Mechanical behaviour of additively-manufactured polymeric octet-truss lattice structures under quasi-static and dynamic compressive loading

Highlights: • Octet-truss lattice structures were 3D printed and tested under static and dynamic loading. • The mechanical behaviour of the printed structures depends on both the relative density and intrinsic material properties. • The Specific Energy Absorption (SEA) of the lattice structures increased monotonically with relative density. -- Abstract: Two different polymer resins were used to create three different octet-truss lattice structures of different densities. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic compressive loading. The structures were printed using stereolithography (SLA) additive manufacturing. The basic building octet unit has a fixed strut length of L = 10 mm, with the designed strut radius varying from R = 0.7 mm to 1.3 mm to provide structures of different densities. It has been found that the mechanical behaviour of the printed octet structures depends on both the relative density and the intrinsic material properties. Higher density structures show larger effective yield and compressive strengths, while the basic printing material fundamentally determines its macroscopic properties: one material provides a brittle mechanical response under compression while the other provides a tough response. The former lattice structures behaved in a brittle manner at all relative densities, fracturing at small strains. For the latter resin lattice structures, on the other hand, under quasi-static compression, the stress-strain curves changed from a slightly stress oscillating mode at low relative density (i.e. $\overline{\rho }$ = 0.13) to a stable stress plateau mode at high relative density (i.e. $\overline{\rho }$ = 0.41). The Specific Energy Absorption (SEA) of both lattice structures had a monotonically increasing relationship with relative density, the SEA of the brittle resin specimen is higher than that of the tough resin specimen, while the tough resin specimen exhibits its excellent energy absorption under a wide displacement range. For the dynamic compressive tests, the tougher resin structures displayed strain-rate effects, while the more brittle ones did not. The numerically predicted response of both lattice structures agreed closely with the experimental results.