and functionality of the device in repeated impacts. Two prototypes were manufactured to prove the concept. The first was produced in Nylon PA 6/66 by fused deposition modelling, while the second was obtained from laser-cut plates of stainless steel AISI 304. The nylon prototype was evaluated in cyclic static compression and dynamic impact tests, while the performance of the steel prototype was assessed only in impact tests. Results show improved values of energy absorption with respect to previous studies using bidimensional NSH energy absorbers and a highly reliable behaviour in multiple dynamic compression tests. Moreover, the nylon prototype featured a novel behaviour during impact tests, with autonomous delayed recovery of deformation after the collision. Our data show that three-dimensional modular NSH approach is effective in obtaining a reusable crash absorber, with improved performance and functionality compared to previously proposed design. This work can be considered a step forward in the search for alternative crash absorbers able to sustain multiple impactsbefore substitution, with potential advantages when their replacement is either impossible or too expensive.