Enhanced Energy Absorption and Unusual Mechanical Behaviors of Continuously Graded Diamond-Shellular Nanostructures

Abstract: Functionally graded cellular materials are garnering increasing interest for their unique structures and superior mechanical properties. Among the various types of cellular materials, shell-based structures have gained advantages over strut-based and hollow structures due to their ability to reduce stress concentration under loading. This study focuses on designing copper-based graded diamond-shell nanostructures, where the relative density varies partially in one direction, to enhance mechanical behavior and boost energy absorption capabilities. Initially, the compressive mechanical behavior and energy absorption capacity of regular diamond-shell nanostructures are examined using molecular dynamics simulations to determine the optimal relative density. Results indicate that the energy absorption of these regular nanostructures varies nonlinearly with relative density, peaking at a density of 0.6. Based on this optimal density, several graded nanostructures are created, which have the same average densities but differ in their density variations. Notably, nanostructures with a density gradient alter the stress–strain response and achieve a 21.8% increase in specific energy absorption compared to the peak value in their regular counterparts. The inclusion of a density gradient facilitates hierarchical, layer-by-layer compression and densification, enhancing overall energy absorption. A detailed analysis of planar defects and dislocation densities elucidates the different mechanical behaviors under compression between the regular and graded nanostructures, with the latter exhibiting a more controlled defect evolution and a stable collapse mechanism during deformation. These insights highlight the potential of graded diamond-shell nanostructures as programmable structures for applications that demand substantial mechanical energy absorption during large deformations. Graphic Abstract: (Figure presented.)