Effects of architecture level on mechanical properties of hierarchical lattice materials

Natural materials often feature hierarchical architectures which result in remarkable mechanical properties. Bio-inspired hierarchical architected materials can be designed and fabricated using 3D printing technology, but the underlying mechanisms on how to manipulate mechanical properties remain unclear. In the present study, second-order hierarchical lattice materials with various lattice configurations were manufactured by selective laser sintering (SLS) and deformed in uniaxial compression. Finite element models validated by experimental results were subsequently developed to assist examination. The role of geometrical parameters, including truss aspect ratios at each level and inclination angel, on mechanical properties was analyzed theoretically together with experiments and simulation. By simulation, hierarchical octet-truss materials with hollow mesoscopic truss members could be 46.1% stronger than the corresponding solid counterparts. Comparing mechanical properties of second-order hierarchical lattices with various configurations, the mesoscopic and macroscopic configurations have almost equal effects on specific stiffness and failure strain, while macroscopic configuration plays a more important role in the specific strength for all the 2nd order lattice materials. Also, with a more generalized analytical model for an nth order lattices, the effect of hierarchy for either self-similar or hybrid type lattices was analyzed. The specific strength was found to increase with hierarchical order by manipulating lattice configurations and strut slenderness ratios. Results provide critical insights into the role of design in regulating the mechanical properties of such mechanical metamaterials.