PSI - Issue 37

3

R. Fernandes et al. / Procedia Structural Integrity 37 (2022) 462–468 R. Fernandes et al./ Structural Integrity Procedia 00 (2019) 000 – 000

464

Building direction

Fig. 1. Specimen geometry used in the low-cycle fatigue tests.

a layer thickness of 30  m, and a maximum power of 350 W. Three batches were prepared, the first in an as-built condition, the second in a stress-relieved condition (300ºC for 2h), and last in a T6 condition (annealing at 550ºC for 2h, followed by aging at 175ºC for 6h). After the manufacturing process, the surface was machined and then polished using progressively finer grades of silicon carbide papers (P600-grit, P1200-grit, and P2500-grit) followed by a 3- μm alumina-based polishing compound. Low-cycle fatigue tests were conducted in a conventional servo-hydraulic machine under fully-reversed conditions (R  = -1) at constant strain rate (d  /dt = 8×10 -3 ) and room temperature. The tests were initiated in tension and were stopped when the total failure has reached. Strain amplitudes (  a ) varied in the interval 0.2%-1.5%. The cyclic stress-strain response was acquired from a from a 12.5 mm-gauge extensometer clamped to the specimen, via two separated knife-edges, and were recorded in appropriate intervals, using a PC-based data acquisition system, with a rate of 200 samples per cycle. Results and discussion The typical stress-strain response collected in the experiments for the different batches obtained for a strain amplitude of 1.25% is plotted in Figure 2. For the sake of clarity, the first cycle and the mid-life cycle are highlighted. Overall, at this strain amplitude, this alloy exhibits a cyclic strain-softening behaviour. However, the cyclic stress strain response is significantly different, which is associated with the manufacturing routes. In the case

400

400

400

 (MPa)

 (MPa)

 (MPa)

300

300

300

200

200

200

100

100

100

 (%)

 (%)

 (%)

0

0

0

-1.25 -0.75 -0.25 0.25 0.75 1.25

-1.25 -0.75 -0.25 0.25 0.75 1.25

-1.25 -0.75 -0.25 0.25 0.75 1.25

-100

-100

-100

-200

-200

-200

Full test 1st cycle Mid-life

Full test 1st cycle Mid-life

Full test 1st cycle Mid-life

-300

-300

-300

-400

-400

-400

(c)

(a)

(b)

Fig. 2. Cyclic stress-strain response of the AlSi10Mg aluminium alloy manufactured by laser-beam powder bed fusion at the (a) as-built condition; (b) stress-relieved condition; and (c) T6 condition.