Flexural Response of Dense Polymeric BCC Lattice Beams: Experimental Benchmark and Limits of Homogenized Beam Descriptions.

The flexural behaviour of body-centred cubic (BCC) lattice beams fabricated by stereolithography remains supported by limited experimental evidence, and available homogenized beam models are rarely confronted with data in the combined regime of high relative density, non-slender struts, and low span-to-depth ratios. This work presents an experimental campaign on polymeric BCC lattice beams with three unit-cell edge lengths (L=3, 4, and 5 mm) and a constant strut-to-cell ratio R/L=1/6, yielding a relative density ρ*≈0.423. Specimens were tested under uniaxial compression and three-point bending for nine combinations of geometry. The experimental data are compared with three analytical frameworks: a classical Euler-Bernoulli homogenized beam model and a BCC-specific shear-corrected formulation at the structural level, both evaluated without calibration to the bending tests, together with a strain-gradient extension whose intrinsic length scale is calibrated against them. For the effective Young's modulus, the closed-form expression of Lee et al. reproduces the compression data within 10%, whereas the Tancogne-Dejean and Mohr model remains markedly stiffer even after the strut-level Timoshenko correction is included. In bending, none of the models proves adequate over the full geometric range: the Euler-Bernoulli model is accurate for several configurations (errors below 16% in five of nine cases) but overestimates the stiffness by up to 108% for the deepest specimen; the shear-corrected model reduces the global root mean square error from 97.94 to 24.44 N/mm (approximately a factor of four), but introduces excessive flexibility in some slender and intermediate configurations; and the strain-gradient correction, being strictly stiffening, yields no appreciable improvement. To avoid assigning the discrepancy to a single mechanism, the bending data are further analysed through an experimental compliance decomposition. The additional compliance relative to Euler-Bernoulli theory is small or negative in several cases, showing that shear flexibility alone cannot explain the full dataset, but becomes dominant for the deepest beams. The results therefore delineate the range of validity of simple homogenized beam models for dense finite BCC lattice structures and identify the combined influence of structural shear, non-slender struts, nodal-region morphology, finite-cell and boundary effects, local roller-contact compliance, and the discrete distribution of struts across the cross-section as the main mechanisms requiring more refined descriptions. These findings correspond to a single relative density (ρ*≈0.423) and a single strut-to-cell ratio (R/L=1/6), so the resulting span-to-depth indicator (L0/h≈2.5) should be regarded as indicative for this class of dense lattices rather than as a general design rule.