PSI - Issue 76

Robin Motte et al. / Procedia Structural Integrity 76 (2026) 74–81

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Fig. 1. Dimensions (in mm) of a four-point bending specimen.

manufacturing new workpieces, WAAM also enables the remanufacturing of worn or damaged components. This has important time, cost and environmental benefits over replacing with a new component. After inspecting the compo nent for damage, material is locally machined away to not only remove the damage but also to prepare a suitable geometry for subsequent material deposition. After that, material deposition by WAAM can take place. As WAAM results in substantial surface waviness due to the deposition of adjacent beads in multiple layers, the final stage of the remanufacturing process typically involves removing excess material by machining and grinding (Li et al. (2019); Priarone et al. (2021); Lee et al. (2022)). These finishing operations are time-consuming and thus also costly (Pri arone et al. (2021)). In cases where a smooth surface finish is not necessary for the functionality of the part, these final machining steps might be omitted to further decrease costs and lead times. However, surface waviness has a signifi cant and detrimental influence on the mechanical properties, especially on the fatigue life of the as-built geometries (Hensel et al. (2023); Bercelli et al. (2023)). Indeed, for bulk WAAM components with as-built surface waviness, fatigue experiments have indicated a fatigue life reduction of around 60% and a fatigue limit reduction of around 35% compared to machined components without surface waviness (Huang et al. (2023)). Although the fatigue performance of as-built bulk WAAM components has been investigated, studies addressing remanufactured parts with unmachined, as-built surfaces in repaired zones are scarce. This work aims to experimentally investigate the fatigue performance of steel components remanufactured by WAAM with as-built surface waviness. To this end, the S-N curves of specimens designed to replicate a repair with as-built surface are compared to reference curves of smooth base materials. Addi tionally, this study focuses on detecting crack initiation and monitoring crack growth during the fatigue experiments by means of infrared (IR) thermography and digital image correlation (DIC), respectively.

2. Materials and methods

2.1. Specimen design and materials

As no dedicated standards are available for fatigue testing of specimens with a pronounced waviness, a novel type of specimen was designed to replicate a steel component repaired by WAAM with as-built surface waviness. The specimens consisted of an S355J2 steel substrate plate with dimensions 185 × 180 × 25 mm³ into which a groove was milled, which was subsequently filled by WAAM. The plate was then machined to specimens with the dimensions as shown in Figure (1). The specimens were designed for four-point bending, ensuring an identical load over the length of the “remanufactured” section. As filler material, a Bo¨hler EMK 8 copper coated wire (voestalpine Bo¨hler Welding (2015)) (G 46 4 M21 4Si1 according to EN ISO 14341-A (International Organization for Standardization (2020)) or alternatively ER70S-6 according to AWS A5.18 (American Welding Society (2023))) with a diameter of 1.2 mm was used. The WAAM deposition was performed at the Belgian Welding Institute using a Kuka K6 robot and Fronius Cold Metal Transfer (CMT) welding source. For the application of the WAAM technique, two di ff erent arc welding processes were selected: conventional short circuit and CMT. During the CMT process, the filler wire is retracted when a short circuit is detected, resulting in increased stability and reduced heat input compared to the conventional process (Selvi et al. (2018)). The welding parameters for both processes are listed in Table 1. The heat input during welding was calculated according to the EN 1011 standard (CEN-CENELEC (2014)) . In the remainder of this paper, “CONV” and “CMT” will be used as naming convention for the specimens manufactured using respectively the conventional short circuit and CMT processes.