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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Fracture tests of different orientations lattice specimens were carried out also using the Instron 8872 hydraulic test machine with displacement control of 1 mm/min. The apparatus is shown in Fig. 4, and the crack mouth opening displacement (CMOD) was measured by Instron 2670-132 extensometer with 10 mm gauge length. Two specimens were tested for each orientation. A 48 MP quad-camera was used in the tests to record the deformation process of lattice specimens in three orientations under loading. The displacement and reaction force of the loading crosshead were recorded during the experiment.

Fig. 4. Experiment set up of lattice fracture test.

2.3. Finite element simulation The fracture response of octet-truss lattice in different orientations was simulated by FEA software Abaqus 2017. Each strut is meshed by using three-dimensional, shear deformable, linear beam element B31 with 0.5 mm seed size to consider the transverse shear deformation of strut. Each strut was meshed by 10 elements also provide convergence of the numerical results (Gu et al. 2018). The explicit dynamics procedure was used in the numerical analysis to model the quasi-static process and geometrical nonlinearity was taken into account. Two controlling points defined at the hole centre were coupled to the motion of nodes around each pin hole. Displacement was applied on the top controlling point in the vertical direction, while the controlling point at the lattice bottom part was constrained over all degrees of freedom. The element deletion method was used to model the strut failure in tests in order to obtain the crack path. The mechanical properties of material were obtained from the above tensile test. The properties for vertical printed photopolymer were used for orientation-X lattice and horizontal printed properties were used for orientations Y and Z lattices because of the printing direction of struts in different orientations lattices. The density is 1.24 g/cm 3 , Poisson’s ratio is 0.23 were from the material supplier (Li et al. 2020). In this simulation, approximately 170000 elements were used in the model. 3. Results and discussion The load-displacement curves of octet-truss lattices in different orientations are shown in Fig. 5. Different curves of lattices in each orientation have similar values, indicating that the specimens have a good consistency. It can be seen that the photopolymer octet-truss lattices exhibit distinctly brittle performance. Once the load reached the critical value, fracture occurred and the specimen failed. The fracture resistance, K R , for octet-truss lattice is calculated according to the ASTM E399-17 standard (2017). = √ ( ) (1) ( ) = (2+ )[0.886+4.64( ) 2 −13.32( ) 3 −5.6( ) 4 ] (1− ) 3/2 (2)