The elasto-plastic analysis of 3D-printed thermoplastics using the NNRPIM and a modified hill yield criterion

Abstract

The Fused Filament Fabrication is a 3D printing technology that allows the production of components and structures with complex geometries at low-cost, using thermoplastic materials as feedstock. This additive manufacturing technique is not yet extensively used in industries mainly due to parts’ anisotropy – which is the consequence of the deposition strategy – and residual stresses, caused by successive heating cycles. Thus, these topics have great influence on the non-linear mechanical performance of 3D printed parts. Additionally, the materials used in the Fused Filament Fabrication have distinct mechanical behaviours under tensile and compression loads. This work proposes a computational framework – using a meshless method as the numeric discretization technique, the Natural Neighbour Radial Point Interpolation method – capable to analyse the elastoplastic response of ductile materials showing distinct compressive and tensile responses, through the implementation of a modified version of the Hill yield surface. In those conditions, 3D-printed specimens of polylactic acid are tested experimentally and numerically using standard tensile and compression tests. The numerical approach is validated by comparing the numerical and the experimental curves. Then, the accuracy of the methodology is proved and the purpose of using the modified Hill yield criterion is clearly shown using a benchmark example.