Synergistic effects of fractal order and microscale layering on the compressive response of 3D-printed architected materials

Architected materials with precisely engineered microstructures have attracted significant interest due to their high mechanical efficiency and multifunctionality. Some monolithic (single material) architectures are limited in ductility and energy absorption due to constrained stress redistribution and fail catastrophically in a brittle manner. Bioinspired multilayered designs offer an alternative paradigm by enabling distributed deformation and enhanced damage tolerance. In this work, we investigate the coupled effects of mesoscale fractal topology and microscale soft-stiff layering on the compressive response of 3D-printed fractal lattices. A design space spanning (i) fractal order ( N = 1–3), (ii) soft material volume fraction, and (iii) number of layers within each cell wall is explored through quasi-static axial compression experiments complemented by calibrated finite element simulations. The results show a pronounced enhancement in energy absorption with increasing fractal order: the N = 3 lattice achieves approximately fivefold higher energy absorption than a honeycomb with the same wall thickness, attributable to the activation of localized short-wavelength buckling modes. Introducing a compliant phase markedly increases energy absorption, while the peak stress and stiffness exhibit trade-offs governed by layer thickness and interlayer constraint effects. In the traditional single-phase honeycomb, replacing 50.9% of the stiff material with an intermediate soft layer resulted in 43% increase in energy absorption. Similarly, we achieved fully ductile behavior in a fractal configuration by including a single soft layer compared to a fully brittle response of the corresponding monolithic fractal. Numerical simulations further revealed non-linear interlayer interactions that lead to a non-monotonic dependence of peak stress on layer number. Collectively, these findings establish mechanistic links between fractal topology, layering configuration, and progressive buckling. The combination of soft and stiff material offers enhanced mechanical properties for applications such as protective helmets, soft robotics, and athletic shoe soles.