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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is 0.5 mm and their nominal length l is 5 mm. The geometry of the specimen is large enough to achieve a high enough ratio of W to l in order to reduce the surface effects.

Fig. 2. Octet-truss lattice samples manufactured by SLA printing.

2.2. Experimental test The material properties of parent material were measured using dog bone specimen based on the ASTM D638 standard (2015). The dog bone specimens were manufactured using the same process parameters as the CT specimens. Tensile tests were performed using an Instron 8872 hydraulic test machine equipped with a 5 kN load cell. Displacement control was used with a rate of 1 mm/min. It is known from literature that the mechanical properties of 3D printed photopolymer are related to the printing direction (Truong 2017). In this research, specimens in two printed directions were used, namely the vertical printed and horizontal printed specimens. Three specimens in each printed orientation were tested using the same test conditions in order to assess the scatter of the results. The strain was measured by a 10 mm gauge length extensometer. The engineering stress-strain curves of the 3D printed photopolymer are shown in Fig. 3. The 3D printed photopolymer showed distinctly brittle performance, and the specimen failed at a relatively small strain under tensile load. The moduli of two direction parent material measured to be 1200 MPa, and the ultimate tensile strengths are 60 MPa and 50 MPa, respectively.

Fig. 3. Stress-strain curves of parent material.