PSI - Issue 28

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 28 (2020) 720–725 M.R. Khosravani and T. Reinicke / Structural Integrity Procedia 00 (2020) 000–000

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raster directions are illustrated. The specimens were printed with two contours (outer layer that is surrounding the internal structure) and infill density of 100%. In FDM process connection is made by adhesive bonding and raster orientation can play a crucial role in the mechanical performance of the 3D-printed part. Indeed, build orientation has significant e ff ect on the mechanical properties of additively manufactured parts. Therefore, a proper design is very important for load-carrying capacity of the 3D-printed structural elements.

= 0

= 30

= 45֯

= 60

= 90֯֯֯֯

13

165

115

R 76

19

Fig. 1. The geometric model and 3D-printed specimens with di ff erent raster orientations (Dim. in mm).

It is noteworthy that the interlayer mesostructural properties such as pore size vary with raster orientation and a ff ect overall mechanical properties of the 3D-printed components. However, similar to composite materials, various defects may occur during printing of the specimens which can lead to the final rupture Khosravani (2012). Quality requirements of 3D-printed parts should be defined in the context of international standards in order to reduce failure and fracture during the service life of these parts.

3. Experimental approach

The development of new materials and processes depend on understanding behavior of materials under di ff erent loading regimes and relies on optimization of the processes. In the present study, a series of quasi-static uniaxial tensile tests was performed by a universal mechanical testing machine. In detail, all the tests were performed with a constant crosshead rate of 5 mm / min and the force was measured with 15 kN load cell. No external extensometer was used for strain measurement. The tensile tests were conducted under temperature and relative humidity of 23 ± 3 ◦ C and 50 ± 5%, respectively. The displacements on the specimens were measured by using a linear variable displacement transducer. By a series of tensile tests di ff erent parameters are determined which are presented and discussed in the following section. It is noteworthy that the tests were repeated six times for each raster orientation and printing speed.

4. Results and discussion

Based on the tests on described specimens we have documented rather brittle fracture behavior in all cases. Indeed, there was a sudden failure in the specimens after reaching the maximum stress. In Fig. 2 close-up pictures of the