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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In detail, Fig. 3 shows that strength and sti ff ness of the examined 3D-printed specimens reached to the highest and the lowest values in 0 ◦ and 90 ◦ specimens, respectively. The obtained results proved that strength and sti ff ness are gradually decreased while raster direction was increased. Based on the experimental results, we determined dependency of elastic modulus and tensile strength on the raster orientation. Fig. 4a shows the relation between raster orientation and elastic modulus in the specimens printed under di ff erent speeds. As can be seen, young modulus is decreased with increase in raster direction. Therefore, the highest elastic modulus was obtained for 0 ◦ specimens. The elastic modulus was decreased with an increase in the raster direction. Therefore, the lowest elastic modulus was achieved for 90 ◦ . Dependency of tensile strength on the raster orientation is depicted in Fig. 4b. Experimental findings confirmed that increase in the raster direction has led to a gradual decrease in the tensile strength. This issue was occurred for all the specimens printed under di ff erent printing speeds.

20 mm/s 80 mm/s

20 mm/s 80 mm/s

(a)

(b)

Fig. 4. Dependency of (a) elastic modulus, and (b) tensile strength on the raster angle for examined 3D-printed specimens.

In analysis of the specimens, the tensile conditions on the specimens can be simplified as plane stress state, there fore, mechanical theory of single-layer composite materials can be utilized. In order to investigate fracture area in the specimens, a fractographic examination is required. Therefore, the frac tured specimens were visually investigated by a free-angle observation system. Fracture surfaces of 3D-printed speci mens with di ff erent raster directions after tensile tests are shown in Fig. 5. It is noteworthy that we have not considered any type of defect in the examined 3D-printed parts. However, during 3D printing process di ff erent type of defects and anomalies might be occurred which have e ff ects on the mechanical behavior of the 3D-printed part.

α = 0°

α = 30°

α = 45°

α = 60°

α = 90°

Fig. 5. Details of fractured surface in 3D-printed specimens with di ff erent raster directions.

As a result of visual investigation it was found that in the 0 ◦ specimens fiber rupture occurred. The fractographic analysis indicated that in the 0 ◦ specimens the crack is oriented orthogonally to the fibers, and in other specimens the cracks are oriented with the raster angle. This visual investigation confirmed that the angle between raster direction and the fracture surface is zero. This fracture was happened in all tested specimens.