PSI - Issue 34

D. Rigon et al. / Procedia Structural Integrity 34 (2021) 199–204

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Rigon D. et al. / Structural Integrity Procedia 00 (2021) 000–000

Virgin and recycled IM specimens were fatigue tested for load ratios R ( σ min /σ max ) equal to -1 and 0.05. The same load ratios were applied to AM specimens for each infill pattern, but only in the recycled condition. The experimental data were statistically analysed, according to BS ISO 12107:2003, under the hypothesis of log-normal distribution of N f and a constant scatter with respect to σ a . After failure, the macroscopic fracture paths were analyzed by using an AM4115ZT Dino-Lite digital microscope with a magnification ranging from 20x to 220x. 3. Fatigue test results and macroscopic damage analyses 3.1 Fatigue test results of virgin and recycled IM specimens The fatigue tests on virgin and recycled IM specimens for load ratios equal to -1 and 0.05 are reported in terms of stress amplitude σ a versus the number of cycle to failure N f in Fig. (2a) and (2b), respectively.

100

100

b) R= 0.05 IM

a) R= -1 IM

k= 62.6 σ A,50% = 33.0 MPa k= 21.4 σ A,50% = 22.7 MPa T σ = 1.25

vPPCC-GF_IM_-1 MF- IM

k= 19.9 σ A,50% = 18.0 MPa k= 21.4 σ A,50% = 15.5 MPa

vPPCC-GF_IM_005 MF- I

rPPCC-GF_IM_-1 MF- I

rPPCC-GF_IM_005 MF- I

σ A,50%

σ a [MPa]

σ a [MPa]

σ A,50%

T σ = 1.23

σ A,50% σ A,50%

T σ = 1.08

N A

N A

scatter bands: 10-90% of survival probability

scatter band: 10-90% of survival probability

10

10

1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07

1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07

Number of cycles to failure

Number of cycles to failure, N f

Fig. 2. Fatigue test results and relevant fatigue curves of vPPMF-GF and rPPMF-GF specimens produced by IM (a) for R=-1 and (b) for R=0.05.

Fig. (2a) shows that the fatigue strength for R=-1 of IM rPPMF-GF is always lower than that of the virgin compound within 10 3 and 2∙10 6 cycles and the difference increases with the number of cycles. At 2∙10 6 cycles (i.e. N A ) the fatigue strength of the recycled compound processed by IM is 31% lower than the virgin one. The stress-based scatter index of the fatigue curves for 10% and 90% of survival probability is approximately the same in the two compounds. However, the virgin material presents a higher inverse slope k, which translates in a life-based scatter index higher than the recycled material. Regarding the results for the R = 0.05 reported in Fig. (2b), the fatigue strength of IM rPPMF-GF is again lower than that of the virgin compound in the lifetime between 10 3 and 2∙10 6 cycles. Opposite to the results relevant to R=- 1, the percentage difference in terms of σ a is approximately constant for the considered range of fatigue life and equal to 28%. A quite narrow scatter has been found in the recycled material processed by IM, while for the virgin one a significant scatter index could not be evaluated, due to the reduced number of broken specimens and therefore it was intentionally omitted. 3.2 Fatigue test results of virgin and recycled IM specimens The fatigue tests on recycled AM specimens for the different infill patterns and load ratios are reported in terms of σ a versus N f in Fig. (3a) and (3b), respectively. Due to the lack a data for R=0.05 related to rPPMF-GF_AM_F90° only the fatigue curve related to 50% of survival probability was calculated and then reported in Fig. (3b). For