Size effect on the mechanical behaviours of pure copper sheet-based triply periodic minimal surface structures fabricated by micro-laser powder bed fusion

Abstract

Advances in micro-laser powder bed fusion (μLPBF) have enabled the utilisation of pure copper in low-density triply periodic minimal surface (TPMS) structures, which are mostly characterised by thin walls. Although coarser-grained pure copper components enhance the conductivity, there are only a limited number of grains along the wall in the thickness direction in the low-density TPMS structures, leading to an unpredictable mechanical performance owing to size effect (SE). In this study, pure copper sheet-based TPMS structures (specifically, gyroid structures) were fabricated via μLPBF followed by different annealing conditions to achieve distinct grain sizes. Compression tests were conducted to investigate SE on the mechanical behaviours of the structures. A constitutive model considering both wall thickness and grain size was developed to explore the uncertain mechanical response induced by SE via finite element (FE) simulations. An optimised FE modelling strategy considering roughness was developed to describe the interactive effect of SE and the surface powder-induced roughness on the deformation behaviours of the TPMS structures. The results show that the mechanical performances of the structures, such as plateau stress and energy absorption, are improved with the refinement of grains and are also highly related to the deformation behaviours influenced by SE. SE offers the potential to achieve the desired multifunctional performance of TPMS structures with acceptable mechanical properties and enhanced electrical conductivity. This study enhances the understanding of SE on the mechanical behaviours of the TPMS structures.