PSI - Issue 37

Yifan Li et al. / Procedia Structural Integrity 37 (2022) 41–48 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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achieve a high enough ratio of W to l in order to reduce surface effects (Gu et al. 2019a). All the octet-truss lattices in three orientations were manufactured by the Stereolithography apparatus (SLA) printing technique. LASTY-702 photopolymer resin was converted from a liquid into 3D solid plastics in a layer-by-layer fashion in Lite 600 SLA printing machine. 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 . After printing, all the specimens were cleaned in 95% ethanol to remove support material and placed in a UV oven for further hardening.

Fig. 2. The designed dimensions of lattice specimens: (a), (b), (c) are X, Y and Z orientations lattice, respectively.

2.2. Static tests Static tests were conducted first to obtain the static critical load. Instron 8872 hydraulic test machine equipped with a 5 kN load cell was used in the tests. Two CT specimens in each orientation were tested under displacement control at a crosshead speed of 1 mm/min. The displacement and reaction force of the loading crosshead were recorded during the experiment. The obtained mean critical loads for orientations X, Y and Z lattices are 359N, 566N and 547N. 2.3. Fatigue tests After static tests, the tension – tension fatigue tests were also conducted using Instron 8872 test machine. The fatigue tests were carried out under load control at fixed load ratio and frequency. The constant tensile load ratio R is 0.1 and a constant loading frequency of 2 Hz (sinusoidal wave shape) were used in the fatigue test. The maximum fatigue loads are 220N, 230N and 240N for X, Y and Z orientations lattices in order to ensure the ratio of maximum fatigue load to static critical load is between 0.4~0.6, which can make sure the failure time of the specimen is within one