Influence of material plasticity and bimodularity on the compressive response of fused-filament fabricated re-entrant honeycombs

Abstract The present study compares four modelling approaches to predict the mechanical behaviour of additively manufactured honeycomb structures. Cellular structures are increasingly employed in energy absorption applications due to their tunable deformation characteristics and lightweight architecture. Accurate modelling of such structures remains challenging, particularly when accounting for the anisotropic and nonlinear behaviour induced by fused-filament fabrication. While detailed modelling approaches based on raster orientation can improve accuracy, they are often computationally expensive and impractical for complex geometries. To address this, isotropic and bimodular assumptions are commonly adopted to simplify the analysis. In this study, the mechanical behaviour of re-entrant honeycomb (RH) structures fabricated using poly(lactic) acid was investigated through a combination of experiments and finite element simulations. Four modelling approaches: (i) elastoplastic (EP), (ii) elastic-perfectly plastic (EPP), (iii) bimodular EP (B-EP), and (iv) bimodular EPP (B-EPP) were evaluated in Abaqus/Standard. Additionally, experimental compression tests were conducted to benchmark numerical predictions of stiffness, peak force, plateau stress, energy absorption, and deformation patterns. All modelling approaches successfully captured the characteristic deformation modes observed experimentally, indicating that the global structural behaviour is primarily governed by geometry. However, significant differences were observed in the quantitative response. The EP model provided the closest agreement with experimental measurements for plateau stress and energy absorption, while the B-EPP model offered improved prediction of the initial stiffness and plateau phase at larger displacements despite underestimating peak force. These findings highlight that, although qualitative deformation patterns are reproduced by all models, an appropriate constitutive formulation is crucial for accurately predicting the mechanical performance of 3D-printed cellular structures.