Size effects in 3D-printed polymeric lattices under three-point bending: Manufacturing, testing, and modelling

Abstract

Architected lattice structures often exhibit pronounced size effects that challenge conventional modelling strategies. This contribution presents a combined experimental and numerical investigation of size effects in 3D-printed lattice beams under three-point bending. Specimens with triangular and square unit cells, manufactured using affordable Fused Deposition Modelling (FDM) with polyethylene terephthalate glycol (PETG), are tested at different lattice refinements while maintaining constant overall dimensions and solid volume fraction. The experiments reveal clear size-dependent behaviour in terms of stiffness, strength, and failure modes. To model these effects, three numerical strategies are employed: Direct Numerical Simulations (DNS), and multi-scale approaches based on first- and second-order computational homogenisation (FE²).DNS provides accurate predictions but is computationally expensive for fine lattices. Second-order FE² captures size effects more efficiently, particularly when micro-scale periodic boundary conditions are applied, although it may overestimate responses for coarser lattices. This work critically assesses the accuracy and applicability of each modelling approach, providing valuable insight into the design and simulation of architected structures where scale-dependent behaviour is significant.