PSI - Issue 54

Martin Matušů et al. / Procedia Structural Integrity 54 (2024) 135 – 142 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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To compare the fatigue strengths for 4 different platforms of recycled/sieved powder, three pairs were made (where the platform n°1 was printed first with the fresh powder and platform n°4 as last with the powder several times reused): a) First the T240 specimens from platform n°1 were compared to the specimens from platform n°3. b) The T200 specimens from platform n°3 were compared to specimens from platform n°4. c) The last pair is comparing the T300 heat treatment of specimen’s from platform n°3 and from platform n°5. However, the platform n°5 is made from one third of the original recycled powder (GE) from previous builds and from two thirds of added fresh powder delivered from a different manufacturer (ECKART).

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Fig. 2. a) Comparison of heat-treated specimen with T240 on two different printing platforms. b) Crack initiation on SEM with the visible crack initiation position on a specimen from platform n°1 of T240 tested on stress amplitude of 90MPa with number of cycles to failure 106 313 cycles. When comparing the results of specimens with the T240 heat treatment from platforms n°3 and n°1, a notable difference can be observed in the fatigue curves, as depicted in Figure 2. The main difference lies in the transition to the fatigue limit domain in the HCF region, where specimens produced from the fresher powder used in platform n°1 exhibit a higher load capacity and longer lifespan, particularly in the region around 1e6 cycles. Conversely, the differences between the two platforms in the region of finite service life, ranging from 1e4 to 1e5 cycles, are negligible. This outcome in this comparison can be caused by the T240 heat treatment, which improves ductility, and which thus can reduce the differences caused in the LCF response.

Table 3. Fatigue strengths at 10 6 cycles 

FS6 according to the K&V regression at and the slope of the power law regression curve k .

Fatigue properties of the regression curves  FS6 [MPa] / k [-]

Series

Platform n°1

Platform n°3

Platform n°4

Platform n°5

T200 T240 T300

68.5 / 4.27 67.1 / 6.60 74.1 / 8.75

47.9 / 4.37

80.5 / 7.09

45.9 / 3.55

Comparing platforms n°3 and n°4 for specimens with the same T200 heat treatment, the differences in fatigue lives become much more pronounced, as depicted in Figure 3 a), compared to the previous case (Figure 2). The S-N curves exhibit a noticeable shift in the region between 10,000 cycles and 100,000 cycles, with a minimum difference of 10MPa in the achieved fatigue strength amplitude. However, the slope of both S-N curves is very similar. The disparity becomes more apparent in the region where the transition to the fatigue limit domain occurs. In the case of run-out specimens, the amplitude of stress differed by 20-25MPa.