Co-authors​ :

 Amin AMIN FARROKH ABADI (BELGIUM), Lu HONYU (BELGIUM), Dimitrios CHRONOPOULOS  

Exceptional stiffness-to-density and strength-to-density ratios are ascribed to auxetic lattice structures. Notable energy absorption capabilities are exhibited by star-shaped honeycombs among various auxetic configurations, thanks to their flexibility and hinge deflection during the application of crushing loads. In contrast, higher equivalent elastic moduli are observed in hourglass honeycomb structures when compared to other configurations.In this study, a novel combined auxetic honeycomb structure, featuring both star and hourglass shapes, is introduced for the first time. This innovative lattice structure can be manufactured using 3D printing techniques, with the option to employ pure or reinforced filaments integrated with continuous fibers. Experimental evaluations of quasi-static compressive loading applied to these structures in the vertical orientations are encompassed by the research. For specimen preparation, the manufacturing process involved fused filament fabrication, commonly known as 3D printing. During the test, the nonlinear response of the star-hourglass-shaped auxetic lattice subjected to compressive loading is analyzed at stepwise quasi-static tests. At each step, the send and receive signals are measured using the ultrasound sensor. The variation and reflection of the ultrasonic wave signals are used to evaluate the health status of the star-hourglass-shaped auxetic structure, as signal alterations are typically associated with damage.
The performed experimental procedure is employed to assess the influence of damage and plasticity modes on wave response under compressive loading of the star-hourglass-shaped auxetic structures, which were fabricated with both pure and reinforced PLA materials. The findings indicate that in structures printed with pure PLA, plasticity dominates as the primary nonlinear phenomenon. Conversely, in lattice structures fabricated with reinforced PLA, damage events and fracture phenomena take precedence, outweighing the nonlinear response attributed to plasticity. Furthermore, it is demonstrated by obtained results that the energy absorption capabilities of composite structures surpass those of structures made exclusively with pure PLA.