Experimental and numerical comparative study on the crashworthiness of pristine and recycled fiber-reinforced polymeric 3D-printed lattice structures

The energy absorption performance of 3D-printed polymeric lattice structures has been recently studied extensively. Different structures, built with different additive manufacturing techniques, have been tested in both quasi-static and dynamic conditions. Recycled plastics are being introduced into the additive manufacturing sector, but research on engineering components that can address their peculiar characteristics is lacking. In this work, 3D-printed closed-cell lattice structures are fabricated using a short fiber reinforced polyamide, both in its pristine and recycled form. Two different printing techniques are used to compare two possible scenarios: printing from filament pristine material and printing from shredded waste of the same material. A direct impact Hopkinson pressure bar setup is used to test the dynamic energy absorption properties of cellular structures with three different overall densities of the same infill geometry. A wave separation technique based on deconvolution is employed to limit the length of the output bar. The dynamic energy absorption performances are compared with the quasi-static ones, observing two different behaviors for pristine and recycled specimens. Quantitatively, the pristine material resulted in an increase of up to 22% in SEA in dynamic conditions, while the recycled one resulted in a decrease of up to 25% in the same conditions. The recycled material had an average 7.8% higher SEA in quasi-static conditions, while it showed an average 25.4% lower SEA in dynamic conditions, compared to the pristine material. Finally, anisotropic finite element models are developed, representing the dynamic behavior of the specimens, proving to be accurate design and verification tools.