PSI - Issue 34

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

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To show the effect of the anisotropy, the yield stress and the failure strain values were plotted in perpendicular (90°) and in parallel (0°) direction in one diagram for both specimen configurations in Fig. 4. The straight line represents the perfect isotropy, the deviation of the points from this isotropy line shows the degree of anisotropy. a b

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0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 notched (BNC) SLS tensile test cylindrical specimens 23 °C, 0.1 to 100 mm/s

SLS tensile test cylindrical specimens 23 °C, 0.1 to 100 mm/s

10

notched (BNC)

8

hollow (HC)

fracture strain 90°, MPa

yield stress for 90°, MPa

hollow (HC)

6

6

8

10

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yield stress for 0°, MPa

fracture strain 0°, MPa

Fig. 4. Comparison of printing directions (a) yield stress; (b) failure strain.

The yield stress values of notched and hollow specimens revealed similar anisotropy. The fracture strain values of notched specimens showed the highest anisotropy.

Fatigue tests The stress amplitude,  vs. cycle number-to-failure, N f , values of the SLS TPU material are plotted in Fig. 5 for both specimen configurations investigated. The corresponding monotonic tensile strength values revealed also a good agreement with the tendency of these curves (see the monotonic tensile strength values in Fig. 5a and 5b).

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SLS TPU fatigue notched cylindrical (BNC) 5 Hz, RT

SLS TPU fatigue hollow cylinder (HC) 5 Hz, RT

 t =10.5 MPa

 t =10.2 MPa (0°)

10

10

 t =8.5

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 t =7.8 MPa (90°)

8

6

6

4

4

0° orientation, R=-1 90° orientation, R=0.1 90° orientation, R=-1 0° orientation, R=0.1

90° orientation, R=0.1 0° orientation, R=-1 90° orientation, R=-1 0° orientation, R=0.1

stress amplitude, MPa

stress amplitude, MPa

2

2

0

10 0

10 1

10 2

10 3

10 4

10 5

10 6

10 7

10 -1

10 0

10 1

10 2

10 3

10 4

10 5

10 6

10 7

cycle numer-to-failure, N f

cycle number-to-failure, N f

Fig. 5. Data points of Wöhler curves for the SLS TPU material; (a) bulk notched cylindrical specimens (BNC); (b) hollow cylindrical (HC).