PSI - Issue 42

Rui F. Fernandes et al. / Procedia Structural Integrity 42 (2022) 1054–1060 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1056

3

LPBF Laser Powder Bed Fusion P op Opening load P max Load maximum P min Load minimum R Stress ratio U Crack closure parameter

2. Experimental procedure A Renishaw machine model “AM 400” was used to produce Compact Tension (CT) specimens, based on the Laser Powder Bed Fusion process. Regarding the process parameters, it was used a laser powder of 350 W, a layer thickness of 0.03 mm and a scanning speed of 1.8 m/s. The feedstock powder of AlSi10Mg used has the chemical composition presented in the table 1. The specimens were produced in the vertical orientation, i.e., with the layers perpendicular to the loading direction. The specimens geometry is presented in the figure 1 and followed ASTM E647 recommendations. Afterwards, it was applied two different heat treatments: Stress relief with a temperature of 250ºC for 2 hours and water quenched, and HIP was done at the same temperature for 2 hours, with a pressure of 100 MPa and cooling to room temperature in air.

Table 1. Chemical composition of the AlSi10Mg aluminum alloy (% wt) (1706 2021)

Al

Si

Mg

Mn 0.45

Cu

Ni

Fe

Zn

Pb

Sn

Ti

Bal.

9-11

0.25-0.45

0.05

0.05

0.55

0.10

0.05

0.05

0.15

Fig. 1. Specimens geometry.

The FCG tests were done at room temperature in mode I loading under constant amplitude at 10 Hz using a 10 kN capacity Instron ElectroPuls machine with a stress ratio (R) of 0.05. The crack length was measured using a traveling microscope (45×) in increments of 0.2 mm, following ASTM E647 recommendations. Crack growth rates were calculated by the incremental polynomial method using five consecutive points and the results were plotted as da/dN versus ∆ K curves. Displacement data was acquired by digital image correlation and the opening load was estimated using the maximization of correlation coefficient method. The crack closure level was represented by the load ratio parameter, U, estimated by the equation: