Investigation on the bending performance of sandwich beams with re-entrant diamond auxetic core

Abstract

ABSTRACT Auxetic metamaterials, characterised by a negative Poisson’s ratio (NPR), exhibit unique mechanical properties where they expand under tension and contract under compression. These structures hold significant potential with applications spanning various industries such as biomedical, construction, sports, aerospace and defence. The re-entrant diamond auxetic metamaterial represents a modified unit cell structure designed to mitigate the bending-dominated failure observed in conventional re-entrant structures. Notably, this modification demonstrates advantages, particularly in uni-axial compression scenarios. However, its performance concerning energy absorption under bending loads has not been explored until now. This study examines the bending behaviour of a re-entrant diamond auxetic metamaterial, both as a core and in sandwich configurations. The samples are fabricated using additive manufacturing (3D printing) and compression moulded glass-epoxy composite skins are added to these cores. Experimental assessments are conducted to evaluate bending performance, facilitated by advanced digital image correlation (DIC) techniques for real-time displacement measurement on the sample surface. The results reveal remarkable 14, 11 and 4-times improvement in energy absorption, specific energy absorption and failure displacement in the sandwich construction compared to the core configuration. Additionally, the study investigates the impact of eccentric loading on the flexural performance of the re-entrant diamond auxetic metamaterial.