PSI - Issue 75

Kalle Lipiäinen et al. / Procedia Structural Integrity 75 (2025) 19–28 Lipiäinen et. al. / Structural Integrity Procedia (2025)

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1. Introduction Additive manufacturing (AM) is a manufacturing method with its own characteristics. Key factors for successful adaption of AM are AM specific design with a consideration of manufacturing requirements and post-treatments. This could be identified as digitized design and manufacturing process. The use of laser powder bed fusion (L-PBF) techniques in titanium alloys have been extensively studied in detailed way from the material characteristics viewpoints. Johnsen et al. (2024) studied factors affecting Ti6Al4V fatigue performance. Kahlin et al. (2017) tested Ti6Al4V specimens in various configurations regarding notch geometry and surface conditions under variable amplitude loading. The surface conditions of L-PBF Ti6Al4V were studied by Kahlin et al. (2020) and improvement in the fatigue strength after shot peening was found. However, in some specimens, the fatigue strength of the shot-blasted samples was similar to that of the as-built samples. Bologna et al. (2024) fatigue tested sandblasted L-PBF manufactured Ti6AL4V unnotched specimens and found run out level above 300 MPa stress range (with stress ratio of R = 0.01). The effect of imperfections in L-PBF manufactured titanium material has been studied and found important together with microstructural features Naab et al. (2024). Hejazi et al. (2024) studied CT-scanned imperfection area on very-high-cycle fatigue tests and found correlation on AM titanium specimens and imperfection sizes. Bonneric et al. (2025) found imperfection morphology important for Ti6Al4V alloy for crack initiation from surface. Dyer & Molaei (2024) studied the effect of overhang using hollow specimens for fatigue testing and found imperfections to be more influential than surface roughness on fatigue strength. Varsha et al. (2024) found fatigue performance improvement for L-PBF manufactured Ti specimens with laser cavitation peening technique. Monaheng et al. (2023) analyzed Ti6Al4V component performance and failure mode and suggested surface treatments for critical components. In this study Laser powder bed fusion (L-PBF) was selected for implementing the component. One case specific component is tested with four different surface treatments. The component was built with two different branded L PBF equipment to study robustness of design independent from physical manufacturing location. 2. Materials and Methods 2.1. Description of the studied component The studied component is a fitting, tailplane hinge, for the BAE Systems Hawk Mk.66 jet trainer (Fig.1). The size of the component is approximately 150 mm in width and 75 mm in height and consequently, enabling easy adoption of L-PBF techniques for manufacturing. The original components are manufactured from forged aluminum alloy. Routine overhaul inspections and non-destructive testing have revealed several cracks in these fatigue-critical components. The crack growth analyses have been analyzed earlier based on the strain gage measurements during flight operations conducted by Finnish Air Forces.

Fig. 1. (a) Hawk Mk.66 tailplane and center box location and (b) Fitting installed on place, LH side. Photo: Patria Aviation