A new porous constitutive model for additively manufactured PLA

Abstract

We introduce a new specific hyperelastic/plastic model and porosity evolution law able to capture the deformation and damage of additively manufactured PLA-N polymers (Fused Filament Fabrication — FFF). Porosity growth is driven by projecting the right Cauchy–Green tensor in the normal to the deposition direction and by solving a local maximization problem. Fracture energy is introduced directly in the resulting law by means of a length scale. A full finite-strain plasticity model is adopted, based on the Hosford yield criterion. Strain softening is regularized with a gradient-enhanced technique, which is solved in tandem with the equilibrium equations. A comprehensive analysis of the hyperelastic transversely isotropic/porous constitutive law is performed, with physical insight on the directional strain softening behavior. A normalized CT test specimen is used to qualitatively assess the effect of deposition direction on the crack path and to investigate the effect of mesh density in the load/displacement curves. We then present a comparison with our experimental results for a cellular PLA-N beam composed of 3 × 13 cells, in terms of crack behavior and load/displacement results. Sequential collapse of the cells and strain localization match the experimental observations.