PSI - Issue 76

R. Fernandes et al. / Procedia Structural Integrity 76 (2026) 43–49

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After L-PBF production, the specimens were divided into four batches, depending on the surface and heat treatments: as-built (AB); shot peening, referred to as as-built shot-peened specimens (AB+SP); stress relief heat treatment (SR) at 250 °C for 2 hours, with a subset of these subsequently subjected to shot peening (SR+SP). Shot peening was performed using Z100 ceramic shots, with an Almen Intensity of 10A ensuring full surface coverage.

Fig. 1. Geometry of Compact Tension (CT) specimen (dimensions in mm).

2.2. Fatigue crack growth tests The fatigue crack growth (FCG) tests were conducted in an Instron ElectroPuls E10000 machine with a 10 kN capacity, operating at 10 Hz under sinusoidal waveforms and mode I loading conditions, for constant amplitude and a stress ratio R=0.05. Crack lengths were measured using a traveling microscope with 45x magnification and crack growth rates were calculated using the incremental polynomial method, which utilized five consecutive points from the a-N curves. Transient behaviour was evaluated after single tensile overloads applied at specific stress intensity factors, using the overload ratio (OLR) of 2. Crack closure was estimated using Digital Image Correlation (DIC) data, which enabled the acquisition of load-displacement measurements. A total of 180 images were captured at a rate of one image per second, covering the load cycle from minimum to maximum values. Crack closure is quantified using the load ratio parameter U, which represents the percentage of the stress range during which the crack tip remains open. The parameter U is calculated using the following equation: = − − = ∆ ∆ (1) where, , and are the maximum load, minimum load and crack-opening load, respectively. As-built and stress-relieved series have been previously studied by the authors, Fernandes et al. (2024), showing that the microstructure of as-built AlSi10Mg exhibits a supersaturated silicon cellular-dendritic structure, consisting of an aluminium matrix that contains a fibrous network of silicon. The stress relief heat treatment at 250 °C for 2 hours, followed by water quenching, induced minor microstructural changes. The L-PBF technology inherently generates defects, particularly porosities and lack of fusion. Then, in order to observe porosity level, micro-computed tomography (micro-CT) was performed using a Werth TomoScope XS Plus X-ray system, with samples measuring 21.5×28×6 mm extracted from both as-built and stress-relieved CT specimens. Figure 2 presents the relationship between the equivalent diameter and the sphericity of the pores. Both the as built and stress-relieved conditions exhibited a similar trend: the equivalent diameter decreases as the sphericity increases, indicating that smaller pores tend to be more rounded, which trend to align with observations reported by Hastie et al. (2021).