PSI - Issue 37

P.N.B. Reis et al. / Procedia Structural Integrity 37 (2022) 934–940

937

4

P.N.B. Reis et al. / Structural Integrity Procedia 00 (2021) 000 – 000

Table 1. Printing parameters used in this study. Material Extrusion Temperature [ºC]

Speed [mm/s]

Layer Height [mm]

Infill [%]

G6- Impact™

235

10

0.25

100

The static characterization was carried out for different loading modes. In terms of three-point bending (3PB) static tests, they were performed using specimens with dimensions of 85×12.7×4 mm 3 and tested with a span length of 64 mm according to EN ISO 178:2003. Compressive tests were performed using specimens with dimensions of 12.7×12.7×25 mm 3 and tested according to ASTM D695-15. For both conditions, a Shimadzu testing machine, model Autograph AG-X, was used and the tests were carried out at room temperature. Finally, tensile tests were performed using specimens and testing conditions according to ASTM D638-14 and using a Shimadzu testing machine model Autograph AGS-X. For each condition, five specimens were tested. For both conditions, stress relaxation tests were carried out on the same machines and with similar samples to those used in the static tests. A fixed deflection/strain was applied, and the stress was recorded during the loading time. In terms of creep tests, a fixed stress/load was applied, and the displacement recorded during the loading time. For each condition, three specimens were tested. 3. Results and Discussion Experimental tests were performed to obtain the static properties. In this context, Figure 1 shows the load displacement curves obtained for each loading mode, which are representative of the others.

10 15 20 25 30 35 40 45

100 150 200 250 300 350 400

Tensile load [N]

Bending load [N]

0 50

0 5

Compressive load (×25) [N]

0 2 4 6 8 10 12 14 16 18 20

Displacement [mm]

Fig. 1. Tensile, compressive and bending versus displacement curves.

For all loading modes a linear region is observed, where the material elastically deforms and returns to its original length when the load is removed. This region ends when the yield point is reached, and the material starts to have a plastic behaviour. In this case, it no longer regains its original length when the load is removed. However, depending on the loading mode, the linear region presents different extensions. From these curves, it is possible to select the displacement and load used, respectively, on the stress relaxation and creep studies. Regarding the creep and stress relaxation behaviour, the results obtained from those tests are shown in Figure 2. The load values were selected to ensure that all tests were performed in the elastic regime in all loading modes. This means that the tensile and bending creep tests were carried out for 40% of the maximum load, while the compression creep tests were carried out for 40% of the yield stress. Regarding the stress relaxation tests, they were carried out at constant displacement and corresponding to the same load value used in the creep tests. Three curves obtained from the experimental tests and respective average curve (blue colour) are shown in Figure 2, which are also representative