On fracture mechanism of additively manufactured triply periodic minimal surface structures using an explicit phase field model

Triply periodic minimal surface (TPMS) structures have been extensively studied for their exceptional mechanical characteristics. However, numerical analysis of their fracture behaviour remains insufficient due to the complexity of the fracture mechanisms. This study aims to utilise a new phase field model to predict the mechanical responses and analyse the fracture mechanism of TPMS gyroid and primitive structures. Firstly, the gyroid (G) and primitive (P) structures were additively manufactured using Ti-6Al-4V titanium and tested under both axial and oblique compression. Secondly, an explicit phase field model was developed by incorporating the Bao-Wierzbicki fracture model to capture damage initiations. It was found that the explicit phase field enables accurate reproduction of experimental force-displacement responses, deformation modes, crack initiations and propagations for G and P structures under both loading conditions. It is noted that medium stress triaxiality tension was the dominant stress state to trigger material damage, regardless of structure and loading conditions. Thirdly, compared with axial compression, it is found that oblique loading introduced a more non-proportional loading history, leading damage initiation points to being far away from the fracture locus. Further, in comparison with the G structure, the P structure involved more medium and high stress triaxiality tension induced fracture initiations, resulting in more damaged material points. This study offers valuable insight into the fracture mechanism of triply periodic minimal surface structures, which is beneficial to improving the design of those structures.