PSI - Issue 19

Wolfgang Schneller et al. / Procedia Structural Integrity 19 (2019) 556–565 Author name / Structural Integrity Procedia 00 (2019) 000–000

561

6

3.4. Fatigue test results The presented HCF test results are normalized to the nominal ultimate tensile strength (UTS) of the base material in as-built condition. This value is given by the powder manufacturer [28]. The results are presented in Figure 4 and summarized in Table 5. In this Figure, the solid lines stand for the machined condition and the dashed lines represent the test results of the unprocessed test series. Furthermore, black with square marking indicates the AB condition, blue with triangle markings stands for the HIP test series and green with circular markings represents the SA post treatment condition. The experimental results are evaluated based on the ASTM E739 standard within the finite life region [29]. The fatigue strength at 1E7 load-cycles was statistically determined by applying the arcsin√P-transformation given in [30]. Specimens that reached the run-out criterion of 1E7 load-cycles are reinserted at higher load levels in order to obtain more data points within the finite life region. The evaluation of the SN-curves reveals a significant decrease of the fatigue strength for each unprocessed test series referring to the corresponding machined condition. Respectively a reduction by -65.6% for the AB condition, -62.2% for the HIP condition and -59.3% for the SA condition is observed, evaluated for a survival probability of 50%. Furthermore, a positive effect of the HIP and SA treatment is observed for both, the machined and unprocessed condition, referring to the AB test series without any post treatment. Concerning the machined condition, HIPing leads to an improvement of +13.8%, and the SA condition shows an increase of +5.9% in fatigue strength. Regarding the unprocessed condition, both post treatments lead to an enhanced fatigue strength of +25.3%. The improved fatigue behavior for the HIP and SA condition can be attributed to the demonstrated influencing factors. The mitigated surface roughness, decreased residual stresses at the crack initiation spot as well as the microstructure favor the fatigue resistance.

0.5

AlSi10Mg (AB,HIP,SA)

R = -1

0.4

0.3

4x 1x 4x 1x

1x 3x

0.2

M-AB (P s = 50%) UP-AB (P s = 50%) M-HIP (P s = 50%) UP-HIP (P s = 50%) M-SA (P s = 50%) UP-SA (P s = 50%)

1x 2x

1x 2x

0.1

Normalized stress amplitude [-]

1x

2x

10 5

10 6

10 7

Number of load-cycles [-]

Fig. 4. SN-curves of the high-cycle fatigue test series