Design and Mechanical Performance of Cylindrical-Coordinate Ti-6Al-4V Octet Lattices: Influence of Outer-Shell Hybridization and Strut Diameter on Compressive Strength

Lattice structures are increasingly used in lightweight engineering applications, particularly in the aerospace, biomedical, and automotive sectors. However, their limited stiffness and narrow linear elastic region can restrict their use in load-bearing applications. This study investigates a hybrid design strategy for improving the compressive performance of Ti-6Al-4V octet lattice structures generated in polar coordinates. Hybrid lattices incorporating a 0.5 mm outer and inner tubular shell and reference lattices without a shell were designed using implicit modeling techniques and manufactured by laser powder bed fusion (LPBF). The mechanical response was characterized through uniaxial compression testing showing an increase in the compressive strength of 900 to 1000% and a strength-to-weight ratio similar to that of bulk titanium in the case of the hybrid samples. Geometrical analysis revealed systematic manufacturing deviations, with all lattice struts exhibiting larger diameters than their nominal dimensions. The hybrid design significantly increased the compressive modulus and yield strength while introducing a moderate increase in mass. Furthermore, the as-printed quality of the polar-generated lattices followed trends reported for equivalent Cartesian-coordinate lattice structures or produced even better results. Overall, the results demonstrate that hybridization can increase compressive strength and modulus significantly while improving the strength-to-weight ratio, with polar lattices exhibiting geometry-dependent trends consistent with Cartesian structures and curved-cell designs providing more uniform volume filling and improved suitability for axisymmetric components.