PSI - Issue 75

J. Havia et al. / Procedia Structural Integrity 75 (2025) 43–52 Havia et al./ Structural Integrity Procedia (2025)

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1. Introduction Additive manufacturing (AM) can be used to add geometrical features to larger assemblies and structures. Directed energy deposition (DED)-manufactured aluminum material has been studied recently. Qin et al. (2025) studied the properties of DED-arc manufactured 7075 aluminum alloy. Bruzzo et al. (2024) studied AlSi10Mg reinforcement structures manufactured with a laser beam and powder (DED-L). DED-L with aluminum wire was also studied by Zapata et al. (2024) and its potential has been highlighted for aluminum AM especially. Unsupported aluminum lattices were studied by (Fu et al., 2024). Lattices were found promising for larger scale structures. DED manufactured aluminum coupon specimens were studied by Lipiäinen et al. (2025) with focus on quality-based fatigue strength analysis. Scharf-Wildenhain et al. (2023) studied the effect of residual stress formation during DED, in respect to build layers and location on specimen with steel samples. Lower residual stresses were measured at beginning of the build than on top of the build. This study examines different configurations of longitudinal gussets added to a plate. The potential of DED could be further utilized for hybrid structures including both AM components and conventional plate structures. A fatigue life of conventional welded structures can be evaluated with nominal or local methods according to Hobbacher & Baumgartner (2024). For longitudinal gusset-like feature, that is studied in this work, fatigue life can be assessed with nominal stress method (FAT 25 MPa, m = 3) or with the effective notch stress (ENS) with reference curve of FAT 71 MPa, m = 3 with 1 mm reference radius. The sequence of deposition and welding operations affects the local material properties and residual stress state. Additionally, manufacturing impacts the local geometry. Fig. 1 illustrates the three cases studied: (1) deposition directly on the plate, (2) welding separate deposited features onto the plate, and (3) depositing features on an arc-DED cladded surface on the plate. The longitudinal gusset-like DED feature creates a high stress concentration factor (SCF) at the weld toe. The aim of the study is to evaluate the effect of residual stresses and local SCFs on fatigue strength assessment and performance on aluminum DED hybrid structures.

Fig. 1. Introduction of studied cases.

2. Materials and methods 2.1. Materials and specimens

A 5000-series aluminum plate with the thickness of 12 mm was used for the study. The longitudinal gusset-like specimen dimensions and manufacturing process are illustrated in Fig. 2 and Table 1 shows the chemical composition of the studied 5083 H111 plate used. The oval shape with reduced perimeter was designed to enable residual stress measurement with the X-ray diffraction technique. Consequently, 20° angle on DED feature were applied.

Table 1. Chemical composition of aluminium plate. Si Fe Cu Mn Mg Cr Ti 5083 H111 Mat. Cert. 0.123 0.291 0.058 0.539 4.79 0.07 0.12 0.027 Zn