PSI - Issue 37

Md Niamul Islam et al. / Procedia Structural Integrity 37 (2022) 217–224 Md Niamul Islam et al. / Structural Integrity Procedia 00 (2019) 000 – 000

221

5

1 = 2 * 3 * 12 = * 13 * 23

230 MPa 125 MPa 30 MPa 20 MPa

*

1e-9

Density

1.17 g cm -3

3. Results and discussion 3.1. Experimental results and discussion

The mean outputs of tensile and compressive tests of 5 specimens for each experiment are displayed in Fig. 5. The average tensile strength of the material was estimated equal to 53.8 MPa and the average compressive strength was 229.8 MPa. The average tensile modulus was found equal to 1.97 GPa while the corresponding mean value at compression was 0.97 GPa. Also, the area under the curve was determined to calculate the toughness of the material. The tensile toughness of the material was on average 5.15 MJ m -3 and the average compressive toughness was 68.11 MJ m -3 . Toro et al. (2020) also performed tensile-compressive test for the same filament material but with different printing parameters and print orientation. The unidirectional 100% infill structure had a tensile strength of 52 MPa and a tensile modulus 6.2 GPa. The compressive strength was approximately 72 MPa and the compressive modulus was 3.9 GPa. Although the tensile strength in both cases was similar, the lower compressive strength and significantly higher tensile and compressive modulus for unidirectional parts were due to the orientation of all the extruded filaments along the loading direction. Further, the unidirectional structure exhibited ductile behaviour for both tension and compression tests, whereas the quasi-isotropic structure in our study showed brittle behaviour. The strain to failure for both structures under tension was fairly close (8% for unidirectional and 12% for quasi isotropic); however, in compression, the quasi-isotropic structure had significantly higher stain at failure (46%) compared to that of the unidirectional structure (24%) The difference in this behaviour can be attributed to the influence of printing parameters and orientation on material structural characteristics.

250

10 15 20 25 30 35 40 45 50 55 60

200

150

100

Tensile Compressive

Tensile stress (MPa)

50

Compressive stress (MPa)

0 5 10 15 20 25 30 35 40 45 50 55 0 5

0

Strain (%)

Fig. 5. Tensile and compressive stress-strain curves for Nylon SCF.

Visual observation of the fracture surface of the tensile-test specimen (Fig. 6a) revealed brittle fracture with a slightly rough surface, indicating that the material exhibited an elastic-brittle behaviour. A post-mortem inspection of the compressive sample (Fig. 6b) also showed a rough brittle fracture surface at the bottom; however, a ‘V’ shaped fracture was noted, indicating that the sample failed in shear. Additionally, the dynamic characteristics of the material, namely, its storage and loss moduli, as well as tan delta for a frequency sweep of 0 Hz to 150 Hz with the DMA in flexure at 25 °C, are provided in Fig. 7. The average