Preparation and compression properties of negative stiffness honeycomb cell structure

Negative stiffness honeycomb cell structures were fabricated by fused filament fabrication (FFF) based on chopped carbon fiber reinforced nylon composites (MarkForged Onyx). In order to analyze the printing properties and compression properties, compression tests for negative stiffness honeycomb cell structure specimens were carried out. The influence mechanism of three process parameters, including building directions, fill patterns and wall layers, on the printing properties and compression properties of the structure was analyzed. The results show that the combination of flat building directions, hexagonal fill pattern and one wall layer can effectively reduce the printing time and cost of the structure. The compression properties of the flat building directions are superior to that of the on-edge and up-right. Compared with quadrilateral and hexagonal fill pattern, triangular fill pattern improves the energy absorption capacity of the structure significantly. Two wall layers have a great impact on the compressive strength of the structure. Cell structures show pronounced negative stiffness behavior during the loading process with percent energy absorbed up to 70%, and force threshold of about 185 N. Through the cycle tests, there is only 6% of the compression deformation, realizing the recoverable energy absorption of negative stiffness honeycomb core structures based on Markforged Onyx chopped carbon fiber reinforced nylon composites.