PSI - Issue 37

Yifan Li et al. / Procedia Structural Integrity 37 (2022) 49–56 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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exhibit higher strength to density ratio than the bending-dominated lattices. So, octet-truss lattice is one of the good solutions for lightweight structural applications. Studies have shown that the lattice structures in different orientations also exhibit different mechanical properties. Gu et al. (2019) performed a numerical method to study the mechanical properties of octet-truss lattices in three different orientations. The study shows effects of lattice orientations on elastic modulus, tensile strength and fracture toughness. Li et al. (2020) conducted experimental and numerical analysis to investigate octet-truss lattices under compressive load. The research investigated the mechanical behaviours and compressive response of octet-truss lattices in different orientations. However, there are few studies on the effects of different orientations on the fracture properties of octet-truss lattice structures, especially in experimental research. In the present research, the orientation effects on fracture behaviours of octet-truss lattices were studied by experimental and numerical methods. Specimens in different orientations have been designed using compact tension geometry and manufactured by stereolithography (SLA) printing technique. Fracture properties such as load displacement curves, fracture resistances and crack paths have been measured and compared with the FE method simulating results. 2. Experimental procedures 2.1. Specimen design and manufacture Compact tension (CT) fracture specimen was used to study the fracture properties of octet-truss lattices in different orientations. The lattice samples printed in three orientations referred to as orientation-X, orientation-Y and orientation-Z are shown in Fig. 1. The tensile CT solid in Fig. 1. represents the lattice structure and the cell orientations are defined by loading direction and local coordinate of the unit cell. For orientation-X specimen, the X-axis in the local coordinate system is parallel to the loading direction. The dimensions of the CT specimens were designed according to the ASTM- E399 standard (2017).

Fig. 1. Definition of lattice orientations.

Octet-truss lattices in three different orientations were manufactured by the Stereolithography apparatus (SLA) printing technique because SLA printing has high printing precision and can print smooth surface. Fig. 2. shows the printed octet-truss lattice samples using a Lite 600 SLA printing machine with LASTY-702 photopolymer resin. The Lite 600 printing machine equipped with 2000mW laser and 8‒15 m/s scanning lens system. The layer resolution controlled by the optical size of the UV laser is range from 50 to 250 μm . The designed nominal radius r of the struts