Effect of angle and thickness of cell wall on bending behavior of auxetic beam

Abstract

Auxetic (Aux) structures, which exhibit unique mechanical properties due to the tunability of negative Poisson's ratio (NPR), have become great attention in recent years. In this work, the bending response and energy absorption behavior of beam structure in which the auxetic cells are oriented along the beam axis under bending are systematically investigated for various thicknesses and angles (55–85 degree) of walls experimentally and numerically. The beam structure was manufactured from AISI 316 L stainless steel by Powder Bed Fusion (PBF) additive manufacturing method, and three-point bending test was employed to determine the mechanical properties. The results revealed that the auxetic cross-section subjected to loading shrinks relating to NPR, orienting the outer wall inward thus reducing local buckling effect causing the main damage mechanism. It was also found that increasing the cell wall angle with the same relative density (ρ̅=0.485) owing to the change in the negative Poisson's ratio of the cross-section was beneficial in improving the load carrying and energy absorption capacity of Aux beam. However, increasing the cell wall angle up to a certain value (75 degrees) provides a significant benefit in the bending performance of the beam. The cell wall angle takes larger values resulting in a negligible increase in performance, whereas damage occurs at lower displacements. Moreover, the performance of the Aux beam can be improved by functionally graded thickness of the auxetic cell wall, increasing the specific load carrying (SLC) and specific energy absorption (SEA) capacity. By grading the cell wall thickness of the structure with the best mechanical performance according to the cell angle 75 degrees, it is understood that SLC and SEA values can be increased by 19.4% and 25.4%, respectively. This research is estimated to ensure a valuable reference for improving the bending response of the auxetic cross-section beams.