PSI - Issue 47

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 47 (2023) 454–459

457

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Author name / Structural Integrity Procedia 00 (2023) 000–000

which are identical, and attached to the specimen by means of a clevis pin arrangement. The two grips are aligned during set up and secured with a pre-load in that alignment. In CT tests, the loading is an imposed cross-head speed of 10 mm / min under the displacement-control conditions according to the relevant standard. Fig. 2 shows CT test conditions on a 3D-printed PLA specimen.

Fig. 2. A CT specimen under test conditions; prior to applying load (left), and after fracture (right).

As the physical properties of materials can be a ff ected by ambient temperature, all tests were performed at room temperature. In detail, the room conditions for tests of the specimens were 23 ± 3 ◦ C and 50 ± 5% temperature and relative humidity, respectively.

3. Results and discussion

In the experimental tests on the dumbbell-shaped specimens, the crosshead displacement and the applied load were recorded. After tensile tests, the load experienced by the grip was converted into engineering stress by dividing through by the initial sample cross-sectional area. The values obtained from tensile tests are summarized in Table 1. As presented in Table 1, the maximum fracture load in dumbbell-shaped PLA specimen was 5475.2 N belongs to the specimen with -45 ◦ / 45 ◦ raster direction and printed at 20 mm / s. The specimens printed with higher speed (80 mm / s) showed the low values of sti ff ness. In fact, the bonding between adjacent filaments is significantly reduced at the higher printing speed. All specimens showed brittle failure without any plastic deformation. It is noteworthy that failures were occurred within the gauge length in all dumbbell-shaped specimens.

Table 1. The results of the tensile tests on the dumbbell-shaped specimens. Material Printing direction Printing speed (mm / s)

Fracture load (N)

Displacement (mm)

20 80 20 80

5475.2 4367.7 4923.8 4147.8

6.1 5.6 5.1 5.2

45 ◦ / − 45 ◦

PLA

0 ◦ / 90 ◦

Since CT test can be used for determining the fracture toughness, ASTM D5045-14 (ASTM D5045, 2014) recom mended the following equation to calculate stress intensity factor:

4

W − 13 . 32 1 − a W

+ 14 . 72

− 5 . 6 a

a W 0 . 886 + 4 . 64 a

a W 3 / 2

a W

W

F e √ W

2

3

2 +

K I =

(1)

where F is the applied load, and a is crack length. Moreover, W is the width of the specimen, and e denotes the specimen thickness. When applied to the peak load F c , this formula gives the toughness K IC . Tests indicate that the