Date of Award


Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Engineering Mechanics (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Susanta Ghosh

Committee Member 1

Parisa Pour Shahid Saeed Abadi

Committee Member 2

Bhisham Sharma


Structural metamaterials, such as lattice metamaterials, are engineered cellular structures designed to achieve properties not achievable by natural materials. They enable mechanical properties unattainable by homogeneous solid materials and offer optimal properties for these materials tunable for specific applications in industries such as automotive, medical, and aerospace. Recent findings have revealed unique tunable mechanical properties such as negative Poisson's ratio, high strength-to-weight ratio, anisotropic stiffness, and much more. While the elastic and wave propogation properties of many lattice metamaterials are well investigated, the fracture properties are not well explored. However, their low fracture toughness is a bottleneck for their use in applications. In particular, the effect of 3D printing parameters on the fracture properties of lattice metamaterials has not yet been investigated. This study investigates the fracture characteristics of 3D printed periodic octet structures in relation to the build direction and relative density. Polylactic acid (PLA) single edge notch bend (SENB) samples were 3D printed in different build directions and relative densities. These samples were then notched in the mid span and tested in three-point-bend following ASTM standard testing procedures. Our results suggest that the work of fracture of octet structures with printed layers perpendicular to the crack plane is much higher than that of the same structures with printed layers parallel to the crack plane. Our results also show that this difference in specific work of fracture between build directions is more pronounced at lower relative densities. Furthermore, the fracture behavior between the two build directions changes from brittle mode 1 fracture to delamination in mode 2. This phenomenon is largely due to the direction of the 3D printed layers which act as a weak interface. These results present an important design consideration when applying 3D printed octet lattice structures in practice.