Exploring flexural behavior of additively manufactured sandwich beams with bioinspired functionally graded cores

Sandwich composite structures have been widely used in aerospace and marine applications for many years due to their remarkable specific strength and stiffness. Despite their widespread use, there has been a constant effort to further improve their mechanical properties. This investigation delves into the influence of a Functionally Graded (FG) core, inspired by nature, in the enhancement of flexural properties of additively manufactured sandwich beams. The design space of the proposed sandwich beam with FG core of cellular cells in triangular shape is explored using an analytical formulation combining the Euler-Bernoulli theory and the Gibson-Ashby approach to develop a flexural performance index. The study involves examining a linear variation of the core density. To validate the analytical predictions, linear-elastic Finite Element (FE) models are created in the ABAQUS commercial FE program. Subsequently, the sandwich beams with FG core are additively manufactured using a polyjet printer (Stratasys J55), eliminates the need for secondary bonding between the face sheet and core. Two different build orientations are examined to investigate the influence of build orientation on flexural properties. The numerical and experimental results closely align with the analytical findings, indicating an approximate 31% increase in the performance index with the FG core. Noteworthy is that sandwich beams featuring FG cores exhibits a progressive failure, whereas those with uniform cores displayed sudden and catastrophic failure. As a result, the suggested FG core design not only contributes to a slight improvement in energy absorption capacity but, more significantly, displays fail-safe failure characteristics. These findings present significant potential for high-performance, lightweight sandwich structures in aerospace and biomedical applications. Graphical Abstract