PSI - Issue 34

Zoltan Major et al. / Procedia Structural Integrity 34 (2021) 191–198 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

195

5

modulus, yield stress and fracture strain are obvious. These differences are, of course, expected by everybody with minor knowledge in polymers, and these simple data can be useful for designers and engineers for specific applications. Furthermore, elastic-plastic and elastic-viscoplastic models for further FE simulations can also be derived using these curves. It is notable here, however, that the SLS printed TPUs reveled a distinct semi-brittle failure behavior for printing directions perpendicular to the loading (90°). The smooth notch effect was partly overshadowed by the influence of the printing directions, that is, by the weak interfaces between the layers. a b

1500

8000

Cylindrical specimens PA12 23 °C, 0.1 mm/s

Cylindrical specimens TPU 23 °C, 0.1 mm/s

1250

6000

1000

750

4000

500 load F, N

load F, N

notched transverse notched parallel hollow transverse hollow parallel

notched transverse notched parallel hollow transverse hollow parallel

2000

250

-10 0 10 20 30 40 50 60 70 80 0

0

0

1

2

3

4

5

6

displacement s, mm

displacement s, mm

Fig. 2. Load-displacement curves for cylindrical test specimen configurations of the polymers investigated at 0.1 mm/s loading rate and RT (a) PA12; (b) TPU.

Stress-displacement curves of the investigated SLS printed TPU materials at various loading rates (from 0.1 mm/s to 100 mmm/s) are shown in Figs. 3a and b. As expected, a pronounced loading rate dependence of the deformation and failure behavior was observed. The increase of the loading rate up to 100 mm/s did not influnce the shape of the stress-strain curves and the failure mode observed. As usual, the tensile modulus, yield strength and fracture (failure) strain values were determined. a b

15,0

15,0

SLS TPU notched (BNC)

SLS TPU hollow cylinder

0° orientation

12,5

12,5

100mm/s

0° orientation

100mms

10,0

10,0

10mm/s

1mm/s

10mms

1mms

7,5

7,5

90° orientation

90° orientation

0,1mm/s

0,1mms

5,0 stress, MPa

5,0 stress, MPa

2,5

2,5

0,0

0,0

0

5

10

15

20

25

0

20

40

60

80

displacement, mm

displacement, mm

Fig. 3. Stress-displacement curves for cylindrical test specimen configurations of the polymers investigated (a) bulk notched specimens (BNC); (b) hollow cylindrical (HC) specimens.