Characterization of additively manufactured architected cellular polymers: Influence of specimen size and cell type on compressive behavior

Mechanical metamaterials are characterized by their hierarchical and periodic structures, which give rise to unusual mechanical properties at macroscopic scales. The greater availability of additive manufacturing technology has sparked a surge in the development of novel mechanical metamaterials in recent years, creating new opportunities in materials science and engineering. Nevertheless, most studies on the design and characterization of lattice structures use ad-hoc experimental methods, with a wide range of specimen shapes, sizes, cell-to-sample size ratios, and preparation that make any direct comparison impossible. This study explores the role of specimen size and cell type on the compressive response of lattices. Samples of three different lattice structures (truncated octahedron, Kelvin cell, and body-centered cubic) of varying cross-section and height were built via vat polymerization and tested under compression. The compressive behavior is influenced by the cell-to-sample size ratio and the aspect ratio of the specimens, even at larger cell sizes where mechanical properties typically converge to a definite value, and these effects are expected to disappear. This behavior challenges our current understanding of the size effect derived from analytical models and highlights the necessity for standardized compressive testing of additively manufactured polymer metamaterials.