PSI - Issue 77

Roman Hofmann et al. / Procedia Structural Integrity 77 (2026) 237–247 Roman Hofmann et al. / Structural Integrity Procedia 00 (2026) 000–000

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specimens, and cantilever geometries. Distortion measurements by cantilever proved to be particularly useful for comparing how the thermal stability of the di ff erent strategies a ff ected the residual stresses. In the project di ff erent methods for residual stress measurements were compared (x-ray di ff raction, specimen deflection and hole drilling). The deflection method was selected for the scan strategy investigation, as it provides more better information on the residual stresses within the component. The cantilever dimensions were defined according to preliminary work [11]. The resulting deflection was measured using a GOM ATOS optical 3D scanner. Fatigue testing provides insight into the impact of the approaches on the thermic history and thus on structural integrity. Therefore fatigue specimens are used with a round cross-section and a diameter of 4.5 mm. The samples were loaded with di ff erent amplitudes under a stress ratio of R = 0.1. In addition to the development of scan strategies, active thermography was integrated as an in-situ monitoring tool to capture the thermal history during the build. A FLIR X6900sc infrared camera, combined with a Euresys frame grabber, was employed to record the entire build process at frame rates of up to 1000 Hz. For the purpose of this study, selected snapshots obtained during the fabrication of demonstrator parts with di ff erent scan strategies are presented to illustrate qualitative di ff erences in heat distribution. The snapshots were taken with the same scaling colourization and were recorded using superframing with three calibrated temperature ranges. A detailed analysis of the thermographic data, however, lies beyond the scope of this paper. A first qualitative assessment of the developed scan strategies was performed using cantilever specimens. These geometries are designed to analyze residual stresses by deflection. Due to their simple cross-sectional changes, cantilevers are also suitable for visualizing the influence of thermal history, which is evident by changes to the surface. As illustrated in Figure 5, cantilevers produced with di ff erent scan strategies show distinct surface discolorations, which can be directly related to heat accumulation and cooling conditions. Even such a simple visual observation demonstrates that simple linear scan strategies do not provide homogeneous thermal conditions, especially in geometries with varying cross-sections, as commonly encountered in additive manufacturing. Specimens processed with index-based reordering strategies (Index 2, 3, and 4 - Figure 5a,b,d) exhibited noticeable discoloration changes at the rib layers, confirming a non-uniform thermal history. In contrast, cantilevers produced with the Voronoi scan strategy showed a far more consistent surface appearance, independent of local geometry changes. This e ff ect was observed both for variants with and without contouring of the individual Voronoi cells, and even when a reduced laser power is applied. The uniform surface appearance suggests a more homogeneous temperature distribution across layers. Similarly, the specimen manufactured using the Pilger strategy displayed a 3. Results and Discussion

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Fig. 5. Printed cantilever specimens with di ff erent scan strategies (a, b, d) Index Reorder (c, e, f) Voronoi (g) Pilger (bottom 8mm conventional linear hatched)