Design of novel isosurface strut-based lattice structures: Effective stiffness, strength, anisotropy and fatigue properties

This paper proposes a novel methodology to design a family of strut-based lattice structures derived from isosurfaces. Here the methodology is applied on isosurfaces obtained from Triply Periodic Minimal Surfaces (TPMSs). A Schoen’s Gyroid TPMS morphology was employed to generate an isosurface strut lattice structure (ISLS). The structural element of ISLSs were modeled as solid tetrahedral and beam elements. Finite element simulations were performed to compute the effective mechanical properties such as stiffness, anisotropy index and fatigue properties for range of relative densities, i.e., 5% to 35%. An isosurface strut mesh sensitivity study was performed to determine number of mesh points required for consistency in mechanical properties. Stretch dominated sheet Gyroids are found to be most superior lattices for mechanical properties in literature and hence the truss based ISLS is compared to sheet Gyroids. The scaling laws demonstrated that Gyroid ISLS modelled with both beam elements and solid elements exhibited bending dominated behavior and yet ISLS solid elements show an elastic modulus, bulk modulus, and shear modulus, comparable to stretch-dominated sheet Gyroids. Anisotropy analysis showed that ISLS exhibit near isotropic behavior for all relative densities. Results exhibited that for the same relative density, ISLS modelled with beam elements showed lower elastic modulus, but higher fatigue performance as compared to the solid elements. Highly porous, low elastic modulus and superior fatigue resistance demonstrate suitability of ISLS beam as biomaterial scaffolds whereas ISLS solid having high modulus are useful in applications requiring enhanced mechanical strength.